# Fm 6-40 Mcrp 3-10E.4 (Formerly Mcwp 3-16.4) Tactics, Techniques, And Procedures For The Field Artillery Manual Cannon Gunnery

## U.S. Marine Corps

DISTRIBUTION RESTRICTION A: Approved for public release; distribution is unlimited.


                                                                                                                        2 May 2016



# Erratum To Mcwp 3-16.4 Tactics, Techniques And Procedures For Field Artillery Manual Cannon Gunnery

##

1. Change all instances of MCWP 3-16.4, Tactics, Techniques and Procedures for Field Artillery Manual Cannon Gunnery, to MCRP 3-10E.4, Tactics, Techniques and Procedures for Field Artillery Manual Cannon Gunnery. 2. Change PCN 143 000003 00 to PCN 144 000267 00. 3. File this transmittal sheet in the front of this publication.

## Foreward

This publication may be used by the US Army and US Marine Corps forces during training, exercises, and contingency operations.

Lieutenant General, USMC
Commanding General Marine Corps Combat Development Command General, USA
Commanding Training and Doctrine Command

## Preface

This field manual (FM) explains all aspects of the cannon gunnery problem and presents a practical application of the science of ballistics. It includes step-by-step instructions for manually solving the gunnery problem and applies to units organized under tables of organization and equipment (TOE) of the L series. The material concerns nonnuclear solutions to the gunnery problem. Automated procedures are covered in ST 6-40-2, ST 6-40-31, and ST 6-50-60.

This publication is a guide for field artillery (FA) officers (commanders and fire direction officers [FDOs]), FA
noncommissioned officers (NCOs), and enlisted personnel in the military occupational specialty (MOS) of cannon gunnery (MOS 13E; United States Marine Corps [USMC] MOS 0844/48). This publication implements the following North Atlantic Treaty Organization (NATO) Standardization Agreements
(STANAGs)/Quadripartite Standardization Agreements (QSTAGs):

STANAG
QSTAG
TITE
Artillery Procedures, Artillery Procedures,
Artillery Procedures, Artillery Procedures,
Battlefield Illumination
Call for Fire Procedures
Target Numbering System (Nonnuclear)
Radio Telephone Procedures for the Conduct
2934 (Chap 10) (Ed 1)
182 (Ed 2)
2934 (Chap 6) (Ed 1)
255 (Ed 3)
2934 (Chap 7) (Ed 1)
221 (Ed 2)
2934 (Chap 5) (Ed 1)
246 (Ed 3)
2934 (Chap 3) (Ed 1)
217 (Ed 2)
2963 (Ed 1)
802 (Ed 1)
4119 (Ed 1)
220 (Ed 2)
none
224 (Ed 2)
4425 (Ed 1)
none
of Artillery Fire
Artillery Procedures, Tactical Tasks and Responsibilities for Control
of Artillery
Coordination of Field Artillery Delivered Scatterable Mines
Adoption of a Standard (Cannon) Artillery Firing Table Format
Manual Fire Direction Equipment, Target Classification, and Methods of Engagement for Post-1970 Procedure to Determine the Degree of Interchangeability of NATO Indirect Fire Ammunition-APO-29

The proponent of this publication is Headquarters (I-IQ), US Army Training and Doctrine Command (TRADOC). Send comments and recommendations on DA Form 2028 (Recommended Changes to Publications and Blank Forms) directly to Commandant, US Army Field Artillery School (USAFAS), ATTN: ATSF-GD, Fort Sill, OK 73503-5600.

Unless this publication states otherwise, masculine nouns and pronouns do not refer exclusively to men.

## Tactics, Techniques, And Procedures For Field Artillery Manual Cannon Gunnery

FM 6-40/MCWP 3-16.4, April 1996, is changed as follows: 1.  Change the following paragraphs or sections (changes are in bold type):
Replace Paragraph 6-1, Page 6-1 with the following:

## 6-1.  Description

A firing chart is a graphic representation of a portion of the earth's surface used for determining distance **(or range)** and direction **(azimuth or deflection).**  The chart may be constructed by using a map, a photomap, a gridsheet, or other material on which the relative locations of batteries, known points, targets, and observers can be plotted.  Additional positions, fire support coordinating measures, and other data needed for the safe and accurate conduct of fire may also be recorded.

Replace  Step 5, Table 6-6, Page 6-19 with the following:

5
Place a plotting pin opposite the number on the azimuth scale (**blue** numbers) on the arc of the
RDP corresponding to the last three digits of the azimuth in which the arm of the RDP is oriented.  The location of the pin represents a temporary index and will not be replaced with a permanent index.  The value of the pin is the value of the first digit of the azimuth in which the arm o f the RDP is oriented.  Use the rules outlined in step 4 of Table 6-5 to determine where the pin should be placed.  In Figure 6-15, the azimuth of lay is 1850, so the RDP has been oriented east (1600 mils).
Replace Figure 7-1, Page 7-1 with the following:

STANDARD CONDITIONS
WEATHER
1
AIR TEMPERATURE 100 PERCENT (59 F)
2
AIR DENSITY 100 PERCENT (1,225 gm/m3)
3
NO WIND
POSITION
1
GUN, TARGET AND MDP AT SAME ALTITUDE
2
ACCURATE RANGE
3
NO ROTATION OF THE EARTH
MATERIAL
1
STANDARD WEAPON, PROJECTILE, AND FUZE
2
PROPELLANT TEMPERATURE (70 F)
3
LEVEL TRUNNIONS AND PRECISION SETTINGS
4
FIRING TABLE MUZZLE VELOCITY
5
NO DRIFT

LEGEND: gm/m3 - grams per cubic meter Replace Table C-6, page C-18, with the following

| TLE = 0 Meters (CEP)        | TLE = 75 Meters (CEP)      |
|-----------------------------|----------------------------|
| TLE = 250 Meters (CEP)      |                            |
| Counterbattery Radar        |                            |
| Airborne infrared system    |                            |
| Flash ranging               |                            |
| Countermortar radar         |                            |
| Forward observer with laser |                            |
| Target area base            |                            |
| Photointerpretation         |                            |
| Airborne target location    |                            |
| Sound ranging               | Forward observer w/o laser |
| Air observer                |                            |
| Tactical air                |                            |
| Forward observer (non FA)   |                            |
| Long-range patrol           |                            |
| Side-looking airborne radar |                            |
| Communications intel        |                            |
| Shell reports               |                            |

2.
Remove old pages and insert new pages indicated below:

| REMOVE PAGES   | INSERT PAGES   |
|----------------|----------------|
| 8-16           | 8-16           |

15-7 TO 15-25
15-7 TO 15-45

(Including Figure 15-22
on page 15-26)
3.
Insert new pages as indicated below:
INSERT PAGES

13-77 to 13-82

4.
File this transmittal sheet in the front of the publication for reference.

## Distribution Restriction:  Approved For Public Release; Distribution Is Unlimited.

By Order of the Secretary of the Army: Official:
Secretary of the Army
                  0011015
By Direction of the Commandant of the Marine Corps:
Marine Corps Combat Development Command

## Distribution:

Active Army, Army National Guard, and U.S. Army Reserve:  To be distributed in accordance with initial distribution  number 110044, requirements for FM 6-40/MCWP 3-16.4.

## 8-15.  Determination Of 10-Mil Site Factor Without A High-Angle Gft

The 10-mil site factor is the value of high angle site for every 10 mils of angle of site.  The 10-mil site factor can be determined manually by solving two equal equations for the 10-mil site factor.

SI = < SI + CAS (FOR LOW AND HIGH ANGLE) SI = < SI + ( | < SI | X CSF)
FOR POSITIVE ANGLES OF SITE:
HIGH ANGLE SITE = < SI ( 1 + CSF )
FOR NEGATIVE ANGLES OF SITE:
HIGH ANGLE SITE = < SI ( 1 - CSF )
USING THE HIGH ANGLE GFT:
HIGH ANGLE SITE = (< SI / 10)  X  10-MIL SI FACTOR
HOW TO DETERMINE 10-MIL SI FACTOR WITHOUT A GFT:
FOR POSITIVE ANGLES OF SITE:  10-MIL SI FACTOR  = 10 ( 1 + CSF ) FOR NEGATIVE ANGLES OF SITE:  10-MIL SI FACTOR =  10 ( 1 - CSF )
NOTE:  If the 10-mil site factor is not listed on the high angle GFT, use the last listed value or change charges The FDC can compute high angle site by manually determining the 10-mil site factor for those situations when a high angle GFT is not available.  The 10-mil site factor from the GFT actually reflects the complementary angle of site for a positive VI. Therefore, this method will introduce a slight inaccuracy when estimating for negative VI's

## 13-42. Sense And Destroy Armor (Sadarm M898)

The M898 SADARM projectile is a base ejecting munition carrying a payload of two target sensing submunitions.  The projectile is a member of the DPICM family, and is ballistically similar to the M483A1.  The technical fire direction computations are similar to those used for the ADAM projectile, in that low level wind corrections must be applied to the firing solution (because of the high Height of Burst) in order to place the payload at the optimal location over the target area.

## 13-43. M898 Firing Data Computations

Firing data are computed for SADARM by using the FT 155 ADD-W-0 or FT 155 ADD-
W-1 in conjunction with the FT 155 AN-2.  The difference between the  ADD-W-0 and ADD-
W-1 is the Height of Burst of the projectile.  The ADD-W-1 increases the HOB to correct for changes in the operational parameters of the projectile.  The ADD-W-1 is the preferred method of producing data, although the ADD-W-0 procedure may be used in lieu of the FT ADD 155- W-1 if it is unavailable.  (Note:  BCS Version 11 will incorporate the ADD-W-1 solution.  BCS Version 10 has the incorrect HOB, and automated firings must also incorporate the change in HOB discussed in the ADD-W-0 method).

## 13-44. Technical Fire Direction Procedures

Technical fire direction procedures consist of four steps (following the Fire Order):
a.  Determine chart data to the target location.  Chart range, chart deflection, and angle
"T" are recorded on the DA-4504 (Record of Fire) in the Initial Fire Commands portion of the form.  AN-2 site, elevation, QE, and angle "T" are determined to this target location.  Fire commands are not determined from this data!  (See Figures 13-33 and 13-34, Sample Records of Fire for SADARM)
b.  Offset aimpoint for low level winds.  The HCO places a target grid over the target location from step 1.  He then applies the Direction of Wind from the Meteorological Message (Extracted from Line 3) and offsets the aimpoint by the distance determined by multiplying the Wind Speed (Extracted from Line 3) times the correction factor from Table "A", Column 5, expressed to the nearest 10 meters.  This is the offset aimpoint which is used to determine firing data for SADARM.

c.  Determine AN-2 graze burst data to the corrected aimpoint.  The HCO announces chart range and deflection to the corrected aimpoint from step 2.  These values are recorded in the Subsequent Fire Commands portion of the DA-4504.  AN-2 graze burst data are determined to this offset aimpoint, to include Fuze Setting, Deflection to fire, and Quadrant Elevation (Site and angle "T" were determined in step (a.)).

d.  Determine SADARM firing data from the ADD-W-0 or ADD-W-1.  If data are being determined with the ADD-W-0, use paragraph (1.) below.  If data are being determined with the ADD-W-1, then use paragraph (2.) below.

(1)  ADD-W-0.  First determine SADARM firing data from the ADD-W-
0.  Then the Height of Burst correction must be applied.  Table 13-33 contains the HOB corrections by charge and AN-2 Quadrant Elevation.  To extract values from the table, enter with Charge on the left, and with the AN-2 graze burst Quadrant Elevation on the top.  If your Quadrant Elevation is less than or equal to the QE listed in Column 2, then use the up correction in Column 2.  If it is greater than the value listed in column 3 and less than 800 mils, apply the up correction from column 3.  If it is greater than 800 mils, apply the up correction from column 4.  The extracted up correction is used to determine the change in Quadrant Elevation (from Table "A", Column 3) and change in Fuze Setting (from Table "B", Column 3) for the change in HOB.  These values are then algebraically added to the ADD-W-0 data to determine the data to fire.  The FT 155 ADD-W-0 use the following formulas:

## Deflection To Fire

AIMPT CHT DF+ADD-W-0 DF CORR+GFT DF CORR+AN-2 DFT=M898 DF

## Fuze Setting To Fire

AN-2 FS+ADD-W-0 FS CORRECTION+HOB FS CORRECTION=M898 FS

## Quadrant Elevation To Fire

AN-2 QE+ADD-W-0 QE CORRECTION+HOB QE CORRECTION=M898 QE

               Column 1                                Column 2                             Column 3                          Column 4
CHARGE
AN-2 QE <=
AN-2 QE> and <800
AN-2 QE >800
3G (M3A1)
QE<=498, U200
QE>498, U200
U250
4G (M3A1)
QE<=430, U100
QE>430, U150
U250
5G (M3A1)
QE<=366, U100
QE>366, U150
U250
3W (M4A2)
QE<=434, U100
QE>434, U200
U250
4W (M4A2)
QE<=388, U150
QE>388, U150
U250
5W (M4A2)
QE<=343, U150
QE>343, U150
U250
6W (M4A2)
QE<=305, U100
QE>305, U200
U300
7W (M4A2)
QE<=251, U100
QE>251, U200
U300
7R/8W (M119/A1/A2)
QE<=205, U100
QE>205, U200
U300
8S (M203/A1)
QE<=173, U100
QE>173, U200
U300

Table 13-34 contains the specific step action drill required to compute SADARM firing data using the ADD-W-0 method.

| STEP                                                                    | ACTION                                                                     |
|-------------------------------------------------------------------------|----------------------------------------------------------------------------|
| 1                                                                       | The call for fire is received                                              |
| 2                                                                       | FDO issues Fire Order                                                      |
| 3                                                                       | The computer records the target information on the Record of Fire.         |
| (Note:  All fire commands are announced as they are determined)         |                                                                            |
| 4                                                                       | The HCO plots the target location on the firing chart and determines       |
| chart range, chart deflection, and angle "T" to the target.             |                                                                            |
| 5                                                                       | The VCO determines and announces AN-2 site to the target location.         |
| 6                                                                       | The Computer determines and announces the data for the offset              |
| aimpoint by extracting the Wind Direction and Wind Speed from line 3    |                                                                            |
| of the meteorological message.  The Wind Direction is announced in      |                                                                            |
| hundreds of mils.  The aimpoint shift correction is determined by       |                                                                            |
| multiplying the windspeed times the value from column 5, Table "A" of   |                                                                            |
| the Firing Table Addendum.  (Note, the entry argument for the           |                                                                            |
| addendum is the AN-2 data determined to the target location)            |                                                                            |
| 7                                                                       | The HCO places a target grid over the target location and applies the      |
| Wind Direction announced by the Computer in step 5.  The aimpoint       |                                                                            |
| shift correction is applied                                             |                                                                            |
| into the wind                                                           |                                                                            |
| .  (Note: the Wind Direction                                            |                                                                            |
| from the MET MSG is the direction the wind is blowing                   |                                                                            |
| from                                                                    |                                                                            |
| .)                                                                      |                                                                            |
| 8                                                                       | The HCO determines and announces chart range and chart deflection          |
| to the offset aimpoint.  The target grid is then reoriented to the OT   |                                                                            |
| direction announced by the observer, as all corrections will be based   |                                                                            |
| on this aimpoint.  Angle "T", however, is determined to the actual      |                                                                            |
| target location in step 4.                                              |                                                                            |
| 9                                                                       | The computer determines AN-2 data to the corrected aimpoint.               |
| 10                                                                      | The computer uses the data from step 9 to determine SADARM data.           |
| 11                                                                      | The computer determines the FS HOB correction necessary by                 |
| dividing the HOB correction from table 13-33 by 50.  This value is then |                                                                            |
| multiplied times the correction factor from Table "B", Column 3 of the  |                                                                            |
| ADD-W-0 addendum to determine the                                       |                                                                            |
| HOB FS CORRECTION.                                                      |                                                                            |
| 12                                                                      | The computer determines fuze setting to fire.  The fuze setting to fire is |
| determined with the following formula:                                  |                                                                            |
| AN-2 FS+ADD-W-0 FS                                                      |                                                                            |
| CORR+HOB FS CORR=M898 FS                                                |                                                                            |
| 13                                                                      | The computer determines the deflection to fire.  The deflection to fire is |
| determined with the following formula:                                  |                                                                            |
| AIMPT CHT DF+ADD-W-0 DF                                                 |                                                                            |
| CORR+GFT DF CORR+AN-2 DFT=M898 DF                                       |                                                                            |
| 14                                                                      | The computer determines the QE HOB correction necessary by                 |
| dividing the HOB correction from table 13-33 by 50.  This value is then |                                                                            |
| multiplied times the correction factor from Table "A", Column 3 of the  |                                                                            |
| ADD-W-0 addendum to determine the                                       |                                                                            |
| HOB QE CORRECTION.                                                      |                                                                            |
| 15                                                                      | The computer determines the Quadrant Elevation to fire.  The QE to         |
| fire is determined with the following formula:                          |                                                                            |
|                                                                         |                                                                            |
| AN-2 QE+ADD-W-0 QE                                                      |                                                                            |
| CORR+HOB QE CORR =M898 QE                                               |                                                                            |
| 13-79                                                                   |                                                                            |

         ADD-W-   TBL B, COL 3 X INC (.1 X 2) =                                                     TBL A COL 3 X INC (16.1 X 2) =

MET MSG LINE 3        19 KTS         (From Met Msg)         AN-2 GFT SETTING: GFT B, CHG5, LOT D/G, RG 5, EL 264, TI 16.7  (M577)
Wind Dir 24 Mils    X 9.9 M/KT    (TBL A, Col 5)
                                                                                                                            GFT DF CORR   L5
Wind Speed 19 Knots  = 188.1~19 Meter Aimpt shift

 (2) ADD-W-1.  No corrections to the Height of Burst are required.  The AN-2
graze burst data are used as entry arguments into the ADD-W-1 and the corrections to DF, FS, and QE are and applied.  The FT 155 ADD-W-1 use the following formulas:

                       FUZE SETTING TO FIRE
               AN-2 FS+ADD-W-1 FS CORRECTION=M898 FS
                        DEFLECTION TO FIRE
AIMPT CHT DF+ADD-W-1 DF CORR+GFT DF CORR+AN-2 DFT=M898 DF
                   QUADRANT ELEVATION TO FIRE
               AN-2 QE+ADD-W-1 QE CORRECTION=M898 QE

| STEP                                                                   | ACTION                                                                |
|------------------------------------------------------------------------|-----------------------------------------------------------------------|
| 1                                                                      | The call for fire is received                                         |
| 2                                                                      | FDO issues Fire Order                                                 |
| 3                                                                      | The computer records the target information on the Record of Fire.    |
| (Note:  All fire commands are announced as they are determined)        |                                                                       |
| 4                                                                      | The HCO plots the target location on the firing chart and determines  |
| chart range, chart deflection, and angle "T" to the target.            |                                                                       |
| 5                                                                      | The VCO determines and announces AN-2 site to the target location.    |
| 6                                                                      | The Computer determines and announces the data for the offset         |
| aimpoint by extracting the Wind Direction and Wind Speed from line 3   |                                                                       |
| of the meteorological message.  The Wind Direction is announced in     |                                                                       |
| hundreds of mils.  The aimpoint shift correction is determined by      |                                                                       |
| multiplying the windspeed times the value from column 5, Table "A" of  |                                                                       |
| the Firing Table Addendum.  (Note, the entry argument for the          |                                                                       |
| addendum is the AN-2 data determined to the target location)           |                                                                       |
| 7                                                                      | The HCO places a target grid over the target location and applies the |
| Wind Direction announced by the Computer in step 5.  The aimpoint      |                                                                       |
| shift correction is applied                                            |                                                                       |
| into the wind                                                          |                                                                       |
| .  (Remember, the Wind                                                 |                                                                       |
| Direction from the Meteorological Message is the direction the wind is |                                                                       |
| blowing                                                                |                                                                       |
| from                                                                   |                                                                       |
| .)                                                                     |                                                                       |
| 8                                                                      | The HCO determines and announces chart range and chart deflection     |
| to the offset aimpoint.  The target grid is then reoriented to the OT  |                                                                       |
| direction announced by the observer, as all corrections will be based  |                                                                       |
| on this aimpoint.  Angle "T", however, is determined to the actual     |                                                                       |
| target location in step 4.                                             |                                                                       |
| 9                                                                      | The computer determines the FS to fire.  The FS to fire is determined |
| with the following formula:                                            |                                                                       |
| AN-2 FS+ADD-W-1 FS CORR = M898 FS                                      |                                                                       |
| 10                                                                     | The computer determines the DF to fire.  The DF to fire is determined |
| with the following formula:                                            |                                                                       |
| AIMPT CHT DF+ADD-W-1 DF CORR+GFT                                       |                                                                       |
| DF CORR+AN-2 DFT=M898 DF                                               |                                                                       |
| 11                                                                     | The computer determines the QE to fire.  The QE to fire is determined |
| with the following formula:                                            |                                                                       |
|                                                                        |                                                                       |
| AN-2 QE+ADD-W-1 QE CORR=M898 QE                                        |                                                                       |
| 13-81                                                                  |                                                                       |
|  AN-2 AIMPOINT DATA                                                                                                  |
|----------------------------------------------------------------------------------------------------------------------|
|                                                                                                                     |
| L9      (3269)                                                                                                       |
|                                                                                                                      |
| 464                                                                                                                  |
|                                                                                                                     |
| +9        241        (250)                                                                                           |
| SADARM AIMPOINT DATA                                   -1.8      13.5                     L                          |
|                                                                                                                     |
| 3269                                                   + 161         41                                              |
| 1                                                                                                                    |
| 12     SAD                                                                                                           |
| DRIFT (L4) + GFT (L5) =                                                                                              |
| ADD-W-1, TBL B, COL 2                 TBL A, COL 8                                                      TBL A, COL 2 |

## Section Ii Manual Computation Of Safety Data

          Minimum and maximum quadrant elevations, deflection limits, and minimum fuze settings must be computed to ensure that all rounds fired impact or function in the target area.  These data are presented and arranged in a logical manner on a safety T.  This section describes the manual computation of safety data by use of tabular and graphical equipment.  As stated earlier, the range officer gives the OIC the lateral safety limits and the minimum and maximum ranges of the target areas.  These data must be converted to fuze settings, deflections, and quadrants.  The computations discussed in this section should be done by two safety-certified personnel working independently.

## 15-4. Manual Computational Procedures

Manual safety computations are accomplished in four steps, beginning with receipt of the range safety card and ultimately ending with the production of the safety T.  These steps are listed in Table 15-1.

STEP
ACTION
1
Receive the Range Safety Card (Produced by unit or from Range Control).
2
Construct the Safety Diagram in accordance with Table 15-2.
3
Construct and complete the computation matrix using Figure 15-3 for Low Angle
Safety and Figure 15-12 for High Angle Safety.
4
Construct the Safety T and disseminate in accordance with unit SOP

NOTE:  Figures 15-16 and 15-17 are reproducible safety computation forms

## 15-5.  Safety Card

A Range Safety Card (Figure 15-1), which prescribes the hours of firing, the area where the firing will take place, the location of the firing position, limits of the target area (in accordance with AR 385-63/MCO P3570) and other pertinent data is approved by the range officer and sent to the OIC of firing.  The OIC of firing gives a copy of the safety card to the position safety officer, who constructs the safety diagram based on the prescribed limits.

NOTE:  The range safety card depicted in Figure 15-1 is used for all safety computation examples in this chapter.

## Range Safety Card

Unit/STR     K 3/11
ScheduledDateIn     5/30/98
ScheduledDate Out     5/30/98
TimeIn
       7:
TimeOut
           23:59
Firing Point  185       (626     411)     HT   37.
Impact Area     S. CARLTON AREA
Weapon         M198   (155)       Ammunition  M17, M11, M116, M825, M485, M557, M582, M732,M577
Type of Fire    LOW ANGLE: HE, WP, M825, ILA, M116
Type of Fire    HIGH ANGLE: HE, M825, ILA Direction Limits:(Ref GN):
Left
134 MILS
Right
19 MILS
Low Angle PD Minimum Range
39 METERS
Min Charge 3GB
Fuze TI and High Angle Minimum Range
4 METERS
Min Charge 3GB
To Establish MIN Time for Fuze VT Apply +5.5 seconds to the Low Angle PD Min Rg Maximum Range to Impact
62 METERS
Max Charge 4GB

## Comments

From AZ 134 TO AZ 15 MAXIMUM RANGE IS 57

## Special Instructions 1.  Shell Illumination (All Calibers)

A.  MAX QE WILL NOT EXCEED QE FOR MAXIMUM RANGE TO IMPACT B.  ONE INITIAL ILLUMINATION CHECK ROUND WILL BE FIRED TO INSURE ILLUMINATION FLARE REMAINS IN IMPACT AREA C.  IF INITIAL ILLUMINATION FLARE DOES NOT LAND IN IMPACT AREA, NO FURTHER ILLUMINATION WILL BE FIRED AT THAT DF AND QE. D.  INSURE THAT ALL SUCCEEDING ROUNDS ARE FIRED AT A HOB SUFFICIENT TO PROVIDE COMPLETE BURNOUT BEFORE REACHING THE GROUND. E.  FOR 155MM HOWITZER, CHARGE 7 NOT AUTHORIZED WHEN FIRING PROJ ILLUM , M485.
UNCLEARED AMMUNITION(FUZES, PROJECTILES, POWDER) WILL NOT BE USED

## Figure 15-1.  Example Of A Range Safety Card 15-6.  Basic Safety Diagram

          a.  The FDO, on receipt of the safety card, constructs a basic safety diagram.  The basic safety diagram is a graphical portrayal of the data on the safety card or is determined from the surface danger zone (AR 385-63, Chapter 11) and need not be drawn to scale.  Shown on the basic safety diagram are the minimum and maximum range lines; the left, right, and intermediate (if any) azimuth limits; the deflections corresponding to the azimuth limits; and the azimuth of lay.

Table 15-2.  Construction of a Basic Safety Diagram.
STEP
ACTION

1
      On the top third of a sheet of paper, draw a line representing the AOL for the firing
      unit.  Label this line with its azimuth and the common deflection for the weapon
      system.
      NOTE:  If the AOL is not provided, use the following procedures to determine it:
      Subtract the maximum left azimuth limit from the maximum right azimuth limit.  Divide
      this value by two, add the result to the maximum left azimuth limit, and express the
      result to the nearest 100 mils.  Expressing to the nearest 100 mils makes it easier for
      the aiming circle operator to lay the howitzers.

| 2                                                                                      | Draw lines representing the lateral limits in proper relation to the AOL.  Label these   |
|----------------------------------------------------------------------------------------|------------------------------------------------------------------------------------------|
| lines with the corresponding azimuth from the range safety card.                       |                                                                                          |
| 3                                                                                      | Draw lines between these lateral limits to represent the minimum and maximum             |
| ranges.  Label these lines with the corresponding ranges from the range safety card.   |                                                                                          |
| These are the                                                                          |                                                                                          |
| Diagram Ranges.                                                                        |                                                                                          |
| NOTE:                                                                                  |                                                                                          |
| If the minimum range for fuze time is different from the minimum range, draw           |                                                                                          |
| a dashed line between the lateral limits to represent the minimum range for fuze time. |                                                                                          |
| Label this line with the corresponding range from the range safety card.  This is the  |                                                                                          |
| minimum time                                                                           |                                                                                          |
| Diagram Range.                                                                         |                                                                                          |
| 4                                                                                      | Compute the angular measurements from the AOL to each lateral limit.  On the             |
| diagram, draw arrows indicating the angular measurements and label them.               |                                                                                          |

5
Apply the angular measurements to the deflection corresponding to the AOL
(Common Deflection) and record the result.  This will be added to the *Drift* and GFT
Deflection Correction determined in the Safety Matrices to produce the Deflection
Limits on the Safety T.  (Note:  If no GFT Deflection Correction has been
determined, then the Deflection Limits = Drift + Diagram Deflection.  If a GFT setting has been determined, then the Deflection Limits = Drift + GFT Deflection
Correction + Diagram Deflection). Drift is applied to the Basic Safety Diagram by
following the "least left, most right" rule.  The lowest (least) drift is applied to all left deflection limits, and the highest (greatest) drift is applied to all right deflection limits.

| 6                                                                                           |
|---------------------------------------------------------------------------------------------|
| point location (grid and altitude), charge, shell, fuze, angle of fire, and azimuth of lay. |

           c.  When the basic safety diagram is complete, it will be constructed to scale, in red, on the firing chart.  Plot the firing point location as listed on the range safety card.  Using temporary azimuth indexes, an RDP, and a red pencil to draw the outline of the basic safety diagram.  To do this, first draw the azimuth limits to include doglegs.  Then, by holding the red pencil firmly against the RDP at the appropriate ranges, connect the azimuth lines.

          d.  Only after drawing the basic safety diagram on the firing chart may the base piece location be plotted and deflection indexes be constructed.  Should the diagram be drawn from the base piece location, it would be invalid unless the base piece was located over the firing point marker.

          e.  After the basic safety diagram has been drawn on a sheet of paper and on the firing chart, it is drawn on a map of the impact area using an RDP and a pencil.  These limits must be drawn accurately, because they will be used to determine altitudes for vertical intervals. Determine the maximum altitude along the minimum range line.  This is used to ensure that the quadrant fired will cause the round to clear the highest point along the minimum range line and impact (function) within the impact area.  At the maximum range, select the minimum altitude to ensure that the round will not clear the lowest point along the maximum range.  Once the altitudes have been selected, label the basic safety diagram with the altitudes for the given ranges.

NOTE:  The rule for determining the correct altitude for safety purposes is called the mini-max rule.  At the minimum range, select the maximum altitude; at the maximum range, select the minimum altitude.  If the contour interval is in feet, use either the GST or divide feet by 3.28 to determine the altitude in meters.   (Feet  3.28 = Meters)  This rule applies to both manual and automated procedures.

## 15-7.  Computation Of Low Angle Safety Data

          Use the steps outlined in Table 15-3 and in the matrix in Figure 15-3 as examples for organizing computations.  The Low Angle Safety Matrix is used for all munitions except M712 CLGP (Copperhead).  Paragraph 15-13 describes M712 safety computations.  The data are determined by either graphical or tabular firing tables.  In the case of expelling charge munitions, the Safety Table located in the Firing Tables or Firing Table Addendums is utilized to determine Elevation, Time of Flight, Fuze Setting, and Drift.  (Note: the Safey Tables used for computing the examples in this chapter are located after the Illum and M825 Low Angle examples).  Use artillery expression for all computations except where noted.

STEP
ACTION
1
On the top third of a blank sheet of paper, construct the basic safety diagram
2
In the middle third of the sheet of paper, construct the Low Angle Safety Matrix
3
Record the *Diagram Ranges* from the basic safety diagram.
4
Record the *Charge* from the range safety card.

5
Enter the *Range Correction*, if required.  This range correction is only necessary if a
nonstandard condition exists and is not already accounted for in a GFT setting, such as correcting for the always heavier than standard White Phosphorous projectile.
See figure 2, paragraph (b) to determine range correction.  If a range correction is
required, it is expressed to the nearest 10 meters.  If no range correction is
required, enter 0 (zero).
6
Determine the *Total Range*.  Total range is the sum of the Diagram Range and the
Range Correction.  **Total Range is expressed to the nearest 10 meters**.
7
Enter the *Range K*.  Range K is only required if a GFT setting has been obtained but
cannot be applied to a GFT (i.e., determining Illumination safety with a HE GFT setting).  Range K is simply the Total Range Correction from the GFT setting expressed as a percentage.  This percentage, when multiplied by the Total Range,
produces the Entry Range.  If no GFT setting is available (i.e., pre-occupation
safety), then enter 1.0000 as the Range K.  If a GFT setting is available, (i.e., post occupation safety), then enter the Range K expressed to four decimal places
(i.e., 1.1234).  Step 7a demonstrates how to compute Range K.
7a
Divide Range ~ Adjusted Elevation by the Achieved Range from the GFT setting to
determine Range K: Range ~ Adjusted Elevation       =     Range K, expressed to four decimal places.
     Achieved Range
8
Determine the *Entry Range*.  Multiply the Total Range times Range K to determine the
Entry Range. If Range K is 1.0000, then the Entry Range will be identical to the Total
Range.  **Entry Range is expressed to the nearest 10 meters**.
9
Following the Mini-Max rule, determine the *Vertical Interval* by subtracting the unit
altitude from the altitude corresponding to the Diagram Range, and record it. (Note:
Diagram Range is used for computations of VI and Site because this is the actual location of the minimum range line.  VI is not computed for minimum time range lines. The Range Correction, Total Range, and Range K are used to compensate for nonstandard conditions, and represent the aimpoint which must be used to cause the
round to cross the Diagram Range.)  VI is expressed to the nearest whole meter.

| 10                                                                                      | Compute and record                                |
|-----------------------------------------------------------------------------------------|---------------------------------------------------|
| Site                                                                                    |                                                   |
| to the Diagram Range.  Use the GST from the head of the                                 |                                                   |
| projectile family whenever possible.                                                    |                                                   |
| Site is expressed to the nearest whole mil.                                             |                                                   |
| 11                                                                                      | Determine the                                     |
| Elevation                                                                               |                                                   |
| from Table C (base ejecting) or TFT/GFT (bursting), and                                 |                                                   |
| record it.  (Note:  GFT Settings are not used to determine Elevation, as Range K        |                                                   |
| represents total corrections, and to use a GFT setting would double the effects of      |                                                   |
| those corrections                                                                       |                                                   |
| ).  Elevation is expressed to the nearest whole mil                                     |                                                   |
| .                                                                                       |                                                   |
| 12                                                                                      | Compute the                                       |
| Quadrant Elevation                                                                      |                                                   |
| and record it.  Quadrant Elevation is the sum of                                        |                                                   |
| Elevation and Site.                                                                     |                                                   |
| Quadrant Elevation is expressed to the nearest whole mil.                               |                                                   |
| 13                                                                                      | Determine and record the minimum fuze setting for |
| M564/M565                                                                               |                                                   |
| fuzes.  These fuze                                                                      |                                                   |
| settings correspond to the Entry Range and are extracted from Table C (base ejecting)   |                                                   |
| or TFT/GFT.  (                                                                          |                                                   |
| Note                                                                                    |                                                   |
| :  Minimum Fuze Settings are only determined for minimum range                          |                                                   |
| lines, and may be computed for separate minimum fuze range lines).                      |                                                   |
| Fuze Settings                                                                           |                                                   |
| are expressed to the nearest tenth of a fuze setting increment.                         |                                                   |
| 14                                                                                      | Determine and record the minimum fuze setting for |
| M582/M577                                                                               |                                                   |
| fuzes.  These fuze                                                                      |                                                   |
| settings correspond to the Entry Range and are extracted from Table C (base ejecting)   |                                                   |
| or TFT/GFT.  (                                                                          |                                                   |
| Note                                                                                    |                                                   |
| :  Minimum Fuze Settings are only determined for minimum range                          |                                                   |
| lines, and may be computed for separate minimum fuze range lines).                      |                                                   |
| Fuze Settings                                                                           |                                                   |
| are expressed to the nearest tenth of a second.                                         |                                                   |
| 15                                                                                      | Determine and record the                          |
| Time of Flight                                                                          |                                                   |
| corresponding to the entry range from Table                                             |                                                   |
| C, (base ejecting) or TFT/GFT.                                                          |                                                   |
| Time of Flight is expressed to the nearest tenth of                                     |                                                   |
| a second.                                                                               |                                                   |
| 16                                                                                      | Determine the minimum fuze setting for            |
| M728/M732                                                                               |                                                   |
| fuzes.  Add 5.5 seconds to the                                                          |                                                   |
| time of flight, and express to the next higher whole second. The VT fuze is designed to |                                                   |
| arm 3.0 seconds before the time set.  They have been known to arm up to 5.5             |                                                   |
| seconds before the time set.  That is why this value is added and always expressed up   |                                                   |
| to the next whole second. (                                                             |                                                   |
| Note                                                                                    |                                                   |
| :  Minimum Fuze Settings are only determined for                                        |                                                   |

minimum range lines, and may be computed for separate minimum fuze range lines).

VT Fuze Settings are expressed up to the next higher whole second.

17
Determine and record *Drift* corresponding to the Entry Range from Table C (base
ejecting) or TFT/GFT.  Drift is applied to the Basic Safety Diagram by following the "least left, most right" rule.  The lowest (least) drift is applied to all left deflection limits,
and the highest (greatest) drift is applied to all right deflection limits.  Drift is
expressed to the nearest whole mil.
18
Ensure computations are verified by a second safety-certified person.
19
On the bottom third of the sheet of paper, record the data on the safety T.
(a)                     (b)            (c)        (d)           (e)        (f)    (g)  (h)     (i)       (j)           (k)          (l)         (m)        (n)         (o)         (p) DIAGRAM         RG           TOT      RG       ENTRY                                                 M564/    M582                               M728/ RG              +    CORR   =  RG   x  K     =   RG        CHG  VI   SI  +  EL  =  QE      M565     M577      TOF   +  5.5  =   M732     DFT
(a)   This is the minimum or maximum range from the range safety diagram. (b)   This is the range correction for nonstandard conditions from Table F, if required. This is typically for preoccupation safety or corrections for nonstandard conditions not included in the Range K factor in column (d), such as WP [] weight.  Examples of nonstandard conditions accounted for in (b)  include, but are not limited to, difference in projectile square weight, difference in muzzle velocity, or any nonstandard condition accounted for prior to determining a Range K factor.  If there is no change from standard, or all nonstandard conditions are accounted for in the Range K factor, this value is zero (0). To determine a range correction from Table F, use the following formula: NONSTANDARD      STANDARD         CHANGE IN       RG CORR     RANGE RANGE   CHG   CONDITION          -  CONDITION    =   STANDARD   x  FACTOR  =  CORRECTION (c)   This is the sum of the Diagram Range and the Range Correction.  If there is no range correction, then the Total Range will be the same as the Diagram Range. (d)   This is the Range K factor determined by using Technique 2, Appendix F, Page F-5 in the FM 6-40/MCWP 3-16.4. This is for post occupation safety. It  represents total corrections for a registration, MET + VE,  or other subsequent MET technique. It represents all nonstandard  conditions (unless a separate nonstandard condition such as change in square weight for WP is listed separately in column (b)).   It is multiplied times the Total Range to determine Entry Range.   If there is no Range K, enter 1.0000.


(e)   This is the sum of the Total Range times the Range K factor.  If there is no Range K factor, then the Entry Range will be the same as the Total Range. Entry Range is the range to which Elevation is determined. (f)    This is the charge from the range safety card for this set of safety computations. (g)   This is the Vertical Interval from the range safety diagram. (h)   This is the site determined to the Diagram Range by using the GST or TFT from the head of the projectile family; e.g., site for
        the  M110 WP projectile is determined with the AM-2, M825 site is computed using the AN-2.  Site is computed to the Diagram  Range, as that is where the Vertical Intervals are determined.* (i)    This is the elevation from Table C (base ejecting), or GFT/TFT (bursting).* (j)    This is the sum of Elevation and Site. It is the minimum or maximum Quadrant Elevation corresponding to the Minimum or Maximum Range. (k)   This is the Minimum Fuze Setting for the M564/565 fuze from Table C (base ejecting), or GFT/TFT (bursting), corresponding to the Entry  Range. */** (l)    This is the Minimum Fuze Setting for the M582/M577 fuze from Table C (base ejecting), or GFT/TFT (bursting), corresponding to the Entry  range. */** (Note, this also applies to the M762, M767, and MOFA fuzes) (m)  This is the Time Of Flight from Table C (base ejecting), or GFT/TFT (bursting), corresponding to the Entry Range. */** (n)   This is the safety factor applied to the Time of Flight to determine VT fuze data.  ** (o)   This is the sum of TOF + 5.5.  It is the Minimum Fuze Setting for M728/M732 VT fuzes. **
* - See Table 15-4 to determine the correct source table or addendum for computations. ** - Computed only for minimum Entry Ranges, and only if applicable to the ammunition and the range safety card.

4[] HE/SMK (M116) LOW ANGLE CHG 4GB

DIAGRAM         RG          TOT         RG        ENTRY                                                 M564/    M582                              M728/
RG              +    CORR  =  RG     x    K       = RG       CHG   VI   SI   +  EL  =  QE      M565     M577    TOF   +  5.5  =   M732    DFT
3900
               +       0       =  3900  x  1.0000  = 3900    4GB  +23  +6   +  225  =  231       --          13.7         /  19.2        ~  20.0       L4


4000
                  +       0        =  4000  x  1.0000  = 4000    4GB    --   --
                                                                                                               --         --           --          14.1              --                  --          --

| 5700                                                                          |    +       0       =  5700  x  1.0000  = 5700    4GB  -15  -3     + 362  =     |
|-------------------------------------------------------------------------------|--------------------------------------------------------------------------------|
| 359                                                                           |                                                                                |
| --           --                  --                 --          --            |                                                                                |
| 6200                                                                          | +       0       =  6200  x  1.0000  = 6200    4GB  -25  -5     + 408  =        |
| 403                                                                           |                                                                                |
| --           --                  --                  --       L9              |                                                                                |
| WP (M110, Weight Unknown) Low Angle Chg 4GB                                   |                                                                                |
| Determining Range Correction for [] Weight Unknown Projectile                 |                                                                                |
| NONSTANDARD    STANDARD      CHANGE IN                                        | RG CORR    RANGE                                                               |
| RANGE   CHG                                                                   | CONDITION         -  CONDITION  =  STANDARD         x                          |
| 3900         4GB            8[]                   -      4[]              =   | I 4[]                                                                          |
| 4000         4GB            8[]                     -      4[]              = | I 4[]                 x          +28        =  +112 ~ +110                     |

DIAGRAM         RG          TOT         RG        ENTRY                                                 M564/    M582                              M728/
RG              +    CORR  =  RG     x    K       = RG       CHG   VI   SI   +  EL  =  QE      M565     M577    TOF   +  5.5  =   M732    DFT
3900
                +  (+110)   = 4010  x  1.0000   = 4010    4GB  +23 (+6)  + 232 =  238        --           --                   --              --            --

4000            +  (+110)   = 4110  x  1.0000   = 4110    4GB    --     --         --        --          --         14.6                 --             --             --

## 15-8.  Safety T

         a.  The safety T is a convenient method of arranging safety data and is used to verify the safety of fire commands (Figure 15-5).  The information needed by the FDO, XO, or platoon leader, and section chief is organized in an easy to read format.  The safety T is labeled with a minimum of firing point location, charge, projectiles(s), fuze(s), angle of fire, and AOL.  Other optional entries are subject to unit SOP.  Any time new safety data are determined, new safety Ts are constructed and issued only after the old safety Ts have been collected (that is, after a move or after a registration or MET + VE).  Use only one charge per Safety T.  (**Note**:  The examples in this demonstrate which data is transferred from the Safety Matrix to the Safety Tee.  This data is in bold type in the matrix and the associated safety T).

          b.  It is the FDO's responsibility to ensure that all data transmitted from the FDC is within the limits of the safety T.  It is the section chief's responsibility to ensure that all data applied to the ammunition or howitzer is within the limits of the safety T.  The FDO must ensure that deflection to fire is between the deflections listed on the safety T.  He then must determine if the quadrant elevation corresponding to that deflection is between the minimum and maximum QE on the safety T.  Finally, he must ensure that the fuze setting is equal to or greater than the minimum fuze setting listed on the safety T for the specific fuze type.

NOTE:  A reproducible copy of DA Form 7353-R (Universal Safety T) is included at the end of this manual, in the reproducible forms section.

MIN QE WP
238
MIN HE TI M582
14.1
MIN  WP TI M582
14.6
MIN VT M732
20.0
Firing Table Addendum
Weapon System
Safety Required for:
Base Projectile
Firing Table for Base Projectile
M101A1
M314
M444
HE HE
105-H-7 105-H-7
N/A ADD-B-2
M102/ M119
M314 M444
HE HE
105-AS-3 105-AS-3
N/A ADD-F-1 N/A ADD-I-2 ADD-R-1
ADD-J-2
ADD-T-0 w/ch1
ADD-Q-O w/ch1,2 ADD-T-0 w/ch1 ADD-Q-0 w/ch1,2 ADD-L-1 w/ch1,2 ADD-N-1 w/ch1 ADD-W-0
M198 or M109A3/A5/A6
M485 M449 M483A1 M483A1 M825
M825 M825A1 M825A1 M692/M731 M718/M741 M898
HE HE HE
DPICM
HE
DPICM HE DPICM DPICM DPICM DPICM
155-AM-2 155-AM-2 155-AM-2 155-AN-2 155-AM-2
155-AN-2 155-AN-2 155-AN-2 155-AN-2 155-AN-2 155-AN-2

## 15-9.  Updating Safety Data After Determining A Gft Setting

a.  After a GFT setting is determined (result of registration or MET + VE technique), the FDO must compute new safety data.  The GFT setting represents all nonstandard conditions in effect at the time the GFT setting was determined (Chapter 10 and 11 discuss Total Corrections in detail).  The effect on safety is that the data determined before the GFT setting was determined no longer represent the safety box, and could result in an unsafe condition if not applied to safety computations.  In order to update safety, new elevations are determined which correspond to the minimum and maximum ranges. Deflections are modified by applying the GFT deflection correction to each lateral limit.  Minimum fuze settings are also recomputed.  The basic safety diagram drawn in red on the firing chart **does not change.**  It was drawn on the basis of azimuths and ranges, and it represents the actual limits.

b.  There are two techniques which can be used to update safety computations:  The Range K Method and Applying a GFT setting to a GFT.  Both methods use the same safety matrices, and apply to both low and high angle fire.  The preferred technique for updating safety is to apply a GFT setting to the appropriate GFT.  Unfortunately, not all munitions have associated GFTs. Application of Total Corrections is the same as for normal mission processing. The Total Corrections, in the form of a GFT setting or Range K, must be applied in accordance with the data on which they were determined (i.e., the GFT setting for a HE registration applies to all projectiles in the HE family, while a MET + VE for DPICM would apply to all projectiles in the DPICM family).  If automation is available a false registration with M795 graze burst data may be used to determine total corrections for all projectiles in the DPICM family (see ST 6-40-2 for procedures).  The principle difference between the two techniques is the manner in which minimum fuze setting is determined.

               (1)  Determining Minimum Fuze Setting with a GFT with a GFT Setting Applied:
When a GFT setting is applied and a fuze setting is to be determined, it is extracted opposite the Time Gage Line (if it is the fuze listed on the GFT setting) or as a function of elevation (for all others).  Use the procedures in Table 15-5 to update safety using a GFT with a GFT setting applied.

               (2)  Determining Fuze Setting using the Range K Technique:  In order to simplify updating safety, the Range K technique determines all fuze settings as a function of elevation.  The difference between registered fuze settings and fuze settings determined using the Range K technique in actual firings and computer simulations varies by only zero to two tenths (0.0 - 0.2) of a Fuze Setting Increment/Second.  The safety requirements in the AR 385-63 and incorporation of Minimum Fuze Setting Range Lines adequately compensate for the difference in computational techniques. Figure 15-7 demonstrates how to update safety when no GFT is available, utilizing the Range K technique.  Use the procedures in Table 15-3 (Low Angle) or Table 15-8 (High Angle) to update safety using the Range K method.

| STEP                                                                    | ACTION                                                                                   |
|-------------------------------------------------------------------------|------------------------------------------------------------------------------------------|
| 1                                                                       | On the top third of a blank sheet of paper, construct the basic safety diagram in        |
| accordance with the range safety card.  (See Table 15-1 for procedures) |                                                                                          |
| 2                                                                       | In the middle third of the sheet of paper, construct the Low Angle Safety Matrix (Figure |
| 1).                                                                     |                                                                                          |
| 3                                                                       | Record the                                                                               |
| Diagram Ranges                                                          |                                                                                          |
| from the basic safety diagram.                                          |                                                                                          |
| 4                                                                       | Record the                                                                               |
| Charge                                                                  |                                                                                          |
| from the range safety card.                                             |                                                                                          |

5
Enter the *Range Correction*, if required.  This range correction is only necessary if a
nonstandard condition exists which requires a change in aimpoint and is not already
accounted for in a GFT setting, such as correcting for the always heavier than
standard White Phosphorous projectile.    See figure 2, paragraph (b) to determine
range correction.  If a range correction is required, it is artillery expressed to the
nearest 10 meters.  If no range correction is required, enter 0 (zero).

| 6                                                        |
|----------------------------------------------------------|
| Total Range                                              |
| .  Total range is the sum of the Diagram Range and the   |
| Range Correction.                                        |
| Total Range is expressed to the nearest 10 meters        |
| .                                                        |
| 7                                                        |
| Range K                                                  |
| .  This is                                               |
| not                                                      |
| used when determining data with a GFT with a GFT setting |
| applied, as the Elevation Gage line represents Range K.  |
| 8                                                        |
| Entry Range                                              |
| .  This value is the same as the Total Range.            |
| Entry Range is artillery                                 |
| expressed to the nearest 10 meters                       |
| .                                                        |

9
Following the Mini-Max rule, determine the *Vertical Interval* by subtracting the unit
altitude from the altitude corresponding to the Diagram Range, and record it.    (Note: Diagram Range is used for computations of VI and Site because this is the actual location of the minimum range line.  VI is not determined for minimum fuze range lines.  The Range Correction, Total Range, and Range K are used to compensate for nonstandard conditions, and represent the aimpoint which must be used to cause the
round to cross the Diagram Range).  VI is artillery expressed to the nearest whole
meter.
10
Compute and record *Site* to the Diagram Range.  Use the GST from the head of the
projectile family whenever possible.  Site is artillery expressed to the nearest whole
mil.
11
Place the MHL on the Entry Range and determine the *Elevation*  from the Elevation
Gage Line on the GFT and record it.    Elevation is artillery expressed to the
nearest whole mil.
12
Compute the *Quadrant Elevation* and record it.  Quadrant Elevation is the sum of
Elevation and Site.  Quadrant Elevation is artillery expressed to the nearest whole
mil.
13
Using the procedures from Appendix G, determine and record the minimum fuze
setting for *M564/M565* fuzes.  These fuze settings correspond to the Entry Range.  If
the GFT Setting was determined using the M564/M565 fuze, then determine the fuze setting opposite the Time Gage Line.  If the GFT setting was not determined using the M564/M565 fuze, then extract the fuze setting corresponding to adjusted elevation.
(**Note**:  Minimum Fuze Settings are only determined for minimum range lines, and may
be computed for separate minimum fuze range lines).  Fuze Settings are artillery
expressed to the nearest tenth of a fuze setting increment.

| 14                                                                                              | Using the procedures from Appendix G, determine and record the minimum fuze   |
|-------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------|
| setting for                                                                                     |                                                                               |
| M582/M577                                                                                       |                                                                               |
| fuzes.  These fuze settings correspond to the Entry Range. If                                   |                                                                               |
| the GFT Setting was determined using the M582/M577 fuze, then determine the fuze                |                                                                               |
| setting opposite the Time Gage Line.  If the GFT setting was not determined using the           |                                                                               |
| M582/M577 fuze, then extract the fuze setting corresponding to adjusted elevation.              |                                                                               |
| (                                                                                               |                                                                               |
| Note                                                                                            |                                                                               |
| :  Minimum Fuze Settings are only determined for minimum range lines, and may                   |                                                                               |
| be computed for separate minimum fuze range lines).                                             |                                                                               |
| Fuze Settings are artillery                                                                     |                                                                               |
| expressed to the nearest tenth of a second.                                                     |                                                                               |
| 15                                                                                              | Using the procedures from Appendix G, determine and record the                |
| Time of Flight                                                                                  |                                                                               |
| corresponding to the Entry Range.  Extract the Time of Flight corresponding to                  |                                                                               |
| adjusted elevation from the TOF scale.                                                          |                                                                               |
| Time of Flight is artillery expressed to the                                                    |                                                                               |
| nearest tenth of a second.                                                                      |                                                                               |
| 16                                                                                              | Using the procedures in Appendix G, determine the minimum fuze setting for    |
| M728/M732                                                                                       |                                                                               |
| fuzes.  Add 5.5 seconds to the time of flight, and express to the next                          |                                                                               |
| higher whole second. (                                                                          |                                                                               |
| Note                                                                                            |                                                                               |
| :  Minimum Fuze Settings are only determined for                                                |                                                                               |
| minimum range lines, and may be computed for separate minimum fuze range lines).                |                                                                               |
| VT Fuze Settings are expressed up to the next higher whole second.                              |                                                                               |
| 17                                                                                              | Determine and record                                                          |
| Drift                                                                                           |                                                                               |
| corresponding to adjusted elevation.  Drift is applied to the                                   |                                                                               |
| Basic Safety Diagram by following the "least left, most right" rule.  The smallest (least)      |                                                                               |
| drift is applied to all left deflection limits, and the greatest (most) drift is applied to all |                                                                               |
| right deflection limits.                                                                        |                                                                               |
| Drift is artillery expressed to the nearest whole mil.                                          |                                                                               |
| 18                                                                                              | Ensure computations are verified by a second safety-certified person.         |
| 19                                                                                              | On the bottom third of the sheet of paper, record the data on the safety T.   |

DIAGRAM         RG          TOT         RG        ENTRY                                                 M564/    M582                              M728/ RG              +    CORR  =  RG     x    K       = RG       CHG   VI   SI   +  EL  =  QE      M565     M577    TOF   +  5.5  =   M732    DFT

| 3900                                                                          |    +      0       = 3900   x  1.0449 = 4080     4GB  +23  +6   + 238 =                          |
|-------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------------|
| 244                                                                           |                                                                                                 |
| --         14.5                /  20.0 ~                                      |                                                                                                 |
| 20.0                                                                          |                                                                                                 |
| L4                                                                            |                                                                                                 |
| 4000                                                                          | +      0         = 4000   x  1.0449 = 4180     4GB    --    --       --          --          -- |
| 14.8                                                                          |                                                                                                 |
| --             --            --                                               |                                                                                                 |
| 5700                                                                          | +      0       = 5700   x  1.0449 = 5960     4GB  -15   -3   + 386 =                            |
| 383                                                                           |                                                                                                 |
| --           --                   --              --           --             |                                                                                                 |
| 6200                                                                          | +      0       = 6200   x  1.0449 = 6480     4GB  -25   -5   + 436 =                            |
| 431                                                                           |                                                                                                 |
| --           --                   --              --        L10               |                                                                                                 |
| WP (M110, Weight Unknown) LOW ANGLE CHG 4GB                                   |                                                                                                 |
| Determining Range Correction for [] Weight Unknown Projectile                 |                                                                                                 |
| NONSTANDARD  STANDARD      CHANGE IN                                          | RG CORR    RANGE                                                                                |
| RANGE   CHG                                                                   | CONDITION         -  CONDITION  =  STANDARD       x                                             |
| 3900         4GB            8[]                   -      4[]              =   | I 4[]                                                                                           |
| 4000         4GB            8[]                     -     4[]               = | I 4[]                x           +28        =  +112 ~ +110                                      |

DIAGRAM         RG          TOT         RG        ENTRY                                                 M564/    M582                              M728/ RG              +    CORR  =  RG     x    K       = RG       CHG   VI   SI   +  EL  =  QE      M565     M577    TOF   +  5.5  =   M732    DFT
3900
   +   (+110)   = 4010    x 1.0449 = 4190     4GB  +23  (+6)  +  245 =  251      --           --                   --               --           --
4000           +   (+110)   = 4110    x 1.0449 = 4290     4GB     --     --         --         --        --        **15.3**                  --               --          --

MAX QE
383
431
DF
3309
3469
2915
MIN QE HE
244
251
MIN QE WP MIN HE TI (M582)
14.8
MIN  WP TI (M582)
15.3
MIN VT (M732)
20.0

             FP 185 (GRID 6026 4110 ALT 370) LOW ANGLE, M825, CHG 4GB, AOF 1600

## M825 Low Angle Chg 4Gb

DIAGRAM         RG          TOT         RG        ENTRY                                                 M564/    M582                              M728/ RG              +    CORR  =  RG     x    K       = RG       CHG   VI   SI   +  EL  =  QE      M565     M577    TOF   +  5.5  =   M732    DFT
3900
    +       0       =  3900  x  1.0000  = 3900    4GB  +23   +6  +  254  =   260      --          --
           --                --          L4

 4000
    +       0       =  4000  x  1.0000  = 4000    4GB    --      --
 --           --        --         **15.1**                --                --           --
5700
    +       0       =  5700  x  1.0000  = 5700    4GB   -15    -3  +  423  =  420       --         --                    --                --           --
6200
    +       0       =  6200  x  1.0000  = 6200    4GB   -25    -6  +  486  =  480       --         --                    --                --          L9
                   FP 185, M825 LOW ANGLE, CHG 4GB, AOL 1600
MAX QE
420
  480
DF
3464
3304
2909

## Ballistic Data For Safety Computations Ft Add-T-0 Projectile Improved Smoke M825 Projectile Family = Dpicm Explanation:

These tables contain ballistic data for safety computations.  They are not to be used for computation of firing data, as they do not account for submunition/payload delivery.  These tables are to be used in conjunction with Chapter 15 of the FM 6-40 for safety computations only.

## Table Data:

The tables are arranged by charge, as follows:

| CHARGE:               |   PAGE: |
|-----------------------|---------|
| 3G = Charge 3, M3A1   |       2 |
| 4G = Charge 4, M3A1   |       5 |
| 5G = Charge 5, M3A1   |       8 |
| 3W = Charge 3, M4A2   |      12 |
| 4W = Charge 4, M4A2   |      15 |
| 5W = Charge 5, M4A2   |      19 |
| 6W = Charge 6, M4A2   |      23 |
| 7W = Charge 7, M4A2   |      28 |
| 7R = Charge 7, M119A2 |      34 |

## Columnar Data: Column:

1.
Range - The distance, measured on the surface of a sphere concentric with the earth, from
the muzzle to a target at the level point.
2.
Elevation - The angle of the gun in the vertical plane required to reach the range
tabulated in column 1.  The maximum elevation shown represents the highest angle at which predictable projectile flight is possible under standard conditions of met and material.
3.
Fuze Setting M577 - Fuze setting for a graze burst - numbers to be set on the fuze,
MTSQ, M577 or ET, M762 that will produce a graze burst at the level point when firing under standard conditions.  This setting will produce a graze burst at the time of flight listed in column 4.
4.
Time of Flight - The projectile travel time, under standard conditions, from the muzzle to
the level point at the range in column 1.  Time of flight is used as fuze setting for fuze MTSQ M577 and fuze ET M762.
5.
Azimuth correction to compensate for Drift - Because of the right hand twist of the
tube, the drift of the projectile is to the right of the vertical plane of fire.  This drift must be compensated for by a correction to the left.

FT ADD-T-0 Projectile Improved Smoke M825
Projectile Family = DPICM
Charge 4G
Range
Elevation
Fuze Setting
Time of Flight
Drift
m
mil
M577
sec
mil
0
0.0
0.0
0.0
3800
246.4
14.2
14.2
3.9
3900
254.3
14.6
14.6
4.0
4000
262.3
15.1
15.1
4.2
4100
270.4
15.5
15.5
4.3
4200
278.6
16.0
16.0
4.4
4300
287.0
16.4
16.4
4.6
4400
295.5
16.9
16.9
4.8
4500
304.1
17.3
17.3
4.9
4600
312.9
17.8
17.8
5.1
4700
321.8
18.3
18.3
5.2
4800
330.9
18.8
18.8
5.4
4900
340.2
19.3
19.3
5.6
5000
349.7
19.8
19.8
5.8
5100
359.4
20.3
20.3
6.0
5200
369.3
20.8
20.8
6.2
5300
379.5
21.3
21.3
6.4
5400
389.9
21.9
21.9
6.6
5500
400.5
22.4
22.4
6.8
5600
411.5
23.0
23.0
7.0
5700
422.8
23.5
23.5
7.3
5800
434.5
24.1
24.1
7.5
5900
446.5
24.7
24.7
7.8
6000
459.0
25.4
25.4
8.1
6100
472.0
26.0
26.0
8.4
6200
485.5
26.7
26.7
8.7
6300
499.7
27.3
27.3
9.0
6400
514.6
28.1
28.1
9.4
6500
530.4
28.8
28.8
9.8
6600
547.3
29.6
29.6
10.2
6700
565.4
30.5
30.5
10.7
6800
585.2
31.4
31.4
11.2
6900
607.3
32.4
32.4
11.8
FT ADD-T-0 Projectile Improved Smoke M825
Projectile Family = DPICM
7000
632.5
33.5
33.5
12.5
7100
663.2
34.9
34.9
13.5
7200
705.5
36.7
36.7
14.9
************** ************
***************
**************** ************
7200
852.1
42.4
42.4
21.0
7100
894.3
44.0
44.0
23.2
7000
924.8
45.0
45.0
25.0
6900
950.0
45.9
45.9
26.6
6800
971.9
46.6
46.6
28.2
6700
991.6
47.2
47.2
29.7
6600
1009.7
47.8
47.8
31.2
6500
1026.4
48.3
48.3
32.6
6400
1042.1
48.7
48.7
34.1
6300
1056.9
49.2
49.2
35.6
6200
1071.0
49.6
49.6
37.2
6100
1084.4
49.9
49.9
38.7
6000
1097.3
50.3
50.3
40.3
5900
1109.7
50.6
50.6
42.0
5800
1121.6
50.9
50.9
43.7
5700
1133.2
51.2
51.2
45.6
5600
1144.3
51.5
51.5
47.5
5500
1155.2
51.8
51.8
49.5
5400
1165.7
52.1
52.1
51.7
5300
1175.9
52.3
52.3
54.0
5200
1185.9
52.5
52.5
56.6
5100
1195.6
52.8
52.8
59.3
5000
1205.1
53.0
53.0
62.3
4900
1214.3
53.2
53.2
65.6
4800
1223.3
53.4
53.4
69.3
4700
1232.1
53.6
53.6
73.4
4600
1240.7
53.8
53.8
78.1
4500
1249.1
54.0
54.0
83.4
4400
1257.2
54.2
54.2
89.4
4300
1265.2
54.4
54.4
96.4
4200
1272.9
54.6
54.6
104.5
4100
1280.4
54.8
54.8
113.9
4000
1287.7
55.0
55.0
124.9
3900
1294.7
55.2
55.2
138.0
3800
1301.5
55.4
55.4
153.3
3700
1308.0
55.6
55.6
171.2
3669
1310.0

## M825 Low Angle Chg 4Gb Diagram         Rg          Tot         Rg        Entry                                                 M564/    M582                              M728/ Rg              +    Corr  =  Rg     X    K       = Rg       Chg   Vi   Si   +  El  =  Qe      M565     M577    Tof   +  5.5  =   M732 Dft

| 3900                                                                  |    +       0       = 3900   x  1.0449  = 4080    4GB  +23  +6   +  269  =                     |
|-----------------------------------------------------------------------|-----------------------------------------------------------------------------------------------|
| 275                                                                   |                                                                                               |
| --           --                                                       | --               --           L4                                                              |
|                                                                       |                                                                                               |
| 4000                                                                  | +       0        = 4000   x  1.0449  = 4180    4GB    --    --       --        --          -- |
| 15.9                                                                  |                                                                                               |
| --                --            --                                    |                                                                                               |
| 5700                                                                  | +       0       = 5700   x  1.0449  = 5960    4GB  -15   -3   +  454  =                       |
| 451                                                                   |                                                                                               |
| --            --                   --                --            -- |                                                                                               |
| 6200                                                                  | +       0        = 6200   x  1.0449  = 6480    4GB  -25   -6   +  527  =                      |
| 521                                                                   |                                                                                               |
| --            --                   --                --         L10   |                                                                                               |

                                                                             FP 185 (GRID 6026 4110 ALT 370) LOW ANGLE, ILLUM, CHG 3GB, AOF 1600

| 3900                                                            |    +      0       = 3900    x  1.0000 = 3900    3GB  +23  +7   + 290  =  297        --          --                    --               --         L7   |
|-----------------------------------------------------------------|--------------------------------------------------------------------------------------------------------------------------------------------------------|
| 4000                                                            | +      0       = 4000    x  1.0000 = 4000    3GB    --    --    +   --   =    --         --                                                            |
| 16.2                                                            |                                                                                                                                                        |
| --               --       --                                    |                                                                                                                                                        |
| 5700                                                            | +      0        = 5700    x  1.0000 = 5700    3GB  -15   -4    + 497 =                                                                                 |
| 493                                                             |                                                                                                                                                        |
| --          --                     --               --       -- |                                                                                                                                                        |
| 6200                                                            | +      0       = 6200    x  1.0000 = 6200    3GB  -25   -7    + 587 =                                                                                  |
| 580                                                             |                                                                                                                                                        |
| --          --                     --               --      L16 |                                                                                                                                                        |

## Ballistic Data For Safety Computations Ft 155-Am-2 Projectile Illumination M485/M485A1/M485A2 Projectile Family = He Explanation:

These tables contain ballistic data for safety computations.  They are not to be used for computation of firing data, as they do not account for submunition/payload delivery.  These tables are to be used in conjunction with Chapter 15 of the FM 6-40 for safety computations only.

## Table Data:

The tables are arranged by charge, as follows:

| CHARGE:                    | PAGE:                             |
|----------------------------|-----------------------------------|
| 1G = Charge 1, M3A1        | 2  (Not applicable M198 howitzer) |
| 2G = Charge 2, M3A1        | 4                                 |
| 3G = Charge 3, M3A1        | 6                                 |
| 4G = Charge 4, M3A1        | 9                                 |
| 5G = Charge 5, M3A1        | 12                                |
| 3W = Charge 3, M4A2        | 16                                |
| 4W = Charge 4, M4A2        | 19                                |
| 5W = Charge 5, M4A2        | 23                                |
| 6W = Charge 6, M4A2        | 27                                |
| 7W = Charge 7, M4A2        | 32                                |
| 8 = Charge 8, M119, M119A1 | 38                                |

## Columnar Data: Column:

1.
Range - The distance, measured on the surface of a sphere concentric with the earth, from
the muzzle to a target at the level point.
2.
Elevation - The angle of the gun in the vertical plane required to reach the range
tabulated in column 1.  The maximum elevation shown represents the highest angle at
which predictable projectile flight is possible under standard conditions of met and material.
3.
Fuze Setting M565 - Fuze setting for a graze burst - numbers to be set on the fuze MT,
M565 that will produce a graze burst at the level point when firing under standard conditions.  This setting will produce a graze burst at the time of flight listed in column 4.
4.
Time of Flight - The projectile travel time, under standard conditions, from the muzzle to
the level point at the range in column 1.  Time of flight is used as fuze setting for fuzes MTSQ M577 and fuze ET M762.
5.
Azimuth correction to compensate for Drift - Because of the right hand twist of the
tube, the drift of the projectile is to the right of the vertical plane of fire.  This drift must be compensated for by a correction to the left.

Projectile Family = HE
| Range   | Elevation   | Fuze Setting   | Time of Flight   | Drift   |
|---------|-------------|----------------|------------------|---------|
| m       | mil         | M565           | sec              | mil     |
| 0       | 0.0         | 0.0            | 0.0              |         |
| 100     | 6.4         | 0.4            | 0.1              |         |
| 3800    | 280.9       | 15.1           | 15.2             | 6.5     |
| 3900    | 290.0       | 15.5           | 15.7             | 6.7     |
| 4000    | 299.4       | 16.0           | 16.2             | 7.0     |
| 4100    | 308.8       | 16.5           | 16.6             | 7.2     |
| 4200    | 318.5       | 17.0           | 17.1             | 7.5     |
| 4300    | 328.3       | 17.5           | 17.6             | 7.7     |
| 4400    | 338.4       | 18.0           | 18.1             | 8.0     |
| 4500    | 348.6       | 18.5           | 18.7             | 8.3     |
| 4600    | 359.1       | 19.0           | 19.2             | 8.6     |
| 4700    | 369.8       | 19.5           | 19.7             | 8.9     |
| 4800    | 380.8       | 20.1           | 20.3             | 9.2     |
| 4900    | 392.0       | 20.6           | 20.8             | 9.5     |
| 5000    | 403.6       | 21.2           | 21.4             | 9.8     |
| 5100    | 415.5       | 21.8           | 21.9             | 10.1    |
| 5200    | 427.8       | 22.3           | 22.5             | 10.5    |
| 5300    | 440.5       | 23.0           | 23.2             | 10.9    |
| 5400    | 453.7       | 23.6           | 23.8             | 11.3    |
| 5500    | 467.4       | 24.2           | 24.4             | 11.7    |
| 5600    | 481.7       | 24.9           | 25.1             | 12.1    |
| 5700    | 496.7       | 25.6           | 25.8             | 12.6    |
| 5800    | 512.4       | 26.3           | 26.5             | 13.1    |
| 5900    | 529.1       | 27.1           | 27.3             | 13.6    |
| 6000    | 547.0       | 27.9           | 28.1             | 14.2    |
| 6100    | 566.2       | 28.7           | 28.9             | 14.9    |
| 6200    | 587.3       | 29.6           | 29.9             | 15.6    |
| 6300    | 610.9       | 30.6           | 30.9             | 16.5    |
| 6400    | 638.3       | 31.8           | 32.1             | 17.5    |

FT 155-AM-2 Projectile Illumination M485/M485A1/M485A2
Projectile Family = HE

| Range                                                                      | Elevation   | Fuze Setting   | Time of Flight   | Drift   |
|----------------------------------------------------------------------------|-------------|----------------|------------------|---------|
| m                                                                          | mil         | M565           | sec              | mil     |
| 6500                                                                       | 672.1       | 33.2           | 33.5             | 18.8    |
| 6600                                                                       | 722.3       | 35.2           | 35.5             | 21.0    |
| ************* ************ ***************** **************** ************ |             |                |                  |         |
| 6600                                                                       | 842.7       | 39.7           | 40.0             | 27.1    |
| 6500                                                                       | 892.6       | 41.4           | 41.7             | 30.2    |
| 6400                                                                       | 926.2       | 42.5           | 42.8             | 32.5    |
| 6300                                                                       | 953.2       | 43.4           | 43.7             | 34.5    |
| 6200                                                                       | 976.6       | 44.1           | 44.4             | 36.5    |
| 6100                                                                       | 997.4       | 44.7           | 45.0             | 38.3    |
| 6000                                                                       | 1016.4      | 45.2           | 45.6             | 40.1    |
| 5900                                                                       | 1033.9      | 45.7           | 46.1             | 42.0    |
| 5800                                                                       | 1050.3      | 46.2           | 46.5             | 43.8    |
| 5700                                                                       | 1065.8      | 46.6           | 47.0             | 45.6    |
| 5600                                                                       | 1080.4      | 47.0           | 47.3             | 47.5    |
| 5500                                                                       | 1094.4      | 47.4           | 47.7             | 49.5    |
| 5400                                                                       | 1107.7      | 47.7           | 48.0             | 51.5    |
| 5300                                                                       | 1120.6      | 48.0           | 48.4             | 53.6    |
| 5200                                                                       | 1132.9      | 48.3           | 48.7             | 55.8    |
| 5100                                                                       | 1144.8      | 48.6           | 48.9             | 58.2    |
| 5000                                                                       | 1156.2      | 48.9           | 49.2             | 60.7    |
| 4900                                                                       | 1167.3      | 49.1           | 49.5             | 63.4    |
| 4800                                                                       | 1178.1      | 49.3           | 49.7             | 66.3    |
| 4700                                                                       | 1188.5      | 49.6           | 49.9             | 69.4    |
| 4600                                                                       | 1198.6      | 49.8           | 50.2             | 72.9    |
| 4500                                                                       | 1208.4      | 50.0           | 50.4             | 76.7    |
| 4400                                                                       | 1217.9      | 50.2           | 50.6             | 81.0    |
| 4300                                                                       | 1227.1      | 50.4           | 50.8             | 85.8    |
| 4200                                                                       | 1236.0      | 50.6           | 51.0             | 91.3    |
| 4100                                                                       | 1244.7      | 50.8           | 51.2             | 97.5    |
| 4000                                                                       | 1253.0      | 51.0           | 51.3             | 104.8   |
| 3900                                                                       | 1261.1      | 51.2           | 51.5             | 113.1   |
| 3800                                                                       | 1268.8      | 51.3           | 51.7             | 123.0   |

## 15-10.  Determination Of Maximum Effective Illumination Area

           All illumination safety data are for graze burst.  Therefore, when illumination fire mission data are computed, the QE determined includes the appropriate HOB.  This will prevent achieving a 600 meter HOB (750 meter HOB for 105 mm) at the minimum and maximum range lines.  Before processing illumination fire mission, it is beneficial to determine the maximum effective illumination area for the current range safety card.  This area should be plotted on the firing chart to help determine if illumination can be fired and to let the Forward Observers know where they can fire illumination effectively.  This area will always be significantly smaller than the HE safety area.  See Table 15-6 for steps outlining the general procedure. This area can be increased by computing High Angle data.

NOTE:  The procedures used to determine the Maximum Effective Illumination Area can be used to for all expelling charge munitions to depict their Maximum Effective Engagement Area.

| STEP                                                                                           | ACTION                                                                                    |
|------------------------------------------------------------------------------------------------|-------------------------------------------------------------------------------------------|
| 1                                                                                              | Enter the TFT, Part 2, Column 7 (RTI) with the nearest range listed without exceeding the |
| maximum range.                                                                                 |                                                                                           |
| 2                                                                                              | Determine the corresponding range to target in column 1.  This is the maximum range the   |
| unit can achieve a 600 meter (155mm) HOB and keep the projectile in the safety box if the      |                                                                                           |
| fuze fails to function.                                                                        |                                                                                           |
| 3                                                                                              | Determine the minimum range for which a 600 meter (155 mm) HOB is achieved and have       |
| the fuze function no earlier than the minimum range line.  Enter the TFT, Part 2, Column 3,    |                                                                                           |
| with the nearest listed FS that is not less than the determined minimum FS.  Column 3 is the   |                                                                                           |
| Fuze Setting for the M565 Fuze, so if M577 is to be used, the fuze setting must be corrected   |                                                                                           |
| by using Table B.  Determine the corresponding range to target in Column 1.                    |                                                                                           |
| 4                                                                                              | The area between these two lines is the maximum effective illumination area where a 600   |
| meter HOB (155mm) is achieved, the fuze functions no earlier than the minimum range line,      |                                                                                           |
| and the round does not exceed the maximum range line if the fuze fails to function.            |                                                                                           |
| Note:                                                                                          |                                                                                           |
| High Angle fire produces a much greater effective illumination area.  The FDO must             |                                                                                           |
| use Column 6,  Range to Fuze Function, to determine the minimum effective illumination         |                                                                                           |
| range line.  The maximum effective illumination range line is determined by using fuze setting |                                                                                           |
| corresponding to Column 7, Range to Impact.                                                    |                                                                                           |

## 15-11.  Safety Considerations For M549/M549A1 Rap

          RAP safety data are computed using the Low Angle Safety or High Angle Safety matrix, as appropriate.  The only difference is that a safety buffer must be incorporated for rocket failure or rocket cap burn through.  For firing in the Rocket-Off Mode, a 6000 meter buffer must be constructed beyond the maximum range line to preclude the projectile exceeding the maximum range line.  For firing in the Rocket-On Mode, a 6000 meter buffer must be constructed short of the minimum range line to preclude the projectile falling short of the minimum range line.

## 15-12.  Safety Considerations For M864 Base Burn Dpicm/M795A1 Base Burn He

          Base Burn safety data are computed using the Low Angle Safety or High Angle Safety matrix, as appropriate.  The only difference is that a safety buffer must be incorporated for Base Burn Element Failure.  A 5000 meter buffer must be constructed short of the minimum range line to preclude the projectile falling short of the minimum range line.

## 15-13.  Safety Procedures For M712 Copperhead

          a.  Copperhead safety data are determined from ballistic data developed specifically for the Copperhead projectile.  Computations are much like those for normal projectiles.  The Copperhead round should never be fired with standard data.  Therefore, the computation of safety data requires the solving of a Copperhead Met to Target technique for each listed range using the FT 155-AS-1, as covered in Chapter 13, Section 1.  See Table 15-7 for steps to compute Copperhead safety.  Surface Danger Zones (SDZs) for shell Copperhead are significantly different than normal indirect fire SDZs.  AR 385-63 (MCO P3570), chapter 11, contains the SDZs for Copperhead.

           b.  All ranges listed on the range safety card may not fall within the ranges listed in the TFT charge selection table for that charge and mode.  Therefore, additional safety computations may be required for additional charge(s) and mode(s) to adequately cover the impact area.  If ranges listed on the range safety card overlap charge and mode range limitations in the charge selection table, then safety for both affected charges and modes must be computed.

|   STEP | ACTION                              |
|--------|-------------------------------------|
|      1 | Construct the basic safety diagram. |

2
For low angle, circle the lower left hand corner of the safety diagram.  Proceed in a clockwise
manner, and circle every other corner.  For high angle, start in the lower right hand corner and circle every other corner in a clockwise manner.
3
Complete a Copperhead Met to Target technique for each circled corner.  Record the FS,
deflection, and QE in the safety T.  The lower left hand corner will provide the minimum FS,
maximum left deflection, and minimum QE.  The upper right hand corner will provide the
maximum right deflection and maximum QE.  Intermediate deflections and ranges will
provide intermediate deflection limits.

## 15-14.  Computation Of High Angle Safety

          a.  The safety data for high angle fire is computed in much the same manner as that for low angle fire except for the ballistic variations caused by the high trajectory.  Site is computed differently (by using the 10 mil Site Factor and the Angle of Site/10), and mechanical or electronic fuze settings are not determined.  (**Note**:  It is the FDO's responsibility to ensure that all High Angle Fuze Settings will cause the fuze to function within the safety box).  Table 15-8 contains the steps required for computation of High Angle Safety.

          b. Use the steps outlined in Table 15-8 and in the matrix in Figure 15-12 as examples for organizing computations.  The High Angle Safety Matrix is used for all munitions except M712
CLGP (Copperhead).  The data are determined by either graphical or tabular firing tables.  In the case of expelling charge munitions, the Safety Table located in the Firing Tables or Firing Table Addendums is utilized to determine Elevation, Time of Flight, Fuze Setting, and Drift.  (**Note**:
The Safety Tables which are used to compute the High Angle examples are located after the Low Angle Safety examples).  Use artillery expression for all computations except where noted.

Table 15-8.   High Angle Procedures
STEP
ACTION
1
On the top third of a blank sheet of paper, construct the basic safety diagram in
accordance with the range safety card. (See Table 15-1 for procedures)
2
In the middle third of the sheet of paper, construct the High Angle Safety Matrix
(Figure 2)
3
Record the *Diagram Ranges* from the basic safety diagram.
4
Record the *Charge* from the range safety card.
5
Enter the *Range Correction*, if required.  This range correction is only necessary if a
nonstandard condition exists which requires a change in aimpoint and is not already accounted for in a GFT setting, such as correcting for the always heavier than standard White Phosphorous projectile.    See figure 2, paragraph (b) to determine
range correction.  If a range correction is required, it is artillery expressed to
the nearest 10 meters.  If no range correction is required, enter 0 (zero).
6
Determine the *Total Range*.  Total range is the sum of the Diagram Range and the
Range Correction.  **Total Range is expressed to the nearest 10 meters**.
7
Enter the *Range K*.  Range K is only required if a GFT setting has been obtained but
cannot be applied to a GFT (i.e., determining Illumination safety with a HE GFT setting).  Range K is simply the Total Range Correction from the GFT setting expressed as a percentage.  This percentage, when multiplied by the Total Range,
produces the Entry Range.  If no GFT setting is available (i.e., pre-occupation
safety), then enter 1.000 as the Range K.  If a GFT setting is available, (i.e., post occupation safety), then enter the Range K expressed to four decimal
places (i.e., 1.1234).  Step 7a demonstrates how to compute Range K.
7a
Divide Range ~ Adjusted Elevation by the Achieved Range from the GFT setting to
determine Range K: Range ~ Adjusted Elevation     =     Range K, expressed to four decimal places.
     Achieved Range
8
Determine the *Entry Range*.  Multiply the Total Range times Range K to determine
the Entry Range. If Range K is 1.0000, then the Entry Range will be identical to the
Total Range.  **Entry Range is artillery expressed to the nearest 10 meters**.
9
Following the Mini-Max rule, determine the *Vertical Interval* by subtracting the unit
altitude from the altitude corresponding to the Diagram Range, and record it.
(**Note**:  Diagram Range is used for computations of VI and Site because this is the
actual location of the minimum range line.  The Range Correction, Total Range, and
Range K are used to compensate for nonstandard conditions, and represent the
aimpoint which must be used to cause the round to cross the Diagram Range).  VI
is artillery expressed to the nearest whole meter.
10
Determine and record the *Angle of Site divided by 10*  to the Diagram Range.  This
is performed by dividing the Angle of Site (use the appropriate GST, if possible) by
10. <SI/10 is artillery expressed to the nearest tenth of a mil, and has the same
sign as the VI.
11
Determine and record the *10 mil Site Factor* from the GFT or TFT which heads the
projectile family. (Note:  Remember to use the  Diagram Range to compute 10 mil
Si Fac).  10 mil Si Fac is artillery expressed to the nearest tenth of a mil and is always negative.
12
Compute and record *Site*.  Site is the product of <SI/10 times 10 mil Si Fac.  Site is
artillery expressed to the nearest whole mil.
13
Determine the *Elevation* from Table C (base ejecting) or TFT/GFT (bursting), and

record it.  (**Note**:  GFT Settings are not used to determine Elevation, as Range K
represents total corrections, and to use a GFT setting would double the effects of those corrections**).  Elevation is artillery expressed to the nearest whole mil**.

14
Compute the *Quadrant Elevation* and record it.  Quadrant Elevation is the sum of
Elevation and Site.  Quadrant Elevation is artillery expressed to  the nearest
whole mil.
15
Determine and record *Drift* corresponding to the Entry Range from Table C (base
ejecting) or TFT/GFT.  Drift is applied to the Basic Safety Diagram by following the "left least, right most" rule.  The lowest (least) drift is applied to all left deflection limits, and the highest (greatest) drift is applied to all right deflection limits.  Drift is artillery expressed to the nearest whole mil.
16
Ensure computations are verified by a second safety-certified person.
17
On the bottom third of the sheet of paper, record the data on the safety T.
NOTE:  Minimum  fuze settings are not computed for High Angle safety.  It is the FDO's responsibility to ensure that all fuze settings will cause the projectile to function in the impact area.

    (a)            (b)             (c)       (d)           (e)           (f)      (g)         (h)          (I)                   (j)       (k)         (l)         (m)
DIAGRAM   RG            TOT      RG        ENTRY RG            + CORR    = RG   x  K      =   RG           CHG    VI    <SI/10 X10mil Si Fac  =   SI   +   EL  =   QE      DRIFT
(a)   This is the minimum or maximum range from the range safety diagram. (b)   This is the range correction for nonstandard conditions from Table F, if required. This is typically for reoccupation safety or corrections for nonstandard conditions not included in the Range K factor in column (d), such as WP [] weight.  Examples of nonstandard conditions accounted for in (b)  include, but are not limited to, difference in projectile square weight, difference in  muzzle velocity, or any nonstandard condition accounted for prior to determining a Range K factor.  If there is no change from standard, or all nonstandard conditions are accounted for in the Range K factor, this value is zero (0). To determine a range correction from Table F, use the following formula: NONSTANDARD      STANDARD         CHANGE IN       RG CORR     RANGE RANGE   CHG   CONDITION          -  CONDITION    =   STANDARD   x  FACTOR  =  CORRECTION (c)   This is the sum of the Diagram Range and the Range Correction.  If there is no range correction, then the Total Range will be the same as the Diagram Range.

(d)   This is the Range K factor determined by using technique 2 in the FM 6-40/MCWP 3-16.6. This is for post occupation safety. It represents total corrections for a registration, MET + VE,  or other subsequent MET technique. It represents all nonstandard conditions (unless a separate nonstandard condition such as change in square weight for WP is listed separately in column (b)). It is multiplied times the Total Range to determine Entry Range.  If there is no Range K, enter 1.0000 (e)   This is the sum of the Total Range times the Range K factor.  If there is no Range K factor, then the Entry Range will be the same as the Total Range. Entry Range is the range to which Elevation is determined. (f)    This is the charge from the range safety card for this set of safety computations.

(g).  This is the Vertical Interval from the range safety diagram. (h).  This is the Angle of Site divided by 10, determined by dividing Vertical Interval by Entry Range in Thousands. (i).  This is the 10 mil Site Factor, determined from the GFT or TFT from the head of the projectile family; e.g., 10  mil Site Factor for the M110 WP projectile would be determined with the AM-2, M825 10 mil Site Factor would be computed using the AN-2. * (j).  This is Site, the product of <Site/10 X 10 Mil Site Factor (Note: Site is determined for the Diagram Range). * (k). This is the elevation to impact from Table C (base ejecting), or GFT/TFT (bursting). * (l).  This is the sum of Elevation and Site. It is the minimum or maximum Quadrant Elevation corresponding to
      maximum or  minimum range.

(m).  This is the Drift corresponding to Table C (base ejecting), or GFT/TFT (bursting),   Drift is applied to the range safety diagram by using the "Least, Left; Most, Right;" rule.  The "least" or lowest drift is applied to all left deflection limits, and the "most" or greatest drift is applied to all right deflection limits.
* - see Table 15-8 to determine the correct source table or addendum for computations/

## 4[] He High Angle Chg 3Gb Diagram    Range      Total       Range    Entry Range     + Corr    =  Range  X  K__       =  Range    Chg   Vi   <Si/10   X  10Mil Si Fac  =  Si  +   El    =    Qe    Drift

 4000          +     0        =   4000       x 1.0000   =  4000         3GB  +23  +0.6       x        -1.0          =  -1   + 1247  =   **1246**      L101
 5700          +     0        =   5700       x 1.0000   =  5700         3GB   -15  -0.3        x        -5.2          = +2   + 1052  =   **1054**       -- 6200          +     0        =   6200       x 1.0000   =  6200         3GB   -25  -0.4        x       -15.0         = +6   + 954    =    960        L34

DIAGRAM     RANGE      TOTAL       RANGE     ENTRY
RANGE     +  CORR    =  RANGE  X  __k__  =    RANGE   CHG       VI   <SI/10   X  10mil Si Fac  =  SI  +  EL    =    QE    DRIFT
4000
  +     0      =      4000      x    1.0000  =
4000
4GB    +23   +0.6     x        -0.7           =   0  + 1288  =   **1288**      L125
5700
  +     0      =       5700    x     1.0000  =
5700
4GB    -15    -0.3      x        -2.8           = +1  + 1133  =   **1134**        --
6200
  +     0
DIAGRAM     RANGE      TOTAL       RANGE      ENTRY
RANGE     +  CORR    =  RANGE  X  __k__   =    RANGE    CHG   VI    <SI/10   X  10mil Si Fac  =  SI  +  EL    =    QE      DRIFT
4000
  +      0      =       4000    x    1.0000  =
4000
3GB    +23   +0.6     x        -1.0           =   -1  + 1253  =   **1252**        L105
5700
  +      0      =       5700    x    1.0000  =
5700
3GB    -15    -0.3      x        -5.3           =   +2 + 1066  =   **1068**          --
6200
  +      0      =       6200    x    1.0000  =

Location (Grid/Alt):                               Charge:          Shell(s):                Fuze(s):                     Angle of Fire:
AOL:
Chg:_____ Shell(s):__________ Fuze(s):__________ Projectile Family:__________
 DIAGRAM         RG           TOT      RG       ENTRY                                                 M564/    M582                               M728/
RG              +    CORR   =  RG   x  K     =   RG        CHG  VI   SI  +  EL  =  QE      M565     M577      TOF   +  5.5  =   M732     DFT
Location:____________Charge: _____Shell(s):___________Fuze(s):__________Angle of Fire:___ AOL: ____
Location (Grid/Alt):                                            Charge:          Shell(s):                              Angle of Fire:
AOL:
High Angle Safety Matrix Chg:_____ Shell(s):__________ Projectile Family:__________
DIAGRAM      RG                TOT           RG           ENTRY RG               +   CORR   =     RG     x       K       =    RG           CHG   VI   <SI/10 x 10 mil Si Fac  =  SI  +  EL  =  QE      DFT
                                                                                   Safety T
Location:_________________Charge: _____Shell(s):__________Angle of Fire:_____AOL:________

## Section Iii Minimum Quadrant Elevation

The XO or platoon leader is responsible for determining the lowest QE
that can be safely fired from his position that will ensure projectiles clear all visible crests (minimum QE).

## 15-15.  Elements Of Computation

A minimum quadrant for EACH howitzer is ALWAYS determined.  The maximum of these minimum quadrants is the XO's minimum quadrant.  Use of the rapid fire tables in ST 6-50-20 is the fastest method of computing minimum QE.  The QE determined from ST 6-50- 20 is always equal to or greater than (more safe) than manual computations.  Manual computations are more accurate than the rapid fire tables and are used if the sum of the site to crest and the angle needed for a 5-meter vertical clearance is greater than 300 mils.  Figure 15-18 shows the elements of minimum QE.

a.  Piece-to-crest range (PCR) is the horizontal distance between the piece and the crest, expressed to the nearest 100 meters.  Procedures for measurement are discussed in paragraph 15-16.

## Note:  All Angles Are Determined And Expressed To The Next Higher Mil.

b.  Angle 1 (Figure 15-18) is the angle of site to crest measured by the weapons.  See paragraph 15-16 for procedures.

c.  Angle 2 (Figure 15-18) is the vertical angle required to clear the top of the crest.  For quick, time, and unarmed proximity (VT) fuzes, a vertical clearance of 5 meters is used.  For armed VT fuzes, see paragraph 15-19.

d.  Angle 3 (Figure 15-18) is the complementary angle of site.  It is the complementary site factor (TFT, Table G) for the appropriate charge at the piece to crest range mulitiplied by the sum of angles 1 and 2.  Site is the sum of angles 1, 2, and 3.

NOTE:  The entry argument for Table G is PCR.  If it is not listed, do not interpolate, use the next higher listed value.

e.  Angle 4 (Figure 15-18) is the elevation (TFT, Table F) for the appropriate charge corresponding to the PCR.

 f.  Angle 5 (Figure 15-18) is a safety factor equivalent to the value of 2 forks (TFT, Table F) for the appropriate charge at the PCR.

 g.  The sum of angles 1 through 5 (Figure 15-18) is the minimum QE for the weapon and the charge computed.

## 15-16.  Measuring Angle Of Site To Crest

As soon as the piece is "safed", prefire checks conducted, and ammunition prepared , position improvement begins with verification of site to crest as measured by the advance party. The advance party measures site to crest with an M2 compass or aiming circle.  The section chief measures the angle of site to crest and reports it to the XO or platoon leader.  To measure the angle of site to crest, the section chief sights along the bottom edge of the bore, has the tube traversed across the probable field of fire, and has the tube elevated until the line of sight clears the crest at the highest point.  He then centers all bubbles on the elevation mount and reads the angle of site to the crest from the elevation counter.  This angle of site and the PCR are reported as part of the section chief's report.

## 15-17.  Measuring Piece-To-Crest Range

a.  There are five methods that can be used to measure piece-to-crest range: **(1) Taping.**  This is the most accurate method; however, it is normally too timeconsuming.

     **(2)  Subtense.**  This method is fast and accurate. (3) Map Measurement.  This method is fast and accurate if the obstacle can be accurately located (for example, a lone tree will not appear on a map).

   **(4) Pacing.**  This method is time-consuming and depends on the distance and accessibility to the crest.

      (5) Estimation.  This method is least accurate, but it is used when other methods are not feasible.

b.  Regarless of the method used to measure PCR, the XO or platoon leader must verify PCR before he computes QE.  He can do this by using any of the five methods.

## 15-18.  Computation Of Fuzes Other Than Armed Vt

a.  The XO or platoon leader does the computations indicated in this section if the sum of angles 1 and 2 (Figure 15-18) exceeds 300 mils or if the rapid firing tables (RFTs) are not available.  **All angles are determined and expressed to the next higher mil.**  Table 15-9 lists the steps and solves an example of an XO's or platoon leader's manual computations.

Table 15-9.  Manual Minimum QE Computations.
STEP
ACTION
1
Howitzer 1 (M109A3) reports a site to crest of 16 mils at a PCR of 1,100 meters.  Charge
3GB is used.
2
1 = site to crest = 16 mils
3
2 = (VI x 1.0186) + PCR (in 1,000s)
      = (5 x 1.0186) + 1.1
      = 4.6  5 mils
This VI is a 5-meter vertical clearance safety factor.  It can also be computed using one of the following methods: -
Use the GST.  Solve in the same way as angle of site **(4.6**  5).
-
Use ST 6-50-20, page 2-7 (5).
4
3 = (1 + 2) x CSF
      = (16 + 5) x 0.010
      = (0.210)  1 mil
5
4 = EL = 74.1  75 mils
6
5 = 2 Forks (TFT, Table F, Column 6)
      = 2 x 2 =  4 mils
7
Min QE = 1 + 2 + 3 + 4 + 5
              = 16 + 5 + 1 + 75 + 4
              = 101 mils

b.  The same example is solved in Table 15-10 by using RFTs in the ST 6-50-20, Appendix B.

STEP
ACTION
1
Determine if the RFT can be used (**1 +** 2 [[[[ **300 mils).**  Use the ST 6-50-20, page A-1.
Since the sum of angles 1 and 2 is less than or equal to 300 **(16 +5 = 21),** the RFT can be
used.
2
Determine RFT value.  Enter the appropriate RFT.  The entry arguments are howitzer
(M109A3), propellant (M3A1, GB), fuze (PD), PCR (1100), and charge (3).  The correct table is on page A-7.  The RFT value is 86.  This value equals the sum of angles 2, 3, 4,
and 5 (**2 +** **3 +** **4 +** 5).
NOTE:  Use the RFT labeled "M557, M564" for all minimum QE computations except
armed VT.  For armed VT, use the RFT labeled "M728."
3
Determine the RFT minimum QE.  This value equals the sum of angle 1 and the RFT
value (16 + 86 = 102).

c.  One howitzer section may report a site to crest that is unusually high.  If the XO or platoon leader determines that it is the result of a single narrow obstruction (such as a tree), the piece can be called out of action when firing a deflection that would engage the obstruction.  This would enable the platoon to use the next lower site to crest.  Other alternatives are to remove the obstruction or move the weapon.

d.  Table 15-11 illustrates why minimum QE is computed for all guns, regardless of which has the largest site to crest.

| GUN     | CHG   | PCR   |
|---------|-------|-------|
| SITE TO |       |       |
| CREST   | +     | RFT   |
| 1       | 3GB   | 800   |
| 2       | 3GB   | 1000  |
| 3       | 3GB   | 1500  |
| 4       | 3GB   | 1200  |

## 15-19.  Computations For Armed Vt Fuze (Low-Angle Fire)

a.  The method of computing the XO's minimum QE for firing a projectile fuzed with an M728 or M732 fuze depends on the method in which the fuze is used.  The proximity (VT) fuze is designed to arm 3 seconds before the time set on the fuze; however, some VT fuzes have armed as early as 5.5 seconds before the time set on the fuze.  Because of the probability of premature arming, a safety factor of 5.5 seconds is added to the time of flight to the PCR.

Since time on the setting ring is set to the whole second, the time determined in computing minimum safe time is expressed up to the nearest whole second.  A VT fuze is designed so that it will not arm earlier than 2 seconds into its time of flight, which makes it a bore-safe fuze.

b.  In noncombat situations, the XO or platoon leader determines the minimum safe time by adding 5.5 seconds to the time of flight to the minimum range line as shown on the range safety card.  The minimum QE determined for fuzes quick and time is also valid for fuze VT.

c.  In combat situations, the XO or platoon leader determines the minimum QE and a minimum safe time for fuze VT.  The minimum QE determined for PD fuzes is safe for VT fuzes if the fuze setting to be fired equals or is greater than the minimum safe time determined in paragraph a above.  If the XO or platoon leader finds it necessary to fire a VT fuze with a time less than the minimum safe time, he must modify the minimum QE.  He does this by increasing the vertical clearance to ensure that the fuze will not function as it passes over the crest.  In addition, he must ensure the fuze will not function over any intervening crests along the guntarget line (See paragraph 15-21).

d.  If the projectile is to be fired with the VT fuze set at a time less than the minimum safe time, allowance must be made for vertical clearance of the crest.  Vertical crest clearances for armed M728 and M732 VT fuzes fired over ordinary terrain for all howitzer systems is 70 meters.

e.  If the projectile is to be fired over marshy or wet terrain, the average height of burst will increase.  The vertical clearance is increased to 105 meters.  If the projectile is fired over water, snow, or ice, the vertical clearance is 140 meters.

f.  The minimum QE for armed fuze VT when a fuze setting less than the minimum safe time is fired is based on the piece-to-crest range and a vertical clearance as indicated in paragraphs d and e above.

g.  Figure 15-19 shows a decision tree for application of armed VT minimum QE.

In combat, you have a VT mission with a time setting of ________ and a QE of ________.  Ask the following questions:
h.  Table 15-12 is an example of computations to determine minimum QE for an armed VT fuze.

Table 15-12.  Manual Armed VT Minimum QE Computations.
STEP
ACTION
1
Howitzer 1 (M109A3) reports a site to crest of 16 mils at a PCR of 1,100 meters.  Charge
3GB is used.
2
1 = site to crest = 16 mils
3
2 = (VI x 1.0186) + PCR (in 1,000s)
     =(70 x 1.0186) + 1.1
     = 64.8  65 mils
This VI is a 70-meter vertical clearance safety factor.  It can also be computed by using the
GST.  Solve in the same way as angle of site **(64.7**  65).
4
3 = (1 + 2) x CSF (TFT, Table G)
     = (16 + 65) x 0.010
     = 0.710  1 mil
5
4 = EL = 74.1  75 mils
6
5 = 2 Forks (TFT, Table F, Column 6)
     = 2 x 2 = 4 mils
7
Min QE = 1 + 2 + 3 + 4 + 5
             = 16 + 65 + 1 + 75 + 4
             = 161 mils
8
Determine minimum safe time.  This value is the sum of TOF to PCR and 5.5 expressed up
to the next higher second **(4.1 + 5.5 = 9.6**  10.0 sec).

i.  The same example is solved in Table 15-13 by using the RFT in the ST 6-50-20, Appendix A.

Table 15-13  RFT Minimum QE Computations.
STEP
ACTION
1
Determine if the RFT can be used (1 + 3 [ 300 mils). This is done manually, since page   A-
1 uses a vertical clearance of 5 meters.  See step 3 in table 15-12 for 2.  Since the sum of
angles 1 and 2 is less than or equal to 300 **(16 +65 = 81)**, the RFT can be used.

2
Determine RFT value.  Enter the appropriate RFT.  The entry arguments are howitzer
(M109A3), propellant (M3A1, GB), fuze (M728 or M732), PCR (1100) and charge (3).  The correct table is on page A-13. The RFT value is 147.  This value equals the sum of angles 2, 3, 4, and 5.
NOTE:  Use the RFT labeled "M557, M564" for all minimum QE computations except armed
VT.  For armed VT, use the RFT labeled "M728."
3
Determine the RFT minimum QE.  This value equals the sum of angle 1 and the RFT value
(16 + 147 = 163).
4
Determine the minimum safe time.  Use the same entry arguments as in step 2.  The
minimum safe time is **10.0**.
j.  If the VT fuze setting to be fired is equal to or greater than the minimum safe VT time, the minimum QE for fuzes quick and time applies.  If the VT fuze setting to be fired is less than the minimum safe VT time, the minimum QE determined for armed VT applies.

## 15-20.  Using Minimum Quadrant Elevation

After computing minimum QE for each charge authorized, the XO or platoon leader must compare the minimum QE to the QE required to clear the minimum range line.  The XO must then select the highest quadrant for each charge to be used as the minimum QE to be fired from that position.

## 15-21.  Intervening Crest

a.  FDOs must ensure that artillery fires clear intervening crests.  Intervening crests are defined as any obstruction between the firing unit and the target not visible from the firing unit. The following are the possible options, listed in order of preference.

    **(1)**  Determine firing data to the crest (include all nonstandard conditions) and add 2
forks (Table 15-12).

    **(2)**  Determine a  minimum  QE in a similar  manner as  XO's  minimum QE  (Table
15-13).

    (3)  Use the trajectory tables in the appendix of the TFT.

b.  Option 1 is preferred because it incorporates all current nonstandard conditions that will affect the projectile along the trajectory.  The FDO has the responsibility to determine on the basis of availability of corrections for nonstandard conditions if this really is the best option.  Table 15-12 lists the steps.

STEP
ACTION
1
Upon occupation, the FDO analyzes the terrain for intervening crests.
2
Upon determining the altitude of this crest, he computes firing data to this point (QE).  The best solution includes all available corrections for nonstandard conditions (current and valid GFT setting).
3
Add the value of 2 forks (TFT, Table F, Column 6) to the QE determined in step 2 to ensure
that round-to-round variations (probable errors) will clear the crest.
4
The FDO then records this QE and charge on his situation map as a check to ensure that
rounds will clear the intervening crest.
5
Upon receipt of a fire mission, the FDO will compare his intervening crest QE to his fire
mission quadrant.  One of the three following situations will occur:

1) The target is located short of the intervening crest.  The FDO does not consider the effects of the crest at this time. 2) The mission QE exceeds intervening crest QE by a significant margin, indicating the rounds will clear the crest. 3) Fire mission QE exceeds intervening crest QE by only a small margin or is less than intervening crest QE, indicating the round may or may not clear the crest.  The FDO must determine if the round will clear after considering the following:

Table 15-14. Intervening Crest, Option 1 (Continued).
STEP
ACTION

- Have all nonstandard conditions been accounted for?
- How old is the current met message? - Are registration corrections being applied to this mission?
Upon realizing that the round may not or will not clear the crest, the FDO can either fire high angle or a reduced charge.  The quickest choice would be to fire high angle, but tactical situations may prevent this.  Firing a lower charge will increase dispersion more than high angle.  For example, at a range of 6,000 meters, the following applies:
- Low angle, charge 5:  Probable error in range = 15 meters. - High angle, charge 5:  Probable error in range = 17 meters. - Low angle, charge 4:  Probable error in range = 23 meters.
If a lower charge is selected, steps 2 through 5 must be repeated.
6
If VT fuzes are to be fired (M700 series), the FDO must take additional steps to ensure that
the VT fuze does not arm before passing over the crest.  Follow the steps for determining armed VT minimum QE and FS in paragraph 15-15.
c.  Option 2 does not include current conditions for all nonstandard conditions.  Table 15-
20 lists the steps.

Table 15-15.  Intervening Crest, Option 2.
STEP
ACTION
1
Upon occupation, the FDO analyzes the terrain for intervening crests.
2
The FDO determines and announces the grid and map spot altitude to the crest.
3
The HCO plots the grid and determines and announces range to crest.
4
The VCO computes angle of site to the crest.  This is the same as determining site to crest
with a howitzer
5
Determine if RFT can be used (**1 +** 2 [[[[ **300 mils)**.  Angle 1 equals angle of site to the crest.
Refer to ST 6-50-20, page A-1.  Since 1 and 2 decrease with range, this should not be a
problem.

6
Determine RFT value.  Enter the appropriate RFT.  The entry arguments are howitzer,
propellant, fuze, PCR (chart range to the crest), and charge.  This value equals the sum of angles 2, 3, 4,  and 5.
NOTE:  Use the RFT labeled "M557, M564" for all minimum QE computations except armed
VT.  For armed VT, use the RFT labeled "M728."
7
Determine RFT intervening crest QE.  This value is the sum of the angle of site to the crest
and the RFT value.
8
If VT is fired, enter the appropriate table and extract the correct information.
9
Follow steps 4 and 5 of table 15-14.
d.  The least preferred option is using the trajectory charts in the appendix of the TFT.

This offers a quicker but less accurate method to clear the intervening crest since it is based off of standard conditions.  The FDO must make a judgment call when to use these charts.  The FDO must use caution when making this decision.

## Chapter 1 The Gunnery Problem And The Gunnery Team

The mission of the Field Artillery is to destroy, neutralize, or suppress the enemy by cannon, rocket, and missile fires and to help integrate all fire support assets into combined arms operations. Field artillery weapons are normally employed in masked or defilade positions to conceal them from the enemy. Placing the firing platoon in defilade precludes direct fire on most targets. Consequently, indirect fire must be used when FA weapons fire on targets that are not visible from the weapons. The gunnery problem is an indirect fire problem. Solving the problem requires weapon and ammunition settings that, when applied to the weapon and ammunition, will cause the projectile to achieve the desired effects on the target.

## 1-1. Gunnery Problem Solution

a.
The steps in solving the gunnery problem areas follows:
Know the location of the firing unit, and determine the location of the target.
(1) (2)
Determine chart (map) data (deflection, range from the weapons to the target,
and altitude of the target).
Determine vertical interval (VI) and site (si).
(3) (4)
(meteorological
Compensate for nonstandard conditions that would affect firing data [met] procedures). Convert chart data to firing data (shell, charge, fuze, fuze setting, deflection, and
(5)
quadrant elevation).
Apply the firing data to the weapon and ammunition.
(6)
The solution to the problem provides weapon and ammunition settings that will cause
b.
the projectile to function on or at a predetermined height above the target. This is necessary so
the desired effects will be achieved.

## 1-2. Field Artillery Gunnery Team

The coordinated efforts of the field artillery gunnery team are required to accomplish the solution of the gunnery problem outlined in paragraph 1-2. The elements of the team must be linked by an adequate communications system.

NOTE:  The terms *battery* and *platoon* used throughout this manual are synonymous, unless otherwise stated.

a. Observer. The observer and/or target acquisition assets serve as the "eyes and ears"
of all indirect fire systems. The mission of the forward observer is to detect and locate suitable indirect fire targets within his zone of observation and bring fires on them. When a target (tgt) is to be attacked, the observer transmits a call for fire and adjusts the fires onto the target as necessary. An observer provides surveillance data of his own fires and any other fires in his zone of observation. Field artillery observers include the following:
Aerial observers (AOs). Forward observers (F0s). Fire support teams (FISTs). Combat observation/lasing teams (COLTs).

Air and naval gunfire liaison company (ANGLICO).

Firepower control teams (FCTs). Any other friendly battlefield personnel.

b. Target Acquisition.

Target acquisition assets also function as observers. They provide accurate and timely detection, identification, and location of ground targets, collect combat and/or target information, orient and/or cue intelligence sources, and permit immediate attack on specific areas. Field artillery target acquisition (TA) assets include the following:
Weapons-locating radar sections. Aircraft radar systems.

NOTE: See FM 6-121 for a discussion of TA assets. See FMs 100-2-1, 100-2-2, and 100-2-3 for information on target characteristics.

c. Fire Direction Center. The fire direction center (FDC) serves as the "brains" of the gunnery team. It is the control center for the gunnery team and is part of the firing battery headquarters. The FDC personnel receive calls for fire directly from an observer or they maybe relayed through the initial fire support automated system (IFSAS) at battalion level. The FDC will then process that information by using tactical and technical fire direction procedures.

Tactical fire direction includes processing calls for fire and determining
(1)
appropriate method of fire, ammunition expenditure, unit(s) to fire, and time of attack. The fire direction officer's decision on how to engage the target is concisely stated as a FIRE ORDER.

(2)
Technical fire direction is the process of converting weapon and ammunition characteristics (muzzle velocity, propellant temperature, and projectile weight), weapon and target locations, and met information into firing data. Firing data consist of shell (sh), charge
(chg), fuze (fz), fuze setting (FS), deflection (df), and quadrant elevation (QE). The FDC
transmits firing data to the guns as fire commands.

d. Firing Battery. The firing battery serves as the "muscle" of the gunnery team. The firing battery includes the battery HQ, the howitzer sections, the ammunition section, and the FDC. The howitzer sections apply the technical firing data to the weapon and ammunition.

Organization and employment considerations of the firing sections are discussed in FM 6-50.

## 1-3. Five Requirement For Accurate Predicted Fire

To achieve accurate first-round fire for effect (FFE) on a target, an artillery unit must compensate for nonstandard conditions as completely as time and the tactical situation permit. There are five requirements for achieving accurate first-round fire for effect. These requirements are accurate target location and size, firing unit location, weapon and ammunition information, met information, and computational procedures.

If these requirements are met, the firing unit will be able to deliver accurate and timely fires in support of the ground-gaining arms. If the requirements for accurate predicted fire cannot be met completely, the firing unit maybe required to use adjust-fire missions to engage targets. Adjust-fire missions can result in less effect on the target, increased ammunition expenditure, and greater possibility that the firing unit will be detected by hostile TA assets.

a. Target Location and Size.

Establishing the range (rg) from the weapons to the target requires accurate and timely detection, identification, and location of ground targets.

Determining their size and disposition on the ground is also necessary so that accurate firing data can be computed. Determining the appropriate time and type of attack requires that the target size (radius or other dimensions) and the direction and speed of movement be considered. Target location is determined by using the TA assets mentioned in paragraph 1-2.

b. Firing Unit Location.

Accurate range and deflection from the firing unit to the target requires accurate weapon locations and that the FDC knows this location. The battalion survey section uses the position and azimuth determining system (PADS) to provide accurate survey information for the battery location. Survey techniques available to the firing battery may also help in determining the location of each weapon. The FDC can determine the grid location of each piece by using the reported direction, distance, and vertical angle for each piece from the aiming circle used to lay the battery.

c. Weapon and Ammunition Information. The actual performance of the weapon is measured by the weapon muzzle velocity (velocity with which the projectile leaves the muzzle of the tube) for a projectile-propellant combination.

The firing battery can measure the achieved muzzle velocity of a weapon and correct it for nonstandard projectile weight and propellant temperature. This is done by using the M90 velocimeter and muzzle velocity correction tables
(MVCT M90-2) for each type of charge and projectile family. Calibration should be conducted continuously by using the M90 velocimeter.

Firing tables and technical gunnery procedures allow the unit to consider specific ammunition information (weight, fuze type, and propellant temperature); thus, accurate firing data are possible.

d. Meteorological Information. The effects of weather on the projectile in flight must be considered, and firing data must compensate for those effects. Firing tables and technical gunnery procedures allow the unit to consider specific met information (air temperature, air density, wind direction, and wind speed) in determining accurate firing data.

e. **Computational Procedures.** The computation of firing data must be accurate.

Manual and automated techniques are designed to achieve accurate and timely delivery of fire. The balance between accuracy, speed, and the other requirements discussed in this chapter should be included in the computational procedures.

f. **Nonstandard Conditions.** If the five requirements for accurate predicted fire cannot be met, registrations can be conducted or a met + VE technique can be completed to compute data that will compensate for nonstandard conditions. Applying these corrections to subsequent fire missions will allow the unit to determine accurate firing data. Accuracy of these fires will be a direct function of the observer's target location.

## Chapter 2 Firing Battery And Battery Fdc Organization

The FA cannon battery is firing unit within the cannon battalion and is organized in one of two ways: a battery-based unit (3 x 6 organization) or a platoon-based unit (3 x 8 organization). In either case, they have the personnel and equipment needed to shoot, move, and communicate. This chapter describes the organization of the firing battery and the battery FDC.

## 2-1. Firing Battery Organization

a. The organization of all cannon batteries is basically the same. Differences in organization stem from differences in weapon caliber, whether the weapon is towed or self-propelled (SP), and whether the battery is in a divisional or nondivisional battalion. The cannon battery is organized as follows:
(1) Battery-based unit--consists of a battery headquarters and a firing battery.

(a)
The battery HQ has the personnel and equipment to perform command and control; food service; supply; communications; nuclear, biological, chemical (NBC), and maintenance functions. (In some units, food service, communications, and maintenance may be consolidated at battalion level.)
(b)
The firing battery has the personnel and equipment to determine firing data, fire the howitzers, and resupply ammunition. (In some units, ammunition assets may be consolidated at battalion level.)
(2) Platoon-based unit--consists of a battery HQ and two firing platoons.

(a)
The battery HQ has the personnel and equipment to perform command and control, food service, supply, communications, NBC, and maintenance functions. (In some units, food service, communications, and maintenance may be consolidated at battalion level.)
(b)
Each firing platoon has the personnel and equipment to determine firing data, fire the howitzers, and resupply ammunition. (In some units, ammunition assets maybe consolidated at battalion level.)

## 2-2. Battery Or Platoon Fdc

a. The battery or platoon FDC is the control center, or brains, of the gunnery team. The FDC personnel receive fire orders from the battalion FDC or calls for fire from observers and process that information by using tactical and technical fire direction procedures (Chapter 1). The battery FDC performs the technical fire direction, while the battalion FDC performs tactical fire direction. If the FDC is operating without a battalion FDC, the battery FDC conducts both tactical and technical fire direction. The battery FDC receives the call for fire and converts the request into firing data. The firing data are then sent to the howitzer sections as fire commands. In addition to an FDC, USMC batteries have a battery operations center (BOC), which is organized and equipped to perform technical fire direction. BOCs enhance unit survivability, simplify displacements, and enable split-battery operations.

In battery positions, BOC personnel may augment the FDC to facilitate 24-hour operations.

b. The FDC is organized to facilitate 24-hour operations (Appendix A). Duties of manual FDC personnel are described below
(1) Fire direction officer. The FDO is responsible for all FDC operations. He is responsible for the training of all FDC personnel, supervises the operation of the FDC, establishes standing operating procedure (SOP), checks target location, announces fire order, and ensures accuracy of firing data sent to the guns. USMC batteries also include an assistant fire direction officer-assistant executive officer (AFDO-AXO). The AFDO-AXO leads the BOC, assists the battery commander during displacement and stands duty in the FDC to enable 24-hour operations.

(2) Chief fire direction computer.

The chief fire direction computer is the technical expert and trainer in the FDC. He ensures that all equipment is on hand and operational, supervises computation of all data, ensures that all appropriate records are maintained, and helps the FDO as needed. He ensures smooth peformance of the FDC in
24-hour operations and functions as the FDO in the FDO's absence. The equivalent USMC billet description is operations chief.

(3) Fire direction computer.

The fire direction computer operates the primary means of computing firing data. He determines and announces fire commands. He also records mission-related data and other information as directed. The equivalent USMC billet description is operations assistant. There is an operations assistant in both the FDC and the BOC.

(4) Fire direction specialist. There are two fire direction specialists per FDC to facilitate 24-hour operations.

In a manual FDC, they serve alternately as horizontal control operator (HCO) and vertical control operator (VCO). The equivalent USMC billet description is fire control man. There are five fire control men in a USMC FDC and three more in a BOC to facilitate 24-hour operations. These fire control men may perform the duties of the HCO, VCO, radio operator, or driver as needed in either the FDC or BOC.

(a)
The HCO constructs and maintains the primary firing chart and determines and announces chart data.

The VCO constructs the secondary firing chart checks chart data, plots
(b)
initial target location on the situation map, and determines and announces site.

(c)
In a manual The radiotelephone operator (RATELO) or driver is normally the operator of the FDC vehicle. He maintains the vehicle and the FDC-associated generators.

FDC, he may also act as the recorder.

## 2-3. Definitions

a. Fire direction is the employment of firepower. The objectives of fire direction are to provide continuous, accurate, and responsive fire support under all conditions. Flexibility must be maintained to engage all types of targets over wide frontages, to mass the fires of all available units quickly, and to engage a number and variety of targets simultaneously.

b. The fire direction center is the element of the gunnery team with which the commander directs artillery firepower. The accuracy, flexibility, and speed in the execution of fire missions depend on the following:

Rapid and clear transmission of calls for free. Rapid and accurate computations. Rapid and clear transmission of fire commands.
Integration of automated and manual equipment into an efficient mutually supporting system.

Efficient use of communications equipment.

## 2-4. Relationship Between Battery Or Platoon And Battalion Fdc

There are two modes of operation under which fire direction can be conducted: battalion directed and autonomous.

a. Battalion Directed. In battalion-directed operations, calls for fire are transmitted from the observer to the battalion FDC. The battalion FDO is responsible for tactical fire direction and selects the unit(s) to fire. A fire order is transmitted to the firing units that are responsible for technical fire direction. The battalion FDC is responsible for transmitting all fire mission related messages (that is, message to observer, ready [if applicable], shot, splash, and rounds complete) to the observer. The firing units are responsible for transmitting all fire mission related messages to the battalion FDC.

b. Autonomous.

In autonomous operations, calls for fire are transmitted from the observer to the firing unit FDC. The firing unit FDC is responsible for tactical and technical fire direction. The firing unit is responsible for transmitting the message to observer, ready (if applicable), shot, splash, and rounds complete to the observer. The battalion FDC and the battalion fire support officer (FSO) monitor the calls for fire. The equivalent USMC billet description for FSO is artillery liaison officer. The battalion FDC may take over control of the mission if the target warrants the massing of two or more batteries. The battalion FDC monitors the battery's message to observer (MTO) to ensure that the battery has selected the appropriate ammunition and method of fire. The battalion FDC may change the battery's plan of attack. If the target requires battalion fire, the firing unit FDO can request reinforcing fires from the battalion FDC.

## 2-5. Battalion Fdc Personnel

A battalion FDC is composed of a fire direction officer, a chief computer, an assistant chief computer, three computers, a horizontal control operator, a vertical control operator, and a radiotelephone operator. USMC battalion FDCs are composed of a fire direction officer, operations chief, two operations assistants, and 10 fire control men to facilitate 24-hour operations. The operations chief is the equivalent of the chief computer, and the operations assistants are the equivalent of the assistant chief computer. The fire control men may perform the duties of computer, HCO, VCO, radio operator, or driver as needed.

## A. Fire Direction Officer's Duties. The Fdo's Duties Areas Follows:

(1) Is responsible for the overall organization and functioning of the battalion FDC. (2) Coordinates with the battalion S3 to ensure that all information regarding the tactical situation, unit mission, ammunition status, and commander's guidance on the method of engagement of targets and control of ammunition expenditures is known and ensures that all information is passed to battery FDOs.

(3) Ensures that all communications are properly established.

(4) Coordinates with the chief computer concerning data input, chart verification, transfer of registration corrections, average site or altitude, terrain gun position corrections
(TGPCs) sectors, and any other special instructions.

(5) Inspects target locations and monitors messages to observer when a mission is received by a battery FDC and intercedes when necessary.

(6) Controls all battalion missions.

## B. Chief Computer's Duties. The Chief Computer's Duties Areas Follows:

(1) Serves as the battalion FDO's technical expert (the actual supervisor and/or trainer of battalion FDC personnel) and assumes the duties of the battalion FDO in his absence.

(2) Ensures that all battalion FDC equipment is operational and emplaced correctly. (3) Ensures coordination of all data throughout the battalion, to include current registration settings.

(4) Ensures that the HCO's and VCO's charts include all pertinent known data. (5) Ensures that the situation map is properly posted, to include fire support coordinating measures and the current tactical situation.

c. Assistant Chief Computer's Duties.

The assistant chief computer's duties are as follows:

(1) Monitors all operations performed by the HCO. (2) Supervises maintenance and care of the generators. (3) Assumes the duties of the chief computer when he is absent.
d. Battery Computers' Duties. The battery computers' duties areas follows:
(1) Provide communications link with the battery FDCs. (2) Monitor the appropriate fire direction net for their battery.
(3) Exchange information with the battery FDCs and pass battalion fire orders to the battery.

(4) Record all data pertinent to fire missions that are sent to their battery.

(5) Compute data for their battery when directed by the chief computer.

(6) Use their fire direction net to communicate with the observer when battalion missions are conducted.

(7) Assume the duties of the assistant chief computer when he is absent.

e. Horizontal Control Operator's Duties. The HCO's duties areas follows:
(1) Plots known data as directed by the assistant chief computer. (2) Determines chart data as appropriate.

(3) Maintains equipment and associated generators.

(4) Plots the initial target location when a mission is received.

f. Vertical Control Operator's Duties. The VCO's duties areas follows:
(1) Plots known data as directed by the assistant chief computer. (2) Plots the initial target location when a mission is received.
(3) Checks chart data with the HCO. (4) Plots the initial target location on the situation map and determines and announces site for the appropriate battery.

## G. Radiotelephone Operator's Duties. The Rto's Duties Areas Follows:

(1) Establishes and maintains communications on the battalion command/fue direction (CF) net.

(2) Determines and transmits the messages to observer when battalion missions are conducted on the battalion CF net.

(3) Encodes and decodes messages, target lists, and fire plans.

(4) Ensures proper authentication of appropriate messages and all fire missions.

## Chapter 3 Ballistics

Ballistics is the study of the firing, flight, and effect of ammunition. A fundamental understanding of ballistics is necessary to comprehend the factors that influence precision and accuracy and how to account for them in the determination of firing data. Gunnery is the practical application of ballistics so that the desired ejects are obtained by fire. To ensure accurate predicted fire, we must strive to account for and minimize those factors that cause round-to-round variations, particularly muzzle velocity. Ballistics can be broken down into four areas: interior, transitional, exterior, and terminal. Interior, transitional, and exterior ballistics directly affect the accuracy of artillery fire and are discussed in this chapter. Terminal ballistics are discussed in Appendix B.

## 3-1. Interior Ballistics

Interior ballistics is the science that deals with the factors that affect the motion of the projectile within the tube. The total effect of all interior ballistic factors determines the velocity at which the projectile leaves the muzzle of the tube, which directly influences the range achieved by the projectile. This velocity, called muzzle velocity (MV), is expressed in meters per second
(m/s). Actual measurements of the muzzle velocities of a sample of rounds corrected for the effects of nonstandard projectile weight and propellant temperature show the performance of a specific weapon for that projectile family-propellant type-charge combination. The resulting measurement(s) are compared to the standard muzzle velocity shown in the firing table(s). This comparison gives the variation from standard, called muzzle velocity variation (MVV), for that weapon and projectile family-propellant type-charge combination. Application of corrections to compensate for the effects of nonstandard muzzle velocity is an important element in computing accurate firing data. (For futher discussion of muzzle velocity, see Chapter 4.) The following equation for muzzle velocity is valid for our purposes:

## Mvv (M/S) = Shooting Strength Of Wpn + Ammunition Efficiency

Tube wear, propellant efficiency, and projectile weight are the items normally accounted for in determination of a muzzle velocity. Other elements in the equation above **generally** have an effect not exceeding 1.5 m/s. As a matter of convenience, the other elements listed below are not individually measured, but their effects are realized to exist under the broader headings of shooting strength and ammunition efficiency.

## Shootingstrengthofweapons                  Ammunitionefficiency

1.  Tube wear
1. Propellant efficiency
2.  Manufacturer tolerances
2.   Projectile efficiency
3.   Reaction to recoil
a. Projectile weight (fuzed)
b. Construction of
(1) Rotating band (2) Bourrelet (3)  Obturating band

## A. Nature Of Propellant And Projectile Movement.

(1) A propellant is a low-order explosive that burns rather than detonates. In artillery weapons using separate-loading ammunition, the propellant burns within a chamber formed by the obturator spindle assembly, powder chamber, rotating band, and base of the projectile. For cannons using semifixed ammunition, the chamber is formed by the shell casing and the base of the projectile.

When the propellant is ignited by the primer, the burning propellant generates gases. When these gases develop enough pressure to overcome initial bore resistance, the projectile begins its forward motion.

(2) Several parts of the cannon tube affect interior ballistics. (See Figure 3-l.)
(a) The caliber of a tube is the inside diameter of the tube as measured between opposite lands.

(b) The breech recess receives the breechblock. The breech permits loading the howitzer from the rear.

(c) The powder chamber receives the complete round of ammunition. It is the portion of the tube between the gas check seat and the centering slope.

The **gas check seat**  is the tapered surface in the rear interior of the tube on weapons firing separate-loading ammunition. It seats the split rings of the obturating mechanism when they expand under pressure in firing. This expansion creates a metal-to-metal seal and prevents the escape of gases through the rear or the breech. Weapons firing semifixed ammunition do not have gas check seats since the expansion of the ease against the walls of the chamber provides a gas seal for-the breech.

The **centering slope** is the tapered portion at or near the forward end of the chamber that causes the projectile to center itself in the bore during loading.

(d) The forcing cone is the tapered portion near the rear of the bore that allows the rotating band to be gradually engaged by the rifling, thereby centering the projectile in the bore.

(e) The bore is the rifled portion of the tube (lands and grooves). It extends from the forcing cone to the muzzle. The rifled portion of the tube imparts spin to the projectile increasing stability in flight. The grooves are the depressions in the rifling. The lands are the raised portions. These parts engrave the rotating band. All United States (US) howitzers have a right-hand twist in rifling.

(f) The bore evacuator is located on enclosed, self-propelled howitzers with semiautomatic breech mechanisms. It prevents contamination of the crew compartment by removing propellant gases from the bore after firing. The bore evacuator forces the gases to flow outward through the bore from a series of valves enclosed on the tube.

(g) The counterbore is the portion at the front of the bore from which the lands have been removed to relieve stress and prevents the tube from cracking.

(h) The muzzle brake is located at the end of the tube on some howitzers. As the projectile leaves the muzzle, the high-velocity gases strike the baffles of the muzzle brake and are deflected rearward and sideways. When striking the baffles, the gases exert a forward force on the baffles that partially counteracts and reduces the force of recoil.

(3) The projectile body has several components that affect ballistics. (See Figure 3-2.)
Three of these affect interior ballistics--the bourrelet the rotating band and the obturating band.

(a) The bourrelet is the widest part of the projectile and is located immediately to the rear of the  ogive. The bourrelet centers the forward part of the projectile in the tube and bears on the lands of the tube. When the projectile is fired, only the bourrelet and rotating band bear on the lands of the tube.

(b) The rotating band is a band of soft metal (copper alloy) that is securely seated around the body of the projectile. It provides forward obturation (the forward gas-tight seal required to develop pressure inside the tube). The rotating band prevents the escape of gas pressure from around the projectile. When the weapon is fired, the rotating band contacts the lands and grooves and is pressed between them. As the projectile travels the length of the cannon tube, over the lands and grooves, spin is imparted. The rifling for the entire length of the tube must be smooth and free of burrs and scars. This permits uniform seating of the projectile and gives a more uniform muzzle velocity.

(c) The obturating band is a plastic band on certain projectiles. It provides forward obturation by preventing the escape of gas pressure from around the projectile.

(4) The sequence that occurs within the cannon tube is described below.

(a) The projectile is rammed into the cannon tube and rests on the  bourrelet.

The rotating band contacts the lands and grooves at the forcing cone.

(b) The propellant is inserted into the chamber. (c) The propellant explosive train is initiated by the ignition of the primer.

This causes the primer, consisting of hot gases and incandescent particles, to be injected into the igniter. The igniter burns and creates hot gases that flow between the propellant granules and ignite the granule surfaces; the igniter and propellant combustion products then act together, perpetuating the flame spread until all the propellant granules are ignited.

(d) The chamber is sealed, in the rear by the breech and obturator spindle group and forward by the projectile, so the gases and energy created by the primer, igniter, and propellant cannot escape. This results in a dramatic increase in the pressure and temperature within the chamber. The burning rate of the propellant is roughly proportional to the pressure, so the increase in pressure is accompanied by an increase in the rate at which further gas is produced.

(e) The rising pressure is moderated by the motion of the projectile along the barrel. The pressure at which this motion begins is the shot-start pressure. The projectile will then almost immediately encounter the rifling, and the projectile will slow or stop again until the pressure has increased enough to overcome the resistance in the bore. The rotating band and obturating band (if present) or the surface of the projectile itself, depending on design, will be engraved to the shape of the rifling.

The resistance decreases, thereby allowing the rapidly increasing pressure to accelerate the projectile.

(f) As the projectile moves forward, it leaves behind an increasing volume to be filled by the high-pressure propellant gases. the propellant is still burning, producing highpressure gases so rapidly that the motion of the projectile cannot fully compensate. As a result, the pressure continues to rise until the peak pressure is reached. The peak pressure is attained when the projectile has traveled about one-tenth of the total length of a full length howitzer tube.

(g) The rate at which extra space is being created behind the rapidly accelerating projectile then exceeds the rate at which high-pressure gas is being produced;
thus the pressure begins to fall. The next stage is the all-burnt position at which the burning of the propellant is completed. However, there is still considerable pressure in the tube;
therefore, for the remaining motion along the bore, the projectile continues to accelerate. As it approaches the muzzle, the propellant gases expand, the pressure falls, and so the acceleration lessens. At the moment the projectile leaves the howitzer, the pressure will have been reduced to about one sixth of the peak pressure. Only about one-third of the energy developed pushes the projectile. The other two-thirds is absorbed by the recoiling parts or it is lost because of heat and metal expansion.

(h) The flow of gases following the projectile out of the muzzle provides additional acceleration for a short distance (transitional ballistics), so that the full muzzle velocity is not reached until the projectile is some distance beyond the muzzle. The noise and shock of firing are caused by the jet action of the projectile as it escapes the flow of gases and encounters the atmosphere.

After this, the projectile breaks away from the influence of the gun and begins independent flight.

(i) This entire sequence, from primer firing to muzzle exit, typically occurs within 15 milliseconds but perhaps as much as 25 milliseconds for a large artillery howitzer.

## (5) Pressure Travel Curves Are Discussed Below.

(a) Once the propellant ignites, gases are generated that develop enough pressure to overcome initial bore resistance, thereby moving the projectile. Two opposing forces act on a projectile within the howitzer. The first is a propelling force caused by the high-pressure propellant gases pushing on the base of the projectile.

The second is a frictional force between the projectile and bore, which includes the high resistance during the engraving process, that opposes the motion of the projectile. The peak pressure, together with the travel of the projectile in the bore (pressure travel curve), determines the velocity at which the projectile leaves the tube.

(b) To analyze the desired development of pressure within the tube, we identify three types of pressure travel curves:
An elastic strength pressure travel curve represents the greatest interior pressure that the construction of the tube (thickness of the wall of the powder chamber, thickness of the tube, composition of the tube or chamber, and so on) will allow. It decreases as the projectile travels toward the muzzle because the thickness of the tube decreases.

A permissible pressure travel curve mirrors the elastic strength pressure travel curve and accounts for a certain factor of safety. It also decreases as the projectile travels through the tube because tube thickness decreases.

An actual pressure travel curve represents the actual pressure developed during firing within the tube. Initially, pressure increases dramatically as the repelling charge explosive train initiated and the initial resistance of the rammed projectile is overcome. After that resistance is overcome, the actual pressure gradually decreases because of the concepts explained by Boyle's Law. (Generally, as volume increases, pressure decreases.) The actual pressure should never exceed the permissible pressure.

Initial Excessive Pressure. This  is undesirable pressure travel curve. It exceeds the elastic strength pressure and permissible pressure. Causes of this travel curve would be an obstruction in the tube, a dirty tube, an "extra" propellant placed in the chamber, an unfuzed k projectile, or a crac ed projectile.

Delayed Excessive Pressure. This is an undesirable pressure travel curve. It exceeds the elastic strength pressure and remissible pressure. Causes that would result in this travel curve would be using wet powder or powder reversed.

Desirable Pressure Travel Curve. This curve does not exceed permissible pressure. It develops peak pressure at about one-tenth the length of the tube.

(6) The following general rules show how various factors tiect the velocity performance of a weapon projectile family-propellant type-charge combination
(a) An increase in the rate of propellant burning increases the resulting gas pressure developed within the chamber. An example of this is the performance of the multiperforated propellant grains used in white bag (WB) propellants. The result is that more gases are produced, gas pressure is increased, and the projectile develops a greater muzzle velocity. Damage to propellant grains, such as cracking and splitting from improper handling, also affect the rate of burn and thus the muzzle velocity.

(b) An increase in the size of the chamber without a corresponding increase in the amount of propellant decreases gas pressure; as a result, muzzle velocity will be less (Boyles Law).

(c) Gas escaping around the projectile decreases chamber pressure.

(d) An increase in bore resistance to projectile movement before peak pressure increases the pressure developed within the tube. Generally, this results in a dragging effect on the projectile, with a corresponding decrease in the developed muzzle velocity. Temporary variations in bore resistance can be caused by excessive deposits of residue within the cannon tube and on projectiles and by temperature differences between the inner and outer surfaces of the cannon tube.

## B. Standard Muzzle Velocity.

(1) Applicable firing tables list the standard value of muzzle velocity for each charge. These standard values are based on an assumed set of standard conditions. These values are points of departure and not absolute standards. Essentially, we cannot assume that a given weapon projectile family-propellant type-charge combination when fired will produce the standard muzzle velocity.

(2) Velocities for each charge are indirectly established by the characteristics of the weapons. Cannons capable of high-angle fire (howitzers) require a greater choice in the number of charges than cannons capable of only low-angle fire (guns). This choice is necessary to achieve range overlap between charges in high-angle fire and the desired range-trajectory combination in low-angle fire. Other factors considered are the maximum range specified for the weapon, the maximum elevation and charge, and the maximum permissible pressure that the weapon can accommodate.

(3) Manufacturing specifications for ammunition include a requirement for velocity performance to meet certain tolerances. Ammunition lots are subjected to test firings, which include measuring the performance of a tested lot and comparing it to the performance of a control (reference) lot that is tested concurrently with the same weapon. An assumption built into the testing procedure is that both lots of ammunition will be influenced in the same manner by the performance of the tube. This assumption, although accurate in most instances, allows some error to be introduced in the assessment of the performance of the tested lot of propellant. In field conditions, variations in the performance of different projectile or propellant lots can be expected even though quality control has been exercised during manufacturing and testing of lots. In other words, although a howitzer develops a muzzle velocity that is 3 meters per second greater (or less) than standard with propellant lot G, it will not necessarily be the same with any other propellant lot. The optimum method for determining ammunition performance is to measure the performance of a particular projectile family-propellant lot-charge combination (calibration).

However, predictions of the performance of a projectile family-propellant lot-charge group combination may be inferred with the understanding that they will not be as accurate as actual performance measurements.

c. Factors Causing Nonstandard Velocities. Nonstandard muzzle velocity is expressed as a variation (plus or minus so many meters per second) from the accepted standard.

Round-to-round corrections for dispersion cannot be made. Each of the following factors that cause nonstandard conditions is treated as a single entity assuming no influence from related factors.

(1) Velocity trends. Not all rounds of a series fired from the same weapon and using the same ammunition lot will develop the same muzzle velocity. Under most conditions, the first few rounds follow a somewhat regular pattern rather than the random pattern associated with normal dispersion. This phenomenon is called velocity trends (or velocity dispersion), and the magnitude varies with the cannon, charge, and tube condition at the time each round is fired. Velocity trends cannot be accurately predicted; thus, any attempt to correct for the effects of velocity trends is impractical. Generally, the magnitude and duration of velocity trends can be minimized when firing is started with a tube that is clean and completely free of oil. (See Figure 3-4.)
(2) Ammunition lots. Each ammunition, projectile, and propellant lot has its own mean performance level in relation to a common weapon.

Although the round-to-round variations within a given lot of the same ammunition (ammo) types are similar, the mean velocity developed by one lot may differ significantly in comparison to that of another lot. With separate-loading ammunition, both the projectile and propellant lots must be identified.

Projectile lots allow for rapid identification of weight differences. Although other projectile factors affect achieved muzzle velocity (such as, diameter and hardness of rotating band), the cumulative effect of these elements generally does not exceed 1.5 rids. As a matter of convenience and speed, they are ignored in the computation of firing data.

(3) Tolerances in new weapons. All new cannons of a given caliber and model will not necessarily develop the same muzzle velocity. In a new tube, the mean factors affecting muzzle velocity are variations in the size of the powder chamber and the interior dimensions of the bore. If a battalion equipped with new cannons fired all of them with a common lot of ammunition a variation of 4 meters per second between the cannon developing the greatest muzzle velocity and the cannon developing the lowest muzzle velocity would not be unusual. Calibration of all cannons allows the firing unit to compensate for small variations in the manufacture of cannon tubes and the resulting variation in developed muzzle velocity. The MVV caused by inconsistencies in tube manufacture remains constant and is valid for the life of the tube.

(4) Tube wear. Continued firing of a cannon wears away portions of the bore by the actions of hot gases and chemicals and movement of the projectile within the tube. These erosive actions are more pronounced when higher charges are fired. The greater the tube wear, the more the muzzle velocity decreases. Normal wear can be minimized by careful selection of the charge and by proper cleaning of both the tube and the ammunition.

(5) Nonuniform ramming. Weak  ramming decreases the volume of the chamber and thereby theoretically increases the pressure imparted to the projectile. This occurs because the pressure of a gas varies inversely with volume. Therefore, only a partial gain in muzzle velocity might be achieved. Of greater note is the improper seating of the projectile within the tube. Improper seating can allow some of the expanding gases to escape around the rotating band of the projectile and thus result in decreased muzzle velocity. The combined effects of a smaller chamber and escaping gases are difficult to predict. Weak, nonuniform ramming results in an unnecessary and preventable increase in the size of the dispersion pattern. Hard, uniform ramming is desired for all rounds. When semifixed ammunition is fired, the principles of varying the size of the chamber and escape of gases still apply, particularly when ammunition is fired through worn tubes. When firing semifixed ammunition, rearward obturation is obtained by the expansion of the cartridge case against the walls of the powder chamber. Proper seating of the cartridge case is important in reducing the escape of gases.

(6) Rotating bands. The ideal rotating band permits proper seating of the projectile within the cannon tube. Proper seating of the projectile allows forward obturation, uniform pressure buildup, and initial resistance to projectile movement within the tube. The rotating band is also designed to provide a minimum drag effect on the projectile once the projectile overcomes the resistance to movement and starts to move. Dirt or burrs on the rotating band may cause improper seating. This increases tube wear and contributes to velocity dispersion. If excessively worn, the lands may not engage the rotating band well enough to impart the proper spin to the projectile.

Insufficient spin reduces projectile stability in flight and can result in dangerously erratic round performance. When erratic rounds occur or excessive tube wear is noted, ordnance teams should be requested to determine the serviceability of the tube.

(7) Propellant and projectile temperatures. Any combustible material burns more rapidly when heated before ignition. When a propellant burns more rapidly than would be expected under standard conditions, gases are produced more rapidly and the pressure imparted to the projectile is greater. As a result, the muzzle velocity will be greater than standard and the projectile will travel farther. Table E in the tabular firing tables lists the magnitude of change in muzzle velocity resulting from a propellant temperature that is greater or less than standard. Appropriate corrections can be extracted from that table; however, such corrections are valid only if they are determined relative to the true propellant temperature. The temperature of propellant in sealed containers remains fairly uniform though not necessarily at the standard propellant temperature (70 degrees Fahrenheit [F}).

Once propellant has been unpacked, its temperature more rapidly approaches the air temperature. The time and type of exposure to the weather result in temperature variations from round to round and within the firing unit. It is currently impractical to measure propellant temperature and apply corrections for each round fired by each cannon. Positive action must be taken to maintain uniform projectile and propellant temperatures. Failure to do this results in erratic firing. The effect of an extreme change in projectile or propellant temperature can invalidate even the most recent corrections determined from a registration.

(a) Ready ammunition should be kept off the ground and protected from dirt, moisture, and direct rays of the sun. At least 6 inches of airspace should be between the ammunition and protective covering on the sides, 6 inches of dunnage should be on the bottom, and the roof should be 18 inches from the top of the stack. These precautions will allow propellant and projectile temperatures to approach the air temperature at a uniform rate throughout the firing unit.

(b) Propellant should be prepared in advance so that it is never necessary to fire freshly unpacked ammunition with ammunition that has been exposed to weather during a fire mission.

(c) Ammunition should be fired in the order in which it was unpacked.

(d) Propellant temperature should be determined from ready ammunition on a periodic basis, particularly if there has been a change in the air temperature.

(8) Moisture content of propellant. Changes in the moisture content of propellant are caused by improper protection from the elements or improper handling of the propellant. These changes can affect muzzle velocity. Since the moisture content cannot be measured or corrected for, the propellant must be provided maximum protection from the elements and improper handling.

(9) Position of propellant in the chamber. In fixed and semifixed ammunition the propellant has a relatively fixed position with respect to the chamber, which is formed by the cartridge case. In separate-loading ammunition, however, the rate at which the propellant burns and the developed muzzle velocity depends on how the cannoneer inserts the charge. To ensure proper ignition of the propellant he must insert the charge so that the base of the propellant bag is flush against the obturator spindle when the breech is closed. The cannoneer ensures this by placing the propellant flush against the Swiss groove (the cutaway portion in the powder chamber). The farther forward the charge is inserted, the slower the burning rate and the lower the subsequent muzzle velocity. An increase in the diameter of the propellant charge can also cause an increase in muzzle velocity. Loose tie straps or wrappings have the effect of increasing the diameter of the propellant charge. Propellant charge wrappings should always be checked for tightness, even when the full propellant charge is used.

(10) Weight of projectile. The weights of like projectiles vary within certain zones
(normally termed square weight). The appropriate weight zone is stenciled on the projectile (in terms of so many squares). Some projectiles are marked with the weight in pounds. In general terms, a heavier-than-standard projectile normally experiences a decrease in muzzle velocity. This is because more of the force generated by the gases is used to overcome the initial resistance to movement. A lighter-than-standard projectile generally experiences an increase in velocity.

NOTE: Copperhead projectiles are not marked with weight in pounds. The precision manufacturing process used guarantees a weight of 137.6 pounds.

(11) Coppering. When the projectile velocity within the bore is great, sufficient friction and heat are developed to remove the outer surface of the rotating band. Material left is a thin film of copper within the bore and is known as coppering. This phenomenon occurs in weapons that develop a high muzzle velocity and when high charges are fired. The amount of copper deposited varies with velocity. Firing higher charges increases the amount of copper deposited on the bore surfaces, whereas firing lower charges reduces the effects of coppering.

Slight coppering resulting from firing a small sample of rounds at higher charges tends to increase muzzle velocity.

Erratic velocity performance is a result of excessive coppering whereby the resistance of the bore to projectile movement is affected. Excessive coppering must be removed by ordnance personnel.

(12) Propellant residue.

Residue from burned propellant and certain chemical agents mixed with the expanding gases are deposited on the bore surface in a manner similar to coppering. Unless the tube is properly cleaned and cared for, this residue will accelerate tube wear by causing pitting and augmenting the abrasive action of the projectile.

(13) Tube conditioning. The temperature of the tube has a direct bearing on the developed muzzle velocity. A cold tube offers a different resistance to projectile movement and is less susceptible to coppering, even at high velocities. In general, a cold tube yields more range dispersion; a hot tube, less range dispersion.

(14) Additional effects in interior ballistics. The additional effects include tube memory and tube jump.

(a) Tube memory is a physical phenomenon of the cannon tube tending to react to the firing stress in the same manner for each round, even after changing charges. It seems to "remember" the muzzle velocity of the last charge fired. For example, if a fire mission with charge 6 M4A2 is followed by a fire mission with charge 4 M4A2, the muzzle velocity of the first round of charge 4 may be **unpredictably** higher. The inverse is also true.

(b) Tube jump occurs as the projectile tries to maintain a straight line when exiting the muzzle. This phenomenon causes the tube to jump up when fired and may cause tube displacement.

## 3-2. Transitional Ballistics

Sometimes referred to as intermediate ballistics, this is the study of the transition from interior to exterior ballistics. Transitional ballistics is a complex science that involves a number of variables that are not fully understood; therefore, it is not an exact science. What is understood is that when the projectile leaves the muzzle, it receives a slight increase in MV from the escaping gases. Immediately after that, its MV begins to decrease because of drag.

## 3-3. Exterior Ballistics

Exterior ballistics is the science that deals with the factors affecting the motion of a projectile after it leaves the muzzle of a piece. At that instant, the total effects of interior ballistics in terms of developed muzzle velocity and spin have been imparted to the projectile.

Were it not for gravity and the effects of the atmosphere, the projectile would continue indefinitely at a constant velocity along the infinite extension of the cannon tube. The discussion of exterior ballistics in the following paragraphs addresses elements of the trajectory, the trajectory in a vacuum, the trajectory within a standard atmosphere, and the factors that affect the flight of the projectile.

a. Trajectory Elements.

The trajectory is the path traced by the center of gravity of the projectile from the origin to the level point. The elements of a trajectory are classified into three groups--intrinsic, initial, and terminal elements.

(1) Intrinsic elements.

Elements that are characteristic of any trajectory, by definition, are intrinsic elements. (See Figure 3-5.)
(a) The origin is the location of the center of gravity of the projectile when it leaves the muzzle. It also denotes the center of the muzzle when the piece has been laid.

(b) The ascending branch is the part of the trajectory that is traced as the projectile rises from the origin.

(c) The summit is the highest point of the trajectory.

(d) The maximum ordinate is the difference in altitude (alt) between the origin and the summit.

(e) The descending branch is the part of the trajectory that is traced as the projectile is falling.

(f) The level point is the point on the descending branch that is the same altitude as the origin.

(g) The base of the trajectory is the straight line from the origin to the level point.

(2) Initial elements. Elements that are characteristic at the origin of the trajectory are initial elements. (See Figure 3-6.)
(a) When the piece is laid, the line of elevation is the axis of the tube extended.

(b) The line of departure is a line tangent to the trajectory at the instant the projectile leaves the tube.

(c) Jump is the displacement of the line of departure from the line of elevation that exists at the instant the projectile leaves the tube.

(d) The angle of site is the smaller angle in a vertical plane from the base of the trajectory to a straight line joining the origin and the target. Vertical interval is the difference in altitude between the target and the origin.

(e) The complementary angle of site is an angle that is algebraically added to the angle of site to compensate for the nonrigidity of the trajectory.

(f) Site is the algebraic sum of the angle of site and the complementary angle of site. Site is computed to compensate for situations in which the target is not at the same altitude as the battery.

(g) Complementary range is the number of meters (range correction)
equivalent to the number of mils of complementary angle of site.

(h) The angle of elevation is the vertical angle between the base of the trajectory and the axis of the bore required for a projectile to achieve a prescribed range under standard conditions.

(i) The quadrant elevation is the angle at the origin measured from the base of the trajectory to the line of elevation. It is the algebraic sum of site and the angle of elevation.

(3) Terminal elements. Elements that are characteristic at the point of impact are terminal elements. (See Figure 3-7.)
(a) The point of impact is the point at which the projectile strikes the target area.

(The point of burst is the point at which the projectile bursts in the air.)
(b) The line of fall is the line tangent to the trajectory at the level point.

(c) The angle of fall  is the vertical angle at the level point between the line of fall and the base of the trajectory.

(d) The line of impact is a line tangent to the trajectory at the point of impact.

(e) The angle of impact is the acute angle at the point of impact between the line of impact and a plane tangent to the surface at the point of impact. This term should not be confused with angle of fall.

## B. Trajectory In A Vacuum.

(1) If a round were fired in a vacuum, gravity would cause the projectile to return to the surface of the earth. The path or trajectory of the projectile would be simple to trace. All projectiles, regardless of size, shape, or weight, would follow paths of the same shape and would achieve the same range for a given muzzle velocity and quadrant elevation.

(2) The factors used to determine the data needed to construct a firing table for firing in a vacuum are the angle of departure, muzzle velocity, and acceleration caused by the force of gravity. The initial velocity imparted to a round has two components--horizontal velocity and vertical velocity. The relative magnitudes of horizontal and vertical components vary with the angle of elevation. For example, if the elevation were zero, the initial velocity imparted to the round would be horizontal in nature and there would be no vertical component.

If, on the other hand, the elevation were 1,600 mils (disregarding the effects of rotation of the earth), the initial velocity would be vertical and there would be no horizontal component.

(3) Gravity causes a projectile in flight to fall to the earth. Because of gravity, the height of the projectile at any instant is less than it would be if no such force were acting on it. In a vacuum, the vertical velocity would decrease from the initial velocity to zero on the ascending branch of the trajectory and increase from zero to the initial velocity on the descending branch, Zero vertical velocity would occur at the summit of the trajectory. For every vertical velocity value on the upward leg of the ascending branch there is an equal vertical velocity value downward on the descending branch. Since there would be no resistance to the forward motion of the projectile in a vacuum, the horizontal velocity component would be a constant. The acceleration caused by the force of gravity (9.81 m/s) affects only the vertical velocity.

## C. Trajectory In A Standard Atmosphere.

(1) The resistance of the air to projectile movement depends on the air movement, density, and temperature. As a point of departure for computing firing tables, assumed conditions of air density and air temperature with no wind are used. The air structure is called the standard atmosphere.

(2) The most apparent difference between the trajectory in a vacuum and the trajectory in the standard atmosphere is a net reduction in the range achieved by the projectile. A
comparison of the flight of the projectile in a vacuum and in the standard atmosphere is shown in Figure 3-8.

(3) The difference in range is due to the horizontal velocity component in the standard atmosphere no longer being a constant value. The horizontal velocity component is continually decreased by the retarding effect of the air. The vertical velocity component is also afected by air resistance. The trajectory in the standard atmosphere has the following characteristic differences from the trajectory in a vacuum:
(a) The velocity at the level point is less than the velocity at the origin. (b) The mean horizontal velocity of the projectile beyond the summit is less than the mean velocity before the projectile reaches the summit; therefore, the projectile travels a shorter horizontal distance. Hence, the descending branch is shorter than the ascending branch.

The angle of fall is greater than the angle of elevation.

(c) The spin (rotational motion) initially imparted to the projectile causes it to respond differently in the standard atmosphere because of air resistance. A trajectory in the standard atmosphere, compared to a trajectory in a vacuum, will be shorter and lower at any specific point along the trajectory for the following reasons:
Horizontal velocity is not a constant value; it decreases with each succeeding time interval.

Vertical velocity is affected by both gravity and the effects of the atmosphere on the projectile.

The summit in a vacuum is midway between the origin and the level point; in the standard atmosphere, it is actually nearer the level point.

The angle of fall in a vacuum is equal to the angle of elevation; in the standard atmosphere, it is greater.

## D. Relation Of Air Resistance And Projectile Efficiency To Standard Range.

(1) This paragraph concerns only those factors that establish the relationship between the standard range, elevation, and achieved range.

(a) The standard (chart) range is the range opposite a given elevation in the firing tables. It is assumed to have been measured along the surface of a sphere concentric with the earth and passing through the muzzle of a weapon. For all practical purposes, standard range is the horizontal distance from the origin of the trajectory to the level point.

(b) The achieved range is the range attained as a result of firing the cannon at a particular elevation.

If actual firing conditions duplicate the ballistic properties and met conditions on which the firing tables are based, then the achieved range and the standard range will be equal.

(c) The corrected range is the range corresponding to the elevation that must be fired to reach the target.

(2) Air resistance affects the flight of the projectile both in range and in direction.

The component of air resistance in the direction opposite that of the forward motion of the projectile is called drag. Because of drag, both the horizontal and vertical components of velocity are less at any given time along the trajectory than they would be if drag was zero (as it would be in a vacuum). This decrease in velocity varies directly in magnitude with drag and inversely with the mass of the projectile. Several factors considered in the computation of drag areas follows:
(a) Air density. The drag of a given projectile is proportional to the density of the air through which it passes. For example, an increase in air density by a given percentage increases drag by the same percentage. Since the air density at a specific place, time, and altitude varies widely, the standard trajectories reflected in the firing tables were computed with a fixed relationship between air density and altitude.

(b) Velocity. The  faster a projectile moves, the more the air resists its motion.

Examination of a set of firing tables reveals that given a constant elevation, the effect of a 1
percent change in air density (and corresponding 1 percent increase in drag) increases with an increase in charge (with the greater muzzle velocity). The drag is approximately proportional to the square of the velocity except when velocity approaches the speed of sound. At the speed of sound, drag increases more rapidly because of the increase in pressure behind the sound wave.

(c) Projectile diameter. Two projectiles of identical shape but of different size will not experience the same drag. For example, a large projectile will offer a larger area for the air to act upon; thus, its drag will be increased by this factor. The drag of projectiles of the same shape is assumed to be proportional to the square of the projectile diameter.

(d) Ballistic coefficient. The ballistic coefficient of a projectile is a measure of its relative efficiency in overcoming air resistance. An increase in the ballistic coefficient reduces the effect of drag and consequently increases range. The reverse is true for a decrease in the ballistic coefficient. The ballistic coefficient can be increased by increasing the ratio of the weight of the projectile to the square of its diameter. It can also be increased by improving the shape of the projectile.

(e) Drag coefficient. The drag coefficient combines several ballistic properties of typical projectiles. These properties include yaw (the angle between the direction of motion and the axis of the projectile) and the ratio of the velocity of the projectile to the speed of sound.

Drag coefficients, which have been computed for many projectile types, simplify the work of ballisticians. When a projectile varies slightly in shape from one of the typical projectile types, the drag coefficient can be determined by computing a form factor for the projectile and multiplying the drag coefficient of a typical projectile type by the form factor.

## E. Deviations From Standard Conditions. Firing Tables Are Based On Actual Firings Of

a piece and its ammunition correlated to a set of standard conditions. Actual firing conditions, however, will never equate to standard conditions. These deviations from standard conditions, if not corrected for when computing firing data will cause the projectile to impact at a point other than the desired location. Corrections for nonstandard conditions are made to improve accuracy.

(1) Range effects. Some of the deviations from standard conditions affecting range are:
Muzzle velocity. Projectile weight.

Range wind.

Air temperature.

Air density. Rotation of the earth.

(2) Deflection effects.

Some of the deviations from the standard conditions affecting deflection are:
Drift.

Crosswind.

Rotation of the earth.

## 3-4. Dispersion And Probability

If a number of rounds of ammunition of the same caliber, lot, and charge are fired from the same position with identical settings used for deflection and quadrant elevation, the rounds will not all impact on a single point but will fall in a scattered pattern. In discussions of artillery fire, this phenomenon is called dispersion, and the array of bursts on the ground is called the dispersion pattern.

## 3-5. Causes Of Dispersion

a. The points of impact of the projectiles will be scattered both in deflection and in range. Dispersion is caused by inherent (systemic) errors. It should never be confused with round-to-round variations caused by either human or constant errors. Human errors can be minimized through training and supervision.

Corrections to compensate for the effects of constant errors can be determined from the TFT. Inherent errors are beyond control or are impractical to measure. Examples of inherent errors are as follows:
(1) Conditions in the bore. The muzzle velocity achieved by a given projectile is affected by the following:
Minor variations in the weight of the projectile, form of the rotating band, and moisture content and temperature of the propellant grains.

Differences in the rate of ignition of the propellant. Variations in the arrangement of the propellant grains. Differences in the rate of ignition of the propellant. Variations in the ramming of the projectile.

Variations in the temperature of the bore from round to round.

For example, variations in the bourrelet and rotating band may cause inaccurate centering of the projectile, which can result in a loss in achieved range because of instability in flight.

(2) Conditions in the carriage.

Deflection and elevation are affected by the following:
Play (looseness) in the mechanisms of the carriage.

Physical limitations of precision in setting values of deflection and quadrant elevation on the respective scales.

Nonuniform reactions to firing stress.

(3) Conditions during flight. The flight of the projectile may be affected by the difference in air resistance created by variations in the weight, achieved muzzle velocity, and projectile. Also, the projectile may be affected by minor variations in wind, air density or air pressure, and air temperature from round to round.

b. The distribution of bursts (dispersion pattern) in a given sample of rounds is roughly elliptical (Figure 3-9) in relation to the line of fire.

c. A rectangle constructed around the dispersion area (excluding any erratic rounds) is called the dispersion rectangle, or 100 percent rectangle. (See Figure 3-10.)

## 3-6. Mean Point Of Impact

For any large number of rounds fired, the average (or mean) location of impact can be
-
determined by drawing a diagram of the pattern of bursts as they appear on the ground. A line drawn perpendicular to the line of fire can be used to divide the sample rounds into two equal groups. Therefore, half of the rounds will be over this line when considered in relation to the weapon. The other half of the rounds will be short of this line in relation to the weapon. This dividing line represents the mean range of the sample and is called the mean range line. A second line can be drawn parallel to the line of fire, again dividing the sample into two equal groups. Half of the rounds will be to the right of this line, and half will be to the left. This line represents the mean deflection of the sample and is called the mean deflection line. (See Figure
3-9.) The intersection of the two lines is  the mean point of impact (MPI). (See Figure 3-10.)

## 3-7. Probable Error

Probable error is nothing more than an error that is exceeded as often as it is not exceeded. For example, in Figure 3-11, consider only those rounds that have impacted over the mean range line (line AB). These rounds all manifest errors in range, since they all impacted over the mean range line. Some of the rounds are more in error than others. At a point beyond the MPI, a second line can be drawn perpendicular to the line of fire to divide the "ovens" into two equal groups (line CD, Figure 3-11). When the distance from the MPI to line CD is used as a measure of probable error, it is obvious that half of the overs show greater magnitude of error than the other half.  This distance is one probable error in range. The range probability curve expresses the following:
a. In a large number of samples, errors in excess and errors in deficiency are equally frequent (probable) as shown by the symmetry of the curve.

b. The errors are not uniformly distributed. Small errors occur more frequently than large errors as shown by the greater number of occurrences near the mean point of impact.

## 3-8. Dispersion Zones

If the dispersion rectangle is divided evenly into eight zones in range with the value for 1
probable error in range (PER) used as the unit of measure, the percentage of rounds impacting within each zone is as indicated in Figure 3-12. The percentage of rounds impacting within each zone has been determined through experimentation. By definition of probable error, 50 percent of all rounds will impact within 1 probable error in range or deflection of the mean point of impact (25 percent over and 25 percent short or 25 percent left and 25 percent right).

## 3-9. Range Probable Error

The values for range probable error at various ranges are given in Table G of the tabular firing tables (TFT). These values may be used as an index of the precision of the piece at a particular charge and range. The values for range probable error are listed in meters. Firing Table (FT) values have been determined on the basis of actual firing of ammunition under controlled conditions. For example, FT 155-AM-2 shows that the value of range probable error for charge 5 green bag (GB) at a range of 6,000 meters is 15 meters. On the basis of the 100
percent rectangle, 50 percent of the rounds will impact within 15 meters (over and short) of the mean range line, 82 percent will impact within 30 meters (over and short), 96 percent will impact within 45-meters (over and short), and 100 percent will impact within 60 meters.

## 3-10. Fork

The term *fork* is used to express the change in elevation (in mils) needed to move the mean point of impact 4 probable errors in range. The values of fork are listed in Table F of the firing tables. For example, FT 155-AM-2 shows that the value of fork for a howitzer firing charge 5GB at a range of 6,000 meters is 4 mils. On the basis of the value for probable error in range (paragraph 3-9), adding 4 mils to the quadrant elevation would cause the MPI to move 60 meters. Fork is used in the computation of safety data (executive officer's minimum QE).

## 3-11. Deflection Probable Error

The values for probable error in deflection (PED) are listed in Table G of the firing tables. For artillery cannons, the deflection probable error is considerably smaller than the range probable error. Values for PED are listed in meters. With the same parameters as those used in paragraph 3-9, the deflection probable error is 4
meters.

Therefore, 50 percent of the rounds will impact within 4 meters of the mean deflection line (left and right); 82 percent, within 8 meters (left and right); 96 percent, within 12 meters (left and right); and 100 percent, within 16 meters.

## 3-12. Time-To-Burst Probable Error

The values of time-to-burst probable error (PETB) (Figure 3-13) are listed in Table G of the firing tables. Each of these values is the weighted average of the precision of a time fuze timing mechanism in relation to the actual time of flight of the projectile. For example, if a 155-mm howitzer fires charge 5GB at a range of 6,000
meters, the value for probable error in time to burst is 0.11 second. As in any other dispersion pattern, 50 percent of the rounds will function within 0.11 second; 82
percent, within 0.22 second; 96 percent, within 0.33 second; and 100 percent within
0.44 second of the mean fuze setting.

## 3-13. Height-Of-Burst Probable Error

With the projectile fuzed to burst in the air, the height-of-burst probable error
(PEHB) (Figure 3-13) is the vertical component of 1 time-to-burst probable error. The height-of-burst probable error reflects the combined effects of dispersion caused by variations in the functioning of the time fuze and dispersion caused by the conditions described in paragraph 3-5(a). The values listed (in meters) follow the same pattern of distribution as for those discussed for range dispersion. These values are listed in Table G of the firing tables.

## 3-14. Range-To-Burst Probable Error

Range-to-burst probable error (PERB) (Figure 3-13) is the horizontal component of 1 time-to-burst probable error. When this value is added to or subtracted from the expected range to burst, it will produce an interval along the line of fire that should contain 50 percent of the rounds fired. These values are listed in Table G of the firing tables.

## Chapter 4 Muzzle Velocity Management

The achieved muzzle velocity is the result of forces acting on the projectile. To obtain accurate artillery fire, the performance of the weapon projectile family-propellant type-charge combination must be known. If it is not known, the result can be reduced effects on the target or friendly casualties (for example, danger close, final protective fire [FPF], converged sheafs, and so on). Firing tables give standard muzzle velocities for a standard weapon firing standard ammunition under standard conditions. However, muzzle velocities achieved in actual firing may differ from the standard muzzle velocities because of variations in the manufacture of the weapon and ammunition, wear in the weapon tube, projectile weight, propellant temperature, propellant lot efficiency, or a combination of these factors.

The M90 velocimeter enables a firing unit to continually update muzzle velocity data. This chapter describes muzzle velocity management with the M90 velocimeter.

## 4-1. Muzzle Velocity Terms

The following terms are associated with muzzle velocity management.

a. Muzzle velocity-- the velocity achieved by a projectile as it leaves the muzzle of the weapon (measured in meters per second).

b. Standard muzzle velocity-- An established muzzle velocity used for comparison. It is dependent upon the weapon system, propellant type, charge, and projectile. It is also referred to as reference muzzle velocity.

c. Muzzle velocity variation-- the change in muzzle velocity of a weapon (expressed in meters per second) from the standard muzzle velocity.

d. Projectile family-- a group of projectiles that have exact or very similar ballistic characteristics. Projectile types within the family are identified by model number.

e. Propellant type-- the  nomenclature of the propellant used for a particular charge.

f. Charge group-- the charges within the propellant type associated with a projectile family, within which MVVs can be transferred. (See Table 4-1.) This has been referred to as propellant model or powder model in the past and in other references. In separate-loading ammunition (155 mm) these terms are synonymous, but in 105-mm ammunition, three charge groups are within a propellant type.

g. Preferred charges-- the charges preferred for measuring and transferring muzzle velocities. These charges produce consistent predictable muzzle velocities. The MVVs they produce **should** not vary more than 1.5 meters per second for the same charge or other charges of the same charge group. Therefore, the MVV determined for one charge of a propellant type will be similar (1.5 rids) to another charge of the same propellant type and lot. Preferred charges are identified in Table 4-1.

NOTE: The principle of MWs not varying by more than 1.5 m/s **generally** holds true within **preferred subsonic charges** of a propellant type. However, the convenience gained by this assumption more than offsets losses in accuracy, and it is sufficiently valid to allow for accurate massing.

h. Restricted charges-- those charges within a charge group to which it is not preferred to transfer measured MVVs or for which it is not authorized to fire (is based on the weapon TM).

The performance of a restricted charge is not indicative of the performance of other charges within the charge group.

i. Adjacent charge-- charges within a charge group which are 1 charge increment greater or less than the charge calibrated. Used in the conduct of a calibration and subsequent lot inference techniques.

j. Propellant lot-- a group of propellants made by the same manufacturer at the same location with the same ingredients.

k. Calibration-- measuring the muzzle velocity of a weapon and then performing a comparison between the muzzle velocity achieved by a given piece and the accepted standard. There are two types of calibration--absolute and comparative.

(1) In absolute calibration, the weapon muzzle velocity is compared to the firing table reference muzzle velocity.

(2) In a comparative calibration, the achieved muzzle velocities of two weapons are compared.

l. M90 Readout average-- the average MV measured by the M90 which has not been corrected to standard projectile weight and standard propellant temperature.

m. Calibrated muzzle velocity-- an M90 readout average that has been corrected to standard projectile weight and propellant temperature.

n. Historical muzzle velocity-- a calibrated muzzle velocity which has been recorded in a muzzle velocity logbook.

o. Inferred calibration--   the MV of a weapon is determined through mathematical procedures by using data from a first lot calibration (baseline data) and the relative efficiency of a second lot of propellant.

p. Erosion-- the wear in a howitzer tube that is the result of firing rounds. It is measured from a pullover gauge reading, which is described in inches, or estimated by computing the equivalent full charges (EFCs) for erosion.

This is determined by multiplying the number of rounds fired with a given charge and the number of EFCs per round for that charge and projectile.

q. Shooting strength-- the change in the achieved muzzle velocity of a howitzer over time caused by erosion, which is a function of erosion and projectile family ballistics.

r. Ammunition efficiency-- the change in velocity which is the sum of the projectile efficiency and propellant efficiency.

s. Projectile efficiency-- known deviations from the standard for a particular projectile which effect the achieved velocity. For example, a high-explosive (HE) Ml 07 projectile which weighs 3   , 93.9 pounds, vice the standard 4    , 95.0 pounds, would have a predictable change in velocity, depending on the charge fired.

t. Propellant efficiency-- known deviations from the standard for a particular propellant which effects the velocity of the projectile. For example, a lot of M3A1 propellant may perform differently than the standard for that propellant type but is still acceptable for firing.

 NOTE:   Refer to ST 6-40-16 for information on the chare group and preferred charges for the 8-inch (203-mm) howitzer.

## 4-2. Calibration

Three techniques can be used to determine calibration data. The accuracy and complexity of these different techniques varies greatly. Each of the techniques must be understood and applied correctly to the tactical situation. The following order of preference can be used as a guideline. The techniques are listed in order of decreasing preference.

M90 chronograph calibration or baseline calibration. Subsequent lot inferred calibration. Predictive muzzle velocity techniques.

## A.  M90 Chronograph Calibration.

(1) Determine calibration data. The howitzer section installs the M90
velocimeter and records the administrative (admin) data at the top of the M90 Velocimeter Work Sheet (DA Form 4982-l-R). The M90 readout values are recorded in the center portion of the form. Normally, data from six usable rounds, all preferably fired within 20 minutes, are used to ensure the most accurate calibration data. These six rounds can be from any fire mission conducted by the firing unit. Specially conducted calibration missions are not required. If the howitzer tube is cold (that is, has not been engaged in firing or in low air temperatures) the firing of warm-up rounds is recommended. Fewer than six rounds can be used. In these situations, the calibration validity is reduced in the same way that the validity of a registration is reduced when the number of rounds fired is less than normal. In these situations, refer to Chapter 10, Table
10-1 for validity information and the effect of reduced rounds on the calibration data. Powder temperature differences between rounds decrease the validity of the calibration. To reduce powder temperature changes from round to round, use proper propellant handling and storing procedures in the firing unit and fire all rounds measured for a calibration within a 20-minute period. Follow these procedures in the calibration of all weapons. When the admin data and the M90 velocimeter readout data are entered on DA Form 4982- l-R for all weapons, the form is given to the fire direction center.

(2) Determine M90 readout average. The FDO inspects the readout values for all rounds and deletes any invalid readout values, those exceeding the readout average by 3.0 m/s.

This  3.O m/s approximates 4 PER in the target area for the given charge. The FDC personnel then determine the new readout average for the usable rounds by adding all usable readout values and dividing the sum by the number of usable rounds. This value includes the effects of nonstandard propellant temperature and projectile weight.

(3) Correct to standard. The M90 velocimeter readout average is not used in its original form because it includes the effects of projectile weight and propellant temperature on the muzzle velocity.

The MV can be used when the corrections for projectile weight and propellant temperature are applied by extracting the value from the appropriate table in the MVCT M90-2 manual and applying that value to the readout average. The correction tables contain data to correct the readout average to what it would have been if the reading had been determined with a standard square-weight projectile and a standard propellant temperature of
70oF. Enter MVCT M90-2 for the appropriate weapon system and projectile family.

Locate the page containing the table for the same charge fired in the calibration. Enter the table with the average propellant temperature and the weight of the projectile fired. Interpolate the value to correct the readout average to standard, and apply that value to the readout average.

The result is the calibrated muzzle velocity for the weapon.

(4) Complete HE M90 velocimeter worksheet. Once the velocity of the rounds fired has been determined, FDC personnel are responsible for verifying and completing the DA
Form 4982-l-R. This will include the steps in Table 4-2. A completed DA Form 4982- l-R is
.

.

shown in Figure 4-1.

## (5) Complete The Muzzle Velocity Record (Da Form 4982-R).

(a) DA Form 4982-R is the record of a calibration kept in the battery or platoon muzzle velocity log book. The top part of the form (FIRST-LOT
CALIBRATION) is used to determine the weapon MVV for a specific charge, when corrected to standard. For future reference, place the completed muzzle velocity record into the unit muzzle velocity logbook under the appropriate weapon projectile family-propellant type-charge group. Ensure this information is given to the platoon leader or XO for entry on DA Form 2408-4 (Weapon Record Data) or NAVMC 10558
(Weapon Record Book, Part 1) and 10558A (Weapon Record Book, Part H) for the weapon.

(b) The determined MVV is used in the solution of concurrent and subsequent met techniques and terrain gun position corrections. The lower part of the form (SECOND-LOT CALIBRATION AND SECOND-LOT INFERENCE) is used to infer muzzle velocity data for a second lot of propellant and/or ammunition.

(c) Table 4-3 provides the steps for completing DA Form 4982-R, and Figure 4-2 shows the form completed through the first nine steps.

## B. Subsequent Lot Inferred Calibration.

(1) Inferred subsequent lot calibration techniques allow a firing unit to quickly update muzzle velocity information for a given projectile family-propellant type combination, when firing a new lot of propellant.

Subsequent lot calibration is used to isolate the difference in efficiency between two propellant lots for one howitzer firing the same projectile family. This difference is applied to the first lot calibration data for the other howitzers to determine calibration data for the second lot. This technique can be used when the situation does not permit the calibration of the new lot with all guns.

(2) To accomplish this technique, the following requirements must be met:
Calibration of the first lot must be completed for the entire unit.
Calibration of a second lot must be completed for one gun.
(3) A calibration should be completed with all howitzers as soon as the situation allows. Table 4-4 provides the steps for conducting a subsequent lot calibration. Figure 4-3 shows DA Form 4982- 1-R completed for a second-lot inferred calibration. Figure 4-4 shows DA Form 4982-R completed for a second-lot inferred calibration.

c. Predictive Muzzle Velocity Technique. While it is not practical to predict (within
0.1 m/s) the velocity of every round, it is possible to approximate velocities to within 1 or 2 m/s with current available information. This may be useful when calibration is not possible, when updating calibration data, or when trying to increase the accuracy of inferred MV techniques.

(1) When calibration is not possible, the shooting strength of the howitzer can be used as the MVV. While this may be enough when no other data are available, it is important to understand that an MVV consists of more than just shooting strength. An equation can be created for determining an MVV by using its basic parts. (See Figure 4-5.)
(2) If all three elements are known, it is possible to determine a value for MVV. It is neither practical nor necessary to quantify round-to-round variation. This element is usually small and subject to rapid change. Projectile efficiency, as a part of ammunition efficiency, is accounted for in solving the concurrent and subsequent met techniques. Therefore, if the round-to-round variation and the projectile efficiency are eliminated from the equation, the howitzer shooting strength and the propellant efficiency of the propellant lot to be fired can approximate the MVV. (See Figure 4-6.)
(3) If calibration is not possible, adding the propellant efficiency to the shooting strength will result in a more accurate MVV for determining firing data than if the shooting strength is considered alone. This MVV can be used as the MVV for manual fire missions. Each howitzer has a value for shooting strength for each projectile family. Also, the value of propellant efficiency applies to any projectile family with which the propellant lot is fired.

## 4-3. Estimating Shooting Strength

a. There may be times when calibration is not possible. If the M90 is not available or there is not time to conduct a calibration, it may be necessary to determine the shooting strength of the howitzer by other means. The shooting strength of a howitzer can be determined by using pullover gauge readings and/or **erosion EFC** service round effects with the appropriate TFT for the weapon-projectile combination to be fired. (See Table 4-5.) DA Form 2408-4 provides the information to determine the shooting strength of each howitzer. (See Figure 4-7.)
b. The number of EFCs is determined by multiplying the number of rounds fired for a specific projectile and propellant by the equivalent erosion effect in decimals for the charge fired listed in the introduction of the TFT. Different projectile families have different TFTs and consequently different values for equivalent erosion effect in decimals. Pullover gauge readings can be determined regularly by the maintenance section in conjunction with borescoping the howitzer. The most accurate technique is to combine the pullover gauge reading and the erosion EFCs fired after the pullover gauge reading to determine an expected loss in muzzle velocity. The most recent pullover gauge reading or total erosion EFCs may be used to determine the approximate loss in muzzle velocity. Table 4-6 provides the steps for determining the pullover gauge reading.

## 4-4. Updating Mvv Data

Once determined, the calibration data represent the best indicator of the expected MVV.

But the MVV is not valid forever since the howitzer shooting strength changes as more rounds are fired. Calibration data can be made indefinitely valid if the shooting strength is continually updated. If the shooting strength of the howitzer is determined at the time of calibration, the changes in shooting strength can be added to the calibrated MVV over time. The current shooting strength can be determined from the Approximate Losses in Muzzle Velocity table in the TFT introduction on the basis of the pullover gauge readings and/or EFCs. The change in shooting strength is determined by subtracting the shooting strength at the time of calibration from the current shooting strength. This difference is then applied to the calibrated MVV to determine a current or updated MVV.

## 4-5. Other Applications

a. The possible applications of the basic equation, Figure 4-6, provide enough flexibility to determine any of the three parts of the equation (MVV, shooting strength, and propellant efficiency). If any two parts are known, the third can be determined. For example, if a replacement howitzer is received without its DA Form 2408-4, its shooting strength would be unknown. However, if it was calibrated and the propellant efficiency of the calibrated propellant lot is known, the shooting strength can be approximated (a modification of the formula found in Figure 4-6). This approximated shooting strength could then be applied by using the techniques described in paragraphs 4-2 and 4-3.

b. A useful  application of the basic equation is the ability to solve for the propellant efficiency of a given propellant lot. The propellant efficiency could then be used to predict an MVV for a different projectile family. (See the example below.)

## 4-6. Mvv Logbook

Once MV data have been determined, these data are used for numerous techniques. MV
data must be recorded on DA Form 4982-R which is then filed in an MV logbook. The MV
logbook allows for quick referencing of howitzer performance when firing a particular projectile family-propellant lot-charge combination. The major sections in the MV logbook are for the projectile families. Each one of the sections should be tabbed for each authorized propellant type-charge group for the projectile family.

## 4-7. Frequency Of Calibration

Ideally, calibration occurs continuously. If that is impractical or impossible, the following methods identify when to consider calibrating.

a. Initial Receipt or Retubing. All new pieces of a given caliber and model will not necessarily develop the same muzzle velocity because of the tolerances that are allowed in the size of the powder chamber and in the dimensions of the bore. Therefore, pieces should be calibrated as soon as possible after receipt or when retubed. Muzzle velocities should be recorded on DA Form 2408-4.

b. Change in Propellant Lot. Calibration should be conducted as soon as possible after an uncalibrated propellant lot is received.

c. New Projectile Family. Calibration should be conducted if a new projectile; for example, M825 smoke (projectile family DPICM), is received for which there are no previous MV records for that projectile family.

d. Annually.

Any piece in service should be recalibrated at least annually. The primary factor contributing to the loss in muzzle velocity for a piece is the number of rounds that have been fired through the tube  and the charges used in firing them. Higher charges increase tube wear, which, in turn, tends to decrease muzzle velocity. Guns, because of their higher velocities, tend to display tube wear more quickly than howitzers. If a great deal of firing takes place, recalibration will be needed more often than annually. Methods of determining when recalibration may be needed are outlined below. The following situations assume that firing takes place with a previously calibrated projectile family-propellant lot.

e. Changes in VE.

If an accurate record of the changes in VE determined from concurrent met solutions is maintained, it may be used as a guide for determining the need for recalibration. When the velocity loss since the last calibration is equivalent to 2 range probable errors, the need for recalibration is indicated. (An indicator of this is a loss of 1.5 m/s, which generally approximates 2 probable errors in range.)
f. Tube Wear. The extent of tube wear near the beginning of the rifling of the bore indicates the loss in muzzle velocity and the remaining tube life. Precise measurement of the distance between the lands in the bore near the start of the rifling can be made with a pullover gauge. Organizational or direct support maintenance has this gauge and makes the measurement. The wear measurement, when compared with the data in the "wear" table (Approximate Losses in Muzzle Velocity table) in the introduction of each firing table, can be used in estimating the loss in muzzle velocity.

g. EFCs. A change in the number of **erosion** EFC service rounds as depicted in the weapon record book may also indicate a need for recalibration. (Refer to paragraph 4-3 for more information about EFCs.) The change in erosion EFC rounds compared with data in the Approximate Losses in Muzzle Velocity table (in the introduction of each TFT) that corresponds to a loss of 1.5 m/s in muzzle velocity may indicate a need for recalibration. A loss of 1.5 m/sin MV generally equates to the effects of 2 probable errors in range (2 PER).

## 4-8. Transferring Mvvs

a. Ideally, every charge should be calibrated. However, this may not always be feasible.

Therefore, the calibration of a few charges, one within each charge group that results in an MVV
applicable to other charges within a charge group, is imperative. For calibration purposes, there are two categories of charges within a charge group. These are preferred charges and restricted charges. The following guidance is established as an order of preference when selecting a charge to calibrate:
(1) If you know the charge you will be firing calibrate that charge. (2) If the charge you will be shooting is unknown, calibrate the middle charge of the preferred charge group.

b. Calibration data determined should only be applied to a subsequent fire mission when the mission meets the following requirement: It is the same calibrated howitzer firing the same calibrated projectile family-propelant lot combination. Once calibration data are determined for a particular charge, these data can be transferred to other charges in the same lot. The order of preference for transferring is as follows:

(1) Transfer down 1 charge.
(2) Transfer up 1 charge.
NOTE: Shooting strength and ammo efficiency make up the achieved MV. With higher charges, there is more erosion but less variance in ammo efficiency. For lower charges, there is less erosion but more variance in ammo efficiency.

Therefore, the general overall effect is less variance when transferring down as opposed to up.

(3) Transfer down 2 charges within the preferred charges.
(4) Transfer up 2 charges within the preferred charges.
(5) Transfer from a preferred charge to a restricted charge.
NOTE: MWs should not be transferred from a restricted charge to any other charge on the basis of the nature (large round-to-round variances) of restricted charges.

## Chapter 5 Fire Mission Messages

The processing of a fire mission involves three essential messages. These are the fire order, message to observer, and fire commands. These messages contain the necessary information to tactically engage the target, control the mission, and transmit technical fire direction to the howitzers.

## Section I Fire Order

This section implements STANAG 2934, Chapter 7, and QSTAG 221.

In the fire order, the FDO specifies how the target will be attacked. This is tactical fire direction.

## 5-1. Overview

When the FDC receives a call for fire (CFF), the FDO must determine if and how the target will be attacked. This decision (part of tactical fire direction) may be made at the battalion or battery or platoon FDC. In battalion missions, the battalion FDO is responsible for issuing the fire order. In autonomous operations, the battery or platoon FDO is responsible for issuing the fire order. A fire order is the FDO's decision on what unit(s) will fire and how much and what type of ammunition will be fired. It is based on the FDO's analysis of the target.

## 5-2. Target Attack Considerations

In determining how, if at all, to attack a target, the FDO must consider several factors.

a. Location of the Target. The FDO must check the location relative to friendly forces, fire support coordinating measures, and zones of responsibility. Target location accuracy must also be considered. The range to the target will affect the choice of unit(s) to fire and charge. The terrain around the target may influence ammunition selection and type of trajectory.

High intermediate crests may require selection of a lower charge or high-angle fire.

b. Nature of the Target. The size and type of target (for example, troops, vehicles, hard, soft, and so on) will affect the following:

Number of units to fire. Type of sheaf. Selection of ammunition. Number of rounds in fire for effect. Priority.
Whether surprise fire (for example, time on target [TOT]) is possible.

c. Ammunition Available. The FDO must consider the amount and type of ammunition available and the controlled supply rate (CSR).

d. Units Available. The number of units available will not only affect which units will be used, but also the type of attack. Sweep and/or zone fire or other techniques may be needed to cover large targets when enough units are not available.

e. Commander's Guidance or Standing Operating Procedures. Restrictions on ammunition, the operations order, and SOPs may govern the selection of units and ammunition, target priority, and method of attack.

f. Call for Fire. The FDO must consider the observer's request carefully since he is observing the target and talks directly to the maneuver commander. The observer's request should be honored when possible.

g. Munitions Effects. The FDO may use the joint munitions effectiveness manual
(JMEM) to determine the type munition and volume of fire to be delivered. The FDO will rely most often on the graphical munitions effectiveness table (GMET), attack guidance matrixes, commander's guidance, and/or experience.

h. Availability of Corrections. The availability of corrections to firing data for nonstandard conditions is a guiding factor in the choice of charge and munitions, since it directly affects accuracy.

i. Enemy Target Acquisition Capability. Knowledge of the current enemy counterbattery radar and sound-ranging capabilities allows the FDO to attack the target in a manner most likely to avoid detection of the unit's location.

NOTE: For a more detailed discussion, refer to Appendix B.

## 5-3. Fire Order Elements

In autonomous operations, the battery or platoon FDO must issue a fire order. The fire order will address all information needed to conduct the mission. The fire order is issued in a prescribed sequence. It consists of 10 elements:
Unit to fire.

Adjusting element and/or method of fire (MOF) of adjusting element. Basis for corrections. Distribution.

Special instructions.

Method of FFE.

Projectile in effect (I/E).

Ammunition lot and charge in effect. Fuze in effect. Target number.

If not standardized by unit SOP, the elements in Figure 5-1 will be addressed in the fire order.

a. UNIT TO FIRE. Indicates the units to follow the mission and to fire for effect.

Normally, BATTERY or PLATOON is announced as the unit to fire.

b. ADJUSTING ELEMENT AND/OR METHOD OF FIRE OF THE ADJUSTING
ELEMENT (if applicable). Indicates the weapon(s) that will adjust. Normally, the base piece is selected and will fire one round in adjustment.

(1) Projectile in adjustment. This is the type of shell to be fired by the adjusting piece in an adjust-fire mission.

(2) Lot and charge in adjustment. This is the ammunition lot (for the shell and propellant) and the charge to be fired by the adjusting piece in an adjust-fire mission.

(3) Fuze in adjustment. This is the type of fuze to be fired by the adjusting piece in an adjust-fire mission.

c. BASIS FOR CORRECTIONS. This element dictates how data will be determined.

Normally, the fastest method is designated.

d. DISTRIBUTION. This element describes the pattern of bursts (sheaf) in or around the target area. The assumed sheaf is a parallel sheaf, which resembles the arrangement of the pieces in the firing position. The sheaf computed may vary from the assumed sheaf on the basis of the number of howitzers available, target size, attitude, and description received from the observer (obsr). If the FDO desires a sheaf other than the assumed sheaf, he will announce it here.

e. SPECIAL INSTRUCTIONS.

This element is any method of control or coordinating instructions deemed appropriate by the FDO.

f. METHOD OF FIRE FOR EFFECT. This element indicates the number of rounds in the fire for effect phase of a mission. This element will always be announced by the FDO.

g. PROJECTILE IN EFFECT. This element is the projectile to be freed in effect.

h. AMMUNITION LOT AND CHARGE I/E. This element is the ammunition lot(s)
and charge used in fire for effect.

i. FUZE I/E. This element is the fuze to be fired in effect.

j. TARGET NUMBER. This element is the specific target number assigned to a fire mission.

## 5-4. Battery Or Platoon Fire Orders

The guidance in Table 5-1 will be used in issuing the fire order.

## 5-5. Fire Order Standing Operating Procedures

a. In most cases, a particular element of the fire order may remain the same from one mission to the next. On the basis of the tactical situation, type and amount of ammunition available, and commander's guidance, the FDO establishes an SOP for each element, which should be displayed in the FDC. When the FDO does not address an element in his fire order, the standard for that element will apply. The FDO need only announce what has changed from the standard. However, the method of fire for effect must be announced.

b. The FDO must ensure that the fire order is clear, concise, and in the proper format.

The fire order format is designed to disseminate information clearly and rapidly with minimal discussion. It is impossible to provide a textbook solution for every conceivable situation, but a combination of technical knowledge and common sense should be enough to avoid confusion. It is better, if any confusion exists, to be redundant rather than too brief.

c. The use of a good SOP to clarify certain missions is essential. Immediate suppression, immediate smoke, illumination (illum), and mixed shell missions (HE and WP, for instance), can be handled more responsively when governed by an SOP. For example, an FDO
needs only to say **IMMEDIATE SUPPRESSION** to mean a platoon will fire two volleys of HE/variable time (VT).

d. The example below shows the fire order elements and the fire order SOP for a four-howitzer platoon.

- (See Figure 5-2.)
(See Figure 5-3, which shows all elements addressed in the previous example.

## 5-6. Battalion Fire Order

Battalion fire orders must be issued to mass the fires of the battalion on a single target.

The battalion fire order differs from the battery or platoon fire order since all the units of the battalion may not be able to receive the call for fire. The battalion fire order must be able to convey all information to cause the units to engage the target. A battalion fire order (Figure 5-4) follows the same basic format as a battery or platoon fire order except for the following:
a. WARNING ORDER. A warning order is issued to indicate the type of mission (AF
or FFE) to be fired (not standardized).

b. UNIT TO FIRE. This is the unit to fire for effect. If the fire order originates at the battalion FDC and the FDO decides to fire the entire battalion, the element is announced as BATTALION. To designate less than the entire battalion, the individual elements are announced (for example, **ALPHA** and **CHARLIE).** When the designation of the unit to fire is transmitted outside the FDC, the unit call sign should be used.

c. UNIT TO ADJUST or METHOD OF FIRE OF THE ADJUSTING UNIT. This is the battery that conducts the adjustment. The battalion FDC will not try to direct a specific piece to adjust; however, the adjusting battery's base piece should be the adjusting piece. When the battalion fire order is transmitted, the last letter of the unit call sign will be used (can be standardized). The battalion may specify the number of rounds, projectile type, lot, charge, and fuze to use in the adjustment by the adjusting unit.

d. BASIS FOR CORRECTIONS. This is the same as the battery-or platoon-level fire order (can be standardized).

e. DISTRIBUTION or TARGET LOCATION. This is the FO's target location, to include target altitude, from the call for fire. If adjustment is necessary, the nonadjusting units will follow the adjustment and fire for effect on the adjusted grid. In adjust-fire missions, the battalion FDO may direct the adjusting unit to transmit the replot location and altitude to the battalion FDC after the completion of the adjustment. The battalion FDC may choose to segment the target, sending aimpoints to the units of the battalion, before fire for effect or direct the units to mass on the adjusted grid by sending the adjusted or replot grid (not standardized).

NOTE: The remaining elements of the battalion fire order are similar to the battery or platoon fire order except for standards.

f. SPECIAL INSTRUCTIONS. This element can be standardized.
g. METHOD OF FIRE FOR EFFECT. This element is not standardized.
h. PROJECTILE I/E. This element can be standardized.
i. AMMUNITION LOT AND CHARGE I/E. This element can be standardized;
however, normally the battery or platoon FDO will select it.

j. FUZE I/E. This element can be standardized.
k. TARGET NUMBER. This element is not standardized.

## 5-7. Massing Of Fires

a. Massing. What does an artilleryman mean when he uses the word *massing?* By definition, it means simultaneous execution of two or more firing elements to achieve maximum effects on a critical target. The 3 x 8 battery bringing its two platoons to bear on a single target, a battalion massing on one point, and even a division artillery (divarty) or corps artillery commander bringing all his battalions onto a single target are all examples of massing. Regardless of the level of command, certain fundamental requirements must be met for two or more units to engage targets **effectively** together.

(1) The first requirement for massing is that all firing units must be on a common location and azimuth system; that is, **common survey.** This includes all platoons, radars, met stations, and observers. The survey control should extend into the target area as well.

(2) The second requirement is accurate MV information for each weapon. Manual corrections for MVVs will occur during concurrent and subsequent met procedures and through determining TGPCs with the Ml 7 plotting board.

(3) The third requirement is valid met corrections considered by each of the firing platoons. This includes the met message valid for the firing platoon, propellent temperature, projectile weight, vertical interval, and corrections for earth rotation.

(4) The final requirement is accurate location. This is the reason the target-locating assets must be on common survey with the firing units. Ensure the target location determined by the observer is the same location plotted by the FDC.

(5) If the target is accurately located and the first three requirements are satisfied, then you can mass without having to adjust each unit onto the target. However, if it is an adjust-fire mission, the adjusting unit must determine the accurate target location and then announce it to the other units. To determine the accurate target location, the adjusting FDC must perform replot procedures discussed in Appendix D. The FDC must then announce the replot grid. The controlling FDC is responsible for the fire order and control of the mission.

## B. Control Of Battalion Mass Missions.

(1) When massing the fires of more than one battery either firing for effect or adjusting, AT MY COMMAND, TIME ON TARGET, or **WHEN READY** can be used. The most effective technique is **TIME ON TARGET,** which achieves the greatest surprise to the enemy.

(2) Control of FFE mass missions on stationary targets can best be affected by using TOT techniques. Accurate time coordination is essential to ensure the simultaneous impact of all initial rounds; lengthy countdowns are unnecessary.

(a) The TOT may be announced as a specific time (for example, TOT 0915).

The battalion would announce a time check to synchronize the units designated to fire. This is done by using the following procedure:
The battalion FDC will announce the time (for example, AT MY
MARK THE TIME WILL BE 0908).

The battalion FDC will give a short countdown starting 5 seconds before the mark (for example, 5, 4, 3, 2, 1, MARK).

Each FDC would start its clock at **MARK.** From that moment, each FDC would control its own firing.

Each FDC would respond to the battalion FDC with **ROGER OUT** if they received a good mark.

If a good mark was not received, the unit FDC will request a new mark and the previous four steps will be done again.

(b) Another technique to execute a TOT is to specify the amount of time before it is to occur (for example, **TOT 5 MINUTES FROM MY MARK).** Each FDC would start its stopwatch at **MARK.** From that moment, each FDC would control its own firing.

(c) The preferred technique is the short countdown TOT (for example, TOT
40 SECONDS FROM MY MARK). The short countdown allows the FDO to decrease the amount of time between receiving a call for fire and massing on the target. The FDO will announce as part of the special instructions in his fire order SHORT COUNT TOT FOLLOWS. This alerts the firing units that the mission is **AT MY COMMAND** and that they will report **READY, TOF** to the battalion FDC. The battalion FDO will add 10 seconds
(reaction time) to the longest time of flight reported. If the longest TOF is 30 seconds, he will announce **TOT 40 SECONDS FROM MY MARK, 5, 4, 3, 2, 1 MARK.** The firing units will quickly subtract their TOF from the number of seconds the battalion FDO announced. The result is the number of seconds after **MARK** until they command FIRE.

(3) Control of an FFE mass mission on moving targets is best achieved by using AT MY COMMAND or **WHEN READY.** The time consumed during a TOT countdown may result in the rounds missing the target.

(a) **AT MY COMMAND.** All units will fire at the same time. The battalion FDO will select this technique if he is willing to accept some loss of surprise caused by varying times of flight to get the rounds on the target quickly. This technique is particularly effective when the unit's times of flight as reported by each FDC are similar.

(b) **WHEN READY.** Unless otherwise specified, each battery will fire when ready. This technique is used more often with adjust-fire missions (particularly those with lengthy adjustment phases) than with fire-for-effect missions. (When surprise has been lost, the difference in reaction times and times of flight between units is less significant.)
(4) Control of the FFE phase in an adjust-fire mass mission can be achieved by the same means as an FFE mass mission.

(a) **TIME ON TARGET.** If the observer is able to enter the FFE phase with one correction and he judges that the target has not been warned, a TIME ON TARGET
(paragraph (2) above) may be used to control time of firing in effect. If the battalion FDO
decides a TOT is unsuitable (for example, loss of time outweighs simultaneous impacting of all initial FFE rounds), he will direct use of AT MY COMMAND or **WHEN READY.** It is rare, however, that a target would not be warned during adjustment. Therefore, TOT to control time of firing in effect after adjustment is not normally used.

(b) **AT MY COMMAND.** The considerations for the selection of this technique are the same as in paragraph (3)(a) above. In addition, it is useful if the observer is able to enter the FFE phase with a large correction.

(c) **WHEN READY.** In most adjust-fire mass missions, no control of time of firing in effect will be used. Since most targets would be warned during adjustment, the battalion FDO would allow units to fire when ready.

c. Examples of Battalion Fire Orders. Examples of battalion fire orders are shown below.

## Section Ii Message To Observer

This section implements STANAG 2934, Chapter 5, and QSTAG 246.

After the FDC receives the call for fire, the FDO analyzes the target. If the target is to be attacked the FDO issues the fire order as his decision on how the target will be attacked. The observer is informed of this decision through the message to observer.

## 5-8. Description

The message to observer consists of four elements and is composed by the RATELO.

a. Units to Fire. The first element is the unit(s) that will fire the mission. It is always announced. If a battalion is firing in effect with one battery or platoon adjusting, the MTO will designate the FFE unit (battalion) and the adjusting unit (battery or platoon). The units to fire are identified by their radio call signs, using long call signs, short call signs, or the first letter of the short call sign. Some examples are listed below.

b. Changes or Additions to the Call for Fire. The second element of the MTO allows the FDC to inform the observer of changes and/or additions made by the FDO to the call for fire.

If high-angle fire is to be used, **HIGH ANGLE** must be included in the MTO if the observer did not request it. The following examples use the previously stated call signs.

c. Number of Rounds. The third element is the number of volleys in fire for effect.

The number of rounds to be fired in effect is **always** announced. The following example uses the previously stated call signs and change to the call for fire.

d. Target Number. The last element is the target number assigned to the mission for reference purposes, it is always announced. This is done to avoid confusion if multiple missions are being fired or if more than one observer is operating on the radio net. Target numbers are used in sequential order based on the units target block. The following example uses the previously stated call signs, change(s) to the call for fire, and number of rounds.

## 5-9. Additional Information

The following additional information may be announced with or after the message to observer.

a. Probable Error in Range. If the probable error in range for an area fire mission is equal to or greater than 38 meters, the FDC will inform the observer. For precision fire, the FDC
will inform the observer if the probable error in range is equal to or greater than 25 meters. The actual value is not announced. For example, the RATELO would announce PROBABLE
ERROR IN RANGE GREATER THAN 38 METERS.

b. Angle T. Angle T is sent to the observer when it is equal to or greater than 500 mils or if the observer requests it. It is announced to the nearest 100 mils. For example, if angle T is
580 mils, it is expressed and announced as ANGLE T 600.

c. Pulse Repetition Frequency Code. The pulse repetition frequency (PRF) code for a Copperhead mission is transmitted in voice operations; for example, the RATELO will announce PRF CODE 241. The range and direction of approach (left or right of the observer-target line)
are needed to orient the footprint.

d. Time of Flight. Time of flight (TOF) is announced to the nearest whole second. It is announced to observers when targets are engaged with Copperhead, when moving targets are engaged, when conducting high-angle missions, when using an aerial observer, or when requested by the observer. For example, the RATELO would announce TIME OF FLIGHT 34 SECONDS.

e. Splash. Splash informs the observer that the round(s) fired will impact in 5 seconds.

It must be sent to aerial observers and during high-angle fire missions. It can also be sent at the observer's request.

f. Shot and Rounds Complete. SHOT is announced to the observer to report when a round has been fired. Rounds complete is announced to the observer when all rounds for a particular mission have been fired. During an adjust-fire mission **SHOT** is announced after each round. Once the FFE
phase is initiated, **SHOT** is announced only on the initial round. Once all rounds have been fired, rounds complete is announced to the observer. For an FFE mission, **SHOT** is announced only on the initial round; once all rounds have been fired, rounds complete is announced to the observer.

## Section Iii Fire Commands

Fire commands are used by the FDC to give the howitzer sections all the information needed to conduct a fire mission. Initial fire command include all elements needed for orienting, loading, and firing the howitzer. Subsequent fire commands include only those elements that have changed from the previous command(s), except quadrant elevation. Quadrant elevation is announced in every set of fire commands and allows the howitzer section to fire if in a WR status.

## 5-10. Fire Command Elements

a. The elements of fire commands are always announced in the same sequence (Table
5-2). This saves time and eliminates confusion; each member of the howitzer section knows the sequence and should be ready for the next command.

b. Certain elements of the fire commands may be standardized. Once the standards are established and announced to the howitzer sections, the standard (std) elements will not be announced.

Quadrant elevation may never be standardized. It is announced in-each set of fire commands.

## 5-11. Battery Or Platoon Fire Commands

The procedures and sequence for announcing fire commands are in Table 5-3; all other fire commands are in Table 5-4.

## 5-12. Examples Of Fire Commands

a. Following is an example of an adjust-fire mission without fire command standards applied for a four-howitzer platoon.

b. Following is an example of an FFE mission without fire command standards applied.

## 5-13. Standardizing Elements Of The Fire Commands.

Certain elements of the fire commands may be standardized after the tactical situation, weapon and personnel capabilities, ammunition status, and enemy counterfire threat have been considered. As shown in Table 5-2, the following elements of the fire commands may be designated as standard: pieces to fire, method of fire, projectile, ammunition lot, and fuze. Only one set of standards can be in effect at any particular time. Once standards are placed in effect, the unit will fire the standard data unless the fire commands specify something different.

## Chapter 6 Firing Charts

One of the elements to the solution of the gunnery problem is the determination of chart data. Chart data consist of chart range, chart deflection, and angle T. The determination of chart data requires the construction and operation of firing chart.

## Section I Types Of Firing Charts

This section implements a portion of QSTAG 224.

Two types of firing charts may be constructed in the FDC. They are surveyed firing charts and observed firing charts. Regardless of the type constructed two firing charts are maintained in a manual FDC. The horizontal control operator (HCO)
maintains the primary firing chart, and the vertical control operator (VCO) maintains a backup, or check, chart and a 1:50,000-scale situation map with tactical overlay(s).

## 6-1. Description

A firing chart is a graphic representation of a portion of the earth's surface used for determining distance and direction. The chart may be constructed by using a map, a photomap, a grid sheet, or other material on which the relative locations of batteries, known points, targets, and observers can be plotted. Additional positions, fire support coordinating measures, and other data needed for the safe and accurate conduct of fire may also be recorded.

## 6-2. Firing Chart Construction

The most commonly used materials for constructing firing charts are as follows:
a. Grid Sheet. A grid sheet is a plain sheet of paper or plastic (mylar) on which equally spaced horizontal and vertical lines, called grid lines, are printed. The intervals between these grid lines will create 1,000-meter grid squares on a scale of 1:25,000. This scale provides the best compromise between accuracy and convenience and is therefore the scale for which standard plotting equipment is graduated. The locations of all points plotted on the grid sheet must be determined either by survey data, map inspection, or firing. The grid sheet is numbered to correspond to the map area of the zone of operation of the supported force. The FDO assigns the lower left-hand corner casting and northing coordinates, and the direction of the long axis (east-west or north-south) also is specified. The rightmost and topmost grid lines are not labeled because data are not determined from these grid lines.

b. Map. A map is a graphic representation, drawn to scale, of a portion of the earth's surface.

Only maps based on accurate ground survey should be used for constructing firing charts. If the map scale is other than 1:25,000, the range readings obtained from plotting equipment must be adjusted.

For example, if a 1:50,000-scale map is used, the ranges determined with the RDP must be doubled. Deflections and azimuths are not affected. If a map is not based on accurate and adequate ground survey control, it should be used only to obtain approximate locations and vertical control to supplement a grid sheet firing chart.

c. Photomap. A photomap is a reproduction of an aerial photograph or a mosaic of aerial photographs on which grid lines, marginal information, and place names are superimposed.

A photomap must not be considered exact until its accuracy has been verified. Photomaps may include errors caused by tilt, distortion caused by relief, and errors caused by poor assembly, If points cannot be located on the photomap by inspection, the photomap scale must be determined before points can be located on the photomap survey. Normally, vertical control can be established by estimation only. Determination of the scale of vertical control of photographs is discussed in FM 21-26. Some photomaps have spot altitudes, but interpolation for altitude is difficult and inaccurate.

## Section Ii Plotting Equipment And Firing Chart Preparation

To ensure the accuracy of the data shown on the firing chart, FDC personnel should construct and plot from a standing position directly above the chart. Plotting pins must be kept perpendicular to the firing chart. Personnel, equipment and the firing chart should be kept as clean as possible at all times. If two charts are present in the FDC, they must be checked against each other for accuracy. If one chart is a backup for another system, it should be verified against that system for accuracy.

(Refer to Appendix E for automated FDC procedures.)

## 6-3. Pencils

a. 6H Pencil. The 6H (hard lead) pencil is sharpened to a wedge point and is used to draw fine index lines from which measurements are made. If a 6H pencil is not available, a 5H
pencil is an acceptable substitute. (See Figure 6-1.) Place a 1-inch piece of tape on the end to differentiate between a 4H pencil.

b. 4H Pencil. The 4H pencil is sharpened to a conical point and is used to label and construct tick marks and to label azimuth and deflection indexes. If a 4H pencil is not available, a 3H pencil is an acceptable substitute. (See Figure 6-2.)
c. Red and Blue Pencil. The red and blue pencil is sharpened to a conical point and is used to label and construct tick marks and label deflection indexes, as required by the color code.

(See Figure 6-2.)
d. Orange Pencil. The orange pencil is sharpened to a conical point and is used to label tick marks and deflection indexes, as required by the color code. (See Figure 6-2.)
e. Green Pencil. The green pencil is sharpened to a conical point and is used to label tick marks for radars, as required by the color code. (See Figure 6-2.)

## 6-4. Plotting Pins

Plotting pins are used to mark indexes and temporary positions on the firing chart. On a
1:25,000-scale chart, the thickness of the plotting pin shaft equals 20 meters.

## 6-5. Plotting Scale

The plotting scale is a square-shaped scale used to plot or determine grid coordinates.

The scale is graduated in meters and yards at scales of 1:25,000 and 1:50,000. Using the four-step plotting method, locations are normally plotted to an accuracy of 10 meters with the plotting scale.

Personnel must be careful not to confuse the meter and yard scales on this instrument (newer plotting scales only have meter scales on them). (See Figure 6-3.) If there is a yard scale, tape over it so this scale is not accidentally used.

NOTE: Ten-digit grid coordinates are expressed to an 8-digit grid coordinate when plotting because of the limitations of the plotting scale.

## 6-6. Range-Deflection Protractor

The RDP is used to measure angles in mils and distances in meters. Range and deflection are measured from a firing unit to a target. Direction and distance are measured from an observer to a target. (See Figure 6-4.)
a. The left edge of the instrument is the arm and is used to measure range or distance. It is graduated in 50-meter increments and labeled every 500 meters on a scale of 1:25,000. Ranges and distances are visually interpolated to an accuracy of 10 meters. The arm can be labeled to represent charge or range spans and other pertinent data to aid the FDO.

b. The 1,000-mil arc of the RDP is graduated in 5-mil increments. The 50-mil increments are indicated by longer graduations and are permanently numbered. The are is visually interpolated to an accuracy of 1 mil.

c. The vertex, the slotted portion of the RDP, is placed against a plotting pinto properly position the RDP for determining data.

d. There are four different RDP models. They differ by the maximum range of the arm
(12,000, 15,000,25,000, and 30,000 meters).

e. RDPs are also available on a 1:50,000 scale.

NOTE: When labeling the RDP, label azimuth values in blue and deflection values in red.

## 6-7. Target Grid

The target grid is a circular paper device on which grid lines are printed. Normally, the target grid used is DA Form 4176 (Target Plotting Grid, Field Artillery). Grid lines on the target grid match the scale of the 1:25,000 firing chart, dividing a 1,000-meter grid square into
100-meter squares. An azimuth scale is printed around the outer edge of the target grid. It is graduated in 10-mil increments and is numbered every 100 mils. An arrow extends across the center of the target grid and is used to indicate the observer-target line (or other line of known direction). The target grid should be labeled as shown in Figure 6-5. (The L and - are written in blue pencil; the R and +, in red.) Transparent tape should be applied to the reverse side of the target grid to prevent the center hole from becoming enlarged. The target grid is used for three distinct operations:

Plotting the position of targets located by a shift from a known point.
Plotting observer subsequent corrections.
Determing angle T.

## Section Iii Surveyed Firing Chart

A surveyed firing chart is a chart on which the location of all required points
(battery or platoon positions, known points, and OPs) are plotted. These locations can be based on survey or map inspection. All plotted points are in correct relations to one another and reflect actual map coordinates.

## 6-8. Selection Of Lower Left-Hand Corner And Azimuth Of Lay

For the chart operator to construct a firing chart correctly, he needs to be provided guidance on what coordinates to assign to the lower left-hand comer (LLHC) of the grid sheet and the azimuth of lay. The FDO is responsible for providing this information. The azimuth of lay can be determined on the basis of the zone of operations or the guidance from the battery commander or higher HQ. After the azimuth of lay is determined, the LLHC coordinates need to be carefully selected. The selected LLHC coordinates should include all critical points on the firing chart and allow full use of the RDP. The steps in Table 6-1 will help to serve as a guide in determining the LLHC and azimuth of lay.

## 6-9. Firing Chart Preparation

The steps in Table 6-2 are the recommended sequence for the preparation of a firing chart.

## 6-10. Four-Step Plotting Method

Points commonly plotted on a firing chart include battery or platoon base piece locations, known points, targets, observer locations, and maneuver checkpoints. Base piece locations can be determined by using the M17 plotting board and protractor. To plot points located by grid coordinates, use the steps in Table 6-3.

## 6-11. Tick Marks

The tick mark is the symbol used to mark and identify the location of a point plotted on a firing chart. The tick mark is constructed in the form of a cross with each arm beginning 40
meters from the pinhole on the chart and extending 160 meters in length (1:25,000 scale).

NOTE: Tick marks will be constructed with a 4H pencil with the following exception: To construct a tick mark for a target that has been located through firing, use a red pencil.

Table 6-4 uses the 3,5,7, method to construct a tick mark.

## 6-12. Construction Of Azimuth Indexes

Azimuth indexes are constructed for points located on the firing chart from which the polar method of target location may be expected.

The RDP is prepared by numbering the
100-mil azimuth graduations in blue as shown in Figure 6-4. Azimuths are always read as four digits. The first digit (thousands of mils) is read from an index that is constructed on the firing chart. The last three digits are read from the arc of the RDP. Azimuth indexes are constructed on the firing chart in 1,000-mil intervals throughout the target area, except the 6000 and 0 indexes, which are 400 mils apart. The steps for constructing azimuth indexes can be found in Table 6-5.

NOTE: To help determine the four digits of a deflection or azimuth, use the memory aid CLUE.

C - Chart index/pin is first digit.
L - Label on RDP arc is second digit.
U - Unit graduation is third digit. E - Estimate (visually) to nearest mil is fourth digit.

## 6-13. Construction Of Deflection Indexes

Direction from a battery or platoon to a target normally is measured and announced in terms of deflection. Deflection is the horizontal clockwise angle from the line of fire, or the rearward extension of the line of fire, to the line of a designated aiming point with the vertex of the angle at the sight. In addition to the deflection as a fire command, the firing battery is concerned with common deflection. The RDP will be used to measure deflection so it must be prepared by numbering the graduations of the arc in red as shown in Figure 6-4. Orient the RDP on the azimuth of fire, and place a pin opposite the common deflection for that weapon system. Table 6-6 contains the steps required for constructing deflection indexes.

## 6-14. Plotting Targets

The observer can use three methods of target location: grid coordinate, polar plot, and shift from a known point. The steps for plotting targets on a firing chart are listed in Table 6-7.

## 6-15. Determining And Announcing Chart Data

Chart data consist of chart range and chart deflection from the firing unit to the target and angle T. In a manual FDC, two firing charts will be constructed and will be used to check each other. Use the steps in Table 6-8 to determine chart data.

## 6-16. Chart-To-Chart Checks

a. One chart may differ slightly from another because of small differences in construction caused by human limitations in reading the graphical equipment. Because of these differences, the following tolerances between charts are permissible:

Range and/or distance 30 meters. Azimuth and/or deflection 3 mils.
Angle T 30 mils.
b. All firing unit locations must be checked for accuracy. For checking the accuracy of two or more charts, plot the same grid intersection on all charts. Determine range and deflection to that grid intersection. If all ranges agree within 30 meters in range and 3 mils in deflection, the charts are accurate for that firing unit location. If not, all charts must be checked for errors.

c. To ensure accuracy, enough points in the zone of operation of a firing unit should be checked. For example, an error in plotting the unit location on one chart could compensate for an error in constructing the deflection index on the other chart. Checking at least two points will reveal the error. This should be done as a matter of unit SOP.

## Section Iv Observed Firing Charts

When survey control and maps are not available, delivery of indirect fires is possible by using observed firing charts. An observed firing (OF) chart is a firing chart on which all units and targets are plotted relative to each other from data determined by firing a registration. Observed firing charts are an expedient method that should only be use under emergency conditions and every attempt should be made to construct a surveyed firing chart as soon as possible. Since all locations are based upon firing data, observed firing charts contain errors because of nonstandard conditions.

## 6-17. Overview

a. All observed firing charts are based on a registration. Once a registration is complete, the unit location is polar plotted from the point of registration (normally assumed to be a grid intersection)
by using the direction that is based on the back azimuth to the point and a range corresponding to the adjusted elevation, or more preferably, a range corresponding to the adjusted time.

b. Because maps and survey are not available, altitudes cannot be accurately determined. When vertical interval and site are assumed to be zero, a false range is introduced into the polar plot range. This inaccuracy can be reduced by trying to determine site. Site may be determined by estimating vertical interval or by conducting an XO's high burst.

c. The general procedures for constructing an OF chart are listed below:
(1) Mark the center of sector for observers.

(2) The observer selects a point in the center of the sector of fire that can be identified on the ground.

(3) Assign the point an arbitrary grid coordinate and altitude. Plot this location on the firing chart. The grid coordinates assigned to the point are completely arbitrary. A grid intersection is preferred for simplicity. The grid coordinates of the known point will serve as the basis for establishing a common grid system. For example, the point could be assigned the grid coordinates of easting (E):20000 northing (N):40000, altitude 400 meters. (See Figure 6-23.)
(4) Conduct a precision registration (fuze time, if possible) on the point by using emergency firing chart procedures. (See Chapter 14.)
(5) Determine the adjusted data (to include orienting angle, if possible). (6) From the adjusted data, determine direction (azimuth) and distance (range) from the point to the unit.

(7) Polar plot the base piece from the point.

## 6-18. Methods Of Determining Polar Plot Data

a. All observed firing charts are constructed by using polar plot data. The method for obtaining these data depends on the type of registration conducted and whether site can be estimated or whether it is unknown.

b. Percussion plot is used when an impact registration has been conducted.

(1) When VI is not known and cannot be estimated, the method is known as percussion plot, VI unknown.

(2) When vertical interval can be estimated, a site can be determined and inaccuracies reduced. This method is known as percussion plot, VI estimated.

c. Time plot is used when a time registration has been conducted.

(1) When VI is not known, the method is known as time plot, VI unknown. (2) When VI can be determined by using an XO's high-burst registration, the method is known as time plot, VI known.

## 6-19. Constructing Observed Firing Charts

The step-by-step procedures for construction of an observed firing chart are listed in Table 6-9.

## 6-20. Determination Of Direction For Polar Plotting

a. Once the registration has been completed, the azimuth of the line of fire must be determined. No matter what technique (percussion or time plot) is used, the direction (azimuth) of the firing unit from the known point is computed in the same manner.

b. There are two methods to determine the azimuth of the line of fire. They are as follows:
(1) The XO or platoon leader will determine the azimuth of the line of fire in accordance with FM 6-50 and report it to the FDC.

(2) The drift corresponding to the adjusted elevation is stripped out of the adjusted deflection; the result is the chart deflection. The chart deflection is then converted to an azimuth.

For example in Figure 6-24, the firing unit was laid on grid azimuth 6100; common deflection
3200. The adjusted deflection was 3346, and the adjusted elevation was 272.

c. Because the firing unit will be polar plotted from the known point, the FDC must convert the azimuth of the line fire to a back azimuth. The polar plot direction is simply the back azimuth of fire to the known point. The polar plot direction equals the azimuth of the line of fire
3,200 mils. If the adjusted (adj) azimuth of fire is less than 3,200 mils, add 3,200 mils to it. If the adjusted azimuth of fire is greater than 3,200 mils, subtract 3,200 mils from it.

NOTE: When the azimuth of the line of fire is measured, the howitzer is aimed with the adjusted deflection. This will result in a polar plot azimuth that compensates for drift. If the drift corresponding to the adjusted elevation is removed and a chart deflection is determined, all nonstandard conditions (other than drift) affecting the deflection are accounted for in the plot of the known point.

d. Once the polar plot direction has been computed, the remaining polar plot data must be computed by using one of the methods listed below.

(1) If the impact registration was conducted and VI is not known and cannot be estimated, use the percussion plot, VI unknown method, as shown in paragraph 6-21.

(2) If the impact registration was conducted and VI can be estimated, use the percussion plot, VI estimated method, as shown in paragraph 6-22.

(3) If time registration was conducted and VI is unknown, use the time plot, VI
unknown method, as shown in paragraph 6-23.

(4) If time registration was conducted and VI is to be determined by using the XO's high burst, use the time plot, VI known method, as shown in paragraph 6-24.

## 6-21. Percussion Plot, Vi Unknown

Percussion plot is used when an impact registration has been conducted. When VI is not known and cannot be estimated, the method is known as percussion plot, VI unknown. The percussion plot technique assumes that site is zero.

The range used to polar plot is the range corresponding to the adjusted elevation. Since site is zero, the adjusted quadrant elevation is the same as the adjusted elevation.

## Unit Altitude = Known Point Altitude Polar Plot Range = Range Corresponding To Adjusted Elevation 6-22. Percussion Plot, Vi Estimated

When site is assumed to be zero, a large error can be introduced into the computation of range by using the percussion plot technique. This error can be minimized and the accuracy of the chart improved by estimating a vertical interval between the firing unit and the known point.

The firing unit altitude is then determined by applying the estimated VI from the assumed altitude of the known point to the firing unit altitude. (See Figure 6-25.) The estimated VI is used to compute site as shown in Table 6-10.

## 6-23. Time Plot, Vi Unknown

a. The lack of an accurate site and nonstandard conditions are the major sources of error in range on an observed firing chart. If the site is unknown or incorrect, the derived adjusted elevation is in error by the amount of error in site. Determining the polar plot range from the false elevation produces a false range. However, the effect of site on fuze settings is usually small. Therefore, the adjusted time can be used as a good indicator of the adjusted elevation and the polar plot range.

Because the adjusted fuze setting is a function of elevation and complementary angle of site (CAS), the angle of site (
SI) and hence the VI may be determined after the firing of fuze time.

b. To derive angle of site, subtract the elevation corresponding to the adjusted time plus the CAS from the adjusted quadrant elevation. Using the GST, determine the VI by multiplying the polar plot range by the derived angle of site. To determine range, place the MHL of the GFT
over the adjusted time and read range under the MHL from the range scale. Determine altitude of the firing unit by applying the VI to the assumed altitude of the known point.

**ADJ QE = (ADJUSTED ELEVATION + CAS) # SI.**

## 6-24. Time Plot, Vi Known (Preferred Technique)

a. When site can be determined by using an XO's high-burst (HB) registration, the method is known as time plot, VI known. This provides an even more accurate relative location.

(1) This technique is based on a rough approximation of site. This approximation can be refined to an accuracy approaching survey accuracy by the firing of a modified HB registration after the completion of a precision registration with fuze time.

(2) The objective of an XO's HB registration is to determine precisely what portion of the adjusted QE is angle of site and what portion is elevation plus CAS. (See Figure 6-26.)
The vertical interval and site to the known point can be computed by using the angle of site and range corresponding to the adjusted time.

ADJ QE = (ADJ EL + CAS) +  SI
(3) This XO's HB registration is based on the principle that fuze setting is a fiction of elevation plus CAS. The XO's HB registration is fired immediately after the time portion of the registration is completed. The firing of three such high airbursts is specifically what is called XO's HB registration.

The height of burst is raised vertically by an amount sufficient to enable the burst to be seen by an aiming circle located within 30 meters of the registering piece. The burst is raised by increasing quadrant. Three rounds are fired with the adjusted time. The XO measures the angle of site to each burst and determines the average angle of site. Because the fuze setting was not changed (the adjusted time was freed), the elevation plus CAS determined is the true elevation plus CAS. This value is then subtracted from the adjusted QE, yielding a true angle of site. Site is then computed.

b. The procedures for conducting an XO's HB registration are outlined in Table 6-11.

c. After understanding the theory on which the determination of site by firing is based, it may be easier to use the **GOT MINUS ASKED FOR** rule to determine the angle of site. As shown in Figure 6-27, the angle of site to the known point equals **got minus(-) asked for.** The procedures for the GOT MINUS ASKED FOR rule are in Table 6-12.

## 6-25. Setting Up The Observed Firing Chart

At the completion of any of the four techniques demonstrated, the HCO will construct an observed firing chart by using the steps in Table 6-13.

## 6-26. Example Of Percussion Plot, Vi Unknown.

A registration was conducted with shell HE, charge 4GB. The site and firing unit altitude are unknown.

a. The following data are known:

Adjusted quadrant elevation:
272
Azimuth of the line of fire
reported by the XO or
platoon leader:
5959
Adjusted deflection:
3346
Assumed altitude of the
known point:
400

b. Determine the direction, altitude, and range from the known point to the firing unit.
(1) Determine the polar plot direction. The azimuth of the line of fire 3200 equals polar plot direction.

## 5959-3200 = 2759 (Back Az Of Fire)

(2) Determine the firing unit altitude. The firing unit altitude equals the known point altitude.

## Firing Unit Altitude = 400 Meters

(3) Determine the polar plot range.

The polar plot range equals the range that corresponds to the adjusted QE.

## Polar Plot Rg = 4560 To Adj Qe (272) 6-27. Example Of Percussion Plot, Vi Estimated

The observer passes the firing unit position on his way to his location and estimates the VI to be +60 meters. Use the known data from paragraph 6-26.

a. Determine the first apparent site. **RG ~ ADJ QE = 4560 METERS.** Using the GST, set +60 underneath the MHL on the D scale. Move the site-range scale for charge 4GB TAG until range 4560 is underneath the MHL. Read site underneath the M gauge point on the D scale.

## First Apparent Site = +14 Mils

b. Determine the first apparent elevation.

## Rg ~ First Apparent El = 4,370 Meters

c. Determine the second apparent site. RG ~ FIRST APPARENT EL = 4,370
METERS. Using the GST, set +60 underneath the MHL on the D scale. Move the site-range scale for charge 4GB TAG until range 4370 is underneath the MHL. Read site underneath the M
gauge point on the D scale.

## Second Apparent Site = +15

Because the first and second apparent sites are within 1 mil, the last site determined, **+15 mils,** is the true site.

d. Determine the true adjusted elevation.
e. Using the GST, determine the VI.
f. Determine the firing unit altitude.
The introduction of an estimated VI of +60 meters changes the polar plot range from the firing unit to the known point by 200 meters (4560 to 4360). The polar plot direction is determined as shown in paragraph 6-20.

## 6-28. Example Of Time Plot, Vi Unknown

NOTE: Use the known data from paragraph 6-26.

a. At the completion of the registration, the adjusted data areas follows:

| Adjusted time (M582):   |   15.6 |
|-------------------------|--------|
| Adjusted deflection:    |        |
| 3346                    |        |
| Adjusted quadrant:      |    272 |

NOTE: The adjusted data come from the example shown in Figure 6-24.

b. Determine the angle of site.
NOTE: EL+ CAS ~ TO ADJ FS = 257.

c. Using the GST, determine the VI.

## Note: Rg ~ Adj Fs = 4360, Which Is The Polar Plot Range.

d. Determine the firing unit altitude.
e. Determine the polar plot direction as discussed in paragraph 6-20.

## 6-29. Example Of Time Plot, Vi Known, Xo's High Burst

NOTE: Use the known data from paragraph 6-26.

a. The site to crest from the XO's report is +32 mils for the registering piece. This example will demonstrate how to determine the HOB correction by using the 10-mil assurance factor.

b. Determine the asked for HOB correction. c. Determine the XO's high-burst QE. d. The computer announces orienting data to the XO or platoon leader.

## Direction 5959, Vertical Angle +42.

e. Three rounds are fired, and the following angles of site are reported by the XO or platoon leader.

## Note: Avg   Si = +55, Which Equals Got.

f. Determine the angle of site to the known point.
g. Using the GST, determine the VI.
NOTE: RG ~ ADJ FS = 4360, which is the polar plot range.

h. Determine the firing unit altitude.
i. Determine the polar plot direction as discussed in paragraph 6-20.

## 6-30. Locate An Observer

If the observer is equipped with a laser, his location maybe established by resection. The procedures are listed below.

a. The observer lases the known point and determines a direction, distance, and a vertical angle. These are reported to the FDC.

b. The HCO determines the observer location as follows:
Polar plots the back azimuth to the known point. Inserts a plotting pin along the back azimuth at the announced distance. Constructs a tick mark and labels it with the observer's call sign.
c. Using the GST, the VCO determines the observer's VI as follows:
Places the M gauge point opposite the VA on the D scale.
Moves the MHL over the distance on the C scale. Reads the VI under the MHL from the D scale.
d. To determine the observer's altitude, subtract the VI from the known point altitude.

## 6-31. Battalion Observed Firing Charts

a. Battalion observed firing charts are based on the concept that if any two points can be located by reference to a third point, the two points can be located in reference to each other. All batteries register on the same known point. For example, using the techniques for battery or platoon observed firing charts discussed in Section II of this chapter, firing units can be located in relation to the known point. After all the firing unit locations are plotted on a single firing chart in relation to the known point, the firing chart provides an accurate graphical representation of the location of the firing units in relation to each other. (See Figure 6-28.) This accurate portrayal of the relationship among the firing unit locations allows for the accurate massing of fires within the battalion on any target located by adjustment of one of the firing units, or by a shift from a known point (known to all firing units).

b. The techniques used in the construction of a battalion observed firing chart are very similar to those used for the construction of a single firing unit observed firing chart. The direction used for polar plotting each firing unit is determined by using the same procedures as the battery or platoon observed firing chart.

(1) Percussion Plot, VI Unknown.

Range and altitude may be determined for each firing unit by using the procedures in paragraph 6-21. The accurate massing of fires is not possible when this method is used.

(2) Percussion Plot, VI Estimated. Range and altitude for each firing unit maybe determined by using the same procedures listed in Table 6-10. If the relative altitude of the firing units can be estimated, the accuracy of the firing chart can be improved. One firing unit is selected as a reference unit and is assigned the same altitude as the known point. The vertical intervals of the other units are estimated and compared with the altitude of the reference firing unit to obtain their altitudes.

(3) Time Plot. Range and altitude for each firing unit may be determined by using the same procedures listed in paragraphs 6-23 and 6-24. This provides a more accurate means of determining relative location.

One firing unit is selected as a reference unit. The vertical intervals of the other firing units are estimated and compared with the altitude of the reference firing unit to obtain their altitudes.

## 6-32. Observed Firing Chart With Incomplete Survey

a. A position area survey maybe used in conjunction with the observed firing chart until the surveyed firing chart is available. The part of the chart established by firing must be plotted to the same scale as the part obtained by survey.

b. The procedure for constructing a battalion observed firing chart that is based on the registration of one unit and that has position area survey is listed in Table 6-14.

## Section V Using Map Spot Data To Construct Firing Charts

The surveyed location and azimuth of lay should be established as soon as possible. Surveyed locations can be determined by map spot survey or by normal survey procedures.

Map spot is less accurate than actual survey. If survey teams cannot immediately provide the needed data, the firing unit conducts a map spot survey to establish the unit center and azimuth of lay. For a map spot survey, fire direction personnel use hasty survey methods to associate terrain features with the locations of those features on a map and to locate the unit's center in relation to the terrain features.

## 6-33. Map Spot Survey

a. Map spot survey is the application of basic map and terrain association. It should be as accurate as possible. Three-point resection is the preferred technique for establishing the unit center by map spot survey. The map spotted location of the unit center will include an eight-digit grid coordinate and an altitude in meters.

b. Directional control (an orienting station and the direction to the end of the orienting line [EOL]) also must be provided. Common directional control should be established as soon as possible, preferably by simultaneous observation or directional traverse during daylight or by Polaris-Kochab method at night. If none of these procedures can be done quickly, the firing unit must be laid magnetically.

NOTE: FM 6-50 includes a detailed discussion of hasty survey techniques.

## 6-34. Constructing A Firing Chart From Map Spot Survey

a. To construct a firing chart based on map spot survey, the FDC must have three items of information:
Assumed grid coordinates of the firing unit center. Assumed altitude of the firing unit.

Assumed azimuth of lay.
b. When met + VE techniques cannot be used, the firing unit will register as the situation permits.

c. A firing chart based on map spot survey is only as accurate as the following:
The map spotted location of the unit center and the known point. The azimuth of lay. The construction of the chart.
d. When a firing chart based on map spot survey is used, the orienting angle must be recorded when the firing unit is laid. This orienting angle is used to determine the actual azimuth of lay when directional control is provided.

e. The FDC replots all fired targets.

## 6-35. Transferring To A Surveyed Firing Chart

a. When the position and target area surveys are completed, the FDC is provided the following information:
Firing unit center grid coordinates and altitude to the nearest 0.1 meter and azimuth to the EOL to the nearest 0.1 mil.

Known point coordinates and altitude to the nearest 0.1 meter.

b. The surveyed firing chart is constructed to show the accurate locations of the firing unit center, the known point, and the actual azimuth of lay.

c. The firing unit was initially laid, and the orienting angle was recorded. When the surveyed azimuth to the EOL is determined, the actual azimuth of lay is computed by using the following formula:

## Surveyed Az To Eol - Orienting Angle = Az Of The Line Of Fire.

d. The initial (map spot) azimuth of lay may be inaccurate. The actual azimuth of the line of fire may differ from the surveyed azimuth of lay. When survey data are provided, the FDC must--
Construct a surveyed firing chart.

Compute GFT settings.

## Chapter 7 Firing Tables

This chapter implements a portion of QSTAG 224.

Field artillery firing data are determined by use of various firing tables and equipment. These tables contain the fire control information (FCI) under standard conditions and data correcting for nonstanadard conditions. These tables and equipment include the tabular firing tables, graphical firing tables, and graphical site tables. The tabular firing tables are the basic source of firing data. They present fire control information in a tabular format. The data listed are based on standard conditions.

The GFTs and GSTs are graphical representations of the tabular firing tables.

## Section I Tabular Firing Tables

This section implements STANAGs 4119 and 4425 and QSTAG 220.

Tabular firing tables are based on test firings and computer simulations of a weapon and its ammunition correlated to a set of conditions that are defined and accepted as standard (See Figure 7-1.) These standard condition are points of departure. Corrections are used to compensate for variables in the weather-weapon-ammunition combination that are known to exist at a given instant and location. The atmospheric standard accepted in US firing tables reflect the mean annual condition in the North Temperate Zone. TFTs are developed for weapons ranging from crew-served to heavy artillery. The format of artillery firing tables are based on standardized agreements, and with small exceptions, are very similar.

## 7-1. Elements And Purpose

a. The principal elements measured in experimental firings include the following:
Angle of elevation.
Angle of departure. Muzzle velocity.
Achieved range.
Drift.
Concurrent atmospheric conditions.
b. The main purpose of the TFT is to provide the data to bring effective fire on a target under any set of conditions.

Data for firing tables are obtained from firings of a weapon conducted at various quadrant elevations. Computed trajectories are based on the equations of motion and are compared with the data obtained in the firings. The computed trajectories are adjusted to the measured results and data are tabulated. Data for elevations not fired are determined by interpolation. Firing table data define the performance of a projectile of known properties under standard conditions.

## 7-2. Cover Information

The cover of the TFT provides information concerning the weapon system(s) and projectiles to which data in the TFT apply. Projectiles listed on the cover are in the same projectile family because of ballistic similarity.

NOTE: The 155-AM-2 TFT is used as the example throughout this section. Figure 7-2
identifies acronyms and abbreviations for the TFT shown in this section.

a. Introduction. The introduction contains general information about the weapon, ammunition, and the TFT. This information specifically includes the items below.

(1) Table of contents. (2) Table of symbols and abbreviations (used in the TFT). (3) General information.
(4) Interchangeability of ammunition. This table shows the ammunition combination held in stock by other NATO nations for a particular weapon caliber that can be used by the US during combined operations, to include training exercises. Because of safety, the ammunition listed in the **shaded portions** may **only** be used in combat operations. (See Figure
7-3.)

(5) Weapon characteristics. (See Figure 7-4.)
(6) Projectile-fuze combinations and mean weights. (See Figure 7-5.)
(7) Equivalent full service rounds. These tables provide information on tube wear and erosion. These data are used to determine the number of equivalent full service rounds fired and the expected muzzle velocity loss due to wear. The values listed in these tables are based on firings of the highest charge used by that weapon system. (See Figure 7-6.)
(8) Approximate losses in muzzle velocity. The tables maybe used as a guide in estimating muzzle velocity variations from the firing table standard that are due to uniform wear in the M185 and the M199 cannon tubes. (See Figure 7-7.)
NOTE: The M199 cannon tube needs to be corrected for certain increases in muzzle velocity, see FT 155-AM-2, page V.

(9) Explanation of tables. (10) Example of met message and sample problems.
(11) Explanation of the probability table.
(12) Table of natural trigonometric functions.
(13) Charge selection table. This table provides guidance to the FDO on the selection of the charge to fire based on range and probable error. Enter the table with the range to target expressed to the nearest listed value, and choose the charge to fire. The gray shaded area shows those charges with the lowest probable error in range and thereby the charge that should be selected given no other considerations. (See Figure 7-8.)

(14) Table of conversion factors. (See Figure 7-9.)
b. Part 1. Part 1 of the TFT contains firing data and corrections for the base projectile.

It is divided into Tables A through J. Additional Tables K through M may be provided in some TFTs, but the format and content vary.

## 7-3. Table A

a. Table A is used for the solution of a concurrent met. It is used to select the line number of the met message. The entry argument for this table is quadrant elevation. The QE best describes the maximum ordinate of the trajectory and, thus, the portion of the atmosphere through which the projectile will pass. The height of the trajectory is determined by computer simulation using equations of motion. Table A also assumes that the target is at the level point of the trajectory. If there is a large vertical interval (either positive or negative), the met message line number selected will not exactly describe the atmosphere through which the projectile passes. This will cause only a small error in manual computations.

b. Enter Table A by using the left column with the adjusted quadrant elevation to a target. Extract the line number of the met message from the right column. (See Figure 7-10.)

## 7-4. Table B.

a. Table B is used in the solution of concurrent and subsequent met. This table is used to determine the value of complementary range (change in range) to correct for the effects of complementary angle of site. Complementary ranges were determined by computer simulations of the trajectory at each listed range and vertical interval. Table B has two entry arguments; they are chart range to a target expressed to the nearest 100 meters and the height of target above gun (vertical interval) expressed to the nearest 100 meters. Table B is entered from the range column along the left side, with the chart range to a target; and along the top of the table with the height of target above gun (vertical interval). Extract the value of complementary range where the two columns intersect. The complementary range is the number of meters of range correction that corresponds to the complementary angle of site. This range correction is measured at the base of the trajectory. The sum of the complementary range and the chart range, expressed to the nearest
10 meters, equals the entry range.

This is the most accurate range for entry into Table F to extract firing data and range corrections.

b. Table B is also used to determine the line number from a ballistic met message for use in subsequent met applications. The table is divided by heavy black lines. These lines form the boundaries of the met zone. The line number may be determined by following the lines between which the complementary range is extracted to the outer edge of the table. The bold number in the margin is the met line number. The met message line numbers were determined by the same method used in Table A. (See Figure 7-11.)
NOTE: Table A is more accurate in the determination of the met message line number to be used in the solution of concurrent met.

## 7-5. Table C

Table C is used in the solution of concurrent and subsequent met. It is entered with the chart direction of wind. The chart direction of wind is the angle formed by the intersection of the direction of the wind from the met message and the direction of fire (that is, the horizontal clockwise angle from the direction of fire to the direction of the wind). This table divides a
1-knot wind into crosswind and range wind components. Components for crosswind and range wind are then extracted. The extracted values are described as the components of a 1-knot wind.

The range wind component is the percentage of the wind speed that acted as a range factor. The crosswind component is the percentage of the wind force that acts to blow the projectile laterally and is translated into a lateral correction factor. (See Figure 7-12.)
NOTE: Table C is based on chart direction of wind only and, thus, is the same for all charges and all weapons.

## 7-6. Table D

a. Table D is used in the solution of concurrent and subsequent met. The values extracted from the table are standard departure of air temperature and density as a function of height. They have been converted to a percentage of standard. This table provides a correction based on a standard departure to correct the temperature and density in the met message (which is measured at the altitude beginning at the meteorological datum plane [MDP]) to values as if they would be measured initially from the unit altitude.

b. Table D is entered with the height of the unit above or below the MDP or met station.

The difference in height is entered on the left side in hundreds of meters and along the top of the table in tens of meters. Extract the corrections to density and temperature from the intersection of the two columns. (See Figure 7-13.)

## 7-7. Table E

a. Table E is used in the solution of concurrent and subsequent met. The extracted values list the effect on muzzle velocity (in meters per second) of nonstandard propellant temperatures.

b. Table E is entered with the temperature of the propellant in degrees Fahrenheit by using the left column or Celsius by using the right column. An effect in meters per second is extracted from the center column. This is the change in muzzle velocity because of the temperature of the propellant. Interpolation is needed to determine precise values from this table.

(See Figure 7-14.)

## 7-8. Table F

a. Table F lists information needed to determine firing data to attack a target and for solving concurrent and subsequent met. Table F is comprised of 19 columns. Columns 2
through 7 provide information for the computation of basic firing data and are based on a set of standard conditions. The remaining columns provide corrections to range and deflection for nonstandard conditions. The asterisks extending across the table denote the changeover point from low-angle to high-angle fire. (See Figure 7-15.)
(1) Range (Column 1). This is the distance measured from the muzzle to the target on the surface of a sphere concentric with the earth. When range is used as the entry argument for this table, it is expressed to the nearest 10 meters. Interpolation is necessary.

(2) Elevation (Column 2). This is the angle that the cannon tube is elevated from the horizontal plane (base of trajectory) to cause the round to impact at the level point for a given range. The elevations listed are the elevations required under standard conditions to achieve the ranges listed in column 1.

(3) Fuze setting for a graze burst (M564) (Column 3). This is the number of fuze setting increments necessary to cause the fuze to function at the level point at the given range under standard conditions. The values listed are for fuzes M564 and M565. The values are expressed in fuze setting increments.

(4) Change in fuze setting FS) per 10-meter decrease in height of burst
(Column 4). This is the adjustment to fuze setting required to decrease the height of burst 10
meters along the trajectory. To increase the HOB, change the sign of the value given in the table.

(5) Change in range per 1-mil change in elevation (Column 5). This is the number of meters change in range, along the gun target line, that would result from a 1-mil change in elevation.

(6) Fork (Column 6). This is the change in the angle of elevation needed to produce a change in range, at the level point, equivalent to 4 probable errors in range.

(7) Time of flight (Column 7). This is the number of seconds needed for the round to travel from the muzzle to the level point at the given elevation. This column is also used to determine the fuze setting for mechanical time fuzes M582 and M577 and variable time fuzes M728 and M732.

(8) Azimuth correction for drift (Column 8). This is the number of mils added to deflection to compensate for the drift of the projectile. Because projectiles drift right when fired, the drift correction will be to the left.

(9) Azimuth correction for a crosswind of 1 knot (Column 9). This is the correction, in mils, needed to correct for a 1-knot crosswind.

b. Columns 10 through 19 list range corrections for muzzle velocity, range wind, air temperature, air density, and projectile weight. These corrections are used in the solution of concurrent and subsequent met.

Correction factors correspond to increases or decreases in relation to standard values for muzzle velocity, air temperature, air density, and projectile weight, except the correction factors for range wind. The correction factors for range wind are listed for both head and tail winds. The factors listed assume that all other conditions are standard.

(1) Correction for a 1 meter-per-second decrease or increase in muzzle velocity
(Columns 10 and 11). This is a correction to range to compensate for a 1 meter-per-second decrease or increase in muzzle velocity.

(2) Correction for a head wind or tail wind of 1 knot (Columns 12 and 13).

This is a correction to range to compensate for a head wind or tail wind of 1 knot.

(3) Correction for a 1 percent decrease or increase in air temperature
(Columns 14 and 15). This is a correction to range to compensate for a decrease or increase in air temperature of 1 percent of standard.

(4) Correction for a 1 percent decrease or increase in air density (Columns 16
and 17). This is a correction to range to compensate for a decrease or increase in air density of 1
percent of standard.

(5) Correction for a 1 square decrease or increase in projectile weight
(Columns 18 and 19). This is a correction to range to compensate for a decrease or increase of 1
square in projectile weight.

## 7-9. Extracting Basic He Data From Table F

Data may be extracted from Columns 1 through 8 of Table F to compute firing data. It is necessary to relate the data extracted to an entry argument. An element of data is said to be a fiction of another element when changes in one of the elements will cause a change in the other.

a. Elevation is a Function of Range.

Enter Column 1 with range expressed to the nearest 10 meters, and extract the elevation to the nearest 1 mil from Column 2.

b. Fuze Setting is a Function of Elevation. Enter Column 2 with the elevation expressed to the nearest mil, and extract the fuze setting expressed to the nearest 0.1 of an increment from Column 3 for fuzes M564 and M565. Extract the fuze setting expressed to the nearest 0.1 of a second from Column 7 for fuzes M582 and M577.

c.

FS for 10-Meter Decrease in HOB is a Function of Fuze Setting. Enter Column FS expressed to the nearest 0.01 from Column 4.

3 for fuzes M564 and M565 or Column 7 for fuzes M582 and M577 with the fuze setting expressed to the nearest 0.1. Extract the d. D Range for a 1-Mil D Elevation is a Function of Elevation. Enter Column 2 with the elevation expressed to the nearest mil, and extract the change in range for a 1-mil change in elevation expressed to the nearest meter.

e. Time of Flight is a Function of Elevation. Enter Column 2 with the elevation expressed to the nearest mil, and extract the time of flight expressed to the nearest whole second from Column 7.

f. Variable Time Fuze Setting is a Function of Elevation. Enter Column 2 with the elevation expressed to the nearest mil, and extract the time of flight expressed to the nearest 0.1 second from Column 7. Express down to the whole second, g. Drift is a Function of Elevation. Enter Column 2 with the elevation expressed to the nearest mil, and extract the drift expressed to the nearest 1 mil from Column 8.

## 7-10. Table G

Table G is the table of supplementary data containing probable error information and certain trajectory elements. For ranges not listed, data can be determined through interpolation.

The entry argument for this table is range (Column 1). Elevation corresponding to that range is listed in Column 2 for quick reference.

The asterisks extending across the table denote the changeover point from low-angle to high-angle fire. (See Figure 7-16.)
a. Probable Error (Columns 3 through 7). Probable error is defined as the error for a particular charge, and range or elevation that is exceeded as often as it is not exceeded. These errors are based on the standard probability curve and are explained in more detail in Chapter 3.

b. Probable Error in Range to Impact (Column 3). Probable error in range is a value in meters that, when added to and subtracted from the range at the mean point of impact along the gun-target (GT) line, will produce an interval that should contain 50 percent of all rounds fired.

PER will vary according to the charge and range.

c. Probable Error in Deflection at Impact (Column 4). Probable error in deflection is a value in meters when applied to the right and left of the mean point of impact, will produce an interval parallel to the line of fire that should contain 50 percent of the rounds fired. PED will vary based on charge and range.

d. Probable Error in Height of Burst (Column 5). Probable error in height of burst is a value in meters which, when added to and subtracted from the expected height of burst, will define an area that should contain 50 percent of the rounds freed. The factors that contribute to PEHB include variations in the functioning of the time fuze.

e. Probable Error in Time to Burst (Column 6). Probable error in time to burst is a value in seconds, which when added to and subtracted from the expected time to burst, will produce a time interval that should contain 50 percent of the rounds fired.

f. Probable Error in Range to Burst (Column 7). Probable error in range to burst is a value in meters which, when added to and subtracted from the expected range to burst, will produce an interval along the line of fire that should contain 50 percent of the rounds fired.

g. Angle of Fall (Column 8). The angle of fall is the value in mils of the least angle measured clockwise from the horizontal to a line tangent to the trajectory at the level point.

h. Cotangent of Angle of Fall (Column 9). The cotangent (cot) angle of fall is the trigonometric function of the angle of fall. When the probable error in range is divided by this factor, the quotient is the vertical probable error.

The vertical probable error is the height expected to contain 25 percent of the impacts when firing onto a vertical face.

i. Terminal Velocity (Column 10). The terminal velocity (tml vel) is the speed of the projectile at the level point under standard conditions.

j. Maximum Ordinate (Column 11). The maximum ordinate (MO) is the height of the summit above the origin in meters.

This is the height of the trajectory above the howitzer expressed in meters under standard conditions.

k. Complementary Angle of Site for Each Mil of Angle of Site (Columns 12 and
13). This is the correction termed the complementary site factor (CSF) which must be algebraically added to each mil of angle of site to compensate for the nonrigidity of the trajectory. When the CSF is multiplied by the absolute value of the angle of site, the product is the complementary angle of site.

## 7-11. Table H

a. Table H is used in the solution of concurrent and subsequent met. The extracted value is the correction to range in meters for the rotation of the earth at 0 latitude. A correction for any other latitude is extracted from the small table at the bottom of Table H and is multiplied by the correction from the table. The asterisks extending across the table denote the changeover point from low-angle to high-angle fire.

b. Table H is entered along the left side with the entry range expressed to the nearest 500
meters and along the top or bottom with the **exact azimuth** (to the nearest mil) to the target (direction of fire) expressed to the nearest listed value. For example, if the azimuth to the target is 1,499 mils, enter Table H with 1400. Whenever the solution determined is exactly halfway between two entry arguments for azimuth to the target use the next higher value. (See Figure 7-17.)

## 7-12. Table I

a. Table I is used in the solution of concurrent and subsequent met. There are tables for every 10 latitude starting from 0 north or south latitude to 70 north or south latitude. The extracted value is the correction to deflection in mils, for the rotation of the earth. The asterisks extending across the table denote the changeover point from low-angle to high-angle free.

b. Table I is entered along the left side with the entry range expressed to the nearest 500
meters and along the top (for northern latitudes), with the **exact azimuth** (to the nearest mil) to the target (direction of fire) expressed to the nearest listed value. For example, if the azimuth to the target is 1,499 mils, enter Table I with 1600. For southern latitudes, you enter from the bottom with the **exact azimuth** (to the nearest mil) to the target (direction of fire) expressed to the nearest listed value. Whenever the solution determined is exactly halfway between two entry arguments for azimuth to the target, use the next higher value. (See Figure 7- 18.)

## 7-13. Table J

a. Table J is used in the solution of concurrent and subsequent met. Data in this table are arranged in 11 columns. Each column lists a fuze setting correction needed to compensate for the effects of nonstandard conditions.

b. The fuze setting used as an entry argument corresponds to the adjusted elevation from a registration (concurrent met) or corresponds to the elevation determined in the solution of a subsequent met. (See Figure 7-19.)
(1) Fuze setting (Column 1).

The FS corresponding to the adjusted elevation expressed to the nearest whole increment is the entry argument for Table J.

(2) Correction for a 1 meter-per-second decrease or increase in muzzle velocity
(Columns 2 and 3). This is the correction for the FS to compensate for a 1 meter-per-second decrease or increase in muzzle velocity.

(3) Correction for ahead wind or tail wind of 1 knot (Columns 4 and 5). This is the correction to FS to compensate for a head wind or tail wind of 1 knot.

(4) Correction for a 1 percent decrease or increase in air temp (Columns 6 and 7).

This is the correction to FS to compensate for a decrease or increase in air temperature of 1 percent of standard.

(5) Correction for a 1 percent decrease or increase in air density (Columns 8 and
9). This is the correction to FS to compensate for a decrease or increase in air density of 1 percent of standard.

(6) Correction for a 1  square decrease or increase in projectile weight (Columns 10
and 11). This is the correction to FS to compensate for a decrease or increase of 1 square in projectile weight.

7-14. Table K
Table K provides corrections to be applied to M564 fuze settings when time fuze M520A1 is being fired. (See Figure 7-20.)

## 7-15. Illuminating Projectiles

a. Illuminating projectiles are available for the 105-mm and the 155-mm howitzers.

They are used to illuminate a designated area for observing enemy night operations, for adjusting artillery fires at night, for marking locations, or for harassment purposes.

b. Illuminating projectiles are base-ejecting projectiles fired with mechanical time fuzes.

The filler consists of an illuminating canister and a parachute assembly. The FDO selects the charge to fire, selecting the lowest practical charge to prevent a malfunction caused by the parachute ripping when the flare is ejected from the projectile. The two models of illuminating projectiles for the 105-mm howitzer are the M314A2 and the newer M314A3, which has a slightly longer burning time.

The 155-mm howitzer also has two models of illuminating projectiles. These models are the M118 and the newer M485A2, which has a significant increase in illumination time.

NOTE: Data are no longer provided for the M118 projectile. Part 2 of the 155-AM-2 TFT applies to the M485 series only).

c. Part 2 of the 105-mm and 155-mm HE TFT provide data for the illuminating projectile. Most illumination data are provided in a single table. However, TFT may contain additional tables to provide corrections for mechanical time fuzes other than that tabulated in the first table. When more than one table is provided, the tables are identified by letters. The shaded portion of Columns 1 and 2 indicate function during the ascending branch.

(a) Range to target (Column 1). This is the distance measured from the muzzle to the target on the surface of a sphere concentric with the earth. When range is used as the entry argument for this table, it is expressed to the nearest 10 meters.

(b) Quadrant elevation (Column 2). This is the angle of the tube in the vertical plane.

This QE, when used in conjunction with the fuze setting given in Column 3, produces an airburst such that the ignition of the illuminant occurs 600 meters (105-mm is 750 meters) above the level point at the given range.

(c) Fuze setting (Column 3). This is the fuze setting for the M565 fuze. When used in conjunction with the QE given in Column 2, it produces an airburst such that the ignition of the illuminant occurs 600 meters above the level point at the range (105-mm is 750 meters).

(d) Change in QE and FS for an increase of 50 meters in HOB (Columns 4
and 5). These corrections are added to the QE and FS to increase the height of burst by 50 meters. By changing the sign of the correction, the factor is used to lower the height of burst. This factor is also used to correct the QE and FS from Columns 2 and 3 for the VI. These factors must be applied in conjunction with each other.

(e) Range to fuze function (Column 6). This is the horizontal distance from the gun to the point at which the fuze functions.

(f) Range to impact (Column 7). This is the horizontal distance from the gun to the point at which a nonfunctioning projectile will impact.

(2) Table B. Table B provides corrections to fuze setting for mechanical time
(MT), M565 to obtain a fuze setting for fuze MTSQ, M577. The corrections are either added to or subtracted from the fuze setting of the MT, M565 fuze to obtain the fuze setting for fuze MTSQ, M577.

## 7-16. Tft Part 3 And Part 4

Certain TFTs (for example, FT 105-H-7) provide data in two additional parts. Part 3
contains firing data for cartridge, HEP-T, M327 and consists of one table for a single charge.

Part 4 contains firing data for cartridge APERS, M546 and consists of one table for a single charge.

## 7-17. Appendixes

The last portion of the TFT are the appendixes. They contain trajectory charts for HE
projectile. Altitude in meters above the origin is plotted against range in meters for every 100
mils of elevation. Time of flight, by 5-second intervals, is marked on the trajectory.

## Section Ii Graphical Firing Tables

To eliminate the difficulties in computing firing data that result from the need to interpolate, the graphical firing table was created. The GFT provides all the information needed to compute firing data in a slide rule form.

## 7-18. Overview

a. Parts. All GFTs are made in two parts (Figure 7-21). The rule is a rectangular wooden base on which is printed one or more sets of scales. With a few exceptions, GFTs are printed on both sides. The second part of the GFT is the cursor. This is a transparent plastic square that slides on the rule. Engraved in the plastic of the cursor is a manufacturer's hairline used to determine values from the scales.

c. Types. The basic GFT format is the same for all weapons. These formats may be divided into three types: low-angle GFTs, high-angle GFTs, and shell illuminating GFTs.

d. Identification. All GFTs are labeled (Figure 7-22) for identification. The first line of the label on low- and high-angle GFTs indicates the type weapon in bold type; that is, HOW
155mm. Immediately below the weapon type, in smaller print, is the identification of the TFT on which the GFT is based; for example, "155AM2." This is followed by the projectile type and nomenclature, such as "HEM107." The last line of identification of low-angle GFTs tells the charge for which the GFT may be used, such as "CHARGE 4." High-angle GFTs indicate the trajectory "HIGH ANGLE."
Shell illuminating GFTs (Figure 7-23) reverse the label with
"PROJECTILE ILLUMINATING" on the top and the weapon type on the bottom.

## 7-19. Low-Angle Gfts

Low-angle GFTs are available for all weapon systems and were developed from the data contained in the TFT of the weapon and projectile. All GFTs are printed with a base scale which represents the data for the base projectile as indicated on the label; that is, "HEM107." One or more ICM/M825 scales may be provided above or below the base scale. The scales are as follows:
a. Drift Scale. This scale, which is printed in black, gives the projectile drift in mils.

Since the projectile drifts to the right, the drift correction is always made to the left. Each elevation at which the drift is exactly halfway between the values is printed in red. Artillery expression is applied to determine the value of drift at each of these elevations. In determining drift, it is important to note that drift is a function of elevation. The corresponding portion of the TFT is Table F, Column 8.

b. 100/R Scale. This scale lists the number of mils needed to move the burst laterally or vertically 100 meters at a given range. The numbers on this scale are printed in red. The scale is based on the mil relation formula     = W/R x 1.0186). 100/R is a function of range. There is no corresponding table in the TFT for 100/R.

c. Range Scale. This scale is the base scale, and all other scales are plotted in relation to it. Range is expressed in meters, The range scale was developed to give as large a range spread as possible, and still permit graduations large enough for accurate readings. Range is read to the nearest 10 meters. The corresponding portion of the TFT is Table F, Column 1.

d. Elevation Scale. This scale is graduated in mils and is read to the nearest mil. The numbers on this scale are printed in red and black. The red numbers denote elevations that are within range transfer limits for a one-plot GFT setting. The corresponding portion of the TFT is Table F, Column 2.

e. Time of Flight/Fuze Setting M582 Scale. This scale lists the time of flight and the fuze settings for time fuzes M582, M577, M728, and M732 corresponding to a given elevation.

Time of flight is determined to the nearest whole second. Fuze settings for time fuzes M582 and M577 are determined to the nearest 0.1 fuze setting increment. Fuze setting for fuze VT is determined from the TF/M582 scale by vanishing the tenths and applying a .0. Time of flight and the fuze settings for M582, M577, M728, and M732 are functions of elevation. The corresponding portion of the TFT is Table F, Column 7.

f. Fuze Setting M564 Scale. This scale lists the&e settings for time fuzes M564 and M565. The values are read to the nearest 0.1 fuze setting increment. Fuze settings for M564 and M565 are functions of elevation. The corresponding portion of the TFT is Table F, Column
3.

g. FS/10M HOB Scale. This scale lists the corrections to fuze setting for fuzes M582
or M564 that are needed to raise or lower the HOB 10 meters along the trajectory. FS/10M HOB
is a function of fuze setting. The corresponding portion of the TFT
- is Table F, Column 4.

NOTE: GFTs produced before 1983 include a fork scale. Fork represents the value, in mils, of the change in the angle of elevation needed to produce a change in range of 4
PER at the level point. The corresponding potion of the TFT is Table F, Column 6.

h. Met Check Gauge Points. These are red equilateral triangles above the TF/M582
fuze setting scale.

The apex of each triangle points to the QE that under standard conditions results in the maximum ordinate of the trajectory passing through a whole line number of a met message. The range and QE at the met check gauge points are preferred for registration aiming points, for met plus velocity error (met + VE) computations, and for determining GFT settings.

There is no corresponding table in the TFT.

NOTE: Chapter 10 explains registrations and determining GFT settings, and Chapter 11
explains met + VE computations.

i. Height-of-Burst Probable Error Gauge Points. These gauge points appear on some GFTs above the fork scale or on the M564 fuze setting scale. They are red right triangles and indicate the range and fuze settings at which the PEHB is 15 meters. Larger HOB dispersion must be expected when time fuzes are used with a particular charge at ranges exceeding the gauge point. Some charges have two such gauge points. The one on the left of the GFT indicates the range at which the PEHB for the next lower charge is 15 meters. The PEHB can be determined from Table G, Column 5, of the TFT.

j. Range Probable Error Gauge Point.

This is a black equilateral triangle located above the HOB scale. It indicates the range at which the range probable error equals
25 meters. Ranges to the left of the gauge point have a PER of less than 25; ranges to the right of the gauge point have a PER of greater than 25. The PER can be determined from Table G, Column 3, of the TFT.

k. Range K and Fuze K Lines.

These are based on data derived from computer simulations of artillery firing. The computer program uses 50 sets of weighted nonstandard conditions of temperature, density, range wind, and muzzle velocity. Firing simulations were made by using these 50 sets of nonstandard conditions for each of a number of ranges within the range limits for each charge. Every group of 50 firings for each range provided data to calculate a total average range correction (range K) and total average fuze correction (fuze K) for that particular range. These values of range K and fuze K were graphically plotted versus the corresponding range for all simulated ranges for each charge. These curves were simplified as tight line approximations and were used to create the data to construct the range K and fuze K lines on the GFT. These approximations were considered to be acceptable, up to the point where no more than 1 PER was introduced. This acceptable range area is denoted on the GFT by the elevation numbers printed in red. Those numbers corresponding to an error larger than 1 PER are printed in black. From this is derived the range transfer limits for a one-plot GFT setting. The range K and fuze K lines are ignored for multiplot GFT
settings.

l. Improved Conventional Munitions Scales. These scales are on some graphical firing tables. They are located above the DEFL CORR/DRIFT scale. The scales apply to a specific type of ammunition as indicated by the model number at the left end of the scale.

(1) DEFL CORR. This is the top scale on GFT ICM scales. This scale incorporates base scale drift and the ballistic correction as tabulated in Table A of the appropriate addendum.

(2) QE. The next scale (the top scale on older GFTs) is the quadrant scale. This scale provides the quadrant to fire for the ICM projectile. The ICM quadrant is read to the nearest mil by placing the manufacturer's hairline over the base scale quadrant and reading up under the MHL to the appropriate ICM quadrant scale. This QE incorporates the ballistic correction given in Table A of the appropriate addendum.

(3) FS. The last scale provides the fuze setting to fire on the ICM projectile. The ICM FS is read to the nearest 0.1 increment by placing the MHL over the base scale FS and reading up under the MHL to the appropriate ICM FS scale. This FS incorporates the ballistic correction given in Table B of the appropriate addendum.

## 7-20. High-Angle Gft

a. High-angle fire is delivered at elevations greater than the elevation corresponding to the maximum range for a charge. All howitzers can deliver high-angle fire effectively.

b. The high-angle GFT consists of one rule with ballistic data for multiple charges on each side. The scales on the high-angle GFT from top to bottom are as follows:
(1) 100/R. This scale lists the number of mils needed to move the burst laterally or vertically 100 meters at a given range. The scale increases from right to left, is read to the nearest mil, and applies to all charges. There is no corresponding portion in the TFT.

(2) Range. The range scale is expressed in meters and applies to all charges appearing on that side of the GFT. Range increases from left to right and is read to the nearest 10
meters. The corresponding portion of the TFT is Table F, Column 1.

(3) Elevation. Elevation is expressed in mils and increases from right to left. It is visually interpolated to the nearest mil.

The corresponding portion of the TFT is Table F, column 2.

(4) 10-Mil site factor. The values on this scale denote the site for each 10 mils of angle of site. The numbers are printed in red and are negative values. This factor actually reflects the complementary angle of site for a positive VI. Consequently, a slightly more accurate solution for negative angles of site can be determined from the TFT. Because of the minimal effect of site in high-angle fire, these values are acceptable for both a positive and negative VI. The scale increases from left to right and is read to the nearest tenth (0.1) of a mil. There is no corresponding portion in the TFT.

(5) Drift. The values on this scale are in mils. The scale increases from right to left and is read to the nearest mil. The corresponding portion of the TFT is Table F, Column 8.

(6) Time of flight. This scale is graduated in seconds and is used to determine both time of flight (to the nearest whole second) and VT fuze setting (to the next lower whole second).

The scale increases from right to left. The corresponding portion of the TFT is Table F, Column
7.

NOTE: Because the scales increase in different directions, the computer must be careful in reading the high-angle GFT. The elevation, 100/R, drift, and TF scales increase from right to left. The range and 10-mil site scales increase from left to right.

## 7-21. Illuminating Projectile Gft

Graphical firing tables have been developed for use with all 155-mm M485A2
illuminating projectiles and with the 105-mm M314A1, M314A2, and M314A3E1 projectiles.

Illumination scales are provided for enough charges to cover the spectrum of range for the shell and weapon.

a. 100/R. This scale is printed along the top edge of the GFT. For a given range, the
100/R scale denotes the number of mils needed to shift the burst 100 meters laterally or vertically. The 100/R is read to the nearest mil. There is no corresponding portion in the TFT.

b. Range. The range scale is the base scale of the illuminating GFT. All other scales are plotted with reference to the range scale.

Range is read to the nearest 10 meters. The corresponding portion of the TFT is Part 2, Table A, Column 1.

c. Elevation to Impact. This scale is graduated in mils. Low-angle elevation increases from left to right and is read to the nearest mil. The scale is used to determine the range (on the range scale) to which a nonfunctioning projectile will impact. There is no corresponding portion in the TFT.

d. Height of Burst. These scales are graduated in 50-meter increments. The HOB is determined by expressing the VI to the nearest 50 meters and algebraically applying the VI to the optimum HOB. There is no corresponding portion in the TFT.

e. QE. The QE scale shown for each listed height of burst gives the QE needed to achieve the height of burst at the desired range. The scale is graduated in mils and is visually interpolated to the nearest mil. A heavy black arrow on the QE scale indicates the part of the trajectory that is at or near the summit and that does not exceed by 50 meters the height of burst that it represents. (See Figure 7-24.) The corresponding portion of the TFT for a 600-meter (750 meters for 105 mm) HOB is Part 2, Table A, Column 2.

f. FS M565. This scale consists of a series of red arcs. The scale includes a red line for each whole fuze setting increment for the MT, M565 fuze. The value of each line is printed in red at the bottom of the scale. The fuze setting is read for the desired range and HOB to an accuracy of 0.1 FS increment by visual interpolation. The corresponding portion of the TFT for a 600-meter (750 meters for 105 mm) HOB is Part 2, Table A, Column 3.

## Chapter 8 Site

This chapter implements a portion of QSTAG 224.

Site is computed to correct for situations where the target is not at the same altitude as the unit. To understand site, a brief description of the trajectory is necessary.

## 8-1. Initial Elements Of The Trajectory

a. Vertical Interval. The vertical interval is the difference in altitude between the unit or observer and the target or point of burst. (See Figure 8-1.) The VCO determines the vertical interval by subtracting the altitude of the unit or observer from the altitude of the target or point of burst. The vertical interval is determined to the nearest meter and is a signed value.

b. Angle of Site. The angle of site compensates for the vertical interval. The angle of site is the smaller angle in a vertical plane from the base of the trajectory to the straight line joining the origin and the target. The angle of site has a positive value when the target is above the base of the trajectory and a negative value when the target is below the base of the trajectory.

The angle of site is determined to the nearest 0.1 mil and is a signed value. It carries the same sign as the VI.

c. Complementary Angle of Site. The complementary angle of site is an angle that is algebraically added to the angle of site to compensate for the nonrigidity of the trajectory. When large angles of site or greater ranges for any one charge are involved, a significant error is introduced because of changes in the shape of the trajectory. If CAS is not added to angle of site in low-angle fire, the trajectory will pass under the target if the target is at an altitude higher than the unit. The trajectory will pass over the target if the target is at an altitude lower than the unit.

Complementary angle of site is dependent on the following:
Charge.

Range.

Angle of site. Weapon system. Projectile family. Angle of fire (high or low).

(1) For a given charge and range, there is a specific complementary angle of site for every 1 mil angle of site. This specific value is listed in Table G of the TFT, Columns 12 and 13, in the form of the complementary site factor (comp site factor or CSF). The CSF must be applied to a particular angle of site to determine complementary angle of site. The CSF must be determined by interpolation for the chart range to the nearest 10 meters. Complementary angle of site is computed to the nearest 0.1 mil and is a signed quantity. The sign is the same as the CSF
value.

(2) A study of listed values for the CSF reveals that for short ranges the CSF is negligible. As the range increases, the factor increases for any given charge. Thus, at greater ranges, the CSF is significant even for small angles of site. The CSF also varies with the charge for any given range.

d. Site. Site is the algebraic sum of the angle of site and the complementary angle of site. It is determined to the nearest mil and is a signed value.

e. Angle of Elevation. The angle of elevation is the vertical angle between the horizontal and the axis of the bore required for a projectile to achieve a prescribed range under standard conditions.

f. Quadrant Elevation. Quadrant elevation is the algebraic sum of site and the angle of elevation. It is determined to the nearest mil.

## 8-2. Site In High-Angle Fire

Site has a relatively small effect in high-angle fire because of the large angle of fall. In high-angle missions, a minus site must be used to compensate for a positive vertical interval and a Plus site must be used to compensate for a negative vertical interval. Therefore, high-angle site will have the opposite sign of the VI.

## 8-3. Determination Of Altitudes

The altitude of the unit or base piece is nomally known by map spot or survey and labeled on the firing chart. To determine the target altitude, the VCO must analyze the call for fire sent by the observer.

a. The observer may report a target location by using the grid coordinate method. This method requires a map of the target area. The easiest way to determine altitude from a map is by reading the contour lines. The VCO plots the grid sent by the observer and extracts the altitude from the map.

b. The observer may report a target location by using polar coordinates. He locates the target in relation to his own location by sending a direction and distance to the target. The observer may also transmit an up or down vertical shift from his location. If the observer transmits a vertical shift, the altitude of the target is determined in relation to the observer by applying the vertical shift to the observer's altitude. If not, the grid is plotted and altitude is determined as in paragraph a.

c. The observer may report a target location with reference to a known point plotted on the firing chart. This method of target location is known as shift from a known point. The vertical shift sent by the observer is applied to the known point altitude to determine the target altitude.

## 8-4. Determination Of Site Without A Graphical Site Table

In Table 8-1 are the procedures for determining site without a GST.

## 8-5. Determination Of Site Without A Gst, Requiring Interpolation

The example in Table 8-2 uses data for the firing unit location and firing chart from Chapter 6. The following data are given:

Weapon System:
MI09A3
Charge:
4GB
Chart Rg From l/A to the
Tgt (Grid 430 290):
4,340 meters
l/A Altitude:
1062
Target Altitude (Map Spot): 1040

## 8-6. Determination Of Vertical Angle

The vertical angle is the smaller angle in a vertical plane from the horizontal to a straight line joining the observer and target. The angle of site and the vertical angle are essentially the same angles viewed from different perspectives. (See Figure 8-2.) The steps for determining VA
are in Table 8-3.

## 8-7. The Graphical Site Table

a. The computation of site with the TFT is time consuming. The GST was developed to provide a quick and accurate computation of vertical angle, angle of site, and site. The GST can also be used to compute the vertical interval when the site, the charge, and the range are known or when the vertical angle and the distance are known. It can be used to convert yards to meters or meters to yards and to multiply and divide. Each GST is designed for a particular weapon and projectile family, and the computations are valid only for the weapon specified on the GST.

b. The GST consists of three parts: a base, a slide, and a cursor with a manufacturer's hairline. (See Figure 8-3.)
(1) Base. The base is marked by the D scale, which is a logarithmic scale of variable graduations.

This scale is used to determine VI, VA, angle of site, and site. The accuracy depends on the values read off the scale. The back of some GSTs have instructions on how to use it.

(2) Slide. The slide is marked with a C scale, gauge points, and site-range scales.

(a) C (range) scale. This scale is identical to the logarithmic D scale, and there are two sides to the slide. The C and D scales, along with the M gauge point, are used for computing vertical interval, vertical angle, and angle of site. Multiplication and division may also be performed by using the C and D scales.

(b) Gauge points. The C scale is marked with two M (meter) and YD (yard)
=1.0186
gauge points. The M gauge point multiplies the value opposite the C index by 1.0186, which gives a precise solution to the mil relation formula and is used in all computations (
W/R). The YD gauge point multiplies the value opposite the M gauge point by 0.9144, which gives an immediate solution to the formula: (YARDS x 0.9144 = METERS).

(c) Site-range scales. These scales are used to compute site when the VI and range are known or to compute the VI when the site and range are known. For each charge indicated, there are two site-range scales. One is black, marked "TAG," and the other is red, marked "TBG." Each side is placed in relation to the M gauge point so that site is read on the D
scale opposite the M gauge point when VI on the D scale is divided by range on the site-range scale. The TAG and TBG scales are constructed to include CAS. They differ from each other just as the CSF for a plus angle of site differs from the CSF for a minus angle of site. The TAG
scale is used when the VI is plus, and the TBG scale is used when the VI is minus. The value of site is read or placed opposite the M gauge point.

When there are no site range scales for a particular charge or the scale does not include the appropriate gun target range, site for that charge must be computed manually.

(d) Range changeover point. On all GSTs for all charges, there is a point on all site-range scales where the scales begin to "double back"; that is, the cursor is moved to the left rather than to the right for an increase in range for a given VI. The range at which each scale reverses direction is called the range changeover point. The location of the changeover point can be shown by plotting site as a function of site in mils and range in meters (Figure 8-4). Recall that site equals the angle of site plus the complementary angle of site. In Figure 8-4, at the lesser ranges (5,000 to 7,000 meters), the angle of site is decreasing at a greater rate than complementary angle of site is increasing; thus, site decreases. At the longer ranges (8,000 to 9,000 meters), the angle of site is decreasing at a lesser rate than the complementary angle of site is increasing; thus, site increases. The site curve shows decreasing values up to a range of about
7,600 meters and then increasing values beyond. The range at which site is at an absolute minimum value is 7,600 meters and is the range changeover point for that charge and projectile.

(e) Cursor.

The cursor has a vertical hairline, known as the manufacturer's hairline. It enables the user to place or read a value on the slide opposite another value on the base.

## 8-8. Average Site

a. A considerable amount of time can be saved in mission processing if average site can be precomputed for the area of operations. As time permits after occupation, the VCO should develop a color-coded average site map (Figure 8-5). The average sites and altitudes would be listed within each color-coded area. Site is computed for vertical interval segments on the basis of ranges and charges to be used most frequently. The error in site will normally be small and is an acceptable tradeoff of accuracy for speed. When a target is plotted on the average site map, the VCO can read and announce site. This technique may not be practical in certain situations, for example, in mountainous terrain or in fast-moving situations. Here the VCO could use the altitude of the nearest preplotted target to compute site.

b. The VCO creates and improves his average site map by using the following steps.

(1) Plotting of contour intervals. The VCO color-codes his map along with selected contour intervals, creating zones with little variation in altitude. VI is based on the mean altitude in each zone. Compute site for each color-coded zone by using the range to the center of the zone and the appropriate charge. This will result in an average site to use for all targets plotted within a color-coded zone.

(2) Refining average site. As time permits, average site values can be refined by computing additional values for variations in range within a color-coded zone.

This will determine if there are significant changes in site caused by changes in range. For example, site would be computed for a zone between the 300 and 320 contour intervals by using ranges throughout the zone (that is, 5,000, 6,000, 7,000). If site changes by more than 1 mil, the VCO
would announce the refined site.

## 8-9. Determination Of Angle Of Site And Vertical Angle With The Gst

a. The procedures for computing angle of site and vertical angle are the same. Both are computed by using the C and D scales and are not associated with a particular charge or a particular weapon. In each case, two values are needed: the range (or distance) to the target in meters and the number of meters the target is above or below the howitzer or observer (vertical interval., b. The diagram in Figure 8-6 is known as the Magic T. It can be used to help determine angle of site, VA, and site when using the GST. The horizontal line in the Magic T
represents division, and the vertical line represents multiplication.

c. The following steps in Table 8-4 show how to determine angle of site and VA by using the GST.

## 8-10. Determination Of Site With The Gst

Site is computed by using the site-range and D scales. The value determined will be valid for a particular charge, weapon, and projectile family. Two values are needed--the range to the target in meters and the vertical interval. Use the steps in Table 8-5 to determine site with a GST.

## 8-11. Sample Problems

The examples in Tables 8-6 through 8-9 use data for the firing unit location, known point, and observer (T03) from Chapter 6. The following data are given:

Weapon System:
M109A3
Charge:
4GB
Chart Rg From l/A to
Known Point 1:
4,960 meters
Distance from T03 to
Known Point 1:
1,760 meters
l/A Altitude:
1062
T03 Altitude:
1127
Known Point 1 Altitude:
1024

a. Determination of Site (Manual Computation). Table 8-6 shows an example of manually determining site.

b. Determination of Vertical Angle (Manual Computation). Table 8-7 shows an example of manually computing VA.

c. Determination of Angle of Site and Vertical Angle With the GST. Table 8-8
shows an example of determining angle of site and VA with the GST.

NOTE: The values in parentheses pertain to the observer and the determination of VA.

d. Determination of Site With a GST. Table 8-9 shows an example of determining site with a GST.

## 8-12. High-Angle Site

a. Site is always computed for high-angle fire and added to the determined angle of elevation, which yields high-angle QE. However, site may have a relatively small effect in high-angle fire because of the large angle of fall. Therefore, if the angle of site is small  and the FDO directs to ignore it, then site **may be** ignored.

b. In high-angle fire, an increase in the angle of elevation decreases range. A decrease in the angle of elevation increases range. The complementary site factors, found in Table G of the TFT, are relatively large (greater than 1) and are the opposite sign of the VI and angle of site. Therefore, the site will have the opposite sign of the VI and angle of site.

c. High-angle site is determined by using the CSF (TFT) or the 10-mil site factor from the GFT. Using the GFT is the preferred method. The reading obtained from the 10-mil site factor scale is the actual site for each 10 mils of angle of site. The site is computed by multiplying the angle of site, divided by 10, by the 10-mil site factor. The 10-mil site factor is always negative.

## 8-13. Determination Of High-Angle Site With The Tft

The procedures for computing high-angle site with a TFT (Table 8-10) are the same as low-angle manual computations of site (Table 8-l). A GST can be used to compute the angle of site.

## 8-14. Determination Of High-Angle Site With A High-Angle Gft

The use of the high-angle GFT to determine site is the preferred method. (See Table
8-11.)

## 8-15. Determination Of 10-Mil Site Factor Without A High-Angle Gft

The 10-mil site factor is the value of high-angle site for every 10 mils of angle of site.

The 10-mil site factor can be determined manually by solving two equal equations for the 10-mil site factor.

NOTE: If the 10-mil site factor is not listed on the high-angle GFT, use the last listed value or change charges.

The FDC can compute high-angle site by manually determining the 10-mil site factor for those situations when a high-angle GFT is not available. The 10-mil site factor from the GFT actually reflects the complementary angle of site for a positive VI.

Therefore, this method will introduce a slight inaccuracy when estimating for negative VIs.

## Chapter 9 Fire Mission Processing

In the battery or platoon FDC, all actions are oriented toward timely and accurate fire mission processing. All actions must provide the best possible flow of information between FDC
personnel. The battery or platoon FDC must be trained to determine responsive and accurate firing data. Upon receipt of a call for fire, FDC personnel must work as a team to accomplish many tasks at the same time. (See Figure 9-1.)

## Section I Duties And The Record Of Fire

This section implements STANAG 2934 and QSTAG 225.

Understanding the duties within the FDC is imperative. All activity supports the computer. He determines and records firing data on the record of fire. He is also the link to the howitzers, because he transmits the fire commands.

## 9-1. Crew Duties For The Fdc

The procedures in Table 9-1 should be used to facilitate mission processing and ensure responsiveness. (For automated FDC crew duties, see Appendix F.)

## 9-2. Elements Of Firing Data

The data determined from the firing chart must be converted to firing data that can be placed on the weapon and ammunition.

These data consist of the charge, fuze setting (when applicable), deflection, and quadrant elevation to be fired.

a. Shell. Shell is the projectile to be fired. The projectile will have a direct impact on determining the remaining elements since firing tables are based on the projectile.

b. Charge. The amount of propellant to be fired with artillery ammunition is varied by the number of propellant increments. The charge selected is based on the range to the target and the tactical situation.

c. Fuze. Fuze is the fuze to be fired. The fuze will have a direct impact on determining the quadrant elevation when firing mechanical time fuzes.

d. Fuze Setting. When a projectile with a mechanical time or proximity fuze is fired, the computer determines a fuze setting to be set on the fuze that should cause it to function at the desired point along the trajectory. Fuze setting is a function of elevation. This fuze setting is determined from the TFT or GFT. Some projectiles may also be fired with a point-detonating fuze, which can be set for delay action.

e. Deflection. The deflection to fire is the deflection announced to the howitzer. To compute deflection to fire, apply the deflection correction to the announced chart deflection by using the LARS rule (left, add; right, subtract). Determine the deflection correction by adding the GFT deflection correction to the drift corresponding to the initial elevation. (GFT deflection correction is discussed in Chapter 10.)
f. Quadrant Elevation. Quadrant elevation is the algebraic sum of site and the angle of elevation. Quadrant elevation is the angle through which the tube of the howitzer must be elevated from the base of the trajectory to cause the trajectory to pass through the target.

(1) Elevation. The angle of elevation is the vertical angle between the base of the trajectory and the axis of the bore required for a projectile to achieve a prescribed range under standard conditions.

(2) Site. If the target and the howitzer are not at the same altitude, site will be determined. Site is combined with elevation to cause the trajectory to pass through the target. If the target and howitzer are at the same altitude, site is announced as zero.

## 9-3. Recording Firing Data

a. DA Form 4504 (Record of Fire) is a legal document used for determiningg and recording iring data. It is organized to allow a smooth flow in determining and processing afire mission. It is used for the following:

Recording the call for fire.
Computing and recording firing data for all types of fire missions.
Keeping a permanent record of a fire mission, to include the type and amount of
ammo expended during the mission.
b. On DA Form 4504 (Figure 9-2), the heavy black lines indicate major sections of the form. Shaded portions denote items that must be announced to the howitzer sections. The use of each block on the record of fire is explained below.

(1) Call for fire block. The CFF announced by the observer is recorded in this block. (See Figure 9-3.) Table 9-2 explains each item and its use.

(2) Computational space and related data blocks. These blocks are used to compute and record data used in determining firing data. (See Figure 9-4.) Table 9-3 explains each item and its use.

(3) Fire order and initial fire commands block. The fire order announced by the FDO and the initial fire commands transmitted to the howitzers are recorded in this block. (See Figure 9-5.) Table 9-4 explains each item and its use.

(4) Message to observer block. The message to observer, angle T, probable error in range, and time of flight are recorded in this block. (See Figure 9-6.) Data determined but not sent are recorded in parentheses. Table 9-5 explains each item and its use.

(5) Fire planning and observer subsequent corrections block. Fire plans or subsequent corrections transmitted by the observer are recorded in this block. (See Figure 9-7.)
Table 9-6 explains each item and its use.

(6) Subsequent fire commands block. Fire commands are recorded in this block.

(See Figure 9-8.) Data placed in parentheses indicate data that were determined but not sent because of no change. Table 9-7 explains each item and its use.

(7) Computational space and administrative blocks. These are the lower computational areas used to record required data or conduct computations. (See Figure 9-9.) Table 9-8 explains each item and its use.

## Section Ii High Explosives

The HE projectile is the base round for the HE family ofprojectiles. The HE projectile is available in all cannon weapon systems (105 mm, 155 mm). The HE ballistic family includes the antipersonnel improved conventional munitions, illumination, chemical, and smoke.

## 9-4. Overview

a. HE projectiles are hollow steel cases filled with explosives (trinitrotoluene [TNT] or composition B). They can be fuzed for air, surface, or subsurface burst. HE projectiles are used against personnel and material objects because of blast and fragmentation effects.

b. Determination of firing data for a point-detonating (Q), mechanical time super quick, time, or variable time fuze mated to an HE projectile is almost identical. Only minor procedural differences exist. Data are determined from the GFT, GST, and TFT.

c. The HE-quick shell-tie combination is the ammunition used for the basic fire mission. Chart data are determined to the target. The computer determines data with the GFT.

The procedures for computing data **without a GFT setting** areas outlined in Table 9-9.

NOTE: Under normal circumstances, FDC personnel will be able to determine a GFT setting.

The determination and explanation of a GFT setting is covered in Chapter 10. When a GFT setting is applied, certain elements of data will be determined as described below.

EI--Elevation is determined by placing the MHL over the range and reading the elevation scale directly under the elevation gauge line (EGL).

FS--Fuze setting is determined by placing the MHL over the range and reading the appropriate fuze scale directly under the time gauge line (TGL). The TGL
is valid only for the registering fuze.

NOTE: The **fire order SOP and fire command standards** in Figure 9-10 are used for all the examples found in this chapter.

## 9-5. Examples Of Completing The Record Of Fire For He Fire Missions

a. HE/Q Adjust-Fire Mission.

Use the steps in Table 9-10 to process an HE/Q
adjust-fire mission. Figure 9-11 shows an example ROF for this type of mission.

b. Police of Record of Fire. Use the steps in Table 9-11 to police the record of fire.
c. HE/Q Fire Mission. Use the steps in Table 9-12 for a subsequent adjustment of an HE/Q fire mission. An example ROF for this entire mission is shown in Figure 9-ll.

## D. High-Explosive With Mechanical Time (M582).

(1) Determining data for an HE/ti round is exactly the same as HE/Q except for the HOB correction and the fuze setting correction.

(2) A time fuze achieves the best effects on the target when it functions at a
20-meter HOB. To achieve the 20-meter HOB, the trajectory of the projectile must be altered to cause the projectile to pass 20 meters above the target. By applying the mil-relation formula in a vertical plane, the amount of mils the trajectory needs to be altered at any range is 20/R. When the value of 20/R is used as the HOB correction, it will always be a positive value. The HOB
correction is included in the computation of QE. The HOB correction is added to the site (ground site), and a total site is determined. This total site is applied to elevation to determine QE. The HOB correction is applied only to the initial time QE.

(3) If subsequent adjustments for the HOB are necessary, then the FS is the only element of firing data that is recomputed. Deflection and QE will remain the same. A FS correction will be applied to the previous fuze setting. The FS correction will be a multiple of L FS/ L  10M HOB. The L FS moves the functioning of the fuze along the trajectory by increments of 10 meters. The observer will adjust the HOB by transmitting HOB corrections (up or down) to the nearest 5 meters.

The observer's corrections in meters must be converted to corrections in FS. The observer's HOB correction is divided by 10 and then multiplied by L FS/ L l0M HOB. This value is expressed to the nearest tenth (0.1) of a FS increment. Before this can be applied as a FS correction, it must have a sign (). The sign is based on the direction
(up or down) of the observer's correction. If the correction is up, then the fuze functioned late and the FS correction must be subtracted. If the correction is down, then the fuze functioned early and the FS correction must be added. Simply stated, for an up correction, the FS correction is negative; for a down correction, the FS correction is positive. An easy rule to remember is USDA (up, subtract; down, add).

## E. He/Ti (M582) Fire Mission With He/Q In Adjustment.

(1) Process the HE/Q adjustment as outlined in paragraph 9-5. Once the observer has requested a change in fuze type to a mechanical time fuze, process the request as described in Table 9-13. Figure 9-12 shows an example ROF for this type of mission.

(2) If a 20-meter HOB was not achieved, the fuze setting must be adjusted. At this point in the mission, the observer does not make any range or deviation corrections. The only corrections are for HOB. Therefore, the only firing data that will change are the fuze setting. Use the steps in Table 9-14 to adjust the fuze setting, Figure 9-12 shows an example ROF for this type of mission.

f. HE/Ti (M582) FFE Mission. Use Table 9-15 for processing an HE/Ti (M582) FFE
fire mission. Figure 9-13 shows an example ROF for this type of mission.

## G. High-Explosive With Variable Time (M732/M728).

(1) The variable time, or proximity fuze, is designed to function at a predetermined HOB (7 meters for M728/732). No HOB correction is needed because of the low HOB. The VT
has a built-in radio transmitter-receiver. The fuze transmits a signal. When the reflected signal reaches a certain strength, the fuze will function.

(2) The VT fuze setting is determined from the time of flight of the projectile. The TOF is determined to the nearest tenth of a second (0.1). However, a VT fuze cannot physically be set to the nearest tenth. The scales are graduated in whole seconds; therefore, the TOF must be expressed **down** to the whole second. If the TOF extracted is already determined to the whole second, there is no need to express down. The VT memory aid **"vanish tenths"** will help you understand the determination of the VT FS. Expressing down provides a greater assurance of an airburst. About 3 seconds before the fuze is set, the fuze is armed and the radio transmitter is activated. Whenever a VT FS is determined, recorded, or announced, it will always end in point zero.

NOTE:
If the observer transmits a graze repeat, the automatic correction to the VT FS is to subtract 1.0 seconds.

h. HE/VT Fire Mission With HE/Q in Adjustment. Process the HE/Q adjustment as outlined in paragraph 9-5. Once the observer has requested a change in fuze type to a variable time fire, process the request as described in Table 9-16. Figure 9-14 shows an example ROF
for this type of mission.

i. HE/VT FFE Fire Mission. Use Table 9-17 for processing an HE/VT FFE fire
.

mission. Figure 9-15 shows an example ROF for this type of mission.

## 9-6. Example Of Completing The Record Of Fire For A Nonstandard Square Weight Wp Or He Projectile

a. Several projectiles require corrections to firing data because of variations in square weight.

The determination of firing data incorporates the use of the GFT and the TFT. The basic HE mission procedures must be altered to compensate for a deviation from the standard square weight from which the firing tables were developed. The TFTs have tables that correct for nonstandard conditions, one of which is weight. The computer must enter the appropriate TFT with the chart range to the target and the difference in square weight (increase or decrease). The difference in weight is determined by subtracting the standard square weight (or registration square weight) from the actual square weight of the projectile to be fired. The range correction factor is extracted and multiplied by the change in square weight. The result is expressed to the nearest 10 meters and is a signed value (). This value is algebraically added to the chart range. This new range is known as the **adjusted range** and is used to compute elevation and all elements that are a function of elevation. The following steps apply to nonstandard square weight WP and HE projectiles.

NOTE: Normal HE procedures are followed until the observer requests the nonstandard square weight projectile.

b. Table 9-18 lists the procedures for processing a WP/Q FFE mission following HE
adjustment. Figure 9-16 shows an example ROF for this type of mission.

## Section Iii High-Angle Fire

High-angle fire is used for firing into or out of deep defilade such as that found in heavily wooded, mountainous, and urban areas. It is also used to fire over high terrain features near friendly troops (Figure 9-17). The observer may request high-angle fire on the basis of terrain in the target area. The FDO also may order high-angle fire on the basis of a terrain analysis from the firing unit position to the target area. The primary characteristic of high-angle fire is that an increase in elevation causes a decrease in range.

Because high-angle fire involves large quadrant elevations and long times of flight, it will not be as responsive as low-angle fire to the immediate needs of a maneuver force. Trajectories are vulnerable to enemy detection. The long time of flight makes it difficult for the observer to identify his round, and corrections may change drastically from round to round. To help the observer, FDC personnel will announce **SPLASH** 5 seconds before each round impacts. To further help the observer, the FDC announces time of flight in the MTO.

## 9-8. High-Angle Gft

The high-angle GFT (Figure 9-18, page 9-31) consists of one rule with ballistic data for multiple charges on each side. The scales on the high-angle GFT from top to bottom are as follows:
a. 100/R. This scale shows the number of mils needed to move the burst 100 meters laterally or vertically. The scale increases from right to left and is read to the nearest mil.

b. Range. This scale is expressed logarithmically in meters and applies to all charges appearing on that side of the GFT. Range increases from left to right and is read to the nearest 10
meters.

c. Elevation. This scale is expressed in mils and increases from right to left. It is interpolated to the nearest mil.

d. 10-m Site Factor. The values on this scale denote the site for each 10 mils angle of site. The numbers are printed in red and are negative values. The scale increases from left to right and is visually interpolated to the nearest tenth (0.1) of a mil.

e. Drift. The values on this scale are in mils. The scale increases from right to left and is interpolated to the nearest mil.

f. TF. This scale is graduated in seconds and is used to determine both time of flight (to the nearest whole second) and VT fuze setting. The TF scale increases from right to left.

NOTE: Figure 9-19, page 9-31 shows an aid that can be used when reading the high-angle GFT.

## 9-8. Duties Of Personnel In High-Angle Fire

a. Except for differences noted in this section, the procedures for high-angle fire are the same as low-angle fire. Duties of FDC personnel in high-angle fire differ in several ways as described below.

b. The FDO does the following:
(1) Includes the command **HIGH ANGLE** in his fire order.
(2) Considers high-angle fire characteristics in selecting the shell and fuze to fire.
(a) Antipersonnel improved conventional munitions (APICM) and DPICM
can be used in high-angle fire for the same types of targets as in low-angle fire.

(b) The high-angle trajectory has two inherent characteristics that affect munitions selection: a steep angle of fall and large probable errors. The steep angle of fall means the projectile is almost vertical as it approaches the ground. When the HE projectile bursts, the side spray contains most of the fragmentation. Since the projectile is nearly vertical, side spray is in all directions and nearly parallel to the ground (Figure 9-20). Thus, shell HE with fuze quick or fuze VT is very effective when fired high angle. The large probable error in height of burst makes the use of MTSQ time fuzes impractical in high-angle fire.

c. The VCO computes and announces angle of site rather than site.
d. The computer does the following:
(1) Selects the charge to be fired (if it is not announced in the fire order).

High-angle fire has two characteristics that affect the selection of charge: a shorter range span for each charge and a range overlap between charges. The range span within which accurate fire can be delivered by a particular charge is less for high-angle fire than for low-angle fire. This may cause a problem during a high-angle fire mission, because a large observer correction may move the round outside the capabilities of the initial charge fired. This, in turn, will necessitate changing charges.

Changing charges in a high-angle fire mission is sometimes unavoidable, although it is not desirable. For this reason, the computer initially selects the charge that is least likely to require changing. As a guideline, he selects the lowest charge that allows for a range shift of at least 500 meters short of and 500 meters beyond the initial chart range.

(2) Includes drift correction. Drift is appreciably greater in high-angle fire than in low-angle fire. Because drift changes a great amount for a relatively small elevation change, the computer determines drift (recorded as the deflection correction) for each elevation. The correction is always applied to the left. If a GFT setting is available for the high-angle GFT, the computer will determine drift and algebraically add it to the GFT deflection correction. The sum is the deflection correction to be applied to the chart deflection.

(3) Includes site in the computation of QE unless the FDO directs otherwise. Site is included when the angle of site is large or when a high-angle registration or a mass mission is being fired. When several firing units are to mass on a target and only one firing unit is to adjust, site is computed at the initial range for each unit.

Site for the nonadjusting units may be recomputed before FFE (for example, when the adjusting unit changes charge or when the adjusting unit conducted a target replot). When adjustment is required before massing and only one unit is to adjust, the unit that is most centrally located should be designated as the adjusting unit to minimize large differences in range for the nonadjusting units. If site is to be ignored, the FDO announces **IGNORE SITE** in the fire order. Since one of the criteria for ignoring site is a small angle of site, the FDO may have to wait for the VCO to compute and announce angle of site. In this situation, the FDO issues a fire order and later supplements it with the command IGNORE SITE.

(4) Announces **HIGH ANGLE** as a special instruction when sending initial fire commands to the howitzers.

(5) The RATELO announces the time of flight in the message to observer and announces **SPLASH** for each round.

## 9-9. Example Of Completing The Rof For An He High-Angle Adjust-Fire Mission

a. The steps in Table 9-19 are used to process an HE high-angle adjust-fire mission.

Figure 9-21 shows an example ROF for this type of mission.

b. The steps in Table 9-20 are used to process a high-angle subsequent adjustment. An example ROF for this entire mission is shown in Figure 9-21.

## Section Iv Illumination

This section implements STANAG 2088 and QSTAG 182.

Illuminating projectiles are available for the 105-mm and the 155-mm howitzers. They are used to illuminate a designated area for observing enemy night operations, for adjusting artillery fires at night, for marking locations, for friendly direction, or in ground/vehicular laser locator designator (G/VLLD)
missions.

Illuminating projectiles are base-ejection projectiles fired with mechanical time fuzes. The filler consists of an illuminating canister and a parachute assembly. The FDO should select the lowest practical charge to prevent a malfunction caused by the parachute ripping when the flare is ejected from the projectile.

## 9-10. Overview

Illumination is conducted by using one of the following techniques.

a. The **one-gun illumination pattern** is used when effective illumination can be achieved by firing one round at a time.

b. The **two-gun illumination pattern** is used when an area requires more illumination than one gun can furnish. This is commonly used for aerial observers.

  (1) The **two-gun illumination range spread pattern** is fired along the GT line. It is used when the area to be illuminated has greater depth than width.

(2) The **two-gun illumination lateral spread pattern** is fired perpendicular to the GT line. It is used when the area to be illuminated has greater width than depth.

c. The **four-gun illumination pattern** is used to illuminate a large area. Four rounds are fired at the same time by using both the lateral and range spread patterns. This is more commonly referred to as the four-gun illumination range and lateral spread.

NOTE: The decision to use the GT line or observer-target (OT) line for illumination missions should be based on unit SOP and mission, enemy, terrain, troops, and time available (METT-T). When using the OT line, the FDC will use the target grid to plot individual aimpoints. Use of the GT line may be more responsive to the observer's needs, but may not always provide the exact illumination coverage desired. The arguments for using the OT line are:
The observer may not be able to visualize the GT line, but he can always visualize the OT line.

The observer may not know which firing unit will fire his mission, especially if the mission is passed to a reinforcing FA unit. Therefore, he may not have the information needed to visualize the GT line.

The terrain may restrict effective illumination of the target area if the observer desires illumination in respect to his OT direction, but the firing unit computes data by using the GT line.

However, for illustrative purposes with the example fire missions, our unit SOP is to use the GT
line for all illum range spreads, lateral spreads, or combination.

## 9-11. Illuminating Projectile Gft

a. There are two manual computational methods for the illuminating projectile. One method uses a special illuminating projectile GFT, and the other method uses Part 2 of the base HE TFT. Graphical firing tables have been developed for use with all 155-mm M485A1 and A2
illuminating projectiles and with the 105-mm M314A1 and A2 and M314A2E1 projectiles.

Figure 9-22 shows a GFT for the illuminating projectile.

b. The scales of the illuminating GFT, from top to bottom, are described below:
(1) The 100/R scale is printed in red along the top edge of the rule. For a given range, the 100/R scale denotes the number of mils needed to shift the burst 100 meters laterally or vertically. 100/R is read to the nearest mil.

(2) The range scale is the base scale of the illuminating GFT. All other scales are plotted with reference to the range scale. Range is read to the nearest 10 meters.

(3) The elevation-to-impact scale is graduated in mils. The elevation-to-impact scale is used to determine the range (on the range scale) to which a nonfunctioning projectile will impact.

(4) The HOB scales, labeled from 350 to 850 meters, are at the left and right edge of the QE scales. The HOB scales are graduated in 50-meter increments.

(5) The QE scale shown for each listed HOB gives the QE needed to achieve that HOB at the desired range. The QE scale is graduated in mils and is visually interpolated to the nearest mil.

(6) The FS scale consists of a series of red arcs. The scale includes a red line for each whole FS increment for the M565 MT fuze. The value of each line is printed in red at the bottom of the scale. The fuze setting is read for the desired range and HOB to an accuracy of 0.1 FS increment by visual interpolation.

NOTE: The heavy black arrows along the QE scale denote when the trajectory is near or at the summit and does not exceed by 50 meters the HOB it represents.

## 9-12. Illumination Firing Data

a. The illum projectile is not weight-zoned. It is designed to illuminate a large area
(Figure 9-23). The minimum corrections from the observer are 200 meters for range and deviation and 50 meters for HOB. All subsequent HOB corrections are always given in multiples of 50 meters. Because of these characteristics, the determination of firing data is significantly different from HE. Drift, site, elevation, and FS are not determined. However, an illum HOB is determined. The HOB is used in conjunction with range to determine QE and FS. Therefore, any HOB correction sent by the observer will cause both the FS and QE to change.

b. The HCO determines chart data in the same manner as in an HE mission. The VCO
determines VI in the same manner as in an HE mission.

The computer will express the VI
determined by the VCO to the nearest 50 meters.

## 9-13. Determination Of Illumination Firing Data With The Gft

a. The appropriate HOB scale is determined by applying the VI determined by the computer to the optimum HOB for the illuminating projectile being fired. During subsequent adjustments, the observer's HOB correction is applied to the previous HOB determined.

b. QE is determined by placing the MHL over the chart range. The QE is determined by visually interpolating the point of intersection of the MHL and the appropriate HOB scale.

Determine QE to the nearest mil.

c. Fuze setting is determined in the same manner as QE; that is, by placing the MHL
over the chart range. Fuze setting is determined by visually interpolating between the red fuze setting arcs along the selected HOB scale. To determine the value of the arcs, follow the arcs to the bottom of the GFT. This fuze setting is for the M565 MT fuze. To determine a fuze setting for MT M577, enter Table B, Part 2, of the TFT and apply the FS correction to the MT M565
value. Determine FS to the nearest tenth.

## 9-14. Determination Of Illumination Firing Data With The Tft

a. Part 2 of the TFT deals exclusively with illum data. Each charge has two tables, Tables A and B. Table A lists basic data, and Table B lists corrections to fuze setting.

b. FS and QE are determined by entering Table A with the chart range (expressed to the nearest 100 meters). QE is extracted from Column 2 (QUAD ELEV) and M565 FS from Column
3 (FS). These values are for the optimum HOB and must be corrected for VI.

c. HOB corrections are made in 50-meter increments. Columns 4 and 5 of Table A list the corrections to QE and FS for an increase of 50 meters in HOB. The VI is expressed to the nearest 50 meters. Once the VI is expressed, it is divided by 50 to determine the number of
50-meter increments that are needed. The number of 50-meter increments are multiplied by the value in Column 4 (QE) and Column 5 (FS). These values are applied to QE and FS. For a positive VI, the values are added; for a negative VI, the values are subtracted. These corrected values are the FS and QE that should be fired.

d. To process HOB corrections, divide the observer's HOB correction by 50. This will provide the number of 50-meter increments. Multiply the number of 50-meter increments by the values in Columns 4 and 5. Apply this correction value as described above.

e. 100/R can be determined manually by using the mil relation formula by dividing 100
by the range in thousands and multiplying that value by 1.0186. The result is expressed to the nearest mil.

NOTE: The FS determined from the illuminating GFT or from Table A, Part 2, Column 3 of the TFT is for the M565 fuze. A correction value must be applied to determine a fuze setting for the M577 fuze. Table B of the TFT lists the correction values. To determine the correction value, enter Table B with the FS for the M565 fuze. Apply this FS correction to the FS for the M565 fuze. The resulting value is the FS for the M577 fuze.

## 9-15. Processing A One-Gun Illumination Fire Mission

a. The steps in Table 9-21 are used to process a one-gun illum mission. Figure 9-24
shows an example ROF for this type of mission. The time fuze being fired is M577.

b. The steps in Table 9-22 are used to process an illumination subsequent adjustment.

An example ROF for this entire mission is shown in Figure 9-24. The time fuze being fired is the M577.

## 9-16.

Two-Gun Illumination Range Spread a. A two-gun range spread requires two illuminating projectiles to be fired along the GT line to provide the maximum range coverage. The projectiles are fired one effective illum diameter apart
(refer to Figure 9-23). To determine the aimpoints, the computer will add and subtract one-half the illum diameter to the chart range of the aimpoint. The computer will then determine firing data at the adjusted ranges. The chart deflection will remain the same and both illumination rounds are fired with the same deflection.

b. Use Table 9-23 to process a two-gun illumination range spread fire mission. An example ROF for this entire mission is shown in Figure 9-25. The time fuze being fired is fuze M577.

9-17.

Two-Gun Illumination Lateral Spread a. A two-gun lateral spread requires two illuminating projectiles to be fired perpendicular to the GT line to allow for the maximum lateral coverage. The projectiles are fired one effective illum diameter apart (refer to Figure 9-23). To determine the aimpoints, the computer must determine a multiple of 100/R (400/R for 105 mm and 500/R for 155 mm). The computer will add and subtract this value from the chart deflection to the aimpoint. The range will be the same for both projectiles.

Therefore, the FS and QE for both projectiles will be the same.

b. Use Table 9-24 to process a two-gun illumination lateral spread fire mission. An example ROF for this entire mission is shown in Figure 9-26. The time fuze being fired is the M577.

## 9-18. Four-Gun Illumination--Range And Lateral Spread

a. The four-gun illum pattern is used to illuminate a large area in width and depth. Four rounds are fired at the same time by using the range and lateral spread patterns. The observer may request a range and lateral spread in the initial CFF or may request this pattern during a subsequent correction as part of a one-gun or two-gun (range or lateral spread) illum mission.

b. To process a four-gun illum mission, combine the procedures for the two-gun range spread and the two-gun lateral spread illum missions. The flank howitzers will fire the two-gun lateral spread while the interior howitzers will fire the two-gun range spread.

c. If the four-gun illum mission is requested during a subsequent correction, the FDO
must initiate a new fire order and the computer will announce new initial fire commands.

NOTE: An example ROF for this type of mission is shown in Figure 9-27. The time fuze being fired is the M577.

## 9-19. Coordinated Illumination

a. A coordinated illum mission is a combination of an illum mission (one-gun, two-gun, two-gun range or lateral spread, or four-gun range and lateral spread) and another fire mission
(normally HE). The illumination is adjusted by the observer until the target is illuminated. When the best target illumination is achieved, the observer will command the FDC to **MARK** the illumination.

Once the observer has marked the illum round, he will request coordinated illumination and transmit another call for fire. The FDC will process both missions following normal procedures.

The rounds will be fired at a predetermined interval that will ensure the rounds of the second mission function when the target is best illuminated. This allows the observer to make the needed corrections and observe the effects. The firing interval may be controlled by either the FDC or observer. The preferred method is for the FDC to control the firing interval.

b. Every time an illum round is fired, the FDC will start a stopwatch. When the target receives the best illumination, the observer will announce **ILLUMINATION MARK.** The FDC
will stop the stopwatch. This time interval is known as the illumination mark time and this value is recorded. When the second call for fire is received, the FDC must compute the TF for the second mission. This TF plus a five-second reaction time is subtracted from the illum mark time and the difference is the firing interval (ILLUM MARK TIME - (TF + 5 SECONDS) = FIRING INTERVAL). At this point, the FDC must ensure both missions are AMC. The FDC
commands the howitzer(s) firing the illum mission to fire. The stopwatch is started as the illum mission is fired. When the firing interval is reached, the FDC commands the howitzer(s) firing the second mission to fire.

c. The observer may request by round at my command. In this situation, the observer wishes to control the firing of both missions.

The FDC will compute data, ensuring both missions are AMC. The FDC must also transmit the TOF of the second mission to the observer.

When the howitzers for both missions report **READY,** the FDC will relay this information to the observer. The observer commands the firing of the ilhum mission. After determining the firing interval, the observer commands the firing of the second mission at the appropriate time.

d. Use the steps in Table 9-25 to determine the firing interval. Example ROFs for this type of mission are shown in Figures 9-28 and 9-29. The illum time fuze being fired is the M577.

e. An example of determining the firing interval is shown below.

f. When coordinated illumination is requested, the FDO must initiate a new fire order for the second mission and the computer will announce new initial fire commands. If the howitzers that are firing the illumination are also included in the second mission, the FDC must ensure those howitzer sections understand they are firing both missions and inforrn them of the firing interval between missions.

## 9-20. High-Angle Illumination

a. Some impact areas are so small that firing low-angle illumination severely restricts or prohibits the firing of the round because of range-to-impact concerns with the projectile body.

To compensate for this, fire high-angle illumination and use the TFT (Part 2, Illumination). This is not the preferred method of firing illumination.

b. Use Table 9-26 to process a high-angle illumination mission. An example ROF for this type of mission is shown in Figure 9-30. The time fuze being fired is M577.

## Chapter 10 Registrations

Registration is a means of determining cumulative errors and the corrections for those errors.

The purpose of this chapter is to explain registrations and their application to the gunnery problem.

## Section I Reasons For Registrations

Registrations should not be needed if the firing unit can meet their portion of the five requirements for accurate predicted fire (minus target location). If the observer cannot provide an accurate target location, the battalion S3 needs to consider providing a survey team to extend survey into the target area and providing common survey to the observers.

If all conditions of weather, position, and material were standard, a cannon firing at a particular elevation and deflection would cause the projectile to travel the range shown in the firing table corresponding to that elevation and charge. Since all standard conditions will never exist at the same time, firing table data must be corrected.

The purpose of a registration is to determine firing data corrections that will correct for the cumulative effects of all nonstandard conditions. With these corrections applied to firing data, a unit can rapidly and successfully engage any accurately located target within the range of their cannons and have a first round FFE capability.

## 10-1. Accurate Firing Unit Location

Accurate range and deflection from the firing unit to the target also require that the weapons be located accurately and that the FDC knows this location. The battalion survey section uses PADS to provide accurate survey information on the unit location.

Survey techniques available to the firing unit can also help in determining the location of each weapon.

The FDC can determine the grid location of each piece by using the reported direction and distance from the aiming circle used to lay the battery or platoon.

## 10-2. Accurate Weapon And Ammunition Information

The actual performance of the weapon is measured by the weapon muzzle velocity for a projectile family-propellant combination.

The firing unit can measure the muzzle velocity of a weapon and correct for nonstandard projectile weight and propellant temperature. This is done by using the M90 velocimeter and MVCT M90-2 for each charge, propellant type, and projectile family. Calibration should be conducted continuously by using the M90. Firing tables and technical gunnery procedures allow the unit to consider specific ammunition information (weight, fuze type, and propellant temperature); thus, accurate firing data are possible.

## 10-3. Accurate Meteorological Information

The effects of weather on the projectile in flight must be considered, and firing data must compensate for those effects. Firing tables and technical gunnery procedures allow the unit to take into account specific met information (air temperature, air density, wind direction, and wind speed) in the determination of accurate firing data.

## 10-4. Accurate Computational Procedures

The computation of firing data must be accurate. If the five requirements for accurate predicted fire (minus target location) cannot be met, **registrations** can be conducted to compute data that will compensate for nonstandard conditions. Applying these corrections to other fire missions will allow the unit to determine accurate firing data.

NOTE: If the unit is able to meet the five requirements for accurate predicted fire, it will still be necessary to improve the firing data derived from the GFT. The unit will not be able to fire accurately (first round fire for effect capability) by firing "cold stick"
data. Therefore, the use of a met + VE technique will allow the unit to take all measurable nonstandard conditions into account, and derive a GFT setting. Met +
VE techniques are discussed in Chapter 11.

## 10-5. When To Conduct Registrations

a. The FDO must consider the following:
Mission. Equipment. Troops. Time.
Terrain and weather. Commander's guidance.
Tactical situation. Enemy target acquisition assets. Availability and location of observers. Availability, location, and survey accuracy of known points. Type of registration. Assurance of registration validity.
b. A mission conducted only for the purpose of registering does not cause any damage to the enemy. It does, however, expose the firing unit to enemy TA devices. Also, missions conducted solely for the purpose of registering require additional ammunition and time. Therefore, when possible, registration missions should be integrated into other missions, especially when the observer is equipped with a laser.

c. Met + VE GFT settings should be used when accurate MVVS, met data, and survey are available. The amount of corrections needed to adjust onto a target will be minimal. Firing two check rounds from an inferred GFT setting can be an abbreviated registration. Any refinement sent by the observer should be used to adjust the GFT setting.

d. The flow chart shown in Figure 10-1 can be used to help you decide whether or not to conduct a registration.

## 10-6. Types Of Registrations

a. There are two types of registrations: precision registration and high-burst and/or mean-point-of-impact (HB/MPI) registration. Within the two categories are alternate methods of registering that may be more suitable for use in a particular tactical situation.

(1) Precision registration.

The precision registration is a technique for determining, by adjustment, firing data that will place the MPI of a group of rounds on a point of known location. The point of known location is called a known point.

(2) High-burst and/or mean point-of-impact registration. The HB/MPI
registration determines the mean burst location of a group of rounds fired with a single set of firing data. When the mean burst location (or MPI) has been determined, the chart data (should hit data) are determined and compared to the data that were fired (adjusted-data [did hit data]).

b. Alternate registration types are discussed below.

(1) Radar-observed registration. The radar-observed registration is a form of the HB/MPI registration and is thoroughly discussed later in this chapter.

(2) Abbreviated registration. Any registration that is conducted by using fewer usable rounds than recommended for the precision or HB/MPI techniques is an abbreviated registration. The use of fewer rounds degrades the results of total corrections. However, the use of fewer rounds to determine the mean burst location (MBL) or the use of a larger "acceptance box" (for example, 2 PEs rather than 1 PE from the MPI) is acceptable if the decreased assurance is acceptable to the commander.

(a) Abbreviated HB/MPI registration. An abbreviated HB/MPI registration is conducted exactly like an HB/MPI registration, except fewer rounds are fired.

(b) Met + VE and check round(s). This form of abbreviated registration requires the solution of a subsequent met to an accurately located target and determines adjusted data by adjusting a round(s) fired by use of the met + VE firing data. Final corrections are determined on the basis of observer refinement.

(c) Abbreviated laser registration.

The abbreviated laser registration determines total corrections by comparing the data fired to the chart data determined to the burst location.

(d) Adjust-fire missions. Any adjust-fire mission conducted on an accurately located target can be used to improve firing data by determining total corrections on the basis of the observer adjustments.

In this case, refinement data must be sent by the observer. The validity of the GFT setting is directly proportional to the accuracy of the target location.

NOTE: Use of the laser with common directional control enables an observer to accurately locate a target to registration-required accuracy.

(3) Offset registration.

A platoon or offset position as much as 1,000 to 2,000
meters away from the firing unit center can be used to conduct a registration. The GFT setting determined from the offset position is assumed to be valid for the primary position if common survey and common direction exist between the two positions. A registration from a flank platoon may reduce the vulnerability of the firing unit.

## (4) Registration To The Rear.

(a) Registering to the rear (or at some azimuth significantly different from the primary azimuth of fire) results in a GFT setting that does not include the primary azimuth of fire within its deflection transfer limits.

(b) To derive a GFT setting for the primary azimuth of lay, apply eight-direction met techniques as follows:
Determine position constants by working a concurrent met for the registration azimuth.

Using subsequent met techniques, determine the total corrections (in the direction of the azimuth of lay) by reworking the met.

NOTE: The eight-direction met technique is discussed later in this chapter and in detail in Chapter 11.

## 10-7. Assurance Tables

A registration conducted with fewer rounds than recommended will degrade the accuracy of the determined corrections. Table 10-1 lists the percentage of probability that the mean location of a particular number of rounds is within 1 or 2 probable errors of the actual mean point of impact achieved by firing an infinite number of rounds. As more rounds are fired, the assurance of validity of the MPI is increased. If the tactical situation dictates, the lesser assurance from an abbreviated registration may have to be accepted.

## 10-8. Registration Corrections And Gft Settings

a. The final step in every registration is the determination and application of registration corrections.

Registration corrections consist of total range, total fuze, and total deflection corrections. The total corrections are determined by comparing the chart data (should hit data) to the adjusted data (did hit data) resulting from a registration. When it is impractical to conduct a registration, corrections can be obtained mathematically by use of a met technique. (See Chapter
11.)
b. The total corrections are then used as the basis for a GFT setting. This allows the FDC personnel to apply total corrections to the GFT. With the GFT setting properly applied, it is possible to fire for effect without an adjustment phase on accurately located targets within transfer limits. Total corrections, GFT settings, and transfer limits will be discussed in greater detail later in this chapter.

It is important to remember that no registration is complete until
-
registration corrections-are determined and a GFT setting is applied.

NOTE: Should hit data (SHD) are data fired under standard conditions that will cause the round to impact at a point of known location. Did hit data (DHD) are data fired under nonstandard conditions that will cause the round to impact at a point of known location.

## Section Ii Precision Registrations

Precision registration is a technique that requires an observer to adjust a group of rounds fired from the same howitzer so that their mean point of impact occurs at a point of known location (that is, a known point). The point of registration is accurately located (8-digit grid, 10-meter accuracy or 10-digit grid 1-meter accuracy).

It can be determined from survey, can be an easily recognized map spotted terrain feature, or it can be any identifiable point located by a laser and should be on common survey with the firing unit, Corrections are determined by comparing the data that actually did hit the target (adjusted data)
to the data that should have hit the target (chart data) if standard conditions had existed at the time of firing.

## 10-9. Objective

The observer's objective in the impact phase of a precision registration is to obtain spottings of two **OVERS** and two **SHORTS** along the OT line from rounds fired with the same data or from rounds fired with data 25 meters apart (50 meters apart when PER is greater than or equal to 25 meters). This normally requires the spottings of four separate rounds. Four spottings achieved by firing projectiles with the same data or data 25 meters apart is critical. This critical bracket must be formed by the observer making only range corrections since a deviation correction will introduce a difference in firing data greater than the 25-meter requirement. The observer should not make any deviation corrections after establishing the 200-meter bracket. If he does, then any previous rounds cannot be used as part of the 25-meter bracket. However, a TARGET HIT or **RANGE CORRECT** will be spotted by the observer as an **OVER** and a SHORT. The objective of the time portion of the registration is to correct the mean height of burst of four rounds fired with the same data to 20 meters above the target point. The FDC's objective in a precision registration is to determine corrections to firing data on the basis of the observer's corrections and to determine whether or not the objectives were achieved.

## 10-10. Initiation Of A Precision Registration

a. The decision to register is based on the considerations in Section I. After the decision to register has been made, the FDO announces a fire order.

(1) Fire order.

When the FDO announces his fire order, he addresses four questions:

(a) What are we going to do? (for example, precision registration) (b) Where are we going to do it? (for example, known point 1) (c) With whom? (for example, with T03)
(d) With what fire order considerations? (The FDO does not address fire order SOP items unless he feels that it is necessary to avoid confusion.)
(2) Registering piece. Use only one weapon to fire the registration. It is best to select the piece that is plotted on the firing chart and for which we have accurate MVV
information for the registering charge (for example, the BASE PIECE).

(3) Lot. Register the largest calibrated lot of propellant. This lot is used for first-round FFE missions.

(4) Charge selection.

Listed below are a few of the factors an FDO should consider when selecting the charge to register.

(a) At what range will most targets be engaged?

(b) If the enemy has a sophisticated sound ranging capability, a lower charge is preferred.

(c) If the enemy has a sophisticated counterbattery radar capability, a higher charge is preferred.

(d) Which charge has the smallest PER for a given range (see the charge selection table in the TFT).

(e) Lower charges produce less tube wear, residue, and noise. They also have better terminal effects with shell HE.

b. When the RATELO hears the fire order, he will announce a message to observer to alert the observer.

(1) MTO. The MTO includes the information from the fire order that pertains to the observer; for example, type of registration, the known point, and fuzes to be registered. If there is no **known point,** the FDO will direct the observer to select one in a specified area, and the observer will send the location to that point. The FDO will then designate the number of the known point. Because of the possibility of introducing a target location error, this option is least preferred.

(2) Observer's response. After the observer has received the MTO, he will report direction. If the observer is directed to select a known point, he will report the eight-digit grid location and direction. In either case, the report of direction indicates the observer is ready to conduct the registration.

## 10-11. Conduct Of The Impact Phase Of A Precision Registration

a. Fire direction procedures for an impact phase of a registration are identical to those used in the conduct of any adjust-fire mission. All observer corrections are plotted on the firing chart and chart data are announced. The computer sends fire commands to the registering piece.

Although care should be taken during all computational steps, extraordinary measures should not be used for the conduct of a registration.

b. The final location of the plotting pin on the chart represents the point where the howitzer had to be aimed to have rounds impact on the known point (Figure 10-2). It is not the actual location of the known point. The difference between these locations depicts the effects that all nonstandard conditions had during firing.

c. The data announced after the observer's final impact refinement shows the range and deflection to the point where the howitzers must aim to have rounds impact on the known point.

At this point, no projectile is fired and the time phase of the registration begins. The deflection and elevation corresponding to the data measured to the final pin location is called the adjusted data--the data that **did hit** the known point. Adjusted data will be circled on the record of fire.

## 10-12. Conduct Of The Time Phase Of A Precision Registration

a. When the impact phase of the registration is complete, the time phase can be started.

The observer's refinement data moved the mean point of impact of the rounds to the known point. At this point, an adjusted deflection and elevation are determined. The adjusted deflection and elevation are did hit data for the known point and the most accurate data with which to begin the time portion.

b. The first fuze setting fired corresponds to the adjusted elevation. The initial fuze setting to fire is determined by placing the MHL over the adjusted elevation and reading a fuze setting corresponding to that adjusted elevation. At the same time, the computer determines L FS
corresponding to the first fuze setting fired.

c.

As with other fuze time missions, an HOB correction (20/R) is added to the ground site to determine a total site. The total site is added to the adjusted elevation to determine the quadrant to fire for the rest of the mission. The adjusted deflection is fired for the rest of the mission.

d. Normal procedures for application of L FS for up or down corrections are followed to meet the objective of the time phase of the mission, which is to correct the mean height of burst of four rounds fired with the same data to 20 meters above the known point.

e.

The adjusted time is determined after the observer's HOB refinement is applied. The adjusted time is circled. With the observer's correction applied, the adjusted time will produce an airburst 20 meters above the known point. The adjusted time is not fired.

## 10-13. Second Lot Registrations

a. The use of the second lot registration technique has become obsolete with the use of the M90 chronograph and the ability to account for muzzle velocity differences in propellant lots.

The GFT settings for subsequent lots can be determined by using the subsequent met techniques if muzzle velocity information is available.

b. Conduct second lot registrations in the same manner as single lot registrations with the following exceptions:
(1) Fire order. The fire order informs the FDC that corrections are needed for two different lots (of the same charge and propellant type).

(2) MTO. The radio operator transmits the MTO notifying the FO to observe two lots by announcing **TWO LOTS** after the fuze or fuzes to be fired.

## 10-14. Initiation Of The Second Lot Registration

a. After completing the first lot time registration, begin firing the first round of the second lot registration with the adjusted deflection and the adjusted quadrant elevation (adjusted elevation plus ground site) determined for the first lot. **Fire fuze quick only.** To notify the observer that a second lot registration is going to be conducted, the FDC announces: OBSERVE
SECOND LOT, OVER.

b. In the appropriate columns on the ROF, enter the firing data determined from the first lot registration. These data include the following:
Adjusted deflection. Adjusted chart range. Value of ground site. Adjusted elevation.

c. The adjusting piece must be given commands to change the method of fire, lot and fuze. The objective of the second lot registration is the same as that of the first lot. Once the observer has met the objective, he will announce **(any refinement)** and RECORD AS SECOND
LOT REGISTRATION POINT, END OF MISSION.

d. To determine the adjusted fuze setting, add the fuze correction from the first lot to the fuze setting corresponding to the subsequent lot adjusted elevation. To determine the adjusted fuze setting for the second lot registration, follow the steps in Table 10-2.

e. The second lot GFT setting will be constructed in the same manner as the first lot GFT setting.

NOTE: To minimize confusion, the second lot GFT setting should be placed on a different cursor and labeled with the appropriate lot.

f. Determine the total deflection correction by using the following formula:
2D LOT ADJ DF - CHART DF = TOT DF CORR
g. Determine the GFT deflection correction by placing the MHL over the second lot adjusted elevation and reading the value under the MHL on the drift scale. This value is subtracted from the total deflection correction, and the LARS rule is used to determine whether the GFT deflection correction is a L or an R.

TOT DF CORR - DRIFT ~ 2D LOT ADJ EL = GFT DF CORR

## 10-15. Example Of A Completed Precision Registration

a. Use Table 10-3 to process a precision registration with fuzes quick and time.

b. The observer ends the impact phase of the registration by providing refinement data and requesting RECORD AS REGISTRATION POINT (announces the number of the registration point), TIME REPEAT. Record this transmission on two lines of the ROF. The first line is used to determine the adjusted elevation and adjusted deflection. The adjusted data are determined by processing the refinement data. These adjusted data are referred to as DHD
and are recorded and circled on the record of fire for quick reference. The adjusted data are not sent to the howitzer(s).

c. Once the refinement data have been processed, the time phase is initiated. The chart data, deflection to fire (adjusted deflection), and elevation (adjusted elevation) have already been determined. The only data that needs to be computed are the time fuze setting (should hit) and the quadrant elevation. Use the steps in Table 10-4 to process the time phase of the registration.

d. After spotting the last round, the observer will provide final refinement data to adjust the mean height of burst to 20 meters.

The observer will also direct RECORD AS TIME
REGISTRATION POINT, END OF MISSION. Record this transmission on two lines of the ROF. The first line is used to process the final HOB correction and determine the adjusted time
(did hit). The adjusted time is recorded and circled on the record of fire for quick reference.

These data are not sent to the howitzer(s). The second line is used to record end of mission, which is sent to the howitzer(s). Once EOM is sent to the howitzer(s), a final police of the ROF is conducted. A completed ROF for a precision registration using the M582 time fuze is shown in Figure 10-3.

## 10-16. Abbreviated Precision Registration

a. The tactical situation or ammo restraints may prohibit conducting a full-scale registration.

In such cases, the FDO may conduct an abbreviated precision registration.

Although having a lower assurance of validity, an abbreviated precision registration often provides adequate compensation for the effects of nonstandard conditions. The observer ends the registration when he believes that his next correction will put the next round on the registration point. The advantages of this type of registration are fewer rounds are fired so less ammunition is consumed and the registration takes less time so the unit is exposed to enemy TA devices for a shorter period of time.

b. After making the decision to register, the FDO announces a fire order. Once the RATELO hears the fire order, he transmits an MTO to alert the forward observer. After the observer has received the MTO, he sends a direction, which signifies he is ready to observe, to the FDC.

are different than c. The observer procedures for an abbreviated precision registration those used for a normal precision registration.

100-meter bracket
(1) The observer will use normal adjust-fire procedures until the is split.

(2) The correction then sent is an add (or drop) 50 meters FFE or time repeat or time add or drop 50 meters.

(3) The burst which is a result of an add (or drop) 50 meters is spotted. Minor corrections for both deviation and range are sent to the FDC in the following format:
(a) For both a quick and time registration: L10, -40, RECORD AS
REGISTRATION POINT, TIME REPEAT.

(b) For an impact only registration: R30, -10, RECORD AS
REGISTRATION POINT, END OF MISSION.

(c) Normal time adjustment procedures are followed in the time portion.

(d) Once an airburst is obtained, a correction for a 20-meter HOB is determined.

(e) Instead of firing for effect, refinement is sent to the FDC in the following format: U5, RECORD AS TIME REGISTRATION POINT, END OF MISSION.

NOTE: If the abbreviated registration is conducted as part of a normal adjust-fire mission, steps c(2) and c(3)(e) are modified to allow the observer to request FFE.

d. The GFT setting and total corrections are determined in the same manner as in a normal precision registration. A completed ROF for an abbreviated registration using the M582 time fuze is shown in Figure 10-4.

## Section Iii High-Burst/Mean Point Of Impact Registrations

When registration is necessary, clearly defined and accurately located registration points may be limited or not available. Dense vegetation or ground fog may prevent the observers from seeing the ground. At night, adjustment of fire on a registration point is impossible without some type of illumination. The tactical situation may not allow the firing of numerous rounds required for a precision registration.

The HB/MPI registration can overcome these problems.

This section describes HB and MPI registrations.

## 10-17. Description

a. In HB and MPI registrations, the unit fires a number of rounds (ideally six) with the same set of firing data.

These rounds are observed by two observers in surveyed positions, usually designated 01 and 02, who can measure the direction to each bursting round. One observer measures the VA to each round. On the basis of the observers' average directions and the average VA from one observer, determine and plot the MBL or the mean point of impact. Lastly, determine chart data and compare them to the adjusted data that were fired.

b. An MPI registration is fired with fuze quick. The HB registration is freed with time-tied rounds. The HB offers an advantage over the MPI registration by allowing the FDC
to determine a fuze correction. The HB registration is also easier to observe, especially at night, and registration corrections can be determined in areas where the observers cannot see the ground.

c. The requirement for surveyed observer locations with directional control is the primary limitation of HB and MPI registrations.

d. The six basic steps to an HB or MPI registration are as follows:
Select an orienting point. Orient the observers.
Determine firing data to the orienting point.
Fire the HB or MPI registrations. Determine the mean burst location. Determine chart data and registration corrections.

## 10-18. Selecting An Orienting Point

a. The S3 or FDO selects an orienting point at which all of the rounds will be fried.

This point may be located at a grid intersection for convenience. The orienting point is only a temporary point on the firing chart. After computing firing data, the orienting point is no longer needed.

b. The orienting point for either an HB or MPI registration point should meet the following criteria.

(1) It must be visible to both observers.

(2) It should be close to the center of the area of responsibility (unless an eight-directional met technique is to be used to determine a valid GFT setting).

(3) It should ensure an acceptable apex angle (Figure 10-5). (The apex angle is the angle formed by the lines from each observer to the orienting point.) Since two of the methods used to determine the MBL involve the use of trigonometry (polar plot and grid coordinate), a strong apex angle is needed to minimize the effects of small measurement errors. More information can be found in FM 6-2.

(4) For an MPI registration, the orienting point should be in a relatively flat (level)
area to eliminate the need to replot the MBL.

(5) For an HB registration, the orienting point must be high enough to ensure an airburst. The selected height of burst must be at least 2 FE in height of burst above the ground expressed up to the next 10 meters. The FDO can increase the HOB as long as it exceeds the minimum selected HOB. An example of this is below.

c. The FDO initiates the HB/MPI registration with a fire order; for example, HIGH-BURST REGISTRATION AT GRID 4128, HEIGHT OF BURST PLUS 30, WITH
T03 AND C19, 6 ROUNDS, FUZE TIME, BY ROUND AT MY COMMAND. As with any registration fire order, this one specifies what will be done, where it is to be done, with whom, and with what fire order considerations (see paragraph 10-10). The FDO has specified BRAMC
to be sure that the observers have enough time to spot each round fired and transmit spottings before the next round is fired.

## 10-19. Orienting The Observers

a. After selecting the orienting point and issuing the fire order, the two observers must be told whereto look to observe the rounds. Plot the observers' locations on the firing chart (if not already done), and measure the direction and distance from each observer to the orienting point. The VCO uses the distances and the VI between each observer location and the orienting point to determine the VA for each observer. Determine the VA by use of the C and D scales of the GST.

b. Send a message to each observer. The MTO contains the information the observers need to orient their instruments. Record the MTO on DA Form 4201. (See Figure 10-6, page
10-19.) The message contains the following elements:
(1) A warning order (for example, OBSERVE HIGH-BURST
REGISTRATION). The warning order informs the observers for what type of registration they are preparing.

(2) Orienting data for 01 (T03). The HCO measures the chart data from 01 to the orienting point.

The direction reported to the observer is the direction determined on the firing chart. The VCO determines the ground altitude of the orienting point and then adds the HOB to determine the altitude of the orienting point. The VCO subtracts the altitude of the observer from the altitude of the orienting point to determine the vertical interval. The VCO uses the C and D scales of the GST, the vertical interval, and the distance measured by the HCO to determine 01's vertical angle. The vertical angle and direction reported to 01 will enable him to orient on the orienting point.

(3) A directive to 01 to measure the vertical angle. Normally, 01 is the more experienced observer and will measure the VA. Observer 01 measures the vertical angles that will be used to compute the altitude of the mean burst location. Only one observer reports the vertical angle.

(4) Orienting data for 02 (C19). The HCO measures the chart data from 02 to the orienting point.

The VCO subtracts the altitude of the observer from the altitude of the orienting point to determine the vertical interval. The VCO uses the C and D scales of the GST, the vertical interval, and the distance measured by the HCO to determine 02's vertical angle.

The vertical angle and direction reported to 02 will enable him to orient on the orienting point.

(5) A directive to the observers to report when they are ready to observe.

When the observers report that they are ready to observe, the FDC can begin the registration.

c. Each observer orients his instrument on the direction and vertical angle announced to him and announces when he is ready to observe the registration.

## 10-20. Determining Firing Data

a. The HCO determines the range and deflection from the firing unit to the orienting point and announces the data to the computer.

b. The VCO subtracts the altitude of the firing unit from the orienting point altitude to determine the vertical interval. He then uses the D scale and the site-range scale of the GST, the vertical interval, and the range announced by the HCO to determine site. The VCO announces site to the computer.

c. The computer records the site on the ROF and determines and announces the fire commands to the howitzer(s). The HOB correction (20/R) is not used for the HB registration since the HOB was already accounted for in the orienting point altitude. The data fired are the adjusted (did hit) data.

## 10-21. Firing The Hb Or Mpi Registration

a. After both observers and the registering piece have reported ready, the FDO directs FIRE THE REGISTRATION. The first round that is fired may not be observed by either of the observers. There may be cases in which the nonstandard conditions cause the round to impact behind a hill or in a ravine, out of sight of one or both of the observers. Sometimes graze bursts occur at the start of an HB registration. The observers' data for these rounds cannot be used to determine the mean burst location. If this happens, change the firing data to the orienting point by increasing the HOB by at least 2 additional probable errors in HOB (Table G of the TFT) until both observers can see the bursting rounds (see paragraph 10-18). Remember, if the orienting point is changed, new orienting data must be sent to the observers (that is, a new MTO)
so that they can orient on the new location.

b. Once both observers have spotted the round, the firing data are not changed. All rounds used to determine the MBL and/or MPI must be fired with the same set of firing data.

These firing data are adjusted (did hit) data.

c. When both observers have reported that they have observed the bursting round, the computer transfers the firing data from the ROF to DA Form 4201 and writes "SEE ATTACHED
DA FORM 4201" on the ROF. Record all information for the rest of the registration on DA Form 4201.

d. After observing each round, each observer reports the direction to the round and 01
reports the vertical angle. The computer records the data on DA Form 421 as it is sent by the observers. The FDO must determine if any rounds fired were erratic and their spotting discarded. There are no exact rules for determining which rounds are erratic. The following are methods in which erratic rounds may be determined.

(1) Determine the MBL by using graphic intersection (see paragraph 10-22). Using the range to the MBL (expressed to the nearest 100 meters and interpolated), determine the PER
and PED and construct a rectangle (8 PER x 8 PED) centered over the MBL and along the GT line. Reject any rounds that plot outside this rectangle. (See Figure 10-7.)
NOTE: All rounds should have functioned within the 100 percent rectangle defined by 4 PER and 4 PED. Any rounds outside of the rectangle are considered erratic.

(2) At the range to the MBL, expressed to the nearest 500 meters, determine the PEHB.

Using 01's reported vertical angles, the measured distance from 01 to the MBL, and the ground altitude, determine the MBL altitude. Determine the altitude of each round, and compare this altitude with the average altitude. Reject any round that falls outside the average altitude 4 PEHB.

(3) The FDO may use his judgement and experience in determining if a round should be rejected. Care must be taken to ensure that erratic rounds are not used or that usable rounds are not rejected. If a round is considered erratic because of the reported direction from 01 or 02 or because of an incorrect vertical angle, the data from the other observer must also be discarded.

## 10-22. Determine The Mean Burst Location

a. List the observers' measured azimuths (spottings) on DA Form 4201 (Figure 10-8) as they are sent by the observers. As the rounds are fired, circle the round number to record the expenditure of rounds during the registration. Some rounds may be considered erratic. Erratic rounds are crossed out, and additional rounds may be fired to replace them.

b. Once the data from the usable rounds are recorded, the FDC determines the MBL.

Determine the location by one of three methods. The methods are listed below in increasing order of accuracy and time of computation. The method used by the FDC will depend on the tactical situation.

Usually, the graphic intersection method is acceptable. However, when increased accuracy is needed, use one of the other methods if time permits. See paragraph 10-24 for specific steps.

(1) Graphic intersection. Draw the observers' average directions on the firing chart. The point at which the lines intersect is the mean burst location.

(2) Polar plot. Determine the direction and distance from 01 to the mean burst location, and polar plot the MBL on the firing chart.

(3) Grid coordinates. Compute the actual grid coordinates of the MBL, and plot the coordinates on the firing chart.

## 10-23. Example Of An Hb/Mpi Registration

a. The steps in Table 10-5 are used to process an HB/MPI registration.

NOTE: A completed ROF for an HB registration using fuze M582 is shown in Figure 10-9.

## 10-24. Determination Of The Mbl

a. After all rounds have been fired and the observer spottings recorded, the FDO will determine if any rounds fired were erratic and should be discarded. If any round(s) are discarded, the FDO may decide to fire more rounds. If more rounds are to be fired, the method of fire and QE will be recorded on the ROF and announced to the registering piece. Use the procedures in Table 10-6 to determine the average observer readings.

b. The MBL is determined by using one of the methods below.

(1) Graphic intersection.

The HCO orients the RDP by using the average direction of 01. Once the RDP is oriented, a line is drawn along the arm of the RDP by using a 6-H pencil. He repeats the same procedure from 02 by using 02's average direction. The point at which the two lines intersect is the mean burst location. The HCO places a plotting pin at the MBL and determines and announces the distance from 01 to the MBL. The VCO uses the average vertical angle of 01, the 01 distance to the MBL, and the GST to determine and announce the vertical interval between 01 and the MBL. The computer adds the vertical interval to 01's altitude to determine the altitude of the MBL **(01 ALT + VI = MBL ALT).** Figure
10-10 can be used to aid in the determination of the MBL altitude. If this aid is used, it is recorded in the margin of DA Form 4201. A completed DA Form 4201 is shown in Figure 10-11
for the graphic intersection technique.

(2) Polar plot. Use the procedures in Table 10-6 and DA Form 4201 (Figure
10-12) to determine the MBL.

(3) Grid coordinate. The steps in Table 10-7 and a DA Form 4201 (see Figure
10-14) are used to determine the MBL.

NOTE: A completed DA Form 4201 for the grid coordinates technique is shown in Figure 10-14.

## 10-25. Determine Chart Data And Registration Corrections

After plotting the MBL on the firing chart, the HCO determines and announces the chart range and deflection from the firing unit to the MBL. Use Table 10-8 to determine the GFT
setting.

## 10-26. Effect Of Complementary Angle Of Site On Adjusted Fuze Setting

a. Fuze setting is determined as a function of elevation and complementary angle of site.

When the vertical interval is equal to or less than 100 meters, the CAS is generally so small that it has little effect on the quadrant and fuze setting fired and is disregarded. If the vertical interval is greater than 100 meters, the value of the CAS becomes increasingly large and begins to affect the fuze setting. In this case, the CAS must be added to the elevation to determine the proper fuze setting.

b. As the CAS increases, the the setting also must be increased to reach the desired burst location. If the effect of CAS is not included in the fuze setting, the fuze will function before it reaches the desired location.

c. If the vertical interval is greater than 100 meters, modify the adjusted the setting to correct for the inaccuracy introduced by the large complementary angle of site. The 100-meter VI is only a rule of thumb; CAS may affect the adjusted fuze setting at vertical intervals of less than 100 meters. The FDO should check the effects of CAS anytime he feels it will affect the adjusted fuze setting. Use Table 10-9 to correct the effect of complementary angle of site on adjusted fuze setting when VI is greater than 100 meters.

## Section Iv Process An An/Tpq-36 Or An/Tpq-37 Radar Registration

Field artillery radars can be used to observe registrations. The conduct of a radar-observed registration (commonly known as a radar registration) is similar to that of other HB or MPI registrations. This section outlines the unique procedures and requirements for the AN/TPQ-36 (Q-36) and AN/TPQ-37 (Q-37) radar systems.

## 10-27. Characteristics

a. The Firefinder radar has two separate modes of operation. The first mode of operation is the friendly fire mode, which is used by friendly artillery and mortar units for adjust-fire missions and registrations. The second is the hostile mode, which tracks incoming projectiles and is used to locate enemy indirect-fire systems.

b. A peculiarity of the two separate modes of operation is how the radar operator inputs data into his computer to orient the radar. Data can only be input while the radar is in the hostile fire mode. Once the operator has input all the data into the computer, he switches from hostile to friendly mode, and a delay is experienced while the radar orients itself. If a problem is encountered during the registration, such as around being unobserved, the first thing the operator does is verify his data. This requires him to switch back to the hostile mode, verify his data, then return to the friendly fire mode. Each time he changes modes, the radar physically reorients itself, taking from 20 to 30 seconds.

c. The radar has three different mission buffers, and they are used to store all the data needed to conduct a friendly fire mission. The radar also has the capability to store the spottings for six rounds. When the friendly fire storage cues are full and another round is tracked, it will replace the oldest spotting with the new one. Unless an observed round is recorded by the radar operator or transmitted to the FDC, these old data are lost when they are automatically replaced by the radar computer. Therefore, the operator needs to monitor the mission and either transmit each individual spotting to the FDC or clear the buffer by deleting erroneously captured information.

d. A danger area exists to the front of the radar. Theoretically, VT fuzes can function prematurely within the danger area or as a result of passing through the danger area. For the Q-36, the danger area is 107 meters out from the radar; for the Q-37, it is 141 meters.

(1) The radar takes 9 seconds to warm up before operation.

(2) Minimum observing distance for the Q-36 is 750 meters; for the Q-37, 3,000 meters.

(3) The friendly fire mode has five different mission types that the radar can conduct. They are as follows:
Mortar datum plane (MD). Mortar impact prediction (MI). Artillery airburst (AA). Artillery datum plane (AD).

Artillery impact prediction (AI).

e. The two types most commonly used by artillery are the artillery airburst (HB
registration) and the artillery impact prediction (adjust-fire missions and MPI registrations). One of the problems occasionally encountered between the FDC and the radar section is the use of different technical language. For example, in the message to observer, you might announce OBSERVE HIGH BURST REGISTRATION to orient the radar. An inexperienced radar operator unfamiliar with artillery terminology may have selected an incorrect mission type, which will result in rounds unobserved or unsuitable data. By understanding the different mission type requirements for radar, mistakes are prevented.

f. The advantages of a radar registration include the following:
Requires only one observation post--the radar. Requires less survey, fewer communications facilities, and less coordination than
other HB or MPI registrations.
Can be conducted quickly.
Can be conducted in periods of poor visibility. Produces the MBL/MPI grid and altitude or the grid and altitude of each round.
g. The disadvantages of a radar registration include the following:
Exposes radar to detection from the enemy. Keeps radar sections from performing their primary mission. May need to reposition radar to conduct the registration.

## 10-28. Conduct Of A Radar Registration

The six steps in conducting a radar registration areas follows:
Select an orienting point. Orient the radar. Determine firing data to the orienting point.

Fire the HB or MPI registration.
Determine the mean burst location. Determine chart data and registration corrections.

## 10-29. Selection Of An Orienting Point

a. The radar must be properly sighted in relation to friendly units to fully use its capabilities. There are three areas that significantly impact the ability of the radar to track friendly fire. They are as follows:

Electrical line of sight.
Range from the radar to the target. Aspect angle (
 T).
(1) A radar must have electrical line of sight to the point along the descending branch of the trajectory of the round where the burst will occur (HB), or it must be able to track the projectile for enough time to predict its point of impact (MPI). Doctrine calls for radar to be sited in defilade to increase its survivability.

This means that there are intervening crests
(screening crests) between the radar and the area where the rounds are being fired.

(2) If these crests interfere with the radar's electrical line of sight, then the radar search fence must be oriented high enough so that these crests will not mask the emissions.

However, if the radar is oriented above the altitude that the time fuzes are set to function, then ROUND UNOBSERVED will very likely be received from the radar. The easiest way to counteract this problem is to modify the procedures normally used to select a height of burst for HB registrations so that the radar is sure to "see" the burst.

T). The aspect angle should
(3) Aspect angle is the angle that is formed by the intersection of the gun-target line and the radar-target line, with the vertex of the angle at the target (
be less than 1,200 mils, with 800 mils being the optimum. A less than optimum aspect angle is going to decrease the probability of tracking each round. (From 1,300 to 1,600 mils, the tracking picture becomes fuzzy with the probability of track decreasing significantly.) These factors must be considered when determining whereto site your radars to optimize their performance.

b. A high-burst registration conducted with the Q-36 or Q-37 radar requires only an electrical line of sight to the selected point. The on-board computer controls the radar to enable it to intersect the trajectory above the screening crest. The radar tracks the round until the airburst is detected. The Q-36 and Q-37 radar systems set up a "window" through which the projectile will pass. The window is referred to as the friendly fire search fence (Figure 10-15). The search fence allows for the best probability of detection. Because of the size of the radar memory queue, no more than six rounds should be fired without coordination with the radar section. Rounds should be fired at 30-second intervals with an angle T of less than 1,000 mils.

c. MPI Registration. A characteristic of the radar MPI registration is that the rounds usually cannot be observed at impact because the radar usually is positioned behind masking terrain with a screening crest. The projectile is tracked until it reaches the datum plane height.

The radar section reports the grid and altitude of the impact location as predicted by the radar.

## 10-30. Orienting The Radar

a. After selecting the orienting point, the FDO issues his fire order and the FDC
computes orienting data. The registration is initiated by transmitting an MTO. The purpose of this message is to inform the radar section of the mission and to provide the information required to prepare the radar.

b. The message to observer must always include the warning order. It is OBSERVE
HIGH-BURST (or MPI) REGISTRATION FOR (unit call sign). This informs the radar section of the type of registration to be fired and for whom the registration is conducted. Observe communications security procedures in transmitting information.

c. To orient the AN/TPQ-36 or -37 radar, send the radar the following:
Grid and altitude of the orienting point. Grid and altitude of the firing unit. Quadrant elevation. Maximum ordinate (to the nearest meter) from the appropriate TFT. Entry argument is quadrant elevation (interpolate). Special if it is meters or feet and above sea level or above gun. Time of flight. Target number. Angle of fall. (Determined by interpolation from Table G by using quadrant elevation as the entry argument.) This is optional.

d. Regardless of the radar system used, the message to observer must include the report order. It is REPORT WHEN READY TO OBSERVE.

## 10-31. Determination Of Firing Data To The Orienting Point

The determination of firing data for a radar registration is the same as that for a regular HB or MPI registration.

## 10-32. Firing The Hb Or Mpi Registration

The radar on-board computer uses the orienting data to check the trajectory and determine whether it fits the capabilities of the radar. Before firing, the radar operator determines whether the data are acceptable, marginal, or unacceptable. The radar section reports when it is ready to observe (for example, AT MY COMMAND, REQUEST SPLASH, READY TO OBSERVE, OVER). Since the radar operator checks the acceptability of the orienting data before firing begins, all rounds fired should be acquired by radar. If the first round is not visible, an error has occurred. The radar operator informs the FDC that the round was unobserved. The FDC should verify firing data, If no errors are found and the next round is unobserved, the FDC should compute new orienting data and send the new data to the radar operator.

## 10-33. Determination Of The Mean Burst Location

The radar operator normally reports the grid location and altitude of each burst. The grids may be recorded in the observer reading columns of DA Form 4201. The FDO determines which rounds are usable. Once the FDO determines the usable rounds, he averages the grids and altitudes of the usable rounds to compute the mean burst location. The grid and altitude are then recorded in the Location of HB (MPI) block near the bottom of DA Form 4201.

## 10-34. Determination Of Chart Data And Registration Corrections

After determining the MBL and altitude, the procedures for computing chart data and registration corrections are the same as those for regular HB/MPI registrations. Figure 10-16
shows an example of a completed ROF for an HB radar registration. Figure 10-17 shows an example of a completed DA Form 4201 for an HB radar registration.

## 10-35. Dpicm Registrations (M483A1/M509E1)

a. The DPICM projectile may be fired in the self-registration mode to provide corrections for other munitions like the area denial artillery munitions (ADAM) or remote antiarmor mine system (RAAMS). The round can be registered by using either the precision or the HB/MPI method. Normally, the HB/MPI method would be selected to conserve ammunition.

b. Firing data should be computed by using the most current firing table.

c. If point-detonating action is desired for an impact registration, the M577 fuze must be set for PD action. An impact registration is not recommended, since no fuze setting correction is determined.

d. In all cases when the round is used in registrations, it must be prepared for the SR
mode (expelling charge removed and booster attached to fuze). In the SR mode, the entire round will detonate and destroy the submunitions.

e. The GFT setting is constructed and total corrections are determined as per precision and HB/MPI instructions. An example ROF for a completed precision registration for shell DPICM is shown in Figure 10-18. The **HOW 155mm 155AN1M483A1 GFT** was used for the registration.

## Section V High-Angle Registration

On the basis of the tactical considerations, it may become necessary to use high-angle fire instead of low-angle fire. In this situation, a high-angle impact registration can be conducted to improve the accuracy of initial rounds. The use of time fuzes to conduct a time registration is impractical because the height of burst probable error is so large.

## 10-36. High-Angle Gft

When conducting a high-angle impact registration, it is common for the range probable error to be equal to or greater than 25 meters. Since current high-angle GFTs do not have a probable error in range gauge point, the computer must check Table G of the TFT to determine if the probable error in range is equal to or greater than 25 meters. A probable error in range gauge point may be constructed on the high-angle GFT for each charge. The gauge point is constructed on the TF scale.

## 10-37. Procedures For High-Angle Impact Registration

Procedures for high-angle impact registrations are the same as low-angle impact registrations with the following three exceptions:
a. Because of the large CAS in high-angle fire, special procedures must be used to determine the adjusted elevation.

b. The high-angle GFT setting is applied differently to the high-angle GFT.

c. High-angle transfer limits are different from low-angle transfer limits because ranges of various charges are smaller.

## 10-38. Computation Of The Adjusted Elevation

a. The adjusted elevation, determined from an HA impact registration, often includes a false site. This false site is caused by the relationship of the CAS to total site. The CAS is a fiction of elevation. In low-angle fire, small changes in elevation will cause small changes in CAS. On the other hand, in high-angle fire, small changes in elevation will cause large changes in CAS. In a high-angle registration, the CAS determined at the initial elevation and applied throughout the mission will often differ substantially from the CAS corresponding to the adjusted elevation. This false CAS, when added to the angle of site, will produce a false site. To provide accurate data, the FDC must determine the true site and subtract it from the adjusted QE to compute the true adjusted elevation. To determine the true site, successive approximation is used.

b. The steps in Table 10-10 are used to determine the true site and true adjusted elevation.

## 10-39. Dpicm High-Angle Registration

a. Conduct a registration with DPICM (M483A1) in the self-registration mode. This destroys the submunitions and causes the round to detonate like an HE round.

b. If terrain in the target and/or firing unit area requires using high-angle fire, a high-angle **high-burst** registration using the M577 time fuze can be conducted. (The M577 has a small probable error in height of burst in relation to the M564/M565 time fuze family. This type of registration is conducted with the DPICM projectile in the SR mode. The procedures are the same as for those in low-angle HB registration with the following exceptions:
(1) Add a minimum of 4 PE
(DPICM TFT, Table G, Column 5) to the altitude of HB
the orienting point.

(2) The fuze setting to fire in an HB high-angle registration is the fuze setting corresponding to elevation plus CAS. The CAS in high-angle fire is usually a relatively large negative number. To determine CAS, enter Table G of the TFT with the range to the nearest 500
meters and extract from Column 12 or 13 the CSF for a 1-mil angle of site. Multiply the angle of site by the CSF to determine CAS. Apply the CAS to the elevation determined from the high-angle GFT. Move the MHL over the value of elevation plus CAS, and read from the TF
scale to the nearest 0.1 fuze setting increment.

(3) Determine drift and elevation from the high-angle GFT.

(4) Determine site by multiplying the 10-mil site factor corresponding to the adjusted elevation by the angle of site divided by 10.

c. Determine the adjusted elevation for a high-angle HB registration in the same manner as for a low-angle HB registration. Site is based on the altitude of the mean burst location.

d. Determine the adjusted time in the same manner as in a low-angle HB registration.

To determine the total fuze correction, subtract the time corresponding to elevation plus CAS
from the adjusted time.

When firing with a GFT setting, apply the total fuze correction to the fuze setting corresponding to the adjusted elevation to determine the fuze setting to fire.

## Section Vi Offset Registrations Or Registrations To The Rear

The tactical situation may make registering from the unit location or along the primary azimuth of fire impractical. The offset registration or registration to the rear should reduce the vulnerability of the firing unit to detection by enemy counterbattery assets. Both of these registrations may require coordination for firingpositions or known points. The registrations are conducted by using normal precision or HB/MPI registration procedures.

## 10-40. Offset Registration

a. An offset registration is conducted by one howitzer from a position away from the rest of the unit. The offset position must be coordinated to ensure there are no other friendly units in the area as the registration may draw enemy counterbattery fire. The offset position must be on common survey with the firing unit to ensure that any corrections for survey errors in the offset position are valid in the firing unit position.

b. Adjusted data and resulting corrections determined from the offset position are valid for that position within normal range and deflection transfer limits.

c. The registration corrections are based on the azimuth and range from the offset position to the known point. It is assumed that if a registration were conducted from the firing unit area by using the same range and azimuth (as from the offset position), the adjusted data and resulting corrections would be the same as those obtained in the offset position. (See Figure
10-20).

## 10-41. Registrations To The Rear

A registration to the rear (or along some other azimuth significantly different from the primary azimuth of fire) may be either a precision or an HB/MPI registration. The registration will result in corrections, but these corrections must be modified for the primary zone of fire by using the eight-direction
- met technique (Chapter 11). The actual area where the rounds will be bursting must be coordinated to ensure there are no friendly units in the area.

## Section Vii Determination And Application Of Registration Corrections

Registration corrections consist of a total range, total fuze, and total deflection correction. FDC personnel compute these corrections by comparing the chart or **should hit** data (the data that when fired under standard conditions will cause the round to burst at a point of known location) with the adjusted or did hit data (the data that when fired under nonstandard conditions will cause the round to burst at a point of known location).

## 10-42. Computation Of Total Range Correction

a. If standard conditions existed, the elevation fired to achieve the chart range would be the elevation listed in the firing tables for that chart range, When nonstandard conditions exist the range that is achieved by firing a certain elevation is greater or less than the range listed in the firing tables by an amount equal to all of the effects caused by the nonstandard conditions. The difference is the total range correction.

b. The total range correction is the difference in meters between the initial chart range and the firing table range corresponding to the adjusted elevation. Determine the total range correction as follows:
(1) From the TFT or GFT, determine the range (to the nearest 10 meters)
corresponding to the adjusted elevation.

(2) Subtract the initial chart range (or achieved range) from the range corresponding to the adjusted elevation. The result is the total range correction. The total range correction is

## 10-43. Computation Of Total Fuze Correction

a. The time portion of a precision or high-burst registration will result in an adjusted or did hit time (fuze setting). The time corresponding to the adjusted elevation is the should hit time that must be compared to the actual adjusted time determined by firing. The difference between the time corresponding to the adjusted elevation and the adjusted time is the total fuze correction
(DHD - SHD = TOT).

b. To determine the total fuze correction, subtract the time corresponding to the adjusted elevation (or elevation plus CAS if the VI is greater than 100) from the adjusted time. The total fuze correction is always a signed value and is used in solving a concurrent met. See the following example.

## 10-44. Computation Of Total Deflection Correction

a. The total deflection correction is the correction, in mils, that must be added to the chart deflection to correct for all nonstandard conditions.

b. To determine the total deflection correction, subtract the chart deflection from the adjusted deflection. The total deflection correction is used in solving the concurrent met technique, in processing immediate type fire missions, and for updating manual safety computations after a registration. For all other missions, the GFT DF correction plus drift is used.

c. A GFT deflection correction is determined by subtracting the drift corresponding to the adjusted elevation from the total deflection correction. The GFT deflection correction remains the same for all elevations fired with the registered charge. The drift is applied to the GFT deflection correction to determine the deflection correction to be used for that mission. Using the precision registration example in Figure 10-3, determine the total deflection correction as follows:

## 10-45. Determination Of Total Registration Corrections

The computational space on DA Form 4757-R (Registration/Special Corrections Work Sheet) will be used to determine the total corrections. Use Table 10-12 to determine total registration corrections,

## 10-46. Low-Angle Gft Settings

a. The data determined from a registration must be applied to FDC graphical equipment.

This will enable the unit to attack accurately located targets without adjustment (first round fire for effect) within transfer limits.

b. Listed below are the elements of a GFT setting. These elements are recorded in the lower computational space of the record of fire used to process the registration. Additionally, they may also be recorded on DA Form 4757-R and on the record of fire of a mission in which they are being used. For the HB/MPI registration, the GFT setting is recorded on DA Form 4201. The acronym UCARET is used as an aid in recording the GFT setting. It is used to keep the GFT setting preceding the total and GFT deflection corrections in order.

Unit that fired the registration.

Charge fired during the registration and the charge for which the GFT setting applies.

Ammunition lot used in the registration. With separate-loading ammunition, the first letter designates the projectile lot used during the registration. The second letter designates the propellant lot used during the registration.

Range (chart or achieved) from the howitzer to the point of known location. Elevation (adjusted or did hit). Time (adjusted or did hit fuze setting).

the Total deflection correction (the difference between the adjusted deflection and chart deflection). GFT deflection correction (the difference between the total deflection correction and the drift corresponding to the adjusted elevation).

c. The following is an example of a completed GFT setting as it is written.

## Gft 1/A Chg 4 Lot Ag Rg 4950 El 314 Ti 18.5 Tot Df Corr R1 Gft Df Corr R7

d. The following is an example of a completed GFT setting as it is written with total corrections.

## 10-47. Determination Of A Gft Setting When The Registering Piece Is Not The Base Piece

It may not always be possible to register with the base piece. When a howitzer other than the base piece is used to register, corrections must be made to compensate for the displacement of the registering piece from the base piece. Use a DA Form 4757-R and the steps in Table 10-13 to determine the necessary corrections.

## 10-48. Construction Of A Gft Setting

Once the information for the GFT setting has been determined and recorded on DA Form
4757-R, the GFT setting can be constructed on the GFT. Use the steps in Table 10-14 to construct a GFT setting on the GFT.

## 10-49. Construction Of A Two-Plot Or Multiplot Gft Setting

The steps in Table 10-15 are used to construct a two-plot or multiplot GFT setting.

## 10-50. Update Of A Gft Setting When Transferring From A Map Spot Or Observed Firing Chart

a. Field artillery units must be able to deliver responsive, accurate fires immediately upon occupation of a new position. Firing must not be delayed because of lack of survey or suitable maps. An initial firing chart may be based on a map spot or an observed firing chart.

Once the actual survey is brought into the unit's area, the firing charts must be reconstructed on the basis of the firing unit's true location and true azimuth. GFT settings based on map spot or observed fire charts are accurate but must be updated.

b. When a registration is conducted on the basis of the map spot data for the registration point and/or firing unit location, the corrections determined will include corrections for map spot errors and possible human errors in plotting the locations. Once survey data are available, the GFT setting(s) determined must be updated to account for the initial inaccuracies.

c. Once survey data become available, the HCO will construct and plot the locations on a surveyed firing chart. He will determine a new chart range and deflection to the known point.

The new chart range will be the range for the GFT setting. The VCO will use the new chart range and an updated VI to recompute site. The computer will recompute the adjusted elevation and new total and GFT deflection corrections.

The adjusted fuze setting was determined by firing and will not change. Use Table 10-16 to update a GFT setting when transferring from a map spot or observed firing chart to a surveyed firing chart.

## 10-51. Registration Transfer Limits

a. In manual gunnery techniques, the total corrections determined from a registration are valid only within certain range and deflection transfer limits. Transfer limits define the ranges and deflections within which the GFT setting is expected to produce accurate firing data. The total corrections for nonstandard conditions are valid only when the weapons are firing toward the known point. For example, when weapons are firing on a different azimuth than that of the known point, the wind will not affect the round in the same manner as it did along the azimuth to the known point.

## B. Range Transfer Limits.

(1) The range transfer limits for a one-plot GFT setting are shown on the GFT
corresponding to the red numbered elevations.

(2) The range transfer limits for a two-plot GFT setting are between the two ranges used to apply the GFT setting(s). This type of GFT setting becomes less accurate outside these two ranges.

(3) The range transfer limits for a multiplot GFT setting are eliminated when three or more sets of corrections are available for the same charge. The optimum multiplot GFT
setting reflects a plot for each met line number that the charge may cause the projectile to pass through (met check gauge points).

## C. Deflection Transfer Limits.

(1) The total registration corrections are valid only within certain deflection transfer limits.

(2) When the chart range to a target is 10,000 meters or less, the total corrections are valid within an area 400 mils left and 400 mils right of a line between the unit and the known point (mean burst location) (Figure 10-24).

(3) When the chart range to a target is less than 10,000 meters, the total corrections are valid within an area 400 mils left and 400 mils right of a line between the unit and the known point (mean burst location) out to 10,000 meters, and 4,000 meters left and 4,000 meters right of the line for ranges beyond 10,000 meters. (See Figure 10-25.)
(4) Total registration corrections may be determined throughout the entire 6,400
mils around the firing unit by using the eight-direction met technique (Chapter 11).

## 10-52. High-Angie Gft Settings

a. GFT settings for high-angle fire are written in the same manner as those for low-angle fire. An example is shown below.

GFT 1/A, Chg 3, Lot AG, Rg 4970, EI 1111
Tot Df Corr L32 GFT Df Corr R20
b. The high-angle GFT setting is constructed on the GFT by placing the MHL over the adjusted elevation for the charge fired and drawing a range gauge line through the GFT setting range on the range scale parallel to the MHL. The MHL becomes the elevation gauge line, and all data except for range and 100/R are read under the MHL. The GFT deflection correction and charge are recorded on the cursor.

## 10-53. High-Angle Transfer Limits

Standard range transfer limits are not applicable to high-angle fire because the range span of each charge is so short. Corrections in the form of GFT settings and GFT deflection corrections are considered valid for the charge used in determining the corrections and are also considered valid for other charges as shown in Table 10-17.

## 10-54. Transfer Of Gft Settings

a. When only one unit of a battalion equipped with weapons for which the same firing tables are used is allowed to register, the GFT setting determined by the registering unit maybe transferred to the nonregistering units in the absence of better information.

b. Transferring of GFT settings should only occur if a concurrent met technique cannot be performed and position constants cannot be isolated (Chapter 11). To transfer a GFT setting, certain conditions must exist as follows:

Common survey between positions. Azimuth of fire (octant) are the same.
Ability to correct for MVVs for the registered lot.
c. The distance over which the GFT settings are transferred should be monitored closely. The further from the registration point the GFT setting is transferred, the less accurate the GFT setting will be. This is due to the different effects of the met (weather) conditions. The guidance given in chapter 11 on the validity of met messages should be used when transferring GFT settings.

d. The procedures for determining a GFT
setting for a nonregistering unit is listed in the GFT setting and registering piece MVV
Table 10-18 below. The registering unit must send to the nonregistering unit.

## 10-55. Example Of Transferring A Gft Setting

Battery A, 1st Platoon registered, and Battery C, 1st Platoon wants the GFT setting transferred to their unit. Battery A, 1st Platoon registered with their base piece which has an MVV of -1.6 M/s. The base piece for Battery C, 1st Platoon has an MVV of -7.7 m/s.

## Chapter 11 Meteorological Techniques

Met techniques described in this chapter allow a unit to account for the effects of nonstandard conditions and achieve first round fire for effect.

## Section I Principles

Understanding the applications of met techniques requires basic knowledge of registration and met principles.

## 11-1. Purpose And Use Of Met Techniques A. Nonstandard Conditions

(1) Accurate fires can be placed on targets of known location without adjustments.

Under standard conditions, the firing table data would achieve the desired results. However, it is valid to assume that standard conditions will not exist. Corrections need to be applied to firing table data to compensate for the nonstandard conditions of weather, position, and material. The most accurate means of determining these corrections is by registering. Registration corrections are only valid within transfer limits and for a specified period of time. However, conducting a registration may not be an option. Therefore, techniques are needed to mathematically determine corrections and compensate for changing nonstandard conditions. The **met techniques** are used to measure deviations from standard conditions and to compute corrections for them.

(2) The firing tables used to determine firing data for artillery weapons are based on an arbitrary set of standard conditions of weather, position, and material. The standards for weather are established by the ICAO (International Civil Aviation organization). (See Figure 11-1.)
(3) The first seven columns of Table F of the TFT are based on one of two conditions occurring:
Standard conditions are in effect.

The sum of the corrections for all nonstandard conditions in effect equals zero.

It is obvious that the first will never occur and the second has a minimal chance of occurring. Therefore, if a unit wants to provide surprise and massed fires, it must consider the effects of nonstandard conditions in some way. The best solution to correct for all nonstandard conditions in effect is to register. This allows a unit to achieve first round FFE on an accurately located target. To correctly determine registration corrections and the effects of nonstandard conditions as they change over time, a unit must follow the five steps to improve firing data. (See Table
11-1.)

## 11-2. Position Constants

a. When a unit displaces to a new position and cannot register, the position constants from the last position may be used as a basis for determining a GFT setting by solving a subsequent met.

The use of this technique may cause slight inaccuracies, but it will produce the most accurate data possible until the unit can conduct another registration or met + VE with a check round. Once new position constants are determined, the old position constants are not used.

b. The position deflection correction generally accounts for errors in survey and chart construction. The position deflection correction should only be transferred if common survey exists between positions.

c. The position fuze correction should be considered a fuze characteristic and not a correction for existing weather conditions. The position fuze correction should only be applied to the same lot of fuzes.

d.  The position velocity error is expressed in meters per second. It is the position constant which accounts for all range errors not accounted for by met data, muzzle velocity variation, and propellant temperature. Therefore, it will include any errors in survey and should only be transferred if common survey exists. However, the position VE is a constant for projectiles within the registering projectile family.

e. Part of the position VE and position deflection correction are charge independent, specifically errors in the firing chart and survey. The position fuze correction is charge independent because it is a fuze characteristic. Since position constants are relatively small and a portion of the position constants are charge independent, it is possible to compute a GFT setting for other charges and lots. The GFT setting will not be as accurate as a GFT setting derived from a registration, but it will be more accurate than firing with no GFT setting.

## 11-3. Met Messages

a. Among the nonstandard conditions that affect the projectile after it leaves the tube is the atmosphere (weather conditions) through which the projectile passes. The three properties of the atmosphere that the artillery considers in its gunnery computations are wind (both direction and speed), air temperature, and air density.

(1) Wind. The effects of wind on a projectile are easy to understand. A tail wind causes an increase in range and a head wind causes a decrease in range. A crosswind blows the projectile to the right or left, which causes a deflection error. The FDC converts ballistic wind measurements into range and deflection components and applies corrections to the deflection and elevation of the howitzer.

(2) Temperature. Variations in air temperature cause two separate effects on a projectile. One effect is caused by the inverse relationship between density and temperature.

This effect is compensated for when density effects are considered. The second effect is regarded as the true temperature. It is the result of the relationship between the speed of the projectile and the speed of the air compression waves that form in front of or behind the projectile. These air compression waves move with the speed of sound, which is directly proportional to the air temperature. The relationship between the variation in air temperature and the drag on the projectile is difficult to determine. This is particularly true for supersonic projectiles, since they break through the air compression waves after they are formed. As firing tables indicate, an increase in air temperature may increase, decrease, or have no effect on achieved range, depending on the initial elevation and muzzle velocity of the weapon.

(3) Air density.

Density of the air through which a projectile passes creates fiction, which affects the forward movement of the projectile. This affects the distance a projectile travels. The density effect is inversely proportional to the projectile ranges; that is, an increase in density causes a decrease in range.

b. The met section is responsible for sampling the weather conditions at various altitudes. Data determined by these samples are converted, manually or by computer, to provide specific weather information at specific altitudes. These weather data are transmitted to artillery units in fixed formats called **met messages.** The field artillery uses the following four types of met messages:
(1) Ballistic met message. This message is used by cannon units, rocket units, mortar units, and air defense artillery.

(2) Computer met message. This message is used by artillery computer systems.

(3) Fallout met message. This message is used in nuclear and chemical fallout predictions.

(4) Target acquisition met message. This message is used by radar platoons of the target acquisition battery (TAB).

NOTE:  Only the ballistic and computer met messages will be described in the following paragraphs.

## 11-4. Ballistic Met Message

The ballistic met message is a coded message containing information about current atmospheric conditions.

There are two types of ballistic met messages provided for artillery.

Type 2 messages (surface to air) are used in air defense artillery and type 3 messages (surface to surface) are used by FA cannon and rocket units. Type 3 messages are used in solving DA Form
4200 (Met Data Correction Sheet). Type 3 messages are used for all elevations, for all charges, and for all howitzers in manual FDC operations. The ballistic met message is recorded on DA
Form 3675 (Ballistic Met Message) and is divided into an introduction and a body.

a. The introduction of the ballistic met message consists of four six-character groups.
(1) Group 1. The first three letters (MET) in group 1 identify the transmission as a met message. The next letter (B) indicates that it is a ballistic met message. The next digit (3) indicates the type of met message (surface to surface). The last digit (1) designates the octant of the earth in which the met station is located. (See Figures 11-2 and 11-3.) In Figure 11-3, octant 1 indicates that the met station is located between 90W and 180W longitude and is north of the equator.

(2) Group 2. This group designates the center of the area in which the met message is valid. This is expressed in tens, units, and tenths of degrees of latitude and longitude (347= 34.7 and
985 = 98.5). When the longitude is 100 or greater, the initial digit (1) is omitted. If the number 9 is used to designate the octant, the six digits or letters represent the coded location (in latitude and longitude) of the met station that produced the message. (See Figure 11-3.)
(3) Group 3. The first two digits (27) in group 3 represent the day of the month that the met message is valid. The next three digits (125) indicate the hour in tens, units, and tenths of hours (125 = 12.5 hours = time 1230) the met message is valid. The hours refer to Greenwich Mean Time (GMT). The last digit (0) in group 3 indicates the number of hours the message will remain valid. The US does not try to predict the length of time a met message will remain valid. Therefore, the last digit in group 3 of a ballistic met message will always be 0.

Some allied nations predict the length of time a met message will remain valid. These predictions vary from 1 to 8 hours. Code 9 indicates 12 hours. (See Figure 11-3.)
(4) Group 4. The first three digits (055) in group 4 indicate the altitude of the met station (MDP) above mean sea level in multiples of 10 meters (055 = 550 meters). The next three digits (972) indicate the atmospheric pressure at the MDP (972 = 97.2 percent). When a value is equal to or greater than 100 percent the initial digit (1) is omitted (012= 101.2 percent). (See Figure 11-3.)
b. The body of the met message can consist of 16 met message lines (00-15). Each line consists of **two six-number groups.** Each line contains the ballistic data for a particular altitude zone.

Ballistic data are the weighted average of the conditions that exist from the surface up through the altitude zone, indicated by the line number, and back to the surface. (See Figure 11-4.)
(1) The first two digits in the first group on each line identifies the altitude zone (00 [surface] through 15 [18,000 meters]). (See Figure 11-4.) Line 02 is used as an example. (See Figure 11-5.)
(2) The next two digits in the first group (59) indicate the direction from which the ballistic wind is blowing.

It is expressed in hundreds of mils true azimuth
(59 = 5900). (See Figure 11-5.)
(3) The last two digits of the first group (17) indicate the wind speed of the ballistic wind in knots (17= 17 knots). (See Figure 11-5.)
(4) The first three digits of the second group (008) indicate the ballistic air temperature expressed as a percentage (to the nearest 0.1 percent) of the ICAO standard
(008 = 100.8). (See Figure 11-5.)
(5) The last three digits of the second group (958) indicate the ballistic air density expressed as a percentage (to the nearest 0.1 percent) of the ICAO standard density (958 = 95.8). (See Figure 11-5.)
NOTE: When the air temperature or air density is equal to or greater than 100
percent, the initial digit (1) is omitted. A completed ballistic met message recorded on DA Form 3675 is shown in Figure 11-5.

## 11-5. Computer Met Message

Like the ballistic met message, the computer met message is a coded message that reports the atmospheric conditions in selected layers starting at the surface and extending to an altitude that will normally include the maximum ordinate of field artillery weapons that use these data. Unlike the ballistic met message used in manual computations (in which the weather conditions existing in one layer or zone are weighted against the conditions in lower layers and reported as percentages of standard), the computer met message reports actual average wind direction, wind speed, air temperature, and pressure in each layer.

The computer met message is used by the battery computer system (BCS) in the computation of the equations of motion used in the computer program. The computer met message is recorded on DA Form 3677 (Computer Met Message) and is divided into two parts--an introduction and a body.

a. The introduction of the computer met message consists of four six-character groups.

(1) Group 1.

The first five letters (METCM) identify the transmission as a computer met. The last digit (1) designates the octant of the earth in which the met station is located. The octant code key is the same as that for the ballistic met message. (See Figure 11-6.)
(2) Group 2. This is the same as group 2 of the ballistic met message. (See Figure
11-6.)
(3) Group 3. This is the same as group 3 of the ballistic met message. (See Figure
11-6.)
(4) Group 4. The first three digits (049) of group 4 indicate the altitude of the met station MDP above sea level in tens of meters (049 = 490). The last three digits (987) indicate the atmospheric pressure, in millibars, at the met station. When the pressure value is greater than
999, the first digit (1) is omitted. (For example, 009= 1009). (See Figure 11-6.)
b. The body of the met message can consist of 27 met message lines (00-26). Each line consists of **two eight-number groups.** Each line contains the actual average weather data for a particular zone. (See Figure 11-6.)
(1) The first two digits in the first group on each line identifies the altitude zone (00
[surface] through 26 [20,000 meters]). Line 00 is used as an example. (See Figure 11-6.)
(2) The next three digits in the first group (260) indicates the direction from which the wind is blowing. It is expressed in tens of mils true azimuth (260= 2600). (See Figure 11-6.)
(3) The last three digits of the first group (018) indicate the wind speed expressed in knots (01 8 =18 knots). (See Figure 11-6.)
(4) The first four digits of the second group (2698) indicate the actual air temperature expressed in degrees Kelvin (K) to the nearest tenth of a degree (269.8K). (See Figure 11-6.)
(5) The last four digits of the second group (0987), indicate the actual air pressure, in millibars, to the nearest millibar (987 millibars). (See Figure 11-6.)

## 11-6. Met Message Checking Procedures

a. When the FDC receives a met message, it should be checked to ensure that it is valid.

Any peculiarities noted in the message should be questioned. If the timeliness or validity of a met message is doubted, that also should be questioned and referred to the artillery met section, whose personnel are qualified to explain message variations or to correct message transmission errors.

Verbal transmission of met messages may cause copying errors, particularly if the message is copied down on something other than the standard (ballistic or computer) met form. FDC personnel should use the guidelines in subparagraphs b through e below when checking met messages.

b. Check the ballistic or computer met message heading as follows: (See Figure 11-7 or
11-8.)
(1) Check message type, octant, and location entries for correctness.

(2) Check date-time entries to ensure data are current. If the met message is more than 4 hours old, consult with the met section to determine message validity (date-time entries are expressed in Greenwich mean time).

(3) Map-spot the altitude of the MDP by using the latitude and longitude from the location block in the header of the met message. (See FM 21-26 for additional information on how to plot a latitude and longitude. An error of 50 meters or more will affect air temperature and density and/or pressure corrections applied to firing data.)
c. Check the ballistic met message body as follows: (See Figure 11-7.)
(1) Ballistic wind direction should trend in a fairly uniform manner. Question drastic changes (1,000 mils or greater) or sudden reverses of wind direction from line to line, particularly if wind speeds are more than 10 knots. Direction changes greater than 1,000 mils are common when wind speeds are 10 knots or less.

(2) Question severe increases or decreases (10 knots or greater) in wind speed from line to line.

(3) Ballistic temperatures and densities normally show an inverse relationship; that is, as temperature increases, density should decrease.

(4) Check for drastic changes (2 percent or more) in density or temperature.

Ballistic temperature and density should change smoothly between zones.

d. Consecutive messages should show a trend that relates to the actual weather conditions unless weather conditions have changed during sunrise or sunset transition periods or because of a frontal passage, rain, snow, or a rapid increase or decrease in cloud cover.

e. Check for errors in the computer met message as follows: (See Figure 11-8.)
(1) Question drastic wind direction changes (1,000 mils or greater) or sudden reverses of wind direction from line to line, particularly if wind speeds are more than 10 knots. Direction changes greater than 1,000 mils are-common when wind speeds are 10 knots or less.

(2) Question severe increases or decreases (10 knots or greater) in wind speed from line to line.

(3) Question a severe increase or decrease (over 20K) in temperature from line to line. (4) Check for differences in identification line pressure and surface pressure; both should match.

(5) Check for increases in pressure. Pressure should decrease smoothly from line to line. Pressure will never increase with height.

## 11-7. Met Message Space And Time Validity

a. Space Considerations.

The accuracy of a met message may decrease as the distance from the met sounding site to balloon and sensors increases. Local topography has a pronounced effect on the distance that met data can reasonably be extended. In mountainous terrain, distinct wind variations occur over short distances. This effect extends to much greater heights than the mountain tops. Large bodies of water affect both time and space considerations of the met message because of the land and sea breezes and the effect of humidity on density. It would be impossible to compute an exact distance for every combination of weather and terrain. Met messages for artillery are considered valid up to 20 kilometers (km) from the balloon release point (met section). The validity distance decreases proportionately with the roughness of the terrain and the proximity of large bodies of water.

b. Time Consideration. The passage of time may decrease the accuracy of a message because of the changing nature of weather. With existent equipment, the artillery met section has difficulty in providing met messages more often than every 2 hours over an extended period of time. There are no specific rules for determining the usable time, since that determination depends on the following:
Characteristics of the atmosphere. Periods of transition. Met section movement.

Personnel. Supplies and equipment.

Altitude of the met message (line number) required by the artillery firing units.

When the weather pattern is variable, the usable time is variable. If a frontal passage is forecast for the area, the met section will take a new sounding after passage of the front. When the weather pattern is stable and is forecast to remain so, time between messages may be extended to several hours or longer, depending on the time of day and existing weather conditions. (See Figure 11-9.)
c. Criteria for Use of Met Data. Results of many studies that are based on artillery firing and met data show that the order of preference of various sources of met data is as shown in paragraphs (1) through (3) below. A current met message is one that is less than 2 hours old unless an exchange of air mass has occurred since the met message was produced or unless periods of transition are involved.

(1) Current met message from a station within 20 kilometers of the midpoint of the trajectory (upwind is best).

(2) Current met message from the nearest station up to 80 kilometers from the midpoint of the trajectory. A 4-hour old met message may be used except when day-to-night transitions or frontal passages are occurring.

(3) Met messages over 2 hours old but from a station within 20 kilometers of the midpoint of the trajectory.

A 4-hour-old met message may be used except when day-to-night transitions or frontal passages are occurring.

## Concurrent Met Technique

A concurrent met is solved to isolate position constants. To perform a concurrent met technique, the firing unit must have total corrections determined from a registration and the met conditions that were valid at the time of the registration. Met corrections are determined and then subtracted from the total corrections to isolate position constants. Any errors in the met corrections and total corrections will be contained in the position constants. Every effort must be made to obtain the most accurate met corrections available.

## 11-8. Da Form 4200

The concurrent met technique is solved on DA Form 4200. There are two methods to solve a concurrent met technique. The first is the vowel rule. This follows the sequence of the tables in the TFT, and computations are completed after extracting data from a vowel table. Table 11-2 provides the abbreviated steps for this method. The second is the RATT rule. RATT is an acronym for record, apply, transfer, tables. This also follows the sequence of the tables in the TFT, but computations are completed after extracting data from **each** table. Table 11-3 provides the abbreviated steps for this method.

## 11-9. Solution Of A Concurrent Met

Table 11-4 shows a detailed solution of a concurrent met using the RATT rule. The example uses the data shown in Figure 11-10.

## Section Iii Subsequent Met Technique

A subsequent met is computed to determine new total corrections. Total corrections determined from a registration will remain valid only as long as the met corrections do not change.

## 11-10. Overview

Whenever a met condition (weather, propellant temperature, projectile weight, or propellant lot) changes, the GFT setting derived from the registration is no longer valid.

Registering every time one of the conditions changes is not feasible. To update registration corrections, a subsequent met can be solved to quantify new met corrections, which are added to the position constants determined from the concurrent met. The result is new total corrections that are used to determine a new GFT setting.

## 11-11. Solution Of A Subsequent Met

Table 11-5 shows a detailed example of the solution of a subsequent met technique. It uses the previously completed concurrent met (Figure 11-27) and assumes the battery and MDP
have not moved.

## Section Iv Subsequent Met Applications

Subsequent met applications include eight-direction met, met to a met check gauge point, met to a target, and met + VE. These are called subsequent met techniques but they do not necessarily require met conditions that were subsequent to a registration nor are position constants required. They are listed under subsequent met techniques because they are used to determine new GFT
settings or new total corrections. These techniques would also be used if the jive requirements for accurate predicted fire were being met or registration corrections were not available. The procedures would be identical to solving a subsequent met technique, with the exception that all position constants would be zero.

## 11-12. Eight-Direction Met

a. Certain combat conditions may require a firing unit to provide accurate artillery support throughout a 6,400-mil zone.

Transfer limits define an area within which total corrections are-assumed to be valid. These transfer limits place a severe limitation on a 6,400-mil firing capability.

Total corrections could be obtained by conducting a registration in each
800-mil sector of the unit's area of responsibility. Such registrations, however, would be costly and would endanger unit survivability. An alternative to registering in each 800-mil sector is the use of the eight-direction met technique.

b. The eight-direction met technique provides corrections to range, deflection, and fuze setting to compensate for the effects of ballistic wind direction and speed and for rotation of the earth throughout the firing unit's area of responsibility. These corrections are combined with the position constants determined in the concurrent met by solving a subsequent met in each 800-mil sector or selected 800-mil sectors. (See Figure 11-32.)
c. Lateral transfer limits can be eliminated for ranges of 10,000 meters or less by solving an eight-direction met. For ranges greater than 10,000 meters, because the lateral transfer limits are valid 4,000 meters left and right of the battery registration point, there will be areas between the 800-mil segments that are not covered by valid corrections. When needed, corrections to cover these areas must be computed by using the met-to-target technique.

d. The eight-direction met technique consists of two steps:
Solution of a concurrent met technique to determine the position VE correction, position deflection correction, and position fuze correction.

Solving for met corrections for other 800-mil segments by use of the met + VE technique and the position constants to determine GFT settings for those octants.

NOTE: The direction of fire will be different for each octant. The value used for altitude of target is the altitude of the registration point. The **FS ~ ADJ EL** will be determined on the basis of the computed adjusted elevation. The eight-direction met technique could be solved without registering. The procedures would be identical to solving a subsequent met technique, with the exception that all position constants would be zero.

## 11-13. Solution Of An Eight-Direction Met Technique

NOTE: This example illustrates how to solve the eight-direction met following the solution of the concurrent met.

a. All known data remain the same as the concurrent met except for the direction of fire.

The direction of fire must be determined for the new octant by applying 800 roils to the original direction of fire.

b. The steps shown in Table 11-6 give a detailed example of the solution of an eight-direction met technique.

## 11-14. Met To A Target

a. Because of the restrictions of transfer limits for the total corrections represented by a GFT setting, there are areas beyond 10,000 meters that are not covered by normal eight-direction met techniques. If a target that requires accurate surprise fires appears in one of the areas, a met to the target is solved. A met to target may also be solved for situations when the unit needs to fire a projectile that they did not register with (for example, M549A1 RAP). Because of the time needed to solve a met to a target, this technique is usually reserved for those situations requiring FFE fires against a "high-payoff" target.

b. The met-to-target technique consists of the two steps below.
(1) Solution of a concurrent met to determine the position VE, position deflection correction, and position fuze correction.

If position constants are not available, use zero for these values.

(2) Solving for met corrections by using the chart range and direction to the target and the position constants to determine a GFT setting. The chart range used is the range to the target. The direction of fire is determined on the basis of the chart direction to the target. The met line number and complementary range are determined from Table B on the basis of the chart range to the target and the height of target above gun.

## 11-15. Solution Of A Met-To-Target Technique

a. Target AB7450 is located outside the octants for which the GFT settings have been determined.

b. All known data remain the same as those for the concurrent met except for the following:
Target AB7450 is located at grid 440240, altitude 1120. Chart deflection to the target is df 4155. Chart range to the target is rg 5630.
c. Table 11-7 shows a detailed example of the solution of a met-to-target technique.

## 11-16. Computing A Gft Setting For An Unregistered Charge

a. When data from a registration and concurrent met are known, the FDC can derive a GFT setting for an unregistered charge.

b. Total corrections for the unregistered charge are determined by applying the position constants determined for the registered charge to the met corrections for the unregistered charge.

This is done by using the following steps:
(1) Determine the range to a met check gauge point on the GFT for the unregistered charge. This will be used as the chart range on the met data correction sheet. The entry range will be the met check gauge point range expressed to the nearest 100 meters. The altitude of the target is the same as the battery altitude.

NOTE: All corrections from the TFT are based on the unregistered charge.

(2) Compute the total deflection correction as follows:
(a) Compute the met deflection correction by use of the met data correction sheet.

(b) Add the position deflection correction determined from the registered
- -
charge to the newly computed met deflection correction for the unregistered charge. The sum is the total deflection-correction for the unregistered charge.

NOTE: The position deflection correction generally accounts for errors in survey and chart construction.

These errors are independent of charge in that they remain constant regardless of the charge fired.

Therefore, it is valid to apply a position deflection correction determined for one charge to other charges.

(3) Compute total range correction and adjusted elevation as follows:
to the MVV to
(a) Add the position velocity error for the registered charge determine the VE.

(b) Add the MVV correction for propellant temperature to the VE to determine the L V for the unregistered charge.

(c) Multiply the L V by the appropriate MV unit correction to determine the L V range correction.

(d) Add the L V range correction to the met range correction for the unregistered charge to determine the total range correction.

(e)  Add the total range correction to the chart range (range to the met check gauge point) to determine the range corresponding to adjusted elevations.

(f)   Set the adjusted range under the MHL of the GFT, and read the adjusted elevation for the unregistered charge.

NOTE: Position velocity errors caused by survey and chart errors are charge independent and, therefore, can be transferred to other charges. Muzzle velocity variations can be transferred to all preferred charges within the same charge group and lot.

(4) Compute the total fuze correction as follows:
(a) Determine the fuze setting corresponding to the adjusted elevation. (b) Compute the met fuze correction. (c)  Add the met fuze correction to the position fuze correction determined for the registered charge. The sum is the total fuze correction. Apply this correction to the fuze setting corresponding the adjusted elevation to determine the adjusted fuze setting for the unregistered charge.

NOTE: The position fuze correction is a constant fuze characteristic. Fuze characteristics are independent of the charge fired. The position fuze correction is similar to a known fuze setting correction, which is determined historically by observing the performance of a particular lot of fuzes.

(5) Compute the GFT deflection correction by subtracting the drift correction corresponding to the adjusted elevation for the unregistered charge from the total deflection correction. The remainder is the GFT deflection correction for the unregistered charge.

## 11-17. Met To Met Check Gauge Point

a. The one-plot GFT setting determined by registering has limited range transfer limits.

A more accurate GFT setting can be determined by using the data from a registration and one or more met + VE computations to met check gauge points. Solution of a met to met check gauge point using subsequent met techniques will yield total corrections at each met check gauge point range. The met check gauge points selected should be the ones farthest away, in range, from the registration chart range.

b. The met to met check gauge point technique consists of the following steps:
Solution of a concurrent met to determine the position VE, position deflection
correction, and position fuze correction.
Solving for met corrections to the selected met check gauge points and adding the position constants to determine GFT settings for these ranges. The chart ranges will be the ranges to the selected met check gauge points and the line number of the met message will be determined on the basis of that range and a height of target above gun of O. The altitude of target used will be the same as the battery altitude.

c. Combine the data from the registration and the met(s) to met check gauge points to determine a two-plot or multiplot GFT setting.

## 11-18. Met + Ve

a. Registrations may not always be practical or necessary on the basis of the current situation and the factors of METT-T. If a battery is meeting the five requirements for accurate predicted fire (less accurate target location), there is still a need to improve the data read from the GFT. A GFT setting can be determined by solving a subsequent met by using the met + VE technique. The steps for working a met+ VE are similar to the subsequent met technique. Since no registration has been conducted and position constants were not isolated, position constants are not considered (use zero for these values).

b. For accuracy, the chart ranges used for the met+ VE technique should correspond to met check gauge points, unless the met-to-target technique is being used. The altitude of target will be the same as the battery altitude unless the met-to-target technique is used.

c. The direction of fire will correspond to the chart direction to the center of the zone of
responsibility or the target.

d. The values for position deflection correction, position velocity error, and position fuze setting will be recorded as zeros (0).

## Chapter 12 Terrain Gun Position Corrections And Special Corrections

To enhance survivability on the battlefield a unit must take maximum advantage of the natural cover and concealment offered by the terrain and vegetation (Figure 12-1). When pieces are so positioned corrections may be required to obtain an acceptable burst pattern (sheaf) in the target area.

These corrections compensate for the differences in muzzle velocity between pieces and terrain positioning of the weapons. When FFE rounds impact in the target area. the results, to a large extent, depend on how well the sheaf fits the size and shape of the target.

## Section I Types Of Corrections

Artillery fires can be computed to fit the size and shape of the target by computing corrections for the following:
Individual piece displacements (position corrections). Shooting strength of each piece (muzzle velocity corrections). Target size, shape, and attitude (irregularly shaped targets).

## 12-1. Overview

a. Terrain gun position corrections (TGPCs) are individual piece corrections applied to the gunner's aid on the panoramic telescope (pantel), the correction counter on the range quadrant, and the fuze setting of each piece.

b. Special corrections are individual piece corrections applied to fuze settings, deflection, and quadrant elevation to place the FFE bursts in a **precise** pattern on the target.

c. Special corrections and TGPCs include corrections for the location of each weapon in the firing unit area (position corrections) and for the shooting strength of each weapon (muzzle velocity corrections).

(1) The goal of TGPCs is to compute corrections to obtain an acceptable sheaf in the target area.

(2) The goal of special corrections is to compute aimpoints tailored to fit the target size, shape, and attitude.

## 12-2. Piece Displacement

a. To determine position corrections, the relative position of pieces in the firing unit area must be known (piece displacement). Piece displacement is the number of meters the piece is forward or behind and right or left of the base piece. It is measured on lines parallel (forward or behind) and perpendicular to (right or left) the azimuth of fire. (See Figure 12-2.)
b. Piece displacement (Figure 12-2) can be determined by estimation and/or pacing, by hasty traverse, or by survey. Usually, estimation and pacing are not accurate enough for the large displacement distances involved in firing unit positions. The hasty traverse technique is a quick, accurate means of determining piece displacement by using the M10 or M17 plotting board. The survey technique provides grid coordinates for each weapon location.

(1) Estimation is the least desirable method to determine piece displacement. Using this technique, the XO or platoon leader estimates the displacement of the pieces from the base piece both parallel and perpendicular to the azimuth of lay. The pacing technique is fairly accurate in small open areas, but it is time consuming.

The XO or platoon leader uses this technique to determine displacement by pacing from the base piece both parallel and perpendicular to the azimuth of lay.

(2) The hasty traverse technique is a graphic solution of piece displacement that uses the M10 or M17 plotting board. The advance party provides the FDC with the initial lay deflection, distance and vertical angle to each howitzer position from the aiming circle (AC).

(3) The survey method is the most accurate method. Field artillery survey crews provide a surveyed grid and altitude to each weapon position. Piece displacement is computed by determining the difference between the grid coordinates from the base piece to each weapon position.

## 12-3. Sheafs

a. A target is covered by fire through controlling the pattern of bursts (sheaf) on the target.

b. When firing a parallel sheaf, the rounds impact at the target in generally the same pattern formed by the howitzers in the firing unit area. The width and depth of the unit's sheaf are always measured on a line perpendicular to the line of fire. As the line of fire changes, so does the width and depth of the unit's sheaf. (See Figure 12-3.)
c. A parallel sheaf does not require TGPCs or special corrections. All weapons fire the same deflection and quadrant.

d. There are three basic types of sheafs that may be obtained with TGPCs and special corrections.

(1) Converged sheaf. All weapons have the same aimpoint.

(2) Open sheaf. Aimpoints are separated by one effective burst width. Figure 12-4
shows sheaf widths for an open sheaf. The open sheaf width equals the number of howitzers multiplied by the projectile effective burst width. See Figure 12-5 for burst widths.

NOTE: For manual computations of TGPCs and special corrections with an M17
plotting board, a width of 30 meters is used for the 105-mm howitzer for ease of computation.

(3) Special sheafs.

Special sheafs are sheafs other than parallel, converged, or open.

(a) Linear. The sheaf is described by a length, and attitude or by two grids.

Aimpoints are evenly distributed along the length of the sheaf along the attitude specified.

(b) Rectangular. The sheaf is described by a length, width, and attitude.

Aimpoints are evenly distributed along two lines equal to the length and parallel to the attitude specified.

(c) Circular. The sheaf is described by a grid and a radius. Aimpoints are evenly distributed on a concentric circle half the radius specified.

(d) Irregular. The sheaf is described by a series of grids. Aimpoints are evenly distributed along the length of the sheaf.

## Section Ii The M17/M10 Plotting Board

The M17 and M10 plotting boards are versatile pieces of the fire direction set. The M17 and M10 plotting boards are similar and used to determine TGPCs and special corrections. The differences are as follows:
The M17 has a snap-type pivot in the center; the M10 uses a small screw. The M17 has a map scale graduated in metric measure; the M10 scale is graduated in both meters and yards.

NOTE: In further discussions, the term "M17" will refer to the M17 and M10  plotting boards.

## 12-4. Description

The M17 plotting board consists of two parts--the gridded base and the clear disk.

a. The gridded base is a white plastic board. The center area of the board is a circular The grid pattern divides the target area into squares. The at the discretion of the user, but most common scales for gridded area called the target area.

scale assigned to the grid pattern is various operations are as follows:

SCALE
OPERATION
1 Square
= 10 meters
1 Square
= 10 meters
1 Square
= 100 meters
1 Square
= 100 meters
Terrain Gun Position Correction Special Corrections
Laser Adjustment of Fire
Target Location

b. A red arrow is printed from the bottom to the top of the target area. This arrow represents the direction of fire. The arrow points to a vernier scale. The center graduation forms the vernier index, which is used to determine direction from the scales on the clear disk. The vernier scale may be used to determine directions to an accuracy of 1 mil. Along the top edge of the plotting board is a measuring scale graduated in millimeters. On the bottom is a scale in meters. On the right side there is a scale in inches.

c. The clear disk is a transparent circular plastic board that snaps or screws into a center pivot on the gridded base. A single black line is engraved in the clear disk, This line represents the 0-3200 line when weapons are plotted.

d. The edge of the disk is engraved with scales that are graduated every 10 mils. The outermost scale is a black numbered scale (the outer black scale). The scale is numbered every
100 mils starting at 0 and ending at 63. The outer black scale is used to represent azimuth and lay deflection. Immediately inside the outer black scale is a red numbered scale (the red scale).

This scale is numbered every 100 mils from 0 to 32. Past the 32 graduation the numbering continues from 1 to 5. This scale is used to orient the disk on chart deflection. The innermost scale is a black numbered scale (the inner black scale). This scale is numbered every 100 mils from 0 to 3200 and is used to orient the disk for lay deflection for the M12-series pantel when lay deflection is measured from the line of fire.

e. The screw or rivet secures the disk to the base and maybe used to represent one of the following:
Base piece. Target. Observer location. Location of the last burst.

NOTE: In the following sample problems, the Ml 7 plotting board is viewed with the curved edge to the operator's left and the description "top of the plotting board"
refers to the side of the plotting board with the vernier scale.

## 12-5. Plotting Piece Locations For Weapons Equipped With The M100-Series Sight

a. The following is an example of the platoon leader's report for the M100-series sight:

HOWITZER
LAID FROM
LAY DEFLECTION
DISTANCE
VA
1
AC
2595
105
+3
2
AC
2910
55
+1
3 (BP)
AC
3405
90
-2
4
AC
3950
100
-5

NOTE: Howitzer Number 3 is the base piece. The azimuth of lay is 4,800 mils.

the steps required to plot piece locations for weapons equipped b. Table 12-1 shows with the M100-series sight.

NOTE: The following data are an example of piece displacement as shown in step 6.

HOWITZER
LATERAL DISPLACEMENT
RANGE DISPLACEMENT
1
R75
0
2
R35
+35
3
0
0
4
L50
+15

## 12-6. Plotting Piece Locations For Weapons Equipped With The M12-Series Sight

a. The M12-series sight is capable of determining deflection to a maximum value of 3,200
mils. The sight is graduated from 1 to 3200 twice to form a full circle. Consequently, every deflection has a "back deflection" of equal value in the opposite direction. This arrangement is indicated on the plotting board by the inner black scale. This scale is a lay deflection scale graduated from 0 to 3200.

Care must be taken when setting up the plotting board to prevent the use of the wrong scale and thereby creating a **"mirror image"** of the battery. The use of the scales is dictated by the location of the howitzers in relationship to the position of the aiming circle. In the XO's report, the XO must indicate whether each piece is to the **left or right** of the aiming circle in respect to the azimuth of lay.

If the lay deflection for a howitzer is exactly 3200, the XO's report must indicate whether that piece is forward (down range) or behind (the aiming circle is down range) in comparison to the aiming circle. The rules for the use of the scales areas follows:
(1) If the piece is left of the 0-3200 line as viewed from the aiming circle, use the inner black scale.

(2) If the piece is right of the 0-3200 line as viewed from the aiming circle, use the outer black scale.

(3) If the piece is on the 0-3200 line (lay deflection 3200) and behind as viewed from the aiming circle, use the inner black scale,
(4) If the piece is on the 0-3200 line (lay deflection 3200) and forward as viewed from the aiming circle, use the outer black scale.

b. For ease in determining whether a piece is left or right and forward or back, the XO
need only realize that if the piece is laid using the red graduations on the aiming circle it is to the left or forward of the aiming circle as you face the azimuth of fire.

c. A simple alternative to the use of these rules is to have the XO report all lay deflections as they would be determined by using values read from the black numbered graduations of the aiming circle. It is recommended that this method be unit SOP in an attempt to avoid confusion with the plotting board.

d. The plotting of the pieces and establishment of an azimuth index are done by using the same procedures as described for the M100-series sight.

e. Piece displacement is determined by using the same procedures as described for the M100-series sight.

f. The following is an example of the platoon leader's report for the M12-series sight:

| HOWITZER       |   LAID FROM |
|----------------|-------------|
| LAY DEFLECTION |             |
| DISTANCE       |             |
| VA             |             |
| 1              |             |
| AC             |        2595 |
| +3             |             |
| 2              |             |
| AC             |        2910 |
| 55             |             |
| +1             |             |
| 3 (BP)         |             |
| AC             |             |
| 0205           |          90 |
| -2             |             |
| 4              |             |
| AC             |             |
| 0750           |             |
| 100            |             |
| -5             |             |

NOTE: Howitzers 3 and 4 are left of the aiming circle. Azimuth of lay (AOL) equals
4800.

g. Use the steps in Table 12-2 to plot piece locations for weapons equipped with the M12-series sight.

## 12-7. Determination Of Base Piece Grid Coordinates

After the pieces have been plotted on the M17, the **base piece grid** can be determined by using the steps in Table 12-3.

NOTE: The grid determined can be used to plot the base piece on the firing chart.

## Section Iii Terrain Gun Position Corrections

Terrain gun position corrections are the precomputed corrections carried on the howitzers to compensate for terrain positioning and muzzle velocity differences to achieve acceptable results in the target area. TGPCs should be computed each time the firing unit occupies a position. The use of TGPCs will allow the unit to effectively engage targets whose size and orientation requires a sheaf other than a parallel sheaf.

## 12-8. Transfer Limits And Sectors Of Fire

a. Terrain gun position corrections are most accurate at the range and direction for which they are computed. They are considered valid 2,000 meters over and short of the center range and 400 mils right and left of the center azimuth of the sector. (See Figure 12-9.)
b. Terrain gun position corrections will provide an acceptable effect on the target provided the firing unit's position is within a box 400 meters wide and 200 meters deep. This box is centered over the firing unit center and oriented perpendicular to the azimuth of lay. If the firing unit is spread out more than 400 meters by 200 meters, a degradation in effectiveness of sheafs can be expected as fires are shifted throughout the sector for which they were computed.

c. If a firing unit's area of responsibility covers an area larger than the TGPC transfer limits, the unit should compute TGPCs for other sectors. Ranges to the centers of the other sectors may be different.

Overlapping sectors for different charges may be necessary. (See Figure 12-10.)

## 12-9. Fire Order And Fire Commands

a. The FDO must establish a fire order SOP that indicates the corrections for the primary sector are standard. This is done in the special instructions section of the fire order SOP.

b. Fire command standards should direct that the primary TGPCs sector is used unless otherwise specified. The **special instructions** block of the fire commands will indicate which TGPC sector will be used for a mission if other than the primary sector. The absence of any instructions in the initial fire commands indicates that corrections for the primary sector will be fired. The command **LEFT (RIGHT) SECTOR** in the special instructions block of the initial fire commands indicates that the corrections for the left (right) sector are to be set on the howitzers. The command **CANCEL TERRAIN GUN POSITION CORRECTIONS** indicates that all TGPCs are to be zeroed for the mission. After end of mission is announced, the primary sector TGPCs are reapplied to the howitzers.

## 12-10. Determination Of Terrain Gun Position Corrections

a. It is recommended that TGPCs be computed for a converged sheaf. This will generally provide an acceptable sheaf within the transfer limits. TGPCs can be computed by using other sheafs, but the dispersion of bursts can be expected to increase as the target range varies from the range to the center of the sector.

It is preferred that base piece carry no corrections. To do otherwise causes the base piece to "zero" the corrections on adjustment and reapply them during fire for effect, which may lead to error. Therefore, the aimpoint of the base piece should be the center pivot when computing TGPCs.

NOTE: DA Form 4757 (Registration/Special Corrections Work Sheet) is completed regardless of the sheaf used. Before computing any TGPCs, plot the howitzers on the M17.

b. Table 12-4 lists the steps for determining TGPCs and completing DA Form 4757.

c. The note on the bottom of DA Form 4757 lets you know to use the chart range to target wherever there is an * displayed.

d. The steps in Table 12-5 are used to determine TGPCs for all sheafs.

NOTE: Step 1 will be different for each type of sheaf. **Steps 2 through 17** are common to all sheafs.

## 12-11. Hasty Terrain Gun Position Corrections

a. Even with well-trained FDC personnel, computing TGPCs is time-consuming.

this, hasty TGPCs must be determined and used until hasty solution, piece displacement is estimated and fuze Corrections are required for firing shortly after occupation of a position. If the advance party has determined displacement and computed TGPCs, corrections will be available immediately. If the advance party has not been able to do accurate TGPCs are computed. For the corrections are ignored.

are designed to provide a converged sheaf at the center b. Hasty TGPCs computations range of the TGPCs sector.

c. Tables 12-8 through 12-13 show data for hasty TGPCs and special corrections. The data presented in these tables are:
Range in 1,000-meter increments.

Charge most likely to be fired at the listed range.

Deflection correction, in mils, to compensate for lateral piece displacement. These values have been determined to the nearest mil with the GST for each 20
meters of lateral displacement (20 to 200 meters). Position range correction, in mils, to compensate for piece displacement in range. QE corrections to the nearest mil for each 20 meters of front or rear displacement
(20 to 100 meters) were computed by using the range change per mil for the listed ranges. MV correction in mils to compensate for the difference in shooting strengths (battery comparative VEs).

MV corrections were determined by using the following formula.

NOTE: MVUCF is the muzzle velocity unit correction factor from the TFT, Table F, Columns 10 and 11.

## 12-12. Determination Of Hasty Tgpcs

Table 12-6 gives the procedures for determining hasty TGPCs, and Table 12-7 gives the procedures for completing DA Form 4757. Figure 12-11 shows recorded hasty TGPCs.

## Section Iv Special Corrections

The corrections determined by using TGPCs are valid only within the specified transfer limits and produce the sheaf for which they were computed. If a target falls outside the transfer limits or is irregularly shaped, it is necessary to compute special corrections.

## 12-13. Definitions And Use

Special corrections are individual piece corrections applied to time, deflection, and quadrant elevation to place FFE bursts in precise location on a target. Special corrections are used for:

Individual piece locations (position correction).
Shooting strength of each piece (calculated correction).
Target shape and size.
Knowing when to compute special corrections is as important as knowing how to a.

compute them. Some factors that influence the use of special corrections are:

Time available for computation. Target size, shape, and proximity to friendly troops. Accuracy of target location.
b. Special corrections should be applied when and where they will increase the effectiveness of fires on the target. Because of the time required for computation, they are used only for FFE missions.

c. The special corrections are computed in a similar manner to TGPCs, the major difference being the plotting of the target. The following types of sheafs may be computed:

Converged sheaf.
A target described by grid, length, and attitude.
A target described by two grids. A target described by three or more grids. A circular target.

## 12-14. Computation Of Special Corrections

Table 12-13 provides the steps and procedures for the computation of special corrections.

## Section Iv Use Of Plotting Board For Fire Mission Processing

When the use of a firing chart is not possible, the M10 or M17 plotting board and GFT or TFT may be used to compute firing data. The observer transmits the call for fire to the firing unit and describes the target location by using any of the methods of target location.

## 12-15. M17 Plotting Board

The steps in Table 12-14 are used to process fire missions with the Ml 7 plotting board.

See Figure 12-12 for the Ml 7 format for processing fire missions.

## 12-16. Determination Of Subsequent Corrections For A Laser Adjust-Fire Mission

Table 12-15 shows the steps and procedures to determine subsequent corrections for a laser adjust-fire mission.

## 12-17. Examples Of Tgpcs

a. The following is an example of the platoon leader's report for the Ml00-series sight:

HOWITZER
LAID FROM
LAY DEFLECTION
DISTANCE
VA
1
AC
2595
105
+3
2
AC
2910
55
+1
3 (BP)
AC
3405
90
-2
4
AC
3950
100
-5

NOTE: Howitzer Number 3 is the base piece.

b. The following is an example of piece displacement.

| HOWITZER           | LATERAL DISPLACEMENT   |
|--------------------|------------------------|
| RANGE DISPLACEMENT |                        |
| 1                  | R75                    |
| 0                  |                        |
| 2                  | R35                    |
| +35                |                        |
| 3                  | 0                      |
| 4                  | L50                    |
| +15                |                        |

c. A completed DA Form 4757 for each sheaf (converged, open, and circular)
containing TGPCs using the data listed above are shown in Figures 12-13 through 12-15.

## 12-18. Examples Of Special Corrections

a. Using the data listed below, determine special corrections for a linear target described by a grid, length, and attitude.

## Given:

(1) Example of the platoon leader's report for the M1OO-series sight:

| HOWITZER   |   LAID FROM |   LAY DEFLECTION |
|------------|-------------|------------------|
| VA         |             |                  |
| 1          |             |                  |
| AC         |        2595 |                  |
| 105        |             |                  |
| +3         |             |                  |
| 2          |             |                  |
| AC         |        2910 |                  |
| 55         |             |                  |
| +1         |             |                  |
| 3 (BP)     |             |                  |
| AC         |        3405 |                  |
| 90         |             |                  |
| -2         |             |                  |
| 4          |             |                  |
| AC         |        3950 |              100 |
| -5         |             |                  |

NOTE: Howitzer Number 3 is the base piece.

(2) Example of piece displacement.

HOWITZER
LATERAL DISPLACEMENT
RANGE DISPLACEMENT
1
R75
0
2
R35
+35
3
0
0
4
L50
+15

Target Grid: 432275
(3)
Length: 300 M
(4)
Attitude: 1,300
(5) (6) (7)
Chart data to the center grid: Chart range 4260 Chart deflection 3452
(8)
b. A completed DA Form 4757 for the special corrections and the Ml7 plotting board are shown in Figures 12-16 through 12-18.

c. Using the data listed below, determine special corrections for a linear target described by two grids.

## Given:

(1) Example of the platoon leader's report for the M1OO-series sight:
HOWITZER
LAID FROM
LAY DEFLECTION
DISTANCE
VA
1
AC
2595
105
+3
2
AC
2910
55
+1
3 (BP)
AC
3405
90
-2
4
AC
3950
100
-5

NOTE: Howitzer Number 3 is the base piece.

(2) Example of piece displacement.
HOWITZER
LATERAL DISPLACEMENT
RANGE DISPLACEMENT
1
R75
0
2
R35
+35
3
0
0
4
L50
+15

(3) Target Grids: 424275 and 427273

(4)
(5)
(6) Center Grid:
(7) Target Length: 360
(8)
(9) Chart data to the center grid: Chart range 4920 Chart deflection 3438
d. A completed DA Form 4757 for the special corrections and the Ml 7 plotting board are shown in Figures 12-19 through 12-22.

## Chapter 13 Special Munitions

This chapter describes procedures for special munition employment. Appendix H
provides further information on special mission processing.

## Section I Copperhead

The cannon-launched guided projectile (CLGP) M712 (Copperhead) is a
155-mm, separate-loading, laser-guided HE projectile. It is heavier (137.6
pounds) and longer (54 inches) than the standard 155-mm projectile. The A4712
projectile consists of three main sections: a guidance section (forward), warhead section (center), and control section (rear). The guidance section contains the seeker head assembly and the electronics assembly. The nose of the projectile houses a laser seeker in a plastic cone. The warhead section contains an HE
antitank warhead consisting of 14.75 pounds of composition B. The control section includes the fins and wings that deploy
- in flight and allow the round limited maneuverability.

## 13-1. Description

a. The Copperhead projectile is shipped and stored in a sealed container. The projectile requires no assembly or testing at the firing site.

b. The FDC can compute firing data for shell Copperhead by using either a shaped trajectory or a ballistic trajectory.

NOTE: The shaped trajectory is based on a revised targeting logic that was first introduced with FT 155-AS-0 (Rev 1) and continued with FT 155-AS-1. The change essentially results in firing higher charges at lower quadrant elevations, resulting in flatter trajectories. This was done to maximize the employment of Copperhead projectiles under low cloud ceilings. Many of the tables in FT 155-AS-1 refer to ballistic or "glide" mode (for example, Table F). In this current FT, the terms glide and *shaped* are used synonymously, even though they are different trajectories. A
true glide mode is only achieved when computing data by using FT 155-AS-0.

However, this method is **not recommended** because it will produce poor results under low cloud ceilings.

(1) The trajectory of the Copperhead projectile is similar to that of a conventional round. Only when the projectile reaches a point on the descending branch of the trajectory does it differ. At that point, on the basis of the two-digit timer setting included in the fire commands, the guidance and control systems are activated. This enables the projectile to alter the remainder of its trajectory.

(2) At 20 seconds from impact, the FDC cues the laser designator operator, who begins designating the target. The ground laser operator may use a G/VLLD, a laser target designator (LTD), or modular universal laser equipment (MULE). Airborne systems include the AH-64, OH-58D, and unmanned aerial vehicles. The Copperhead projectile acquires the reflected laser energy and initiates internal guidance and control, allowing it to maneuver to the target. If the time of flight of the projectile is less than 20 seconds, the FDC will inform the observer to designate the target concurrent with the shot message (that is, LASER ON, SHOT, OVER).

c. The ground surface area in which the round can maneuver is limited. The optimum limits of maneuverability of the Copperhead round is called a footprint
(Figure 13-l). The size of the footprint is determined by the GT range and the shape of the trajectory, but it can also be affected by cloud height. The ballistic aimpoint is on the GT line, usually short of the target location sent by the laser designator operator.

The distance that the ballistic aimpoint is short of the target location varies and is called the offset correction. This offset distance is used to ensure that the maximum probability of hit occurs at the original target location sent by the observer. The larger the target location error, the lower the probability of hitting the target.

d. Copperhead missions, like conventional missions, can be fired on either planned targets or targets of opportunity. Planned targets are priority targets or on-call targets.

(1) Because of its relatively short response time, the Copperhead planned target is the preferred method for employing Copperhead. Unless otherwise specified on the target list, two Copperhead rounds are prepared in advance for each Copperhead priority target.

DA Form 5711-R (Copperhead Planned Target List Work Sheet) may be used to quickly update data for planned Copperhead targets. These data can then be transferred to DA Form 4504 when the mission is fired. Figure 13-2 shows an example Copperhead planned target list work sheet.

NOTE: A reproducible copy of DA Form 571 I-R is provided at the back of this publication.

(2) On-call target procedures for Copperhead are the same as those for conventional on-call missions.

NOTE: FDC personnel must ensure that at least two howitzers and two Copperhead rounds are prepared for any mission. This action increases firing unit responsiveness if a round or howitzer malfunctions. The criteria in Table 13-1 are used for all Copperhead missions.

## 13-2. Computations For Shell Copperhead

a. When a target list is received from the battalion FDC, Copperhead priority targets are **processed first.** Battery or platoon FDC personnel must know how to use the Copperhead footprint templates and must be aware of the maximum 800-mil angle T requirement. Priority target firing data usually are sent to two adjacent howitzers. The FDC transmits the message to observer and informs the observer when the unit is prepared to fire the priority target. Response time is excessive if the Copperhead rounds and the howitzers are not prepared in advance. Firing data for the rest of the targets on the target list are then computed and recorded by target number in the FDC.

b. As the situation changes, recomputation may be required and is done by the FDC.

## 13-3. Copperhead Sop

a. Unit SOPs dealing with Copperhead (Cphd) missions are helpful in rapidly disseminating mission-essential information with a minimum of discussion. When used with extensive training, a unit SOP can result in more responsive fires.

(1) An observer requesting Copperhead fires on planned targets and targets of opportunity will send a call for fire to the battery or platoon FDC over an established fire net.

(2) The standard target list is used to initiate a planned target. (3) To fire on a planned target, the observer transmits a call for fire that includes the following elements:
(4) To enhance mission responsiveness when engaging priority targets, the observer may omit the target description, method of engagement, and method of control; for example, T46
THIS IS T18, FIRE TARGET AB2213, OVER.

(5) If the number of rounds to be fired is not specified in the call for fire, the FDC
will fire the number of rounds specified for that target on the Copperhead target list. If the number of rounds is not specified on the target list, the FDC will fire one round at the target and direct the howitzer(s) to prepare, but **DO NOT LOAD,** a second round. The MTO will reflect 1
round.

(6) When the observer requests **AT MY COMMAND,** the Copperhead rounds will be freed at intervals of at least 30 seconds when the observer gives the initial command to fire.

When **BY ROUND AT MY COMMAND** is requested, the observer will control the firing of each Copperhead round. The observer must understand this and act accordingly so as not to waste rounds.

b. For targets of opportunity, the call for fire includes the following elements:
NOTE: For a target of opportunity, the call for fire must specify Copperhead.

## 13-4. Message To Observer

After a call for fire is processed, an MTO is sent as soon as possible before firing.

a.
The MTO for Copperhead missions includes the following elements:
b.
c. For a Copperhead mission to be successful, the three-digit pulse repetition frequency
(PRF) code set on the Copperhead round must match the PRF code set on the observer's designator. The FDC should have a list of all observer PRF codes by call sign. The FDC selects the proper PRF code on the basis of the identification of the observer sending the call for fire. The PRF code is then sent to the howitzers in the fire commands and is placed on the Copperhead round. The observer verifies the PRF code announced in the MTO.

## 13-5. Fire Order

The elements established as standard are not addressed unless a change in the standard is desired. Two howitzers will support a given Copperhead fire mission.

## 13-6. Computation Of Firing Data

NOTE: FT 155-AS-1 is used to compute firing data for Copperhead. There are no GFTs for FT 155-AS-1. FT 155-AS-1 supersedes FT 155-AS-0 (Rev 1) firing tables.

a. Initial Chart Data. The computation of firing data for Copperhead begins with the determination of chart data. This applies to both planned targets (target locations taken from the Copperhead target list) and targets of opportunity (target location provided in the call for fire).

The initial chart data required for Copperhead missions is chart range, chart deflection, and angle T. Chart data are determined and announced by the HCO.

b. Trajectory and Charge Selection. Given the chart range to the target, observer visibility, and target cloud height, the FDO enters the Copperhead charge selection table in the Copperhead TFT. Determine the charge to fire by entering the table with the visibility followed by cloud height. Identify the range interval that includes the chart range. To determine the visibility and cloud height to use, see the table on page xxx in the introduction of the TFT. For example, for an Ml09A3 unit with nominal visibility, cloud height of 900, and chart range of 6300, the unit would use the ballistic mode and fire charge 6 white bag.

c. Computations. Met corrections have a large impact on the Copperhead projectile;
therefore, firing data should not be determined without compensating for nonstandard conditions.

(1) Priority or planned targets. Firing data for planned targets is based on the solving of a met to target with the AS-1 TFT.

(2) Targets of opportunity. Because of the decreased response time for targets of opportunity, solving a met to a target is not practical. The following procedures can be used to determine firing data for targets of opportunity.

(a) FDO selects charge(s) to cover area of operations. FDO must also consider expected visibility and cloud height.

(b) Solve a met + VE for selected charge(s) by using the center range of the range interval for the charge(s).

(c) Use the total range correction determined as a "range K" to be applied to other missions with that charge.

(d) When the observer requests a Copperhead target of opportunity, apply the range K to the chart range to determine the entry argument for Table F, Column 1.

(3) Manual met to target. The following guidelines apply when a met to target for Copperhead is solved manually:
(a) Use a position deflection correction of zero. (b) Use MVV calibration data determined from the M90 velocimeter and corrected for nonstandard conditions as the velocity error.

NOTE: In most situations, an MVV for shell Copperhead will be unavailable. The loss in muzzle velocity due to tube erosion (as determined from a recent pullover gauge reading and/or from EFC rounds) can be used as the position VE. Be sure to use the AS-1 TFT to determine an estimated loss in MV base on the current pullover gauge reading.

Refer to Chapter 4 for further information on predictive MVV techniques.

(c) No fuze setting correction is determined.

## 13-7. Angle T And Target Cloud Height Checks

a. The FDO makes the angle T check by listening to the announced angle T and determining if it meets the angle T requirement for Copperhead (800 mils or less). Copperhead should not be fired when the angle T is greater than 800 mils. An angle T of this magnitude may seriously degrade the ability of the round to successfully acquire and engage its intended target.

The FDO should also check the observer location to ensure he is not located "long" along the GT
line. If this were the situation, the Copperhead projectile may not be able to seek the reflected laser energy.

b. Depending on the method used to locate the target, the target cloud height can be computed in one of two ways.

(1) If the target is located by grid coordinates, subtract the OT VI from the observer cloud height to determine the target cloud height.

(2) If the target is located by laser polar plot, as targets of opportunity nomally are, compute the target cloud height as follows: First, use the OT distance and the VA reportedly the observer to compute the OT VI with the C and D scales of the GST. Then subtract the OT VI
from the observer cloud height to determine the target cloud height.

c. The VCO computes the target cloud height and reports it to the FDO. The FDO
enters the table with the target cloud height to determine the cloud ceiling.

d. An OT vertical interval of less than 30 meters can be ignored for targets of opportunity. In such cases, target cloud height equals observer cloud height.

e. Insufficient target cloud height will adversely affect the accuracy of the Copperhead round.

## 13-8. Trajectories

a. The Copperhead projectile travels in a trajectory determined by the switch setting applied. The trajectory used is dependent on the chart range to the target observer visibility, and target cloud height. The targeting logic used in the FT 155-AS-1 allows the FDC to select from one of two trajectories--ballistic or shaped.

b. The ballistic trajectory has a greater angle of fall, resulting in greater target area effects. In the ballistic mode, the projectile travels in a ballistic trajectory. This trajectory is only affected near the end of the descending branch when the projectile acquires and homes in on the reflected laser energy.

If the projectile fails to acquire the designator, the projectile would continue to follow the ballistic trajectory to the ballistic aimpoint. The ballistic aimpoint is the point to which the fining data are computed, usually offset along the GT line by 0 to 500 meters.

c. The angle of fall generated by the ballistic solution is so steep as to limit the time that the projectile has, after exiting the cloud cover, to acquire the laser energy. The shaped trajectory allows the projectile to approach the target at a shallow angle and thus stay below cloud cover.

The projectile may be caused to glide at a constant angle in the descending branch of the trajectory, allowing longer exposure of the projectile to the reflected laser energy and thereby enhancing acquisition probability. (See Figure 13-3.)

## 13-9. Switch Setting

The Copperhead switch setting consists of five digits. (See Figure 13-4.) The first two numbers are the time setting determined by the FDC. The first digit programs the projectile for a specific trajectory. A first digit of 1 or 2 results in a ballistic trajectory, while a first digit of 3
through 8 results in a shaped trajectory. The second digit programs a time delay based on the duration of flight and type of trajectory. The program delay digits of 1 through 8 will result in a delay of 0 to 45 seconds for the ballistic mode and 0 to 48 seconds for the shaped trajectory.

After the time delay has expired, the main portion of the battery will activate, providing power to the electronic circuits and deploying the wings. The last three digits are the PRF code for the G/VLLD or MULE operator. This setting establishes a common laser frequency between the projectile and the G/VLLD or MULE.

## 13-10. Computing Site

The VCO manually computes site for Copperhead by using the ballistic aimpoint.

## 13-11. Computing Deflection Correction

The Copperhead round has no correction for drift. Therefore, the total deflection correction equals the GFT deflection correction and is applied without modification throughout that charge and mode.

## 13-12. Limits Of The Base Piece Solution

a. Firing data for Copperhead is initially computed from the base piece location. If the center of the two howitzers firing the Copperhead mission is within 100 meters of the base piece, the firing data computed at the base piece may be used. If the two howitzers are located father than 100 meters from the base piece, deflection and elevation corrections from the two-howitzer subelement should be computed and applied to the base piece solution.

b. When time for computing data is limited, as is normally the case for targets of opportunity, and the two howitzers are located further than 100 meters from the base piece, the FDC should compute at least a deflection correction. The Copperhead round can compensate for errors in range easier than it can for errors in deflection.

## 13-13. Target Attack Contingencies

a. If the Copperhead round cannot be fired on a target because of insufficient target cloud height, the FDC must inform the observer requesting the mission. Coordination between the observer and the FDC can then be made to fire other types of munitions on the target.

b. If the Copperhead round cannot be fired on a target because the angle T is greater than 800 mils, the battery or platoon FDC should contact the battalion FDC to see if the mission can be taken by another unit having an angle T of 800 mils or less. If another unit is available, the original battery or platoon FDC tells the observer to contact the FDC of the unit taking the mission. If no other units are available, the observer and the FDC can coordinate to fire other types of munitions on the target.

c. The steps in Table 13-2 are used to determine firing data for planned targets.

NOTE: Receipt of the CopperheadMTO by the observer indicates that the unit is ready to fire.

The steps in Table 13-3 are used to process a Copperhead mission with a record of d.

fire.

NOTE: Figures 13-5 through 13-7 show a completed Copperhead fire mission using the 155-AS-1 TFT. The Met + VE Worksheet (DA Form 7352-R) is a new reproducible form located at the back of this book.

## Section  Ii Rocket-Assistedprojectile

Rocket-assisted projectiles are available for the 105-mm and 155-mm howitzers. They are designed to extend the range of the howitzers. The basic rocket-assisted projectiles are filled with HE material. They produce blast and fragmentation in the target area. Computation procedures for the two basic HE
RAPs are identical. Firing tables are available for the rocket on mode only.

## 13-15. Description

a. The 105-mm RAPs are the M548 and M913. The 155-mm projectiles are the M549
and M549A1. For the Ml 09A2/A3 weapons, these projectiles are fired with charges 7 (M4A2),
8 (Ml 19A1), and 7 (Ml 19A2). The M198 howitzers may use charges 7 (M4A2), 8 (Ml 19A1), 7
(Ml 19A2), and 8S (M203 only for the M549A1 projectile).

b. Rocket-assisted projectiles should always be fired by using current GFT settings because most RAP missions are expected to be FFE missions. The multiplot GFT setting is recommended for use with RAP. When no RAP registration data are available, a met-to-target technique should be solved by using MV data, propellant temperature, and rocket motor temperature (assumed to be the same as the propellant temperature).

## 13-16. Manual Computations

a. Procedures for computing HE RAP firing data are identical to those for conventional HE
rounds. The RAP GFTs and GSTs are similar to and are read in the same way as those for conventional HE rounds with two exceptions. The 155-mmM549A1 GFT has no fuze setting scale.

b. Table 13-4 shows the steps for determining firing data for the RAP.

NOTE: Figures 13-8 through 13-10 show a completed RAP fire mission. An Ml 09A3 howitzer, propellant Ml 19AI, and TFT 155-AO-0 were used.

I

## 13-17. Registration And Determining A Gft Setting

a. Units most likely will not register with the rocket-assisted projectile. An inferred GFT setting can be computed without registration data. Use a subsequent met technique such as met + VE, met to target, or met to met-check gauge point. Assume position constants are zero.

As time allows, compute a multiplot GFT setting to improve accuracy  at all ranges. Include range corrections for rocket motor temperature (Table E-1) for solving RAP met techniques for rocket motor on mode. For 105-mm howitzers in the rocket motor on mode, met techniques or registrations for RAP will yield unacceptable fuze corrections because of the large fuze-related probable errors. Therefore, do not compute them. For 155-mm howitzers, there is no Table J for fuze correction computations in the RAP TFT, since it can only be fired in the rocket motor on mode.

b. In a combat environment, the unit may conduct registrations with RAP. All of the probable errors involved in firing RAP force the observer to modify a precision registration and severely degrade its accuracy. For this reason, an MPI registration is the best option. However, probable errors also affect the MPI registration. Since the observer obtains spottings of a number of impacts **without adjustment,** the effects of the probable errors are lessened in comparison to a precision registration. The determined mean point of impact most likely is not as accurate as one determined for an HE MPI registration. However, the RAP MPI registration still provides a GFT
setting and increases accuracy.

If the unit does register, it also solves a concurrent met and derives position constants for use with later RAP missions. Use the position constants and a subsequent met technique to determine a GFT setting for new missions. As time allows, use the position constants and subsequent met techniques to construct a multiplot GFT setting and improve accuracy at all ranges.

## Section Iii Smoke Projectiles

Smoke projectiles are used for smoke screens, obscuring smoke, and marking targets for aircraft.

## 13-18. Description

a. Types. The three types of smoke projectiles areas follows:
(1) Hexachloroethane. Hexachloroethane (HC) smoke (smk) projectiles are available for 105-mm and 155-mm howitzers. They are used for screening, obscuration, spotting, and signaling purposes. The projectile has no casualty-producing effects. This base-ejection projectile is ballistically simailar to the HE projectile. It is fitted with a mechanical time fuze M565 or M577. The round expels smoke canisters that emit smoke for a period of 40 to 90
seconds.

(2) Burster-type white phosphorus. White phosphorus projectiles are available for 105-rnm and 155-mm howitzers. They are bursting-tube type projectiles that can be fired with point-detonating (PD) or MTSQ fuzes. The projectile has an incendiary-producing effect and is ballistically similar to the HE projectile. Normally, shell WP is employed for its incendiary effect. The projectile also can be used for screening, spotting, and signaling purposes.

(3) M825 white phosphorus. The M825 WP projectile is an FA-delivered 155-mm base-ejection projectile designed to produce a smoke screen on the ground for a duration of 5 to
15 minutes. It consists of two major components--the projectile carrier and the payload. The projectile carrier delivers the payload to the target. The payload consists of 116 WP-saturated felt wedges. The smoke screen is produced when a predetermined fuze action causes ejection of the payload from the projectile. After ejection, the WP-saturated felt wedges in the payload fall to the ground in an elliptical pattern. Each wedge then becomes a point or source of smoke. The M825 is ballistically similar to the M483A1 (DPICM) family of projectiles.

b. Employment. Smoke is employed by using the quick smoke and immediate smoke techniques.

(1) Quick smoke. A quick smoke mission is used to build a screen 100 to 1,500
meters in length, depending on the munition selected. It may be fired as a preplanned target or as a target of opportunity. Targets greater than 250 meters in length should be preplanned because of ammunition constraints and the possible need to segment the target. Quick smoke may be processed as an adjust-fire or FFE mission.

Accurate FFE mission processing on preplanned targets presupposes a positive correlation between wind direction at the screen location and that listed on line 00 of the current computer met message, in addition to meeting the five requirements for accurate predicted fire. The following is a list of quick smoke mission characteristics.

Delivery technique: Quick smoke. Type of target: Planned, or target of opportunity, 100 to 1,500 meters.

Number of howitzers: 2 to 16.

Type of ammunition: M825, HC or WP.

Sheaf: Linear.

Obscuration Time: 5 to 15 minutes. Command and Control: Approval of maneuver commander.

Computations (155 mm): FT 155-AM-2 for HC and WP data, FT 155-AM-2 and FT 155-ADD-T-0 or FT 155-AN-2 and FT 155-ADD-Q-0
for M825 data, and/or corresponding GFTs and GSTs.

NOTE: GFTs are available for 155 AM-2 that have M825 scales in place of ICM
scales. The M825 data are determined on the basis of the HE quadrant and fuze setting.

(2) Immediate smoke. An immediate smoke mission may be fired as a separate mission or as a follow-up to immediate suppression. Immediate smoke missions normally are fired by platoon. The initial volley may be fired with shell WP, fuze quick, or a mix of shell  WP and shell HC. If additional volleys are fired, all howitzers should fire HC smoke. When firing the M825 smoke round, all howitzers should fire the M825 projectile for the initial and any subsequent volleys. Unit SOP should dictate the number of volleys and which howitzers will fire WP and which will fire HC smoke, if applicable. The following is a list of immediate smoke mission characteristics.

Delivery technique: Immediate smoke (point suppression). The immediate smoke technique can be used in an immediate suppression mission on a target of opportunity by unit SOP. A mix of WP and HC normally will follow the initial suppression rounds when immediate smoke is requested. Type of target: Point or small area of 150 meters or less.

Number of howitzers: One platoon.

Type of ammunition: First volley, WP and/or HC; subsequent volleys, HC;
or all volleys M825 smoke.

Sheaf: Parallel.

Obscuration time: 30 seconds to 5 minutes.

Command and control: By SOP and/or approval of maneuver commander.

Computations (155 mm):
FT 155-AM-2 for HC and WP data, FT
155-AM-2 and FT 155-ADD-T-0 or FT 155-AN-2 and FT 155-ADD-Q-0
for M825 data, and/or corresponding GFTs and GSTs.

## 13-19. Quick Smoke

a. Quick smoke missions are fired by using linear sheafs and TGPCs or special corrections. Depending on the atmospheric conditions and the type of smoke desired, the FDC may need to determine two sets of firing data--one set for the initial rounds and one set for the sustainment rounds. The initial rounds establish the smoke screen, and the sustainment rounds ensure the smoke screen is in place for the desired duration.

b. For the FDC to provide an effective smoke screen, the FDO needs to obtain additional information not normally provided for other missions. From the observer, the FDO
needs the following:
The center grid of the desired smoke screen. The FDC will compute offset aimpoints on the basis of the type of munition, wind speed, and/or wind direction.

The length of the smoke screen. The maneuver target (MT) direction. The direction from the point at which the maneuver element will be most susceptible to enemy observation to the target.

Wind direction in reference to the maneuver target line. The observer must let the FDC know if the wind is a head wind, tail wind, left crosswind, or right crosswind in relation to the maneuver target line.

The screen time (duration), in minutes.

c. From the met station, the FDO will need to know the relative humidity for line 00 of the latest met message. This should be prearranged by unit SOP.

d. When the call for fire is received, the FDO will use a series of tables to determine the Pasquill weather category, mean wind speed, the number of rounds to fire to establish the smoke screen (initial rounds), and the number of rounds to fire to maintain the screen for the desired duration requested (sustainment rounds). If the number of aimpoints, rounds, or guns exceeds unit capabilities, the FDO will notify higher headquarters per unit SOP.

e. Once the number of rounds has been determined, the FDO will go through a series of computations to determine the number of meters between rounds (separation distance) and the necessary upwind offset corrections.

f. The HCO will plot the center grid of the smoke screen on the firing chart and will plot the upwind offset correction on the basis of the wind direction, the maneuver target direction, and the upwind offset correction. He will then plot the aimpoints and determine chart data to each aimpoint.

NOTE: It is necessary to determine individual piece data to each aimpoint. Proper manual computational procedures entail the use of the Ml 7 plotting board and the TGPC/Special  Correction Worksheet. This must be prepared in advance. Different aimpoint values for the initial and sustainment volleys would normally require the computation of two sets of special corrections for each mission. An alternative method is to plot the aimpoints on the firing chart, and determine firing data for each howitzer on the basis of the base piece location. When converged sheaf TGPCs (recomputed for the appropriate sector and already relayed to each gun section)
are applied, the solution approximates the previous method. Errors induced by this alternate method (that is, because of screen location at other than center of the TGPC sector) are offset by decreased computational time and complexity and the nature of the effects of smoke (large area covered per round). This latter method of computation will be used in this chapter.

g. The computer will determine and announce firing commands for each piece for the initial and sustainment volleys.

## 13-20. Quick Smoke Technique

The steps in Table 13-5 are used to determine firing data for the quick smoke technique.

NOTE: A study of the RI and R2 factors for HC and WP under poor conditions for smoke (calm, clear, warm, daylight) reveals an excessive number of aimpoints for a given screen width. The use of M825 or other means of screening should be considered in those instances.

## 13-21. Smoke Munitions Expenditure Tables And Equations

Smoke munitions (M825, M116, and M110) are used to establish and maintain smoke screens. The following tables  and equations can help you determine data when firing M825, M116, or M110 smoke munitions. (See Tables 13-8 through 13-10.)

## 13-22. M825 Smoke Procedures

The steps in Table 13-11 are used to determine firing data for shell M825.

## 13-23. M825 Examples

The following data are used in the examples shown in Figures 13-12 through 13-14.

## Known Data:

Unit: 1/A, four-gun platoon Azimuth of fire: 4800 Altitude: 1062

## Conditions:

Completely overcast afternoon Wind speed: 10 knots Humidity: 50 percent Wind direction: 3900 (left crosswind) Met line number: 00 Assumed screening: Normal visibility
Screen length: 250 meters
Duration: 15 minutes

## Tactical Solution:

Pasquill category: D Table: I-5 R1:4 R2:2 Firing interval: 5 min Number of volleys: 15 5 = 3

## Aimpoint Separation:

SEP1: 90 meters SEP2: 180 meters
Offset aimpoint: 110 meters

## Section Iv Dual-Purpose Improved Conventional Munitions

Dual-purpose improved conventional munitions are base-ejection (155
mm only), payload-carrying projectiles. These projectiles are fired with M577
MT fuzes and are filled with 88 dual-purpose grenades. During flight, the base of the projectile is blown off and centrlfugal  force  disperses  the grenades radially from the projectile line of flight.

## 13-24. Overview

The 155-mm DPICM projectile contains two types of dual-purpose grenades (64 M42 and 24
M46). Both types are capable of penetrating more than 2.5 inches of rolled homogeneous armor. They are also capable of fragmentation for incapacitating personnel. The M577 MT fuze is preset to function over the target area and initiate the expulsion charge. The expulsion charge pushes the grenades out of the container and onto the target area. The projectile can be modified for the SR
mode. The SR mode causes the round to point detonate so as to be visible to the observer and destroy the submunitions. It also may produce an airburst for high-burst registrations.

## 13-25. Determining Dpicm Firing Data

a. There are three ways to determine DPICM firing data. The preferred method is to use the 155-AM-2 GFT with the DPICM scales and a GFT setting. The second way is to use either the 155-AM-2 GFT without a GFT setting or the FT 155-AM-2 and the addendum for DPICM
(ADD-R-l). The third way is to use the FT 155-AN-2 and the addendum for DPICM (ADD-J-l).

Because the DPICM scales on the 155-AM-2 GFT are based on HE data, HE data from the base
(graze burst) scale must be determined before DPICM data can be determined.

(1) To determine the DPICM fuze setting, you must first determine the HE
fuze setting. Once the HE fuze setting has been determined, move the MHL over the HE fuze setting on the base scale and read up to the DPICM fuze scale. This is the DPICM fuze setting.

Since DPICM is fired with the M577 fuze, the HE fuze setting must be determined from the M582 scale.

(2) To determine the DPICM deflection to fire, you must first have the chart deflection from the HCO. There are three different ways to determine the deflection to fire on the basis of the type of mission being fired.

(a) If DPICM is the only shell fired during the mission, to include the adjustment and fire for effect phases, or if a straight FFE mission was conducted, the drift is taken from the DPICM scale instead of the HE base scale. The MHL is placed over the HE QE
on the base HE EL scale. Read up to determine the proper value for drift on the DPICM scale.

This drift will be used throughout the remainder of the mission.

(b) If HE is used in the adjust-fire phase and DPICM is used to fire for effect, then as soon as the type of shell is changed (HE to DPICM) a new value for drift must be determined from the DPICM drift scale. This drift will be determined by placing the MHL over the HE QE on the base scale and then reading up to the DPICM drift scale. Compare this DPICM drift to the HE drift to determine the change in drift (DPICM DRIFT - HE DRIFT=
CHANGE IN DRIFT). This change in drift is applied to the HE deflection fired (not to be confused with the chart deflection) to determine the DPICM deflection. Another method is to use DPICM DRIFT+ GFT DF CORR + CHART DF = DPICM DF TO FIRE.

(c) The last method is to use the appropriate addendum. As soon as the projectile changes, go to the addendum and extract the drift correction from Table A, Column 8.

Take this new drift correction, express it to the nearest mil, and add it to the HE deflection fired so that anew DPICM deflection can be determined for this mission.

(3) To determine the DPICM QE, first determine the HE QE. Place the MHL over the HE QE on the base HE EL scale. Now read up to the DPICM QE scale, and determine the QE to fire.

(4) To determine HOB corrections for DPICM, we must use the ADD-R-1. Table A is used to determine the correction factor that will be applied to the QE. Table B is used to determine the correction factor that will be applied to the fuze setting. Remember, the HE data are used to enter the tables, but the correction factors extracted are applied to the DPICM data.

b. To determine firing data without a GFT setting for DPICM, use the 155-AM-2 GFT
or the FT 155-AM-2 and the ADD-R-1. This procedure is valid for low-angle fire only.

(1) Using the proper charge and range, begin by determining HE data from the FT
155-AM-2, Table F. Elevation is extracted from Column 2, the fuze setting is extracted from Column 7 (M582), and the drift that will be added to the chart deflection is in Column 8. Site is computed in the normal way and then algebraically added to the elevation.

(2) Once the base HE data have been determined, the ballistic corrections to compensate for the DPICM projectile need to be extracted from the ADD-R-1. Table A of the appropriate charge will yield corrections for QE and deflection. Table A is entered with the HE
QE expressed to the nearest listed value. Column 2 will yield the correction factor that must be added to the HE QE to determine the DPICM QE. Column 8 has the deflection correction that must be applied to the HE deflection (chart deflection plus drift) before firing. Table B contains the correction factor that will be applied to the HE fuze setting. Enter Table B with the HE fuze setting, and extract the fuze correction. Apply this correction to the HE fuze setting to determine the DPICM fuze setting.

(3) The HOB of the DPICM projectile is dependent on the charge fired. If the observer transmits a request for an HOB correction, the ADD-R-1 will be used to determine the correction factors that must be applied to the DPICM fuze setting and QE. Table A, Column 3, of the appropriate charge will yield the correction factor for a 50-meter change in HOB. Multiply the correction factor by the number of 50-meter increments needed. Express the answer to the nearest mil. Apply the HOB correction to the DPICM QE. If it was an up correction, add the HOB correction to the DPICM QE; if it was a down correction, subtract the HOB correction from the DPICM QE. Table B, Column 3, of the appropriate charge will yield the FS correction for a
50-meter change in HOB. Multiply the correction factor by the number of 50-meter increments needed. Express the answer to the nearest FS increment. Apply the HOB correction to the DPICM fuze setting. If it was an up correction, add the HOB correction to the DPICM fuze setting; if it was a down correction, subtract the HOB correction from the DPICM fuze setting.

c. To determine firing data without a GFT setting for DPICM, use the FT 155-AN-2 and the ADD-J-1. This procedure is valid for low-angle fire only.

(1) Begin by determining DPICM graze burst data from the FT 155-AN-2, Table F, by using the proper charge and range. Elevation is extracted from Column 2, the graze burst fuze setting is extracted from Column 3 (M577), and the drift that will be added to the chart deflection is extracted from Column 8. Site is computed manually or by using the 155-AN-1 GST and then algebraically adding it to the elevation.

(2) Once the graze burst DPICM data have been determined, the ballistic corrections to compensate for the HOB of the DPICM projectile need to be extracted from the ADD-J-1. Table A of the appropriate charge will yield the corrections for QE. Table A is entered with the DPICM graze burst QE expressed to the nearest listed value. Column 2 will yield the correction factor that must be added to the DPICM graze burst QE so that the actual DPICM QE can be determined. Table B contains the correction factor that will be applied to the DPICM graze burst fuze setting. Enter Table B with the DPICM graze burst fuze setting, and extract the fuze correction. Apply this correction to the DPICM graze burst fuze setting so that the actual DPICM fuze setting can be determined.

(3) If during the course of a fire mission an HOB correction is sent to the FDC for shell DPICM, the ADD-J-1 will be used to determine the correction factors that must be applied to the DPICM fuze setting and QE. Table A, Column 3, of the appropriate charge will yield the correction factor for a 50-meter change in HOB. Multiply the correction factor by the number of
50-meter increments needed. Express the answer to the nearest mil. Apply the HOB correction to the DPICM QE. If it was an up correction, add the HOB correction to the DPICM QE; if it was a down correction, subtract the HOB correction from the DPICM QE. Table B, Column 3, of the appropriate charge will yield the FS correction for a 50-meter change in HOB. Multiply the correction factor by the number of 50-meter increments needed. Express the answer to the nearest FS increment. Apply the HOB correction to the DPICM fuze setting. If it was an up correction, add the HOB correction to the DPICM fuze setting; if it was a down correction, subtract it from the DPICM fuze setting.

NOTE: APICM data can be determined in a similar manner. The preferred method is to use the 155-AM-2 GFT with the APICM scales and a GFT setting. The other way is to use the 155-AM-2 GFT without a GFT setting or the FT 155-AM-2 and the addendum for APICM (ADD-l-2).

d. Figures 13-15 through 13-17 show completed ROFs for all three methods of determining firing data for shell DPICM.

## Section V Family Of Scatterable Mines

This section implements STANAG 2963 and QSTAG 802.

The family of scatterable mines adds new dimension to mine warfare, providing the maneuver commander with a rapid, flexible means of delaying, harassing, paralyzing, canalizing, or wearing down the enemy forces in both offensive and defensive operations. Mines can force the enemy into kill zones, change their direction of attack, spend time in clearing operations, or take evasive actions. FASCAM presents an array of air and FA-delivered scatterable mines available to maneuver force commanders. The two types of FA-delivered scatterable mines are ADAM and RAAMS.

## 13-26. Types Of Scatterable Mines

a. ADAM is an antipersonnel mine activated by deployed trip lines. There are 36
wedge-shaped mines contained in the 155-mm projectile. Minefield density can be selectively determined by altering the number of rounds applied. There are currently three densities: low, medium, and high. The mines are expelled from the projectile (approximately 600 meters) over the designated target. Shortly after ground impact, up to seven trip line sensors are released out to a maximum length of 20 feet. The detonators are armed to fiction in the event of any small disturbance. The ADAM mine has lethality out to 15 feet. Self-destruct times are 4 hours for short self-destruct (M731 ) and 48 hours for long self-destruct (M692). Figure 13-18 shows an ADAM projectile.

b. RAAMS is effective against armored vehicles. The mines are expelled from the rear of the projectile over the target. After ground impact and roll, the mine is armed and ready to detonate upon sensing a proper armored vehicle signature (electromagnetic). A percentage of the nine RAAMS mines are equipped with an antidisturbance device. RAAMS is highly effective when used in conjunction with the ADAM mine, which helps prevent neutralization by enemy ground troops. There are nine RAAMS mines per 155-mm projectile. Minefield densities and self-destruct times are the same as ADAM (M741 short-destruct, M718 long-destruct). Figure
13-19 shows a RAAMS projectile.

## 13-27. Fascam Tactical Considerations And Fire Order Process

a. Two types of minefields can be developed with FASCAM--planned minefield and target of opportunity minefields.

(1) Planned minefields begin with the development of the scheme of maneuver and then the barrier and/or obstacle plan by the G3 and/or S3 and engineer. Before deciding on the employment of ADAM and/or RAAMS, the FSCOORD is brought into the planning process to provide guidance on the availability of FA mines and delivery units. The process is then initiated with the DA Form 5032-R (Field Artillery Delivered Minefield Planning Sheet).

(2) Minefields employed against targets of opportunity (unplanned) must be emplaced immediately because of the tactical nature of the targets. They are requested through the fire support channels at any level. Once the maneuver brigade or division commander has approved the use of FA mines, they can be emplaced appropriately. Normally, targets of opportunity are used when the delivery of the mines can be observed. Aimpoints for target of opportunity minefields can be computed as in a planned minefield. However, this will be time-consuming and may not meet the demands of the tactical situation. Therefore, it is recommended that units establish an SOP for a "standard minefield" to fire when the tactical situation requires an immediate minefield. For example, the unit SOP may be for a 400 x 400
minefield, high angle, medium density, with two aimpoints. The SOP will allow FSOs to determine the number of target of opportunity minefields that are available for the maneuver commander. This determination is based on the unit's FASCAM unit basic load (UBL).

b. Upon receiving a request for a FASCAM minefield, the FDO must begin a detailed process to determine the fire order. The first thing that the FDO must understand is that FASCAM employment is based on a concept known as planning modules. The planning module for RAAMS low angle is 200 meters x 200 meters. The planning module for RAAMS high angle and for ADAM low or high angle is 400 meters x 400 meters. This does not mean that the minefield planner cannot request a minefield that is larger than the planning module. In any FASCAM minefield, the requesting agency defines the minefield size in terms of the length, width, and attitude. The length of the minefield is always the longest axis. The concept of the planning modules is based on the minefield width. In other words, the width of all minefields must be in multiples of the planning module defined above. The FDO will use the length, width, and planning module to determine the number of linear sheafs required to establish the required minefield. The linear sheafs will evenly divide each module and will be parallel to the long axis
(length) of the minefield. Refer to paragraph (13) for an example that illustrates this concept.

(1) Once the call for fire on a DA Form 5032-R is received, the FDO will plot the target. In FASCAM missions, DPICM graze burst data, battery-minefield angle (BMA), angle of fire, number of aimpoints, and the desired minefield density must be determined before issuing the fire order.

(2) Plot the minefield linear sheaf, determine the minefield center point of each linear sheaf, and determine the chart range and deflection to the minefield center point(s).

Record the chart range and chart deflection on the ROF.

(3) Determine DPICM graze burst data to the center point computed in (2) above.

For RAAMS only, determine chart range. For ADAM, determine chart range and DPICM QE.

(4) Determine the battery minefield angle.

The BMA is defined as the smaller angle formed by the intersection of the attitude of the minefield and the GT line with the vertex at the center point of the minefield. Using the target grid, set off the minefield attitude and with the vertex at the battery or platoon location, place the RDP against the center point. The smaller interior angle is the BMA. BMA is **always** less than 1,600 mils. Record this in the computation block of the ROF.

(5) To determine the appropriate mine employment table to use, the FDO must ask three questions:
What delivery technique am I using?

Met + VE (FFE).

Observer adjust (AF).
What shell and trajectory will I fire?
M718/M741 (RAAMS) low angle.
M718/M741 (RAAMS) high angle.
M692/M731 (ADAM) low or high angle.

What is the BMA?

Less than or **equal** to 800.

Greater than 800.

(6) The matrix key is used to determine the mine employment table to use. The table number that is displayed for each of the three entry arguments is the table used for mine employment. See the matrix shown in Table 13-12.

(7) The trajectory makes a difference in the minefield module that can be achieved.

RAAMS low-angle planning module is 200 x 200. RAAMS high-angle planning module is 400
x 400. ADAM low- or high-angle planning module is 400 x 400. So, only with RAAMS low angle can you achieve a minefield width of 200 meters, or every 200 meters.

NOTE:
If ADAM and RAAMS are employed together, then the process for determination of the appropriate mine employment table is done for each shell.

(8) The mine employment tables are used to determine the number of aimpoints required. Review the header information to verify the appropriate table is being used. The entry argument into the mine employment tables are the length (greatest axis) along the top and chart range for entering along the left side of the table (enter with the nearest listed value). If the chart range falls **exactly** halfway between two ranges, use the lower listed range. The mine employment tables are shown in Tables 13-13 through 13-20.

NOTE: These tables are number of aimpoints per linear sheaf (planning module width).

(9) On the basis of the module size and the number of aimpoints, the location of the aimpoints is determined.

(a) Module size 400- by 400-meters--even number of aimpoints. Place aimpoints 200 meters left and right of the center point along each centerline. Place the others at intervals of 400 meters. (See Figure 13-20.)
(b) Module size 400- by 400-meters--odd number of aimpoints. Place the first aimpoint at the center point of the minefield. Place the others at intervals of 400 meters left and right of the center point along each centerline. (See Figure 13-21.)
(c) Module size 200- by 200-meters--even number of aimpoints. Place the aimpoints 100 meters left and right of the center point along each centerline. Place the others at intervals of 200 meters. (See Figure 13-22.)
(d) Module size 200- by 200-meters--odd number of aimpoints. Place the first aimpoint at the center point of the minefield. Place the others at intervals of 200 meters left and right of the center point along each centerline. (See Figure 13-23.)
(10) On the basis of the desired density, enter Table 13-21 below to determine the number of rounds needed to achieve that density.

NOTE: A density of .001 means that there will be approximately one mine every
1,000 square meters. In other words, there will be one mine in every 32-x 32-meter area. These density numbers are used for planning purposes only. Dispersion of the projectiles in the target area will dictate the actual pattern of mines. Tables 13-22
and 13-23 show recommended minefield densities.

(11) Now, using all available information, the FDO issues the fire order and the computer records it on the ROF.

(12) There are some additional tactical considerations to consider when determining which firing unit(s) will deliver the mines on target.

The FDO must consider the total
.

.

emplacement time, the BMA angles of the firing units, the units available, distribution of FASCAM ammunition, and distribution of aimpoints. When firing a minefield containing both ADAM and RAAMS mines, RAAMS should be fired first to Prevent Premature detonation of ADAM mines.

NOTE: The above example is for illustrative purposes only and does not include the time required to shift between aimpoints.

(13) The FDO must also consider how to segment a target that is larger than the established planning modules. Segmenting a large target may require the FDO to establish two or more linear sheafs in the target area. The tactical considerations discussed in paragraph (12) are considered for each linear sheaf as if it were a separate fire mission. This decision to segment a large target is normally the responsibility of the battalion FDO.

(a) To illustrate this concept, consider the following situation:
Weapon: M109A3
Minefield size: 1,000 x 800 Attitude: 0400 Munitions: RAAMS
Angle of fire: High angle Module size: 400 x 400
(b) Since the width of the minefield is a multiple of the planning module
(800/400 = 2), the FDO can continue with the fire order process. If the establishing agency requests a minefield width that is **not** a multiple of the planning module, this must be resolved before the FDO can properly segment the target to achieve the desired density. In this example, the FDO will segment the minefield into two targets of 1,000 x 400 each. On the firing chart, the FDO will establish a centerline along each separate minefield. The easiest way to do this is to place the target grid over the center of the grid to the minefield and orient along the attitude.

Next, place plotting pins left and right of the attitude (200 meters) to establish the offset center points.

(c) The FDO will use the offset center points to determine chart range and the BMA. In some cases, this may cause the number of aimpoints to be different for each centerline, In this example, the chart operator determined the following data:

Centerline 1: 1/A RG 10,930, BMA 1150
Centerline 2: 1/A RG 11,350, BMA 1170
(d) The FDO will enter the appropriate minefield employment table and determine the number of aimpoints for each centerline. Finally, he will determine the aimpoint spacing along each centerline. In this example, the FDO determined the following data
(e) The remainder of the tactical considerations are performed as described in the steps from paragraph 13-27b(l3). Figure 13-23 depicts the results achieved from the above situation.

## 13-28. Technical Fire Direction Procedures

a. Now that the fire order is issued, technical fire direction must be determined by using DPICM graze burst data and then converting these DPICM data to either RAAMS or ADAM data. To convert these DPICM data, use the FT 155-ADD-L-1 (for ADAM) or FT 155-ADD-N-1
(for RAAMS). The preferred technique is to conduct a DPICM registration and transfer the GFT
setting. Other techniques used are met + VE or met to target. The computer records the initial fire commands through the Fz block and the MTO block on the ROF.

b. Now plot the aimpoints on the (target grid) firing chart (placing plotting pins left and right along the centerline arrow, representing the attitude) and determine chart data to the aimpoints. These are aimpoints where you want the rounds to impact. For ADAM, these chart data are not recorded on the ROF but are used to determine VI and site (we determine site to the actual impact of the rounds, not to an offset aimpoint location). For future use, record the chart range, VI, and site in the computational space of the ROF. For RAAMS, record the chart data, VI, and site for each aimpoint.

c.

Since low-level winds will cause ADAM mines to be blown away from the intended aimpoint, a modification in meters must be made to the location of the aimpoints. This will allow the mines to impact at the intended location. Low-level wind corrections are not computed for RAAMS. For RAAMS, go to paragraph f(3).

d. The computer must enter FT 155-ADD-L-1, Table A, Column 1, with the DPICM
graze burst quadrant determined to the center point grid (paragraph 13-27b(3)) and extract the correction for low-level winds from Column 5. This offset correction allows the delivered ADAM mines to be on target for a wind speed of 1 knot. The Low-level wind correction is recorded in the subsequent fire commands portion of the ROF.

(1) Since ADAM has a 600-meter HOB, line 02 from a current met message is used to determine the wind speed and direction. Line 02 is used because 00 = 0 to 250 meters, 01 =
250 to 500 meters, and line 02= 500 to 1,000 meters.

(2) The computer multiplies the correction factor in paragraph d by the wind speed in paragraph d(1) to determine the total distance, in meters, needed to offset each aimpoint to compensate for low-level winds. Express this value to the nearest 10 meters, and record it on the ROF. This distance in meters, in conjunction with the direction of the wind, will be used to offset the aimpoints.

## E. The Hco Uses The Target Grid To Offset The Aimpoints.

(1) The HCO places the target grid over the center point and sets off the direction of wind. Remember, this is the direction from which the wind is blowing. The HCO then offsets the center point into the wind by the distance determined in step d(2). (See Figure 13-25.)
(2) The HCO reorients the target grid over this point, resets the minefield attitude off, and places plotting pins left and right of the center point as determined in step (9) above, using the target grid centerline (arrow). Note that the "head and tail" of the target grid represents the attitude. (See Figure 13-26.)

f. The computer determines FASCAM firing data to each offset aimpoint.
(1) The HCO determines and announces chart range and deflection to the two aimpoints.

(2) The VCO determines site. Using the location and range to the original aimpoints which are recorded in the computational space of the ROF, the VCO determines VI
and site.

(3) The computer determines DPICM graze burst time, deflection, elevation, and quadrant elevation to each aimpoint.

Since these are not the data to be fired, place the time, deflection, and quadrant in parentheses.

(4) The computer determines and records FASCAM firing data by placing the MHL
over the DPICM graze burst time and quadrant. The deflection to fire is the chart deflection to the aimpoint plus the total deflection correction (GFT DF CORR + DPICM DRIFT).

(5) The preliminary FT 155-AN-2 and FT 155-AN-1 TFTs can be used to determine graze burst data for DPICM. The FT 155-AN-2 supersedes the FT 155-AN-1 and is the preferred source of firing data.

(6) The firing table addendums are used in conjunction with the firing tables to determine the firing data FASCAM.

## 13-29. Adam

a. Firing Table Addendum L-1 is used in conjunction with the AN-l/AN-2 base TFT to determine firing data for shell ADAM.

b. Table A, Column 1, is entered with the graze burst QE that was determined by using the AN-1/AN-2 TFT. The correction to quadrant is found in Column 2 and is added to the graze burst data.

c. Table B, Column 1, is entered with the graze burst fuze  setting that was determined by using the AN-1/AN-2 TFT. The correction to fuze setting is found in Column 2 and is added to the graze burst data.

d. Subsequent corrections for quadrant are determined from Table A, Columns 3 and 4;
for fuze setting, Table B, Columns 3 and 4.

## 13-30. Raams

a. Firing Table Addendum N-1 is used in conjunction with the AN-1/AN-2 base TFT to determine firing data for shell RAAMS.

b. Table A, Column 1, is entered with the graze burst QE that was determined by using the AN-1/AN-2 TFT. The correction to quadrant is found in Column 2 and is added to the graze burst data.

c. Table B, Column 1, is entered with the graze burst fuze setting that was determined by using the AN-1/AN-2 TFT. The correction to fuze setting is found in Column 2 and is added to the graze burst data.

d. Subsequent corrections for quadrant are determined from Table A, Columns 3 and 4;
for fuze setting, Table B, Columns 3 and 4.

## 13-31. Da Form 5032-R

a. DA Form 5032-R (Figure 13-27) is used for planned FA-delivered barrier or obstacle minefields, target of opportunity minefields, and minefields established in conjunction with other munitions.

b. The sections shown on this sheet are completed at different levels during the planning and execution sequence. The purpose of the planning sheet is as follows:
(1) Provide a standard procedure for placing planned minefield data into fire support channels.

(2) Provide data for computation and dissemination of a safety zone after minefield emplacement.

## 13-32. Planned Minefields

The planning sequence starts with the G3, S3, and engineer with guidance from the FSCOORD.

a. Section A is completed by the G3, S3, and/or engineer when requesting an FA-delivered scatterable minefield to support a barrier or obstacle plan.

b. Section B is completed by the G3, S3, and/or engineer to record dissemination of safety zones.

c. Section C is completed by the FSE.
d. Section D is completed by the firing unit FDO.

## 13-33. Target Of Opportunity Minefields And Minefields Established In Conjunction With Other Munitions

These minefields are initiated over fire support channels directly to the firing units.

Therefore, the use of the planning sheet starts in reverse sequence.

a. Section D is completed by the firing unit FDO. b. Section C is completed by the FSE.
c. Section B is completed by the G3, S3, and/or engineer to record dissemination of safety zones.

d. Section A is not applicable.
NOTE: A blank DA Form 5032-R is shown in Figures 13-27 and 13-28, and a description of each block is shown in Table 13-24.

## 13-34. Safety Zone Determination

a. The G3, S3, and/or engineers are normally responsible for determining the safety zones for FASCAM and disseminating them to the appropriate higher, lower, and adjacent units. The FSCOORD at any level can also determine safety zones for minefields that are fired into the maneuver area for which he is providing support. This would only be done for expediency to support maneuver operations.

b. As a safety check, the FDO should also determine the safety zone before firing FASCAM. The determined safety zone should be compared to the situation map to ensure there are no units within the safety zones for FA-delivered scatterable minefields. The two techniques used to determine the safety zone are as follows:

Safety zone tables. Safety zone templates.
NOTE: About 99 percent of all mine delivery missions will result in the entire minefield (minefield modules) being inside the safety squares.

For both techniques, the following information is required:

Type of projectile (ADAM or RAAMS).
Trajectory (high angle or low angle). Range to center of the minefield. Aimpoint coordinates. Delivery technique (met+ VE, or observer adjust).

## 13-35. Safety Zone Tables

The steps for using the safety zone tables are shown in Table 13-25.

## 13-36. Safety Zone Templates

If safety zone templates are available, the steps are basically the same as the safety zone tables. The selected template is centered over the aimpoint locations and the safety zone is traced onto the situation map. The field artillery mine safety template is shown in Figure 13-28.

## 13-37. Fascam Employment Steps

a. Table 13-29 shows the employment  procedures for shell ADAM.

b. Table 13-30 shows the employment procedures for shell RAAMS.

NOTE: Figure 13-31 shows a completed ROF for shell RAAMS.

## 13-38. Base Burn Dpicm (M864)

The M864 projectile is a dual-purpose ICM projectile that incorporates base burn technology to increase its range. Base burn technology was developed to reduce the amount of base drag on a projectile, thereby increasing the achieved range. The drag is reduced by a (base)
burner unit located on the base of the projectile. Once ignited, the base burner unit bleeds hot gas which causes the flow of air at the base to be less turbulent. The decrease in turbulence causes less base drag. (Base drag accounts for about 50 percent of total drag.) The amount of thrust produced by the base burner unit is negligible and does not serve the same function as the rocket motor on RAP. (See Figure 13-32.)

## 13-39. M864 Firing Data Computations

a. The current sources of firing data for M864 are the FT 155-AU-PAD and FT
.
155-ADD-U-PAD. There is also an M864 addendum to the FT 155-AO-0 (RAP). This is an unnamed provisional aiming data (PAD) addendum that is authorized for combat use only. It is used much in the same manner as the FT 155-ADD-R-1 is used to determine M483A1 firing data from M107 firing data.

b. The M864 projectile is not ballistically matched to any projectile currently in the inventory, but because of the similarity of the trajectories, firing data for the M864 can be determined from the M549A1 firing data. Once accurate M549A1 data are determined, corrections for the ballistic difference can be determined from a PAD addendum. The M549A1
QE, which is used to enter Table A of the addendum, can be no higher than 450 mils for charge 7WB (M4A2) or 500 mils for charges 7R (Ml19A2) and 8S (M203). These are the maximum quadrants for which data in the addendum were determined. The quadrant limitations do not allow the maximum range of M864 to be achieved with this technique. Table 13-31 shows the M864 maximum QE and Range to a target (including the desired HOB) that can be determined from M549A1 data. Table 13-32 depicts the designed M864 maximum QE and ranges. This technique can be used for both FFE missions and adjust-fire missions in which RAP is the adjusting projectile. While this technique of applying ballistic corrections to accurate M549A1 firing data has limitations in range, it represents the most accurate technique. The accuracy of this technique will be increased if used in conjunction with a RAP GFT setting.

## 13-40. Met To A Target

Because of the amount of time needed to work a met to a target, this technique would be best employed for planned targets. The FT 155-AU-PAD is designed in the same basic format as the FT 155-AN-2 TFT for DPICM and provides graze burst data. Once the graze burst data are determined, corrections from the FT 155-ADD-U-PAD are applied to the fuze setting deflection and quadrant to determine data to yield the appropriate HOB. If MV information has been determined with the M90 chronograph, the MVV is used as the velocity error.

NOTE: An MVV for M864 determined by calibration may not be available. The loss in muzzle velocity because of tube erosion (as determined from a recent pullover gauge reading and/or from EFC rounds) can be used as the position VE.

## 13-41. M864 Registrations

M864 projectiles can be fired in the SR mode by using the same procedures as for the M483A1. Because of the increased range, registrations may be difficult. Observers may have difficulty determining spottings and corrections, and radar, in the friendly fire mode, has an effective range of 14.7 kilometers.

NOTE: If a registration is conducted with the extended range dual-purpose improved conventional munitions (ERDPICM) projectile, the values for range K and fuze K would be computed in the same manner as conventional techniques.

## Chapter  14 Emergency Fdc Procedures

Field artillery units must be capable of delivering fire at all times. Requests for immediate fires may be received when the unit is moving or when the FDC is not yet set up. The loss of personnel or equipment may cause the battery to rely on some type of emergency backup procedures. The firing battery executing an emergency fire mission has two priority technical fire direction tasks:

Determine initial firing data to the target. Prepare for determination of subsequent data on the basis of the observer's
corrections.

## 14-1. Methods Of Determining Initial Data

The first priority is to compute initial data, announce it to the piece, and fire a round.

Depending on the call for fire, the XO or FDC may accomplish this by using one of several methods:
a. Adjust Fire.

The platoon leader determines direction and range to the target grid location from the map-spotted platoon location. This is done most rapidly by using a map and a range-azimuth fan of the correct scale (Figure 14-1). The platoon leader directs that the platoon be laid on the azimuth to the target, or he may orient the base piece himself by using the howitzer backlay method or a distant aiming point. If he has time, the platoon leader should lay the base piece with an aiming circle. The platoon leader selects a charge, or uses the standard charge, and converts the range to an elevation. The initial firing data are announced to the piece(s).

(1) Deflection equals the common deflection for the weapon system in use.

(2) QE equals elevation corresponding to range to target (GFT, TFT, and so on). Site is ignored unless it is excessively large. The FDO or platoon leader is responsible for analyzing the terrain in the target area and checking intervening crests to determine if he should include site.

b. Mark Center of Sector. This is requested when the observer is not oriented to the terrain. The platoon leader determines direction and range to the center of the supported unit's zone of action from the map-spotted battery location.If the platoon leader is not sure of the situation or the location of the sector center or if he feels a center of sector round may be unsafe, a white phosphorus with fuze time for an airburst should be fired. The platoon leader directs that the platoon be laid on the azimuth he determines to the sector center. The platoon leader determines the elevation corresponding to the range and charge. The initial firing data are announced to the piece.

(1) For a WP or an HE high airburst, the trajectory is raised to a 200-meter HOB by using the100/R factor. The FS corresponding to the initial elevation is used. The error introduced by a vertical interval greater than 100 meters is ignored.

(2) If shell HC smoke or WP is requested, HE data are fired without making corrections for projectile weight. For shell HC smoke, the time fuze setting to fire is determined by subtracting 2 seconds from the FS corresponding to the HE elevation.

NOTE: A grid location is preferred over mark center of sector because the first round fired engages the target directly.

## 14-2. Methods Of Determining Subsequent Data

After the initial fire commands are announced, emergency equipment must be prepared to convert the observer's corrections into subsequent fire commands. There are several expedient means of obtaining subsequent data that are available to the XO. He or the FDO must be able to quickly convert observer corrections into firing data.

a. Emergency Firing Chart.

Use of the emergency firing chart to adjust fire is discussed in paragraph 14-3.

b. M10 or M17 Plotting Board. Use of the Ml 0 or Ml 7 plotting board to adjust fire is discussed in paragraph 14-4.

c. Black Magic.

If no other means of adjusting fire is available, the Black Magic technique may be used as a last resort.

Certain information must be available, as detailed in paragraph 14-5.

## 14-3. Emergency Firing Chart

a. The emergency firing chart employs the same basic techniques as observed firing charts. Establish location and direction by using the relationship between the firing unit and its targets. The relationship is determined by firing and will contain errors. The emergency chart is only a temporary expedient to be used until a surveyed chart can be constructed.

b. The emergency chart may be constructed on any surface suitable for plotting (can accommodate an RDP and plotting pins).

c. Use Table 14-1 to construct an emergency firing chart.

## 14-4. M10 Or M17 Plotting Board

a. The M10 or M17 plotting board may be used for determining data for subsequent corrections in place of an emergency firing chart. Once prepared, observer corrections along the OT line can be converted to corrections along the GT line. For this procedure, the rivet (center)
of the plotting board represents the location of the last burst.

b. Use Table 14-2 to determine data for subsequent corrections in place of an emergency firing chart.

## 14-5. Black Magic

a. Black magic can be used to determine both initial firing data and firing data that are based on subsequent corrections. This technique can be done by FDC personnel or the observer and should only be used as a last resort.

b. Table 14-3 gives the steps for the Black Magic procedure.

c.  Subsequent corrections are processed by using the steps in Table 14-4.
NOTE: Subsequent corrections are made with respect to the GT line.

## 14-6. Emergency Firing Chart Example

a. You receive a call for fire while traveling to your next position. From a map spot, you determine the range to the target to be 4200 and the direction to be 4950.

b. Use Table 14-6 to process the mission.

## 14-7. Black Magic Example

a. You receive a call for fire against a platoon of infantry in a trench line. You estimate the range to be 3,400 meters and the direction of fire to be 4750. The observer requests time in effect.

b. Use Table 14-7 to process the mission.

## Chapter 15 Safety

AR 385-63 (MCOP3570.1A), Chapter 11, implements the chain-of command safety concept. Under this concept, the firing battery chain of command is responsible for safety during firing, training, and combat. This chapter reinforces AR 385-63. However, if local range regulations are more restrictive than the material in this chapter, the local range regulations must be followed.

## Section I Responsibilities And Duties

This section describes safety responsibilities, the duties of safety personnel, and the safety aids used by those personnel.

## 15-1. Responsibilities

a. Commanders of Field Artillery Units. Commanders establish and maintain a safety training and certification program for their personnel. The purpose of this program is to train and qualify personnel of the firing battery in the safety procedures for their specific areas of responsibility. When the commander is satisfied that the personnel are qualified to perform the safety duties as required, he certifies them.

b. Battalion Commander. The FA battalion commander is responsible for safety during all phases of a firing exercise under his control. He selects, trains, and certifies the personnel needed to help him discharge this responsibility. These personnel include, but are not limited to, the following:
Battery commander.

Executive officer.
Fire direction officer. XO or platoon leader. Chief of firing battery.

Gunnery sergeant.

FDC chief computer. Howitzer section chief.

If any position is not filled by a command safety-certified individual, another individual who is certified and qualified to fill that position performs the safety checks.

c. Officer in Charge.

The officer in charge (OIC) is the battery commander or his command safety-certified representative. The OIC is responsible for all aspects of safety in the firing unit and on the assigned firing range. Before the firing exercise, the range officer provides the OIC with the required safety data and any firing limitations. The OIC verifies that the unit is in the proper firing position. He supervises the conversion of the safety data into a safety diagram and ensures that this diagram is verified by another command safety-certified individual. The safety data determined from the safety diagram provide right and left deflection limits, minimum and maximum quadrant elevations for authorized charges, and minimum safe fuze times. The safety T, modified as needed by the XO's minimum QE, is given to the appropriate members of the firing battery.

d. XO or Platoon Leader. The XO or platoon leader is responsible for the safety practices of the firing element. He ensures that the section chiefs have safety data. He is responsible for determining the lowest QE that can be fired safely from his firing position and will ensure that projectiles clear all immediate crests (XO's minimum QE). He is assisted by the FDO, the platoon sergeant, and/or the gunnery sergeant.

e. Fire Direction Officer. The FDO has primary responsibility for computing safety data and for ensuring that all safety data are updated after registrations and receipt of current met data. He is responsible for plotting the impact area on a map or chart in the FDC. He is assisted in his duties by the chief computer. He ensures that all firing data are within prescribed safety limits before they are sent to the firing sections. He is responsible for adjusting minimum QE for intervening crests.

f. Platoon Sergeant. The platoon sergeant helps the XO or platoon leader in his duties and must be prepared to perform many of the duties in his absence. His main responsibilities are laying the battery, performing the duties of the XO or platoon leader, and working in shifts with the XO or platoon leader.

g. Howitzer Section Chief.

The section chief is responsible for supervising all practices that take place at or near his weapon. These include verifying that the announced safety data are applied to his weapon and that the proper charge, fuze, and projectiles are fired. He has the final responsibility for the firing of his weapon.

h. Range Officer.

The range officer gives the OIC of the firing unit the following safety data:
Grid coordinates of the firing position.

Lateral safety limits.
Minimum and maximum ranges. Authorized ammunition to be fired (fuze, projectile, and charge).
Maximum ordinate (high angle or low angle). Hours during which firing is conducted.

## 15-2. Duties Of Safety Personnel

In accordance with AR 385-63 (MCOP3470.1A), a separate battery safety officer is not required during the firing of field artillery. Normally, the XO or platoon leader perforrns this function. The XO or platoon leader is not required to verify all data placed on the on-carriage fire control equipment. He may rely on safety stakes, safety tape, or physical constraints on the weapon to ensure that the safety limits are not exceeded. All key personnel must be thoroughly familiar with six references:
AR 385-63 (MCOP3570.1A).

FM 6-40. FM 6-50. TM 43-0001-28. Appropriate TM for the weapon. Local range regulations.

In case of conflict, the most restrictive, usually local range regulations, takes precedence.

NOTE: The following are guidelines that can help units develop SOPs.

a. Specific duties of safety personnel before firing are, but are not limited to, the following:
(1) Verify that the data the range officer gives the OIC apply to the unit firing, that the unit is in the correct location, and that the data are correct. (OIC and safety officer)
(2) Compute and verify the safety diagram (at least two safety-certified personnel.

(normally XO or platoon leader and FDO)
(3) Check DA Form 581 (Request for Issue and Turn-in of Ammunition) and the range safety card to ensure that only authorized ammunition is fired. (XO or platoon leader or platoon sergeant)
(4) Ensure that no safety violations occur at or near the weapon(s). (all members of the firing unit)
(5) Check the weapons for correct boresighting. (section chief) (6) Verify the lay of the battery. (XO, platoon leader, or platoon sergeant)
(7) Compute and verify minimum QE. (XO, platoon leader, or FDO)
(8) Compare minimum QE with the QE for minimum range shown on the safety diagram. Use the larger of the two as the minimum QE. (XO, platoon leader, or FDO)
(9) Verify that the section chief has safety data (safety T). (XO, platoon leader, or platoon sergeant)
(10) Supervise and check the emplacement of safety aids (stakes, tape, and other devices). (XO, platoon leader, platoon sergeant, or gunnery sergeant)
(11) Verify that range clearance has been obtained. (XO, platoon leader, or FDO)
b. Specific duties of safety personnel during firing are, but are not limited to, the following:
(1) Verify the serviceability of ammunition. (section chief)
(2) Supervise key safety personnel in the performance of their duties. (OIC or safety officer)
(3) Verify that the charges, projectiles, and fuzes being fired are only those prescribed on the safety card. (section chief, XO, platoon leader, or platoon sergeant)
(4) Verify that rounds are not fired below the minimum QE or above the maximum QE. (section chief, XO, platoon leader, or platoon sergeant)
(5) Verify that rounds are not fired outside the lateral (deflection) safety limits specified on the safety card. (section chief, XO, platoon leader, or platoon sergeant)
(6) Verify that time-fuzed rounds are not fired with fuze settings that are less than the minimum time prescribed on the safety T. (section chief, XO, platoon leader, or platoon sergeant)
(7) On all commands that are unsafe to fire, command **CHECK FIRING** and give the reason(s) why the command(s) is(are) unsafe. (any person)
(8) Recompute and issue updated safety Ts under the following conditions: (FDO
or chief computer)
When a registration is completed. When met conditions change.

(9) Suspend firing when any unsafe condition exists. (Any person who sees an unsafe act) Examples of unsafe conditions areas follows:
Powder bags exposed to fire. Personnel smoking near pieces or ammunition. Improper handling of ammunition. Time fuze previously set and not reset to safe. Personnel or aircraft directly in front of the weapon. Primer inserted into the firing assembly before the breech is closed
(separate-loading ammunition).

Failure to inspect the powder chamber and bore after each round is fired. Failure to swab powder chamber after each round of separate-loading ammunition is fired.

c. All safety personnel will perform their duties in a manner that ensures compliance with all safety regulations and limits.

## 15-3. Safety Aids

From the range safety card, the FDO prepares a safety diagram, computes safety data, and safety Ts for use by the safety-certified personnel. Safety aids are used to ensure that only safe data are fired from the position. The most common safety aids are the safety stakes and safety tape. These aids are then used as a visual check to ensure that the howitzer is laid within safety limits.

a. Emplace safety aids for the M102 howitzer as follows:
(1) For deflection safety aids--
Set off the left deflection limit on the pantel by using the deflection counter. Traverse the tube to establish the proper sight picture on the aiming point. Emplace the safety stake against the right side of the lunette, and drive it firmly into the ground. Mark the right deflection limit in the same manner, but emplace the safety stake on the left side of the lunette.

(2) For QE safety aids--
Use the cam follower as an index mark.

Set off the maximum QE on the fire control quadrant. Elevate the tube until the bubbles center in the elevation level vials.

Mark the cam with apiece of tape in line with the cam follower.

Mark the minimum QE in the same manner.

b. Emplace safety aids on the M119 howitzer as follows:
(1) For deflection safety aids--
Determine the left deflection limit. Set off the left deflection limit on the pantel by using the deflection counter. Traverse the tube to the left as much as possible. Traverse the carriage (shift trails) until the correct left deflection limit sight picture on the aiming point is established. Place a left limit safety stake against the right side of the spade. Mark the right deflection limit in the same manner, but emplace the safety stake on the left side of the spade.

(2) For quadrant elevation aids--
Use the stationary bracket on the elevation gear box as an index mark. Set off the maximum QE on the fire control quadrant. Elevate the tube until the bubbles center in the elevation level vials. Mark the elevation arc with a piece of tape in line with the stationary bracket on the elevation gear box. Mark the minimum QE in the same manner.

c. Emplace safety tape on the Ml98 howitzer as follows:
(1) For deflection safety aids--
With the tube parallel to the azimuth of lay, place a piece of tape over the azimuth counter (bottom carriage).

Set off the left deflection limit on the pantel by using the deflection counter. Traverse the tube to establish the proper sight picture on the aiming point. Using a straight edge, draw a line on the tape placed on the bottom carriage directly below the azimuth counter index mark found on the upper carriage. Record the left deflection limit next to that line. Mark the right deflection limit in the same manner.

(2) For quadrant elevation safety aids--
With the tube elevated to 0 mils, place a piece of tape on the trunnion support and draw a straight line as an index. Set off the minimum QE on the fire control quadrant. Elevate the tube until the bubble centers in the elevation level vial.

Place a piece of tape on the quadrant mount, and draw a line across from the index line established on the trunnion support. Record the minimum QE next to that line. Mark the maximum QE in the same manner.

d. Emplace safety aids on the Ml09A3, A4, or A5 howitzer as follows:
(1) Deflection safety aids. These may be marked on the exterior and/or interior of the hull.

Make an index mark on the top carriage with a piece of tape. Set off the left deflection limit on the pantel by using the reset counter. Traverse the tube to establish a proper sight picture on the aiming point. Place a piece of tape on the bottom of the carriage directly under the index mark. Mark the right deflection limit in the same manner.

(2) Quadrant elevation safety aids. These may be marked on the exterior or the interior of the weapon. To emplace the safety aids on the interior of the weapon, follow the steps in paragraph c(2) above. To mark the exterior of the weapon, perform the following steps:
Mark an index on the tube with a piece of tape. Set off the maximum QE on the fire control quadrant. Elevate the tube until the bubble centers in the elevation level vial. Place a mark on the top carriage in line with the index mark. Mark the minimum QE in the same manner.

## Section Ii Manual Computation Of Low-Angle Safety Data

Minimum and maximum quadrants, deflection limits, and minimum fuze settings must be computed to ensure that all rounds fired impact or function in the target area. These data are presented and arranged in a logical manner on a safety T. This section describes the manual computation of safety data by use of tabular and graphical equipment. As stated earlier, the range officer gives the OIC the lateral safety limits and the minimum and maximum ranges of the target areas. These data must be converted to fuze settings, deflections, and quadrants.

The computations discussed in this section should be done by two safety-certified personnel working independently.

## 15-4. Safety Card

A safety card (Figure 15-1), which prescribes hours of firing, the area where the firing will take place, the location of the firing position, limits of the target area (in accordance with AR
385-63), and other pertinent data is approved by the range officer and sent to the OIC of firing.

The OIC of firing gives a copy of the safety card to the position safety officer, who constructs a safety diagram based on the prescribed limits.

## 15-5. Basic Safety Diagram

a. The FDO, on receipt of the safety card, constructs a basic safety diagram. The basic safety diagram is a graphical portrayal of the data on the safety card or is determined from the surface danger zone (AR 385-63, Chapter 11) and need not be drawn to scale. Shown on the basic safety diagram are the minimum and maximum range lines the left, right, and intermediate
(if any) azimuth limits; the deflections corresponding to the azimuth limits; and the azimuth of lay. The safety diagram header is labeled with a minimum of firing point grid and altitude (location) and charge. Other optional entries are angle of fire, shell, fuze and azimuth of lay.

b. The steps for constructing a basic safety diagram are shown in Table 15-1. An example of a completed safety diagram is shown in Figure 15-2.

c. When the basic safety diagram is complete, it will be constructed to scale, in red, on the firing chart. Plot the firing point location as listed on the range safety card. Using temporary azimuth indexes, an RDP, and a red pencil to draw the outline of the basic safety diagram. To do this, first draw the azimuth limits to include doglegs. Then, by holding the red pencil firmly against the RDP at the appropriate ranges, connect the azimuth limits.

d. Only after drawing the basic safety diagram on the firing chart may the base piece location be plotted and deflection indexes be constructed. Should the diagram be drawn from the base piece location, it would be invalid unless the base piece was located over the firing point marker.

e. After the basic safety diagram has been drawn on a sheet of paper and on the firing chart it is drawn on a map of the impact area by using an RDP and a pencil. These limits must be drawn accurately, because they will be used to determine altitudes for vertical intervals. Determine the maximum altitude along the minimum range line. This is used to ensure that the quadrant fired will cause the round to clear the highest point along the minimum range line and impact (function) within the impact area. At the maximum range, select the minimum altitude to ensure that the round will not clear the lowest point along the maximum range. Once the altitudes have been selected, label the basic safety diagram with the appropriate altitudes for the given ranges.

NOTE: The rule for determining the correct altitude for safety purposes is called the mini-max rule. At the minimum range, select the maximum altitude; at the maximum range, select the minimum altitude. If the contour interval is in feet, use either the GST or a feet-to-meters conversion table to convert the altitude to meters. This rule applies to both manual and automated procedures.

## 15-6. Computation Of Low-Angle Safety Data For Shell He, Standard Square Weight (No Gft Setting Available)

Use the steps outlined in Table 15-2 and the matrix in Figure 15-3 as examples for organizing computations. Only charge 4GB is shown. Use artillery expression for all computations except where noted.

## 15-7. Safety T

The safety T is a convenient method of arranging safety data and is used to verify the safety of fire commands (Figure 15-4). The information needed by the FDO, XO or platoon leader, and section chief is organized in an easy-to-read format. The safety T is labeled with a minimum of firing point location, charge, and projectile(s). Other optional entries are angle of fire and effective DTG. Anytime new safety data are determined, new safety Ts are constructed and issued only after the old safety Ts have been collected (that is, after a move or after a registration). Use only one charge per safety T.

NOTE: A reproducible copy of DA Form 7353-R (Universal Safety T) is included at the back of this book.

## 15-8. Computation Of Low-Angle Safety Data For Nonstandard Square Weight (Shell He, Wp, Or Hc) (No Gft Setting Available)

Use the steps outlined in Table 15-3 and the matrix in Figure 15-5 as examples for organizing computations.

a. WP and HC smoke are ballistically similar to HE but often differ in weight. The deflection limits and site computed for HE are accurate for different weight projectiles, but corrections must be applied to determine QEs and minimum FS.

b. At most charges and ranges, heavier projectiles fall short. This phenomenon is a safety concern with all projectiles, especially with shell WP, since WP will **never** weigh the same as a standard HE square weight ( I wt) projectile.

## Notes:

1. The following example uses WP (always heavier than standard square weight HE), since it is the most common nonstandard square weight projectile fired.

2. If the square weight is unknown, assume the worst case (heaviest) for minimum range.

3. Generally, a range correction is not determined for the maximum range, since the QE determined for a standard square weight projectile will cause the heavier square weight projectile to impact short of the maximum range. If a unit wants to maximize the safety box, compute maximum QE by applying the range correction corresponding to the known square weight (if unknown, use lightest possible square weight).

## Warning

For range 9100, M119A1 charge 8, the opposite is true. A heavier than standard projectile actually travels farther than a lighter projectile.

4. For lighter than standard square weight projectiles, compute a maximum QE, since a lighter projectile will generally travel farther than a standard square weight projectile.

5. The easiest way to remember which weight to use at a specific range is minimum range, maximum weight; maximum range, minimum weight.

## 15-9. Updating Safety Data After Registration

a. After a GFT setting is determined (result of registration or met+ VE technique), the FDO must compute new safety data by using the GFT setting. New elevations are determined which correspond to the minimum and maximum ranges (using the elevation gauge line). Deflections are modified by applying the total deflection correction to each lateral limit. Minimum fuze settings are recomputed (using the time gauge line, if applicable). The basic safety diagram drawn in red on the firing chart **does not change.** It was drawn on the basis of azimuths and ranges, and it represents the actual limits.

NOTE: The basic low-angle HE and nonstandard square weight projectile matrixes are shown in Figures 15-6 and 15-7 after applying the following GFT setting. WP
square weight is now known. It is 6 squares. Use Appendix F for help with determining data with a GFT setting.

b. Determine and issue new safety Ts with the corrected data. Figure 15-8 shows the updated safety T for HE only.

## 15-10. Low-Angle Illumination

a. The illuminating GFT is the preferred method for computing low-angle illum safety data. However, illum GFTs do not exist for all charges. Therefore, units may have to use the TFT method for computing safety in some situations. A basic safety diagram is constructed in the same manner as for low angle HE safety. The purpose of computing illum safety is to determine the minimum and maximum QE at which a nonfunctioning (dud) projectile would impact. It is not to determine the minimum and maximum QE that will keep the spent cannister of a functioning projectile in the impact area. There is no way to compute the trajectory of a spent cannister because it becomes ballistically unstable after fuze fiction.

b. The GFT method uses the elevation determined from the illum GFT
elevation-to-impact (ETI) scale at the minimum and maximum ranges. HE site is added to account for the vertical interval.

c. The TFT method uses the range-to-impact (RTI) column of Part 2 of the TFT to extract an elevation (column 2). These data approximate what is obtained from the ETI scale of the GFT. HE site is added to account for the vertical interval. However, this method does not always work at each **minimum** range for which safety is computed because the RTI may not be listed. Therefore, it is necessary to use a method that tries to approximate the value for elevation corresponding to the RTI column. This method assumes an average HOB of 750 meters for the
105-mm illumination and 600 meters for the 155-mm illumination. The QE from Column 2 is adjusted to ground level in 50-meter increments by use of the factor in Column 4 (change in QE
for a 50-meter change in HOB).

d. The GFT ETI method is **always** preferred over the TFT method. When the situation allows, units should try to fire charges for which an illum GFT exists. When a GFT is not available, using the RTI column of the TFT is preferred over the HOB method mentioned above.

## 15-11. Computation Of Safety Data For Illumination, Gft Method, Low Angle (No Gft Setting Available)

NOTE: Use the steps outlined in Table 15-4 and the matrix in Figure 15-9 for organizing computations.

The same range safety card and safety diagram as above are used.

## 15-12. Computation Of Safety Data For Illumination, Tft Method, Low Angle

Use the steps outlined in Tables 15-5 and 15-6 and the matrixes in Figures 15-11, 15-12, and 15-13 for organizing computations. The same range safety card and safety diagram as above are used.

NOTE: Since the maximum range of 7000 is not listed in RTI, Column 7, the maximum QE is determined by using the HOB correction method outlined in Table
15-5. See Figure 15-12.

## 15-13. Determination Of Maximum Effective Illumination Area

All illum safety data are for a graze burst. Therefore, when illurn fire mission data are computed, the QE determined includes the appropriate HOB. This will prevent achieving a
600-meter HOB (750-meter HOB for 105 mm) at the minimum range and maximum range lines.

Before processing illum fire missions, it is beneficial to determine the maximum effective illum area for the current range safety card. This area should be plotted on the chart to help determine if illum can be fired and to let the FOs know where they can fire illum effectively. This area will always be significantly smaller than the HE safety area. See Table 15-7 for steps outlining the general procedure. To increase this area, determine HA illum safety data (paragraph 15-22).

## 15-14. Low-Angle Safety Data For Shell 155 Mm M483A1 Dpicm, M825 Smoke, M692/M731 Adam, M718/M741 Raam, And M449 Apicm (Tft Method, No Gft Setting Available)

a. The procedures for determining safety data for DPICM, M825, FASCAM, and APICM depend on the weapon system and the availability of TFTs and firing table addendums.

See Table 15-8.

b. The steps in Tables 15-9 and 15-10 outline the procedures for determining safety for DPICM. To determine safety data for the other projectiles listed in Table 15-8, replace ADD-R-1 with the appropriate addendum. Use the matrixes in Figures 15-14 and 15-15 for organizing computations.

NOTE: In accordance with AR 385-63 (MCOP3570.1A), Chapter 11, ICM must be fired into a dedicated impact area and the submissive drift factors must be accounted for in safety computations.

Refer to the above manual for specific guidance concerning your situation. This does not apply to M825 computations. The example below is generic and does not include a submissive drift factor.

NOTE: The above matrixes and procedures can also be used to determine ICM/M825 using the AN-2 TFT and appropriate addendum. Replace HE elevation, HE site, HE FS, and HE QE with DPICM graze burst data.

## 15-15. Safety Procedures For M712 Copperhead

a. Copperhead safety data are determined from ballistic data developed specifically for the Copperhead. Computations are much like those for normal HE safety data. The Copperhead round should not be fired with cold stick data. Therefore, the computation of safety data requires the solving of a Copperhead met-to-target technique for each listed range by using TFT AS-1, as covered in Chapter 13, Section 1.

See Table 15-11 for steps to compute Copperhead safety.

Surface danger zones (SDZs) for shell Copperhead are significantly different than normal indirect fire SDZs. AR 385-63 (MCO P3570.1A), Chapter 11, contains SDZs for Copperhead fired in both ballistic and glide mode.

b. All ranges listed on the range safety card may not fall within the ranges listed in the TFT charge selection table for that charge and mode. Therefore, additional safety computations may be required for additional charge(s) and mode(s) to adequately cover the impact area. If ranges listed on the range safety card overlap charge and mode range limitations in the charge selection table, then safety for both affected charges and modes must be computed.

## 15-16. Safety Procedures For M549A1 Rap

RAP safety data are computed in the same manner as Copperhead safety data. Use the FT
155 AO-0. Complete a RAP met-to-target technique for each listed range. Follow the same steps as listed in Table 15-11. Minimum FS is not determined. An additional safety buffer of 6,000
meters is constructed short of the minimum range line in case the rocket motor does not ignite.

No personnel are allowed in this safety buffer.

## 15-17. Safety Procedures For M864 Base Burn Dpicm

a. M864 safety data are computed in the same manner as DPICM safety data (paragraph
15-14) by using one of the following methods:
(1) Use the FT 155-AU-PAD and FT ADD-U-PAD. Solve a met-to-target technique by following the steps in Table 15-11.

(2) Use the FT 155-AO-0 and provisional aiming data addendum to FT 155-AO-0
for projectile HE M864. Use registration data for projectile HE M549A1, low-angle fire only (no short title has been established).

b. An additional safety buffer of 5,000 meters is constructed short of the minimum range line in case the base burner element fails to function. No personnel are allowed in this safety buffer.

c. In accordance with AR 385-63 (MCOP3570.1A), Chapter 11, ICM must be fired into a dedicated impact area and the submissive drift factors must be accounted for in safety computations. Refer to the above manual for specific guidance concerning your situation.

## Section Iii Manual Computation Of High-Angle Safety Data

The safety data for high-angle fire is computed in much the same manner as that for low-angle fire except for the variations caused by the trajectory of high-angle fire.

## 15-18. Safety Data For High-Angle Fire

NOTE: The same range safety card (Figure 15-1) used during low-angle HE safety computations is used in this section.

## A. Deflection.

(1) Before registration. The deflection limits for HA fire are computed in the same manner as those for low-angle fire except that the limits are modified by the large amount of drift characteristic to HA fire. The left deflection limits are moved to the left by the amount of the minimum drift for the charge to be fired within the range limits. The right deflection limits are moved to the left by the amount of maximum drift for the charge to be fired, within the range limits. The values for drift are determined from either the HA GFT or the HA portion of the appropriate TFT.

(2) After high-angle registration. The deflection limits for HA fire are further modified.

Since the elevation changes after registration deflection limits are modified by redetermining new drifts and adding GFT deflection correction.

## B. Quadrant Elevation.

(1) Before registration. The minimum and maximum quadrants for HA fire are SI10 x computed in the same manner as those for low-angle fire except for the computation of site
10-MIL SITE FACTOR). The 10-mil site factor is determined from the GFT. Angle of site is computed from the GST by use of the C and D scales. If a 10-mil site factor is not available, HA site is computed manually (Table 15-13, step 5) by using the procedures in Chapter 8.

(2) After high-angle registration. An HA registration is valid for all charges in that charge group. Fire missions throughout safety limits usually require that more than one charge be used. Minimum and maximum QEs are computed for each charge by using corrections determined from the registration. The minimum and maximum elevations are read under the MHL when a GFT setting has been applied. Site must be recomputed.

c. Fuze Setting. Minimum fuze settings are not computed for HA fire. Mechanical time and/or superquick fuzes (M564 and M582) should not be used because of large probable errors in height of burst. The FDO must verify that VT fuze settings are determined to correspond to the appropriate target range.

## 15-19. Construction Of Basic Safety Diagram

a. Initially compute the deflection limits in the same manner as low angle. Then modify the limits by the large amount of drift that is peculiar to HA fire.

b. For the charges listed on the range safety card, extract from the TFT (or GFT) the HA
drifts corresponding to the elevations appropriate to the minimum and maximum ranges. When extracting from the TFT, express the value to the nearest 1 mil. If the range desired is not attainable for the particular charge, locate the nearest listed range and extract the corresponding value for drift. See Table 15-12.

c. As seen in Table 15-12, the minimum drift is L36 and the maximum drift is L92.

Each deflection limit is now modified by the appropriate drift correction. The example below shows the effect of using the least drift at a right limit.

## 15-20. Computation Of Safety Data For Ha (No Gft Setting Available)

Use the steps outlined in Table 15-13 and the matrix in Figure 15-17 as examples for organizing computations. Only charge 4GB is shown. Use artillery expression for all computations except where noted.

## 15-21. Computation Of Safety Data For Ha Fire (Gft Setting Available)

Like low-angle safety data, HA safety data are updatd a GFT setting is determined. See Chapter 10
for the application of a GFT setting to the HA GFT. Follow the same steps outlined in Table 15-13. Use the matrix in Figure 15-19 to organize computations. Use Appendix F for help with for help with determining data with an HA GFT setting applied. To determine new deflection limits, add the appropriate drift and GFT deflection correction to the low-angle deflection limit. Use the following GFT setting to update HA safety data.

## 15-22. Computation Of Safety Data For Ha Illumination (Tft Method)

Some impact areas are so small that low-angle illumination safety procedures can restrict firing this round.

High-angle illumination will significantly increase the maximum effective illum area for a range safety card or enable a unit to fire illumination when low angle is not practical. Therefore, it is necessary to compute safety data for HA illumination.

NOTE: The adjustments of HOB will be unrealistic. This is because the only movement in HOB
will parallel a change in QE fired.

Use the matrixes in Figure 15-20 and 15-21 to organize computations. The same steps are followed as listed in Tables 15-5 and 15-6. Minimum FS is not determined for HA illumination.

NOTE: Minimum FS is not determined because this FS must then be used with all QEs fired.

## Warning

The FDC is responsible for ensuring that the FS computed and announced will not function short of the minimum range line.

## 15-23. Safety Computations Matrixes

There are many different ways to organize safety computations for the different projectile and fuze combinations. Figure 15-22 shows all the matrixes used throughout this chapter. These are recomeded because they follow a logical flow.

## Section Iv Minimum Quadrant Elevation

The XO or platoon leader is responsible for determining the lowest QE
that can be safely fired from his position that will ensure projectiles clear all visible crests (minimum QE).

## 15-24. Elements Of Computation

A minimum quadrant for EACH howitzer is ALWAYS determined. The maximum of these minimum quadrants is the XO's minimum quadrant. Use of the rapid fire tables in ST 6-50-20 is the fastest method of computing minimum QE. The QE determined from ST
6-50-20 is always equal to or greater than (more safe) than manual computations. Manual computations are more accurate than the rapid fire tables and are used if the sum of the site to crest and the angle needed for a 5-meter vertical clearance is greater than 300 mils. Figure 15-23
shows the elements of minimum QE.

a.

Piece-to-crest range (PCR) is the horizontal distance between the piece and the crest, expressed to the nearest 100 meters. Procedures for measurement are discussed in paragraph
15-26.

NOTE: All angles are determined and expressed to the next higher mil.

b. Angle 1 (Figure 15-23) is the angle of site to crest measured by the weapons. See paragraph 15-25 for procedures.

c. Angle 2 (Figure 15-23) is the vertical angle required to clear the top of the crest. For quick, time, and unarmed proximity (VT) fuzes, a vertical clearance of 5 meters is used. For armed VT fuzes, see paragraph 15-28.

d. Angle 3 (Figure 15-23) is the complementary angle of site. It is the complementary site factor (TFT, Table G) for the appropriate charge at the piece-to-crest range multiplied by the sum of angles 1 and 2. Site is the sum of angles 1, 2, and 3.

NOTE: The entry argument for Table G is PCR. If it is not listed, do not interpolate, use the next higher listed value.

e. Angle 4 (Figure 15-23) is the elevation (TFT, Table F) for the appropriate charge corresponding to the PCR.

f. Angle 5 (Figure 15-23) is a safety factor equivalent to the value of 2 forks (TFT, Table F) for the appropriate charge at the PCR.

g. The sum of angles 1 through 5 (Figure 15-23) is the minimum QE for the weapon and the charge computed.

## 15-25. Measuring Angle Of Site To Crest

As soon as the piece is "safed," prefire checks conducted, and ammunition prepared, position improvement begins with verification of site to crest as measured by the advance party.

The advance party measures site to crest with an M2 compass or aiming circle. The section chief measures the angle of site to crest and reports it to the XO or platoon leader. To measure the angle of site to crest, the section chief sights along the bottom edge of the bore, has the tube traversed across the probable field of fire, and has the tube elevated until the line of sight clears the crest at the highest point. He then centers all bubbles on the elevation mount and reads the angle of site to the crest from the elevation counter. This angle of site and the PCR are reported as part of the section chief's report.

## 15-26. Measuring Piece-To-Crest Range

a. There are five methods that can be used to measure piece-to-crest range:
(1) Taping. This is the most accurate method; however, it is normally too time-consuming.

(2) Subtense. This method is fast and accurate.

(3) Map Measurement. This method is fast and accurate if the obstacle can be accurately located (for example, a lone tree will not appear on a map).

(4) Pacing. This method is time-consuming and depends on the distance and accessibility to the crest.

(5) Estimation. This method is least accurate, but it is used when other methods are not feasible.

b. Regardless of the method used to measure PCR, the XO or platoon leader must verify PCR before he computes QE. He can do this by using any of the five methods.

## 15-27. Computation For Fuzes Other Than Armed Vt

a. The XO or platoon leader does the computations indicated in this section if the sum of angles 1 and 2 (Figure 15-23) exceeds 300 mils or if the rapid fire tables (RFTs) are not available. All angles are determined and expressed to the next higher mil. Table 15-14 lists the steps and solves an example of an XO's or platoon leader's manual computations.

b. The same example is solved in Table 15-15 by using the RFTs in ST 6-50-20, Appendix B.

c. One howitzer section may report a site to crest that is unusually high. If the XO or platoon leader determines that it is the result of a single narrow obstruction (such as a tree), the piece can be called out of action when firing a deflection that would engage the obstruction. This would enable the platoon to use the next lower site to crest. Other alternatives are to remove the obstruction or move the weapon.

d. Table 15-16 illustrates why minimum QE is computed for all guns, regardless of which has the largest site to crest.

## 15-28. Computations For Armed Vt Fuze (Low-Angle Fire)

a. The method of computing the XO's minimum QE for firing a projectile fuzed with an M728 or M732 fuze depends on the method in which the fuze is used. The proximity (VT) fuze is designed to arm 3 seconds before the time set on the fuze; however, some VT fuzes have armed as early as 5.5 seconds before the time set on the fuze. Because of the probability of premature arming, a safety factor of 5.5 seconds is added to the time of flight to the PCR. Since time on the setting ring is set to the whole second, the time determined in computing minimum safe time is expressed up to the nearest whole second. A VT fuze is designed so that it will not arm earlier than 2 seconds into time of flight, which makes it a bore-safe fuze.

b. In noncombat situations, the XO or platoon leader determines the minimum safe time by adding 5.5 seconds to the time of flight to the minimum range line as shown on the range safety card. The minimum QE determined for fuzes quick and time is also valid for fuze VT.

c. In combat situations, the XO or platoon leader determines the minimum QE and a minimum safe time for fuze VT. The minimum QE determined for PD fuzes is safe for VT fuzes if the fuze setting to be fired equals or is greater than the minimum safe time determined in paragraph a above. If the XO or platoon leader finds it necessary to fire a VT fuze with a time less than the minimum safe time, he must modify the minimum QE. He does this by increasing the vertical clearance to ensure that the fuze will not function as it passes over the crest.

d. If the projectile is to be fired with the VT fuze set at a time less than the minimum safe time, allowance must be made for vertical clearance of the crest. Vertical crest clearances for armed M728 and M732 VT fuzes fired over ordinary terrain for all howitzer systems is 70 meters.

e. If the projectile is to be fired over marshy or wet terrain, the average height of burst will increase. The vertical clearance is increased to 105 meters. If the projectile is fired over water, snow, or ice, the vertical clearance is 140 meters.

f. The minimum QE for armed fuze VT when a fuze setting less than the minimum safe time is fired is based on the piece-to-crest range and a vertical clearance as indicated in paragraphs d and e above.

g. Figure 15-24 shows a decision tree for application of armed VT minimum QE.

h. Table 15-17 is an example of computations to determine minimum OE for an armed VT fuze.

i. The same example is solved in Table 15-18 by using the RFT in ST 6-50-20, Appendix B.

j. If the fuze setting to be fired is equal to or greater than the minimum safe time, the minimum QE for fuzes quick and time applies. If the fuze setting to be fired is less than the minimum safe time, the minimum QE determined for armed VT applies.

## 15-29. Using Minimum Quadrant Elevation

After computing minimum QE for each charge authorized, the XO or platoon leader must compare the minimum QE to the QE required to clear the minimum range line. The XO must then select the highest quadrant for each charge to be used as the minimum QE to be fired from that position.

## 15-30. Intervening Crest

a. FDOs must ensure that artillery fires clear intervening crests. Intervening crests are defined as any obstruction between the firing unit and the target not visible from the firing unit. The following are the possible options, listed in order of preference:
(1) Determine firing data to the crest (include all nonstandard conditions) and add 2
forks (Table 15-19).

(2) Determine a minimum QE in a similar manner as XO's minimum QE (Table
15-20).

(3) Use the trajectory tables in the appendix of the TFT.

b. Option 1 is preferred because it incorporates all current nonstandard conditions that will affect the projectile along the trajectory. The FDO has the responsibility to determine on the basis of availability of corrections for nonstandard conditions if this really is the best option. Table 15-19 lists the steps.

c. Option 2 does not include current corrections for all nonstandard conditions. Table
15-20 lists the steps.

d. The least preferred option is using the trajectory charts in the appendix of the TFT.

This offers a quicker but less accurate method to clear the intervening crest. The FDO must make a judgment call when to use these charts.

The FDO must use caution when making this decision.

## Appendix A Battery Or Platoon Fire Direction Center Sop

NOTE: The following SOP is to be used only as a guideline to help the FDO or fire direction section chief in developing an SOP for their unit.

The organization of the FDC generally is standard throughout the Field Artillery. The actual organization will vary depending upon unit size and their particular mission. However, the FDC in any unit must meet certain standards and be able to function on a continuous
24-hour basis. This requires that each individual within the FDC be cross-trained in every job in the FDC and understand that their primary function is to process all fire missions received with the maximum speed consistent with safety by using the most accurate data available, while ensuring necessary checks to preclude errors which might endanger friendlypersonnel. The FDC also receives operational and intelligence information for the platoon. In autonomous operations, the FDC will communicate directly with the observer in receiving the above-mentioned information.

## A-1. Operational Concepts

The organization of the FDC must allow for the following goals to be accomplished:
Continuous, accurate, timely, and safe artillery fire support under all weather conditions and terrain.

Ability to engage all types of targets over a wide area. Massing of fires of all available units within range.
Processing simultaneous missions. Disemmination of pertinent information.
Efficient division of duties.
Adherence to standard techniques and procedures.
Teamwork and adherence to a definite specified sequence of operations to aviod and
elimiante errors and to save time.
Efficient use of communications.

## A-2. Duties And Responsibilities Within The Fdc A. Fire Direction Officer.

(1) Establishes, coordinates, and supervises the operations of the FDC. (2) Issues the fire order.
(3) Ensures that the computer processes all fire missions with technically correct procedures.

(4) Reviews and approves the solution on all fire missions, to include any violations of safety data.

(5) Develops and enforces fire command standards and ensures that proper fire commands are transmitted to the cannon sections.

(6) Ensures that ammo distribution is maintained correctly within the platoon and notifies the platoon leader if an ammo shift becomes necessary.

(7) Ensures that the FDC maintains current tactical data on maps and charts. (8) Ensures that firing unit and ammo status are reported to the battalion FDC.

(9) Supervises the preparation for and execution of prearranged fires.

(10) Computes all safety data, to include verification of the platoon leader's minimum quadrant elevation.

(11) Analyzes intervening crests. (12) Establishes and maintains communications.

## B. Chief Fire Direction Computer (Usmc--Operations Chief).

(1) Responsible for the training of all personnel within the FDC.

(2) Ensures that the FDC is prepared within Army training and evaluation program
(ARTEP) (Marine Corps combat readiness evaluation system [MCRES]) standards to fire missions with the most accurate data available.

(3) Supervises the preparation of the firing chart(s). Ensures that chart checks are performed and are within tolerances between both the horizontal and vertical control operators'
charts.

(4) Determines center range and charge for the computation of TGPCs. Ensures that TGPCs are correctly computed.

(5) Ensures that the safety box is correctly constructed. (6) Supervises the installation of equipment in the FDC.

(7) Assumes the duties of the FDO in his absence.

## C. Senior Fire Direction Specialist (Usmc--Operations Assistant).

(1) Prepares the primary means for computing firing data and processes and records all missions fired on DA Form 4504.

(2) Transmits all firing commands to the howitzer sections in accordance with prepared fire command standards.

(3) Reports current firing unit and ammo status to the battalion FDC. (4) Ensures that accurate information is maintained within the FDC. (5) Ensures that all required equipment for processing missions is present and keeps the FDO and section chief informed of any shortages.

## D. Fire Direciton Specialist (Hco)(Usmc--Fire Control Man).

(1) Prepares the primary chart for operation. The HCO will determine range, deflection, and angle-T.

when
(2) Assists the fire direction computer in manual fire direction procedures necessary.

(3) Updates the primary firing chart in accordance with the tactical situation. (4) Assists the section chief in installation of section equipment when necessary.

## E. Fire Direction Specialist (Vco) (Usmc--Fire Control Man).

(1) Plots known data as directed by the assistant chief computer.
(2) Plots the initial target location and subsequent corrections when received.
(3) Checks chart data with the HCO.
(4) Plots the initial target location on the situation map and determines and announces site for the appropriate battery.

## F. Ratelo/Driver (Usmc--Fire Control Man/Driver).

(1) Maintains the section vehicle. (2) Maintains the generator(s).
(3) Helps the fire direction specialist in posting the current tactical situation on the situation map. Also, helps in maintaining in a current status all charts and records.

(4) Operates and maintains the FDC radios.

g. Advance Party Man. Not mentioned above are the additional duties of the advance party man. This individual is normally selected and trained by the section chief. His duties areas follows:
Prepares the position for the arrival of the FDC.

Establishes wire communications with the aiming circle and the gun guides.

Sets up the OE-254 antenna.

Receives initial data from the aiming circle and inputs it into the BUCS computer. Establishes position voice communication with battalion. Guides the FDC vehicle into position.

Helps set up camouflage nets.

Ensures wire and radio communications are functioning properly. If they are not, he troubleshoots them.

Sets up the second 0E-254 as needed.

NOTE: Successful accomplishment of the battery fire direction mission depends on the fully coordinated efforts of all members of the FDC.

## A-3. Fire Direction Center Operations Checklist

The following checklists are provided to help the FDO or section chief in preparation and sustainment during any major field exercise.

## A. Actions Before Departing Garrison.

(1) Design physical setup of the FDC to allow the FDO and section chief to observe the work of all personnel with a minimum amount of movement and provide each individual ready access to the equipment, forms, and information necessary to perform his duties.

(2) Ensure all necessary supplies and equipment are located within the FDC. (For a complete list of required equipment in a standard FDC, refer to the end of this appendix.)
(3) Ensure muzzle velocity logbook is present. (4) Ensure adequate supply of expendable forms is on hand. The following forms are used in all FA units:
DA Form 4982-R, Muzzle Velocity Record. DA Form 4982-1-R, M90 Velocimeter Work Sheet. DA Form 4504, Record of Fire. DA Form 4200, Met Data Correction Sheet. DA Form 3677, Computer Met Message.

DA Form 3675, Ballistic Met Message.
DA Form 5338-R, Computer Checklist. DA Form 4757, Registration and Special Correction Work Sheet, DA Form 4201, High Burst (Mean Point of Impact) Registration.

DA Form 7353-R, Universal Safety T. DA Form 7352-R, Copperhead Met + VE Work Sheet. DA Form 4655-R, Target List Work Sheet.

NOTE: The following forms are only for use in 155-mm units:
DA Form 5032-R, Field Artillery Delivered Minefield Planning Sheet. DA Form 5711-R, Copperhead Planned Target List Work Sheet.

(5) Ensure that the fire direction vehicle is loaded in accordance with your unit load plan. The load plan located at the end of this appendix maybe used as a guideline.

(6) Ensure the communications system has been verified as operational.

b. Actions Upon Occupation of a Position.

These actions are not listed in any particular order and are as follows:

(1) Establish voice communications with battalion operations center and the FDC,
guns, and other subscribers; that is, observers and range control.

(2) Verify the azimuth of lay with the platoon leader.
(3) Transmit current update to battalion on firing unit and ammo status. (4) Establish fire order and fire command standards, and transmit them to the
howitzer sections.

(5) Maintain the muzzle velocity logbook. (6) Request observer locations.
(7) Complete average site map. (8) Request current met. (9) Verify howitzer ammo count and whether or not the ammo status is readily
available to the FDO and section chief.

(10) Perform all necessary chart checks. (11) Compute safety and have a verification check completed as well.
(12) Verify the platoon leader's minimum QE. (13) Verify the safety computed does not violate the platoon leader's minimum QE. (14) Ensure safety data have been posted within the FDC and distributed to all
howitzer sections and leadership within the platoon.
(15) Ensure the VCO's map is color-coded and marked for average site and
altitude.

(16) Compute TGPCs and special correcitons.
(17) Verify that all sensitive items are accounted for.
(18) Verify GFT settings are applied to the GFTs. (19) Obtain an accurate propellant temperature and projectile weight. (20) Ensure situation map is readily available and posted with the current tactical
situation and fire support coordinating measures.
(21) Ensure the generator has been serviced and started.
(22) Ensure after-operation checks have been completed on the FDC vehicle.
(23) Ensure all howitzers have reported safe and in order. (24) Check for intervening crests.
(25) Check the following to ensure that they are plotted correctly on the firing chart:
Center of battery location or base piece and altitude.

Azimuth of fire. Azimuth and deflection indexes, Safety box. Observer locations. Fire support coordinating measures. Frontline of troops. Radar.

Other batteries within the battalion. TGPC sectors if applicable.

(26) Ensure the firing chart is neat and clean.
(27) Ensure the chart is prepared for 6,400-mil operation, if necessary.
(28) Ensure the five requirements for accurate predicted fire have been met. (29) Ensure a wet code has been requested for live fire from range control.
(30) Ensure the FDC is neat and orderly with equipment readily available but stored so as not to interfere with the FDC operations.

(31) Ensure fire order and fire command standards are visible to all personnel.

(32) Ensure the following information is easily accessible.

Laying data. Piece distribution. MV information.

Call signs.

Residuals. GFT settings. Propellant temperature. Projectile weight.

Terrain gun position corrections.

c. Actions Upon Receipt of a Fire Mission. Upon receipt of a fire mission, the FDC
does the following:
RATELO: Records CFF and announces **FIRE MISSION** to the FDC.

ALL: Announce FIRE MISSION.

COMPUTER: Announces **FIRE MISSION** to gun line.

RATELO: Announces (or records on mission board) the CFF to the FDC (loud readback to FO).

HCO: Reads back target location, plots target, and determines chart range and deflection.

VCO: Plots target and determines chart range and deflection.

FDO AND SECTION CHIEF:
1) Plot the target on the situation map and verify it is safe and does not violate any FSCMs.

2) Determine the fire order and issue it to the computer.

COMPUTER:
1) Reads back the fire order and records it on ROF.

2) Records initial fire commands up to and including fuze on the basis of the FDO's fire order.

3) Announces initial fire commands to the guns. (FDO and section chief monitor.)
RATELO: Composes and transmits the MTO on the basis of the fire order. (FDO and section chief monitor.)
COMPUTER: Requests range; for example, RANGE, ONE ALPHA. HCO: Announces chart range to the computer; for example, ONE  ALPHA, RANGE
5980.

VCO: Announces CHECK or **HOLD** (30 meters) to HCO.

COMPUTER:
1) If the VCO announces **CHECK,** places announced range under MHL on appropriate GFT. If the VCO announces **HOLD,** has the section chief verify charts and determine which range to use.

2) Records and reads back range placed on GFT; for example, RANGE 5980.
3) Requests deflection; for example, DEFLECTION.
HCO: Announces chart deflection to computer; for example, **DEFLECTION** 3286.

VCO: Announces CHECK or **HOLD** (3 mils) to HCO.

COMPUTER:

1) Records chart deflection on ROF and reads back chart deflection.
2) Records elevation on ROF.
3) If time or VT fuze is used, determines time setting.
4) If time or VT fuze is used, announces **FZ TI (or VT), TIME (such-and-such)** to gun line and records on ROF.

5) Determines deflection correction and records it on ROF.
6) Determines deflection to fire.

7) Announces deflection to fire as **DEFLECTION (so much)** to the gun line and records it on ROF.

FDO AND SECTION CHIEF: Ensure all data determined by computer are correct.

(May follow with TFT and GFT or BUCS.)
VCO: Determines and announces site. (FDO and section chief perform common-sense check [VI/RG in thousands].)
COMPUTER:

1) Records site on ROF.
2) Determines QE and records it on ROF.
3) Announces data to FDO and section chief for safety verification.
FDO AND SECTION CHIEF: Verify the data from the safety T are safe. If the data are safe, announce **SAFE.** If the data are unsafe, announce UNSAFE and state the reason why; for example, UNSAFE, QE 3 MILS BELOW MIN SAFE QE.

COMPUTER:

1) If data are safe, announces QE to the gun line.
2) Records MOF I/E, if applicable, as announced in the fire order.
3) Maintains the ROF.
HCO AND VCO: Orient target grid on firing charts and await any subsequent corrections from the observer.

VCO: Updates ammo board as time permits.

d. Actions During Fire Missions. These actions areas follows:

(1) Verify the met was valid with registration.
(2) Ensure safety data have been updated after the registration mission.
(3) Ensure situation map has been checked for occupation of intervening crests by
friendly elements.

(4) Verify fire order has been issued. (5) Ensure the fire mission is from a valid subscriber.
(6) Authenticate the call for fire, if necessary.
(7) Ensure the current communications-electronics operation instructions (CEOI) are available.

(8) Ensure the MTO is transmitted promptly and in accordance with the fire order. (9) Ensure fire commands are being transmitted as soon as individual items are determined and that they are in the correct format.

(10) Ensure ammo count has been updated after every mission by piece.

Verify how old met data are.
(11)
Complete a chart-to-chart check on firing data for each mission.
(12)
Check safety on each and every mission.
(13)
Determine angle T and, if necessary, transmit it to the observer.
(14)
Properly update safety.
(15)
Ensure
proper reports are given to the battalion FDC and tactical operations
(16)
center (TOC).
current situation map has been updated lately to reflect the current
Ensure
(17)
tactical situation.
(18) Ensure the record of fire is legible and complete.
(19) Ensure propellant temperature has been updated within the last hour. (20) Ensure the communications system allows all personnel to hear the call for free.
e. Actions Before Displacement. These actions areas follows:
Ensure FDC is set up for emergency missions.
(1)
Clean off old GFT settings from GFT.
(2)
Ensure start point has been reported to battalion.
(3)
Ensure communications check has been performed with battalion while moving.
(4)
Ensure all sensitive items have been accounted for.
(5)
Ensure chart has been prepared for the next position.
(6)
Ensure checkout information has been obtained from range control. Always keep copies of ROFs and safety computations for permanent records.
(7)
(8)
File forms in an orderly manner.
(9)

## A-4. Fire Direction Center Journal (Logbook)

To maintain a record of FDC activities during field operations, it is recommended that a journal be kept of each day's activities. This journal, or logbook, will reflect all significant events that have occured during all field operations. These significant events include, but are not limited to, the following:

Check firings.
Reports. All range control information. Receipt of all messages (date, time, and content).
Met messages. The journal should be closed out every 24 hours so as to prevent any unnecessary confusion.

## A-5. Fire Direction Center Equipment And Configurations

a. Although this appendix focuses on the manual FDC, it should be noted that the following is the priority in determining the method to be used in the computation of firing data.

(1) The lightweight computer unit (LCU)-BCS is the primary means of computing technical firing data within the platoon.

(2) The LCU-BCS-BUCS is the backup means of computing technical firing data.

(3) The ability to perform manual fire direction must be maintained to change to manual fire direction techniques at any time. Each FDC should maintain one firing chart with the appropriate fire direction equipment and manuals to support all manual cannon gunnery operations. The firing charts should serve as an emergency backup for BCS and BUCS, b. Each FDC is authorized the following:
fire direction set 3, artillery (NSN
1290-00-299-6892), 30,000 meters maximum range (line item number [LIN] H55843), 19200
(Table A-l); fire direction set 4, artillery (NSN 1290-00-299-6893), 15,000 meters maximum range (LIN H55706) (Table A-2); and plotting set, artillery fire control @JSN 6675-00-641 -3630) (LIN P09818) (Table A-3).

c. Figures A-1 through A-5 show suggested layouts of battery FDCs, including manual, automated, and howitzer improvement program (HIP) configurations. Applicability of these configurations will depend on the inherent mission and equipment of the unit concerned. Address questions or comments concerning these layouts to:

Commandant
US Army Field Artillery School
ATTN: ATSF-GSP
Fort Sill, OK 73503-5600

c.  Table A-4 shows a list of components needed for the FDC.

## Appendix B Fire Direction Center Section Evaluation Guide

This evaluation guide tests the skills essential to the accomplishment of the mission of the FDC section. Although many of the tasks are evaluated on the basis of individual performance, the collective skills evaluation will measure the ability of the platoon FDC to function as a team.

Commanders may use the guide to accomplish the following:

Provide a basis for a section training program. Evaluate the current state of training proficiency of the section.
Serve as a supplement to other performance-oriented training.
The tasks laid out in this guide also serve as a program of training objectives. The platoon FDC
section should practice each task to acquire the degree of proficiency required by the standards set in the evaluation.

## B-1. Scope

This is an evaluation guide for the platoon FDC section of a cannon battalion or separate battery. It is generic in scope and can be adapted readily to all platoon FDC sections associated with all artillery units. It is a performance-oriented evaluation and training guide designed to collectively identify the performance objectives for the platoon FDC sections. Commanders should modify this evaluation to meet local mission-essential task list (METL) tasks and current modification tables of organization and equipment (MTOE) requirements.  It may  be administered as follows:

Internally or externally.
With a minimum of admin  support. In the local training area.
In a tactical nonfiring environment.

## B-2. Conduct Of The Evaluation

The evaluation consists of three phases. The first two phases evaluate the ability of the section chief to organize and train his section into a cohesive, effective team. The last phase is a critique of the evaluation. Each phase is a separate annex and can be administered independently.

a. Phase I. This phase begins with an orientation period to include a statement of the purpose, scope, and description of the evaluation. Evaluators give a written test, on military occupational specialty (MOS) knowledge. Soldiers take this phase in a classroom environment before the remaining phases.

b. Phase II. This phase (section performance) evaluates the collective skills needed by the platoon FDC section to perform mission-oriented collective tasks in a tactical environment.

The commander may choose to evaluate during day or night conditions. Live firing is not necessary to complete this phase.

Commanders at various levels may direct the intensity to include all or only part of tasks for evaluation.

c. Phase III. This is a critique of the evaluation by the platoon FDC section.

Evaluators will note and take recommendations from the soldiers to improve training and future evaluations.

## B-3. Evaluation Format

a. Phase I consists of 25 multiple choice and true-false questions.
b. Phase II consists of specific section performance tasks.
(1) The **task** is a general statement of the requirement for the particular evaluation. (2) The **conditions** define the specific environment or situation for the evaluation.

They state what assistance, reference materials, equipment, or personnel are required.

(3) Standards or **evaluation checklists** are the requirements for successful completion of a particular task. Specific technical procedures required in the task are in the appropriate technical or field manual.

c. Phase III consists of a period after the evaluation where the section comments on the evaluated tasks, conditions, and standards.

## B-4. Scoring

Phases I and II combine for a maximum total point value of 1,000 points. The evaluator will base his judgment on the criteria stated in the standards or evaluation checklist and on the most current references for the task.

## B-5. Qualification

a. Formal scoring is optional. The commander can determine the strengths and weaknesses of his section by analyzing the GO-NO GO ratings received for each task performed.

b. The evaluation maybe used to determine the best platoon FDC section in a battalion ard/or div arty by determining a formal score. To determine the score for individual sections, add the numerical scores attained in each of the two phases. (See Table B-1.) Sample score sheets are shown in Figures B-1 through B-3. A sample critique for Phase III is shown in Figure B-4.

## B-6. Phase I: Test And Answer Key

A sample Phase I written test is shown below. The Phase I written test answer key follows the sample written test.

## B-7. Phase Ii: Section Performance Test

A sample Phase II section performance testis shown below.

## B-8. Phase Iii: Critique Instructions

a. The evaluator will address comments to the critique quedstions in the front of this at the end of each e-valuated phase or after Phase annex. The evaluator should conduct this phase II only.

b. The references for this critique are:
FM 6-40. STP 6-13E14-SM-TG, dated Jul 92. Current ARTEP MTP manual.
NOTE: This appendix was taken from examples of div arty FDC evaluation guides.

## Appendix C Target Analysis And Munition Effects And Terminal Ballistics

Target analysis is the examination and evaluation of an enemy target situation to determine the most suitable weapon, ammunition, and method required to defeat, neutralize, or otherwise disrupt, delay, or limit the enemy. Not only does target analysis involve determining the amount and type of ammunition required to inflict a given damage (or casualty) level on a particular target, it also involves a continuous process of consultation and cooperation between the commander and the FDO.

## C-1. Target Analysis

The amount of time devoted to target analysis and the thoroughness of the analysis depends on the following:
Amount of target information. Weapons and ammunition available to attack the target. Urgency of the engagement.

## C-2. Determining The Precedence Of Attack

When an FDO receives a fire mission, his options include the following (see Figure C-1): Attack the target immediately. Defer attacking the target until an existing fire mission is complete. Pass the fire mission to another FDC. Request reinforcing fires. Deny the mission.

An FDO selects a particular precedence of attack after considering the following:
Call for fire.

Terrain. Target location. Weather. Target characteristics. Units available. Commander's criteria. Availability of corrections. Munition effects. Enemy target acquisition. Commander's intent. Ammunition availability.

a. Commander's Criteria.

All phases of target analysis are conducted within constraints established by the commander. In determining the precedence for attacking a target, primary consideration is given to the commander's target priorities.

(1) Attack guidance matrix. The commander's target priorities are organized into an attack guidance matrix that lists the type of target, when to attack, degree of destruction, and any restrictions.

Figure C-2 is an example of a commander's attack guidance matrix. The following example explains how it would be used.

## Example

Your FDC received a call for fire, and the target description was a POL dump. While processing this mission, you received another call for fire requesting fires on an infantry platoon. Referring to the attack guidance matrix, you would determine that the infantry platoon is a higher priority. In this case, you process this mission first. Upon completion of this mission, you would fire on the POL dump.

NOTE: For a more detailed discussion on the attack guidance matrix, see FM
6-20-40.

(2) Target effects categories. On the basis of ammunition constraints, a commander also specifies the type of effects he desires against specific target categories. The three target effects categories are as follows:
(a) Suppression. Suppression of a target limits the ability of enemy personnel to perform their mission. Firing HE, fuze VT reduces the combat effectiveness of personnel and armored targets by creating apprehension and surprise and by causing tracked vehicles to button up. Smoke is used to blind or confuse. The effect of suppressive fires usually lasts only as long as the fires are continued. This type of fire is used against likely, suspected, or inaccurately located enemy units where time is essential. It can be delivered by small delivery units or means and requires little ammunition.

(b) Neutralization. Neutralization of a target knocks the target out of the battle temporarily. Casualties of 10 percent or more neutralize a unit. The unit is effective again when the casualties are replaced and/or damage is repaired. Neutralization fires are delivered against targets located by accurate map inspection, indirect fire adjustment, or a TA device. The assets required to neutralize a target vary according to the type and size of the target and the weapon-ammunition combination.

(c) Destruction. Destruction puts the target out of action permanently. Thirty percent casualties or materiel damage inflicted during a short time span normally renders a unit permanently ineffective. Direct hits are required to destroy hard materiel targets. Targets must be located by accurate map inspection, indirect fire adjustment, or a TA device. Destruction usually requires a large amount of ammunition from many units.

## B. Target Characteristics.

(1) Targets encountered on the battlefield vary considerably in composition, degree of protection, shape, mobility, and recuperability. For simplicity, targets are divided into four categories (Table C-1) to compare the effectiveness of particular weapons and rounds. Examples axe listed for each category. Under certain conditions, some examples could be listed in more than one category.

For example, a motorized rifle battalion could be listed under the first category and the fourth category.

(2) For personnel targets in particular, the posture of the target is extremely important. Normally, target postures us d for personnel targets are standing, prone, and in fighting positions.

For computation, it is assumed that the personnel are wearing helmets and that personnel in fighting positions are in a crouching position. In describing posture of a target, consider the protection afforded by the terrain. For example, an infantry platoon may be attacking in a standing posture. However, irregular terrain may provide protection equivalent to the prone position.

Usually, personnel targets seek a more protective posture during an engagement; for example, from a standing to a prone position. This change is called posture sequencing. Posture sequencing causes considerable degradation of effects as additional volleys are fired and is the reason for the continual emphasis on surprise or mass fires. For the purposes of analysis, personnel targets in the offense are considered to be one-half standing and one-half prone during the first volley of fire and all prone for subsequent volleys. In a defensive configuration, personnel targets are considered to be one-half prone and one-half in fighting positions during the initial volley and all in fighting positions for subsequent volleys.

(3) A target must be analyzed to determine its weak points. Where the target is most vulnerable and what fires will best exploit its weaknesses are influenced by the degree of damage desired. Often there is a tendency to overkill the target when less combat power would suffice. On the basis of the commander's criteria, the FDO must ascertain the degree of effects needed (destruction, neutralization, suppression) to support the tactical plan. The acceptable degree of damage is the level that yields a significant military advantage. For example, fire from a heavily protected machine-gun emplacement may be silenced by obscuration through smoke and subsequent engagement by direct fire as opposed to the expenditure of a large number of HE rounds required for its destruction.

(a) Target location.

The FDO must check the target location relative to friendly forces, fire support coordinating measures, zones of fire, and registration transfer limits.

Target location accuracy is also considered. The range affects the choice of units to fire and charge selection.

The terrain around the target may influence ammo selection or type of trajectory. High intervening crests may require selection of a lower charge or high angle.

(b) Target characteristics. The size of the target affects the number of units to fire, the type of sheaf, the selection of ammo, and the number of rounds in the fire for effect. The type of target (troops, vehicles, hard, soft) influences the ammo type and amount, the priority placed on the mission, and whether surprise fire (for example, time on target) is possible.

(c) Ammo availability.

The FDO must consider the amount and type of ammunition available and the controlled supply rate.

(d) Units available. The number of units available not only affects which units are used, but also the type of attack. Sweep and/or zone fire or other techniques may be needed to cover large targets when enough units are not available.

(e) Commander's criteria or commander's intent. Restrictions on ammo, operation order (OPORD), and SOPs may govern the selection of units and ammunition, target priority, and method of attack.

(f) Call for fire. The FDO must consider the observer's request carefully since he is observing the target and talks directly to the maneuver commander. The observer's request is honored when possible. The call for fire will also include information on the target activity
(for example, attacking, defending, digging in).

(g) Munitions effects.

If time permits, the FDO may use the JMEMs to determine the type munition and volume of fire. The FDO most often relies on the GMET or experience.

(h) Availability of corrections. The availability of corrections to firing data for nonstandard conditions is a guiding factor in the choice of charge and munitions, since it directly affects the ability to provide accurate first round fire for effect.

(i) Enemy target acquisition capability. Knowledge of the current enemy counterbattery radar and sound ranging capabilities allows the FDO to attack the target in a manner most likely to evade detection.

d. Terrain. The terrain in the target area has a direct effect on the vulnerability of the target. Rugged terrain affords considerable natural cover and makes target location difficult.

Certain terrain provides complete protection from some angles of approach but not others and thus influences the unit and munitions to be employed. The nature of the vegetation in the target area should be considered when selecting ammunition.

e. Weather. Weather is of little consequence in evaluating a target to attack with fuze quick or time.

However, precipitation and wind are of particular importance in evaluating a target to attack with ICM, smoke, FASCAM, or illum projectiles. Low clouds, thick fog, surface water, and rain degrade the effectiveness of VT fuze.

## C-3. Determining Most Suitable Weapon And Ammunition

When an FDO decides to attack a target, he selects a weapon-ammunition combination that achieves the desired effect with a minimum expenditure of available ammo. Figure C-3
depicts weapon-ammunition selection.

## A. Munitions.

(1) Type and quantity available. The nature of the target, its surroundings, and the desired effects dictate the type and amount of ammo to use. For a detailed discussion of ammo and fuzes, refer to FM 6-141-1 and (C)FM 6-141-2. The ammo resupply system sometimes rules out the best ammo selection. For example, extensive smoke fires may be needed to screen maneuver movement, but such fires may cause a resupply problem. Some fires require more ammo than others. Suppression and neutralization fires normally use less ammo than destruction fires.

(2) Troop safety.

Troop safety is a major concern in considering the weapon-ammunition selection for firing close-in targets. The FDO must ensure that fires do not endanger friendly troops, equipment, and facilities.

(3) Residual effects in target area. The supported unit must be advised of the residual effects from certain munitions. For example, the self-destruct times from FASCAM
munitions may preclude the desired movement of supported units through a particular area.

Weather changes may alter choices of certain munitions (smoke, illumination, and white phosphorous).

The incendiary effects of certain munitions may make areas untenable for supported forces. However, these effects can also deny the enemy use of selected terrain.

(4) Effectiveness. When properly delivered against appropriate targets, artillery fire support can be the decisive factor in a battle. The FDO must ensure that the desired result is attained from every mission. To match a munition to a target, the FDO must know what damage a munition can produce and the damage required to defeat the target. The lethality of a munition must be matched to the specific vulnerability of the target. Thus, the FDO must understand the damage potential (blast, cratering, fragmentation, incendiary, and penetration) of specific munitions.

Specific information regarding the effects of various munitions is found in the appropriate JMEM, FM 6-141-1, and (C) FM 6-141-2. For details on predicting weapon effects, see paragraphs C-5 through C-8.

## B. Weapons.

(1) Caliber and type available. In certain instances, an FDO may control the fires of reinforcing (R) or general support reinforcing (GSR) units that fire a different caliber. The FDO must have a thorough knowledge of the characteristics, capabilities, and vulnerabilities of each weapon system. Weapons with slow rates of fire and poor delivery accuracy are best suited for long-range fires. Weapons with rapid rates of fire and good delivery accuracy are suited for close fires.

(2) System response time.

An FDO must ascertain the urgency of each fire mission. Small and medium weapons have a quicker firing response time than heavy weapons. Fire missions sent by the direct support (DS) battalion to reinforcing or GSR units require more processing time than those sent directly to the firing batteries of the battalion.

(3) Predicted fire capability.

The FDO must know the current survey, registration, and met status of all firing units under his control. FFE missions should be assigned to units that have the best predicted fire capability.

## C-4. Determining The Method Of Attack

The final step in the FDO's target analysis is the selection of a method of attack. The FDO selects a method of attack that ensures target area coverage and desired target effects. To determine the best method of attack, the FDO must consider aimpoints, density, and duration of fire, Figure C-4 shows the method-of-attack selection considerations.

a. Aimpoints. Normally, the size of the area to be attacked depends on the size of the target or the size of the area in which the target location is known or suspected. A single aiming point in the center of the target is used to attack small targets. For attacking large targets, multiple aimpoints are designated to distribute the fires and ensure adequate coverage. Appendix E gives procedures for establishing multiple aimpoints.

b. Density. For most targets, uniform density of fires is needed. Several techniques for indirect fire weapons produce such results. These include zone and sweep fires either from a single unit or simultaneous attack by multiple units on different portions of the target.

c. Duration. Accurate surprise fires produce the most effective results. Time on target procedures place initial rounds from all units on the target at the same time and achieve the greatest surprise.

While intense fires of short duration generally produce the best results, the tactical situation may require that fires be continued over a longer period of time. Some examples are harassing and interdiction fires, screening smoke, continuous illumination, and suppressive fires supporting a maneuver final assault on an objective.

## C-5. Predicting Weapons And Munitions Effects

a. The most important step in performing target analysis is determining the number and type of rounds required to produce the desired effects on a target. The time available to perform the target analysis largely determines the tools used to predict effects. An analyst at the division fire support level can use the JMEMs for guidance while the FDO at battalion or battery level, because of time constraints, can used the GMET.

b. A JMEM for world artillery and mortar systems will be distributed in fiscal year 1997
on a compact disk (CD). It will be a single source of information on US and foreign weapon systems and their effectiveness and the data and methodologies used to generate these effects.

Information will be provided on the following:

US and foreign artillery and mortar weapon systems characteristics. Damage mechanisms.
Delivery accuracy. Reliability.

Mission planning. Target acquisition. Target characteristics. Target environments. How weapon effectiveness is determined.

Additionally, expected fractional damage and casualties can be generated for user-selected weapon-target-engagement condition combinations. This JMEM on a CD can be used as a training tool and a source of combat effectiveness information.

## A-6. Joint Munitions Effectiveness Manuals

Effectiveness tables published in JMEMs for surface-to-surface weapons (JMEM/SS)
provide guidance for determining the expected fraction of casualties to personnel targets or damage to materiel targets. The JMEM/SS are published as field manuals. The current manuals are as follows:
155-mm, M109A6, M198, and Tactical Missile System: M39 Launch Rocket System (MLRS):
FM 101-60-25, Change 3, Effectiveness Data for Howitzer, 155-mm M198 and M109A2/A3 (23 Oct 94). Revision 1 is scheduled for distribution in fiscal year 1996. It will be titled Effectiveness Data for Howitzer, M109A2/A3/A4 (1 Sep 84). FM 101-60-35, Effectiveness Data for the Army (Army-TACMS Block I) (S) (18 Nov 94). FM 101-60-28, Effectiveness Data for the Multiple 227-mm, M270 (3 May 94).

Each of these manuals contains a personal computer (PC) program and associated database to compute weapon effectiveness for conditions not displayed in the manual. Effectiveness data in these manuals are listed for the following targets and conditions.

a. Personnel Targets. Square target sizes of 100,250,500, and (for MLRS only) 1,000
meters on a side are given.

Data are listed for standing, prone, prone protected, and fighting position postures.

b. Materiel Targets.

A short description of the following targets and their vulnerabilities are included:
 T-62, medium tank. T-72Ml/T-80, medium tank. BMP-1, armored infantry combat vehicle. BDRM-2, armored amphibious reconnaissance vehicle.

 BTR-60pB, armored personnel carrier. 122-mm and 152-mm self-propelled howitzers.

122-mm and 152-mm towed howitzers. 122-mm multiple rocket launcher.

ZSU-23-4, antiaircraft gun. ZIL-157, medium truck. KrAZ-214, heavy truck.

FROG-7B, rocket and launcher.

Scud-B, missile and transporter-erector-launcher. SA-8, missile system.

SA-13, missile system.

Straight Flush radar.

The JMEM/SS are constantly updated, and other materiel targets will be added to the above list as data become available.

c. Environment. Data for personnel targets are listed for open terrain, marsh grass, temperate forrest, coniferous forest, and several urban environments. Data for materiel targets are listed for open terrain and a limited set of targets for several urban environments.

d. Methods of Delivery. Data are given for observer-adjusted and BCS techniques.

e. Aim Policy.

Data are given for BCS aimpoint techniques for howitzers, MLRS
aiming policy for MLRS, and a single aimpoint for the Army tactical missile system (ATACMS).

f. Ammunition. Data are given for HE and DPICM (M483A1 and M864).

## Caution

There is no assurance that the expected fraction of damage or casualties will be provided by any number of volleys in a given situation. Although not precisely within the mathematical definition, the method of averaging data used for the tables will result in less damage being realized for approximately
50 percent of the rounds and, conversely, greater damage for the other 50 percent of the rounds.

## C-7. Graphical Munitions Effects Tables (Gmets)

a. Purpose. Although the JMEMs provide excellent effectiveness data, the usefulness of these publications to the FDO during field operations is limited by their volume and difficulty of easily cross-referencing information.

The GMETs overcome these limitations by providing quick access to munitions effectiveness data. The effectiveness data found on a GMET is not as accurate as the JMEM, but the compromise in accuracy is offset by the speed of obtaining information.

## B. Table Description.

(1) The GMET consists of a loose-leaf binder with introductory text and instructions for use followed by the tabulated data.

The tabulated data allows the user to determine the number of battery or battalion volleys needed to achieve the desired fractional damage. The number of volleys determined is a function of the following:
Weapon system. Environment.

Delivery accuracy.

Target location error (TLE). Size of target.

Target posture.

Ammunition selected.

The following assumptions were made when compiling data for the GMET:
(a) Targets are engaged by using BCS aimpoint techniques. The GMETs for the M102/M119 and M198 assume that you are engaging targets with a six-gun battery. The GMETs for the Ml09-series howitzer assume you are engaging targets with a four-gun platoon.

(b) To maintain a constant probable error, all volleys are considered to be fired at two-thirds of the maximum range of the specific weapon system.

(c) The GMETs use a center-of-battery to center-of-target solution for effects.

(d) If the number of rounds needed to achieve the desired results exceeds 30
battery or 10 battalion volleys, the letter "P" (prohibited) is listed because any additional volleys will not achieve a significant increase in casualties. The letter "E" (excessive) indicates that the casualties obtained would be in excess of the specified casualty level.

(e) The percentage of casualties (%CAS) is expressed as the average expected fraction of casualties. Against personnel targets in an offensive posture, the assumed desired average expected fraction of casualties are 30, 20, and 10 percent (.30, .20, and .10). For targets in a defensive posture, the assumed casualties are 10, 5, and 2 percent. The casualty percentages for the defense are lower than those for the offense because of greater shielding of targets. Also shown is the average expected fraction of casualties for one battalion and one battery volley. The number of expected casualties is the product of the average expected fraction of casualties and the number of personnel in the target area.

(f) The target posture for personnel in an offensive posture is assumed to be one half standing and one half prone for the first volley and all prone for sustaining volleys. For personnel in the defensive posture, one half are assumed to be prone and one half are in foxholes for the initial volley, and all personnel are assumed to be in foxholes for subsequent volleys.

(g) ICM is APICM. The ICM reflected on the GMET are only for APICM.

(h) The effects listed are based on targets located by observer adjustment
(observer adjusted) and met + VE delivery techniques. If the FDO is confident of target location, he may select TLE O, or if the FDO's confidence of the accuracy of target location is suspect, TLE + 75 can be selected.

(i) The target size for various targets is listed on each table of the GMET.

(2) The current GMETs were produced in fiscal year 1996 and represent a significant improvement over previous GMETs.

Previous GMETs consisted of a body and cursor similar to GFTs and used aimpoint techniques used for a six-gun battery firing a parallel sheaf. Also, there were no data for the DPICM family of projectiles. Unclassified versions of the previous editions of the GMETs (with body and cursor) are available and can be used for training purposes only. See Figure C-5.

## C-8. Quick Reference Tables

a. If JMEMs or GMETs are not available, the FDO can use the guide for cannon attack of typical targets (Table C-2).

The table lists selected personnel and materiel targets and indicates the order of effectiveness for each shell-fuze combination. Targets not indicted should be equated to targets that are listed. The table can be used for all calibers.

b. The expected area of coverage table (Table C-3) can be used to determine the appropriate size of a battery one volley or battalion one volley of both HE and ICM for the various caliber weapon systems. The FDO can use Table C-3 to determine the size target that can be attacked by use of battery or battalion volleys. The density of coverage is not considered, but the density of coverage of ICM is much greater than that of HE.

c. The expected fraction of casualties or personnel table (Table C-4) can be used to determine the optimum method of attacking a personnel target of 50 meters radius to achieve the commander's criteria. Table C-4 cannot be used for material targets.

## C-9. Examples

The following examples are to be used for training only. They are based on previous versions (Figure C-5) of the GMET that are still available. To determine the amount and type of munitions needed to achieve suppression, neutralization, and destruction of targets, use the procedures in Tables C-5 and C-7.

## C-10. Terminal Ballistics

Terminal ballistics may be defined as the study of the effects of projectiles on a target.

The theory of terminal ballistics is relatively new compared to the theory of internal and external ballistics.

The techniques of investigation for impact on solid targets consist primarily of empirical relations (based on experiments), analytical models, and computer simulations. In terminal ballistics, we are dealing with the shock caused by the detonation of the HE filler. The effects are most pronounced if the shell penetrates the surface of a target before detonation.

## C-11. Munitions Effects

a. High Explosive.

The use of the HE with its many different fuze combinations
(PD-Superquick or Delay, Ti, or VT) is very effective against personnel targets except when they have a high degree of protection. The HE projectile is available for the 105-mm and 155-mm howitzers.

b. HERA Projectile.

This projectile has two distinct advantages over normal HE--increased range and fragmentation. The RAP round is primarily used against antipersonnel and material targets at increased ranges.

The RAP round is available for the 105-mm and
155-mm howitzers.

c. Smoke. There are four different types of smoke in our inventory: HC smoke, colored smoke, white phosphorus, and M825/M825A smoke. The hexachloroethane, or HC
smoke, and the colored smoke are used for screening, marking, and obscuring targets with no casualty-producing effect. The WP projectile is primarily used for incendiary purposes; that is, POL sites and equipment. White phosphorus may also be used as a screening or marking round.

The M825/M825Al, new smoke, is a WP projectile which dispenses 116 WP impregnated felt wedges. The build-up time is much quicker, and the duration (5 to 10 minutes) is longer than normal HC or WP. The smoke projectile (HC, colored, and WP) are available for the 105-mm and 155-mm howitzers. The M825/M825A1 is only available for the 155-mm howitzer.

d. Chemical (Gas). This munition incapacitates the enemy either by choking, blistering exposed tissue, or attacking the nervous system. The chemical projectile is most effective when deployed with other types of munitions. The chemical projectile is available for the 105-mm and
155-mm howitzers.

e. Illumination. The illum projectile is primarily used for night attack or defense, as a ground marking round for a particular target, and for harassment. The illum projectile is available for the 105-mrn and 155-mm howitzers.

f. Antipersonnel (Beehive). The Beehive projectile was designed for direct fire battery defense. The projectile acquired its name because of the 8,000 flechettes, or "steel darts," housed within the body. The projectile is available for the 105-mm howitzer only and comes fuzed with the M563 fuze set on muzzle action.

g. Antipersonnel Improved Conventional Munitions. This projectile contains antipersonnel grenades (the number varies depending on the caliber of the weapon) which are extremely effective on antipersonnel targets.

APICM is available for 105-mm and 155-mm howitzers.

h. Dual-Purpose Improved Conventional Munitions. This projectile contains antipersonnel and antimaterial grenades. As with APICM, the number of each type of submunition depends on the caliber of the weapon. This projectile was designed for use against equipment, lightly armored vehicles, and personnel.

DPICM is available for the 155-mm howitzer.

i. Family of Scatterable Mines.

There are two types of artillery delivered mines:
ADAM and RAAMS. The ADAM was developed for use against personnel targets, to deny terrain, and to block avenues of approach.

RAAMS was developed for use against armored targets. Both the ADAM and RAAMS have preset self-destruct times of either short (within 4
hours) or long (within 48 hours). FASCAM is available for the 155-mm howitzer only.

j. Copperhead. The CLGP, or Copperhead projectile, was designed for high-payoff targets such as enemy armor or command bunkers.

The projectile has three distinct sections:
guidance, warhead, and control. The round is loaded and fired the same as with other projectiles but with a special switch setting placed on the projectile before firing. It is laser-guided to the target. The Copperhead projectile is only available for the 155-mm howitzer.

k. M864 Base Burn DPICM. This projectile is a 155-mm projectile that extends the maximum range of DPICM to 22.2 km for the Ml09A2/A3 and 28.4 km for the M109A5/A6
M198 howitzers. The projectile contains 72 dual-purpose grenades. A base burner assembly containing 2.6 pounds of HTPB-AP propellant is assembled to the base of the projectile body.

When the weapon is fired, the propelling charge ignites the propellant in the base burner assembly. The gases expelled from the base burner unit greatly reduce drag behind the base, thus increasing projectile range. The projectile will not be used for training; all assets will become war reserve. Data may be computed manually by using FT 155-AU-PAD and FT 155-ADD-U-PAD.

Automated procedures will become available with the fielding of version 10 software for the battery computer system.

## C-12. New Experimental Projectiles

a. M898 Sense and Destroy Armor.

M898 SADARM artillery munitions are in engineering and manufacturing development for the 155-mm howitzer delivery systems. The SADARM submunitions are delivered by a DPICM-family projectile and are dispensed over the target area. The submunitions will orient, stabilize, and descend by parachute over the target area. When a target is identified within the submunition scan area by millimeter wave or infrared sensors, an explosively formed penetrator will fire from the submunition into the target.

b. XM915/916 105-mm DPICM. The XM915 cartridge is a semifixed 105-mm DPICM projectile which is compatible with the Ml19 howitzer. It uses the M229 zone 8 propelling charge. The maximum range is 14 km. The XM916 cartridge is a semifixed 105-mm DPICM projectile which is compatible with the M101A1, M102, and M119 howitzers. It uses the standard M67 propelling charge.

The maximum range is 11 km. Both projectiles contain a submunition payload of 42 dual-purpose XM80 submunitions, which will be approximately twice as effective as the current M444 APICM projectile.

c. M913 105-mm RAP. The M913 cartridge is a semifixed 105-mm RAP which is compatible with the M119 howitzer. It uses the M229 zone 8 propelling charge. The maximum range is 19.5 km. The M913 will be produced for all M119 units Armywide and will be held in war reserve.

## Appendix D Planning Ranges

This appendix provides information on the minimum and maximum ranges for planning purposes for the following weapon systems:
105 mm (Table D-1). 155 mm (Tables D-2, D-3, and D-4).

203 mm. MLRS.

## Appendix E Replot Procedures

In many instances, the refinement data transmitted by the observer after the FFE phase may not reflect the actual location of the target as defined by its grid coordinates and altitude.

This inaccuracy results from errors in initial target location and errors in determining the initial site fired in an adjust-fire mission. For other units to mass fires on the same point and for the observer to accurately shift from a known point located by firing, the actual target location and altitude must be determined as accurately as possible. The replot process is used for this purpose.

Targets are replotted on request of the observer or when directed by the FDO. Replot gives a deflection and range with which the target location can be polar plotted from the location of the firing unit.

The manual replot procedures are the same for PD and VT fuzes. The procedures for the time fuze are somewhat different.

NOTE: The resulting target location reflects any errors that exist in the firing data and unit location. The replot grid and altitude may differ from the survey location of the same target for this reason.

## E-1. Reasons For Replot

a. Inaccurate target location by the observer may result in an inaccurate altitude and an inaccurate site being determined by the FDC.

For example, in Figure E-1, the observer's inaccurate target location included an altitude greater than the actual target altitude. On the basis of the inaccurate target altitude, a false site is determined and used. The observer sends a subsequent correction of **DROP 400.** The firing data computed reflect the data needed to cause the round to impact at Point A. Because no adjustment has been made to altitude, the projectile continues beyond Point A and impacts over the target. As shown in Figure E-2, the observer's next correction **(DROP 50)** results in accurate fire for effect. Figure E-2 also shows that there is a difference between the final pin location on the firing chart and the actual target location.

Target replot is required to correct for this error.

Replot procedures use successive approximation to determine the true site and the actual (replot) range and deflection to the target.

b. Requirements for replot are as follows:
A map. Accurate refinement data from the observer. Valid GFT setting that accurately accounts for the nonstandard conditions existing at the time of firing.
These elements will ensure that the replot procedure is as accurate as possible. Should the GFT
setting or firing chart be later corrected to more accurately reflect the conditions that existed when the mission was fired, the replot should be recomputed with the more accurate data.

## E-2. Replot With Pd And Vt Fuzes

a. Replot Deflection. The replot (true) deflection to the target may or may not be the final piece deflection.

Because drift may have changed during the conduct of the adjustment, determine the true total deflection correction as shown in Table E-1. (See Figure E-3.)
b. Replot Grid and Altitude. Determine the replot grid and altitude by successive approximation: The procedures are described in Table E-2.

## E-3. Time Refinement

To accurately replot targets when firing fuze time, determine refinement data to correct for inaccurate HOB.

a. During the adjustment phase of the mission, the observer usually adjusts the trajectory to within 50 meters of the target before requesting FFE rounds. Upon completion of the FFE phase, the observer sends refinement data to the FDC. Elements of refinement may include deviation, range, and/or HOB. These refinement data place the mean point of the FFE
bursts over the actual target location, thereby allowing the FDC to compute accurate data to the target if future fires are required. Application of refinement is a requirement for replot of targets, which allows for transfer and massing of fires.

b. Fuze time procedures are slightly different. During the time adjustment phase of the has mission, the FDC applies L FS to the fuze setting to correct for the difference in the height of burst above the target. Therefore, when he requests fire for effect, we assume the observer adjusted the height of burst to 20 meters.

c. Time refinement procedures **without** an HOB correction are shown in Table E-3.

e. Time refinement procedures **with** an HOB correction are shown in Table E-4.

## E-4. Replot With Time Fuze

a. When a target is attacked with a mechanical time fuze, the observer adjusts the height of burst to 20 meters above the target. The final fuze setting provides an accurate representation of the target location and the altitude of a point 20 meters above the target. Consequently, when the time gauge line is placed over the final time, the range and 100/R (read under the MHL) and the elevation and drift correction (read under the elevation gauge line as a function of elevation)
are true. The replot grid and altitude can then be determined (See Figure E-4.)
b. Replot deflection procedures are shown in Table E-5. (See Figure E-5 on page E-8.)
c. The procedures for determining replot grid and altitude are shown in Table E-6.

## E-5. Attack Of Large Targets

In a manual FDC or one equipped with the BCS operating autonomously, the FDO
decides how to attack a target. In determining the volume of fire to place on a target, he uses the GMET and the JMEM as guides. Calls for fire may include targets too large to be considered with the GMET, since the largest target radius considered in the GMET is 250 meters. Large or irregularly shaped targets require special fire distribution techniques to ensure proper coverage with the most effective use of the ammunition available. The following paragraphs describe various methods of attacking large targets that have proved successful. The FDO and S3 should use the technique that best accomplishes the mission.

a. Target Division Method. Targets that exceed the firing capability of one battery should be sent to battalion FDC for additional fires. There are times, however, when the battery is forced to fire on targets that exceed its capability. When this occurs, the battery FDO may divide the target into several targets to distribute his fires effectively.

(1) Determining aimpoints for a linear target. Because the basic linear sheaf for a four-gun 155-mm platoon is 200 meters, a linear target must be segmented into 200-meter lengths. For a six-gun 155-mm platoon, the length is 300 meters; 8-inch six-gun platoon, 480
meters; and 105-mm four-gun platoon, 120 meters. The procedures for determining aimpoints for a linear target are shown in Table E-7.

(2) Determining aimpoints for a rectangular target. Because the four-gun platoon optimum rectangular sheaf is a 100- by 100-meter sheaf, the target must be broken into 100- by
100-meter boxes to effectively engage a large rectangular target.

c. Determining Aimpoints for Subtargets.

The battalion could receive a call for fire for a large target, or if a battery receives a call for fire and requests reinforcing fires, the battalion FDO
must also be able to attack a large target. He uses the firing elements of his battalion to attack the large target, and must be able to determine aimpoints for each firing unit. The battalion FDO will normally divide large or irregularly shaped targets into subtargets for each firing unit. The appropriate subtargets are announced for each unit in the battalion fire order. The fire order should include the center grid and if necessary the attitude. The battalion FDO can also issue guidance in the fire order as to how the subtargets should be subdivided. To determine the aimpoints for the subtargets, the FDO can use the same techniques discussed in paragraphs a and b.

If the subtargets described above had required further subdivision (for example, sweep and zone), the battalion FDO could have designated how the batteries were to attack the target:
FIRE FOR EFFECT, BATTALION, ALPHA GRID 618234, BRAVO GRID 617232, CHARLIE
GRID 615229, ALTITUDE 380, VT, EIGHT ROUNDS, SWEEP AND ZONE, TIME ON TARGET.

As an alternate method, the FDO could have said:
FIRE FOR EFFECT, BAITALION, ALPHA GRID 618234, BRAVO GRID 617232, CHARLIE GRID 615229, ALTITUDE 380, AITITUDE 200, PLACE BURSTS 60 METERS APART, VT, EIGHT ROUNDS, TIME ON TARGET.

This indicates to each battery not only center grid, but also the type of sheaf they are to fire.

c. Massed Fire Distribution Template. In this method, the large or irregularly shaped target is plotted on the firing chart. A locally constructed massed fire distribution template drawn to scale for the firing chart is placed over the plotted target to allow the user to determine the optimum aimpoints for the required number of firing elements to mass fires.

(1) Constructing the Template.

Overlay paper is the best material for constructing the template. Each tick mark placed on the template represents an aimpoint for a firing element (Figure E-6). A separate template is required for each caliber, munition type, and size of firing element (one gun, platoon, or battery). (Refer to the appropriate JMEM for this information.) Distance between tick marks is based on the radius of effects of the particular weapon system and munitions to be fired. (Refer to (C) FM 101-60-25.)
(2) Using the Template.  Table E-11 discusses how to use the template.

## Appendix F Automated Fdc

While the means of technical fire direction is different, the basic operation of an automated FDC is similar to that of a manual FDC.

## F-1. Personnel

Duties of the FDO and chief fire direction specialist are the same as in a manual FDC.

The equivalent USMC billet description is operations chief.

a. Senior Fire Direction Specialist. The senior fire direction specialist (computer)
operates the computer that is the primary means of determining firing data. He is responsible for the transmission of fire commands (voice or digital) to the howitzer sections. The equivalent USMC billet description is operations assistant.

## B. Fire Direction Specialist (Usmc--Fire Control Man).

(1) Recorder. The recorder maintains the record of fire, recording information as directed by the FDO. The recorder may also be required to operate the computer that is the backup means of determining firing data.

(2) HCO and VCO. The HCO and VCO maintain a firing chart and follow each mission. The HCO and VCO check the coordinates on the firing chart and provide target altitude as required. The HCO and VCO maybe required to operate the backup computer as well.

## F-2. Fire Order

The FDO considers the same factors when determining a fire order in an automated or manual FDC. The order in which the fire order is announced and the elements of the fire order are also the same. The biggest difference between the fire order for an automated FDC and for a manual FDC is the SOP. On the basis of the computer's ability to determine individual piece firing data and the computer programs, certain elements would be standardized differently.

a. Adjusting Element/Method of Fire of the Adjusting Element. On the basis of the computer's ability to compute firing data based on individual piece locations, muzzle velocities, and aimpoints, the use of base piece is not necessary (a base piece should be selected for ease of transition from automated to manual). Depending on the computer's programming, it may automatically select an adjusting piece in sequential order, or the operator may have to input an adjusting piece. Method of fire of the adjusting element would be included in the SOP, which may or may not be a programmed computer default.

b. Basis for Corrections. The SOP for this element should reflect the primary means of computing firing data.

c. Distribution. As in a manual FDC, the observer or FDO will announce the sheaf to fire. In a manual FDC, the normal sheaf is parallel. In an automated FDC, the normal or default sheaf will be the default sheaf programmed into the computer.

d. Ammunition Lot and Charge. The SOP for this element will allow the computer to select the lot and charge to fire on the basis of its programmed selection routines. Safety constraints, availability of registration corrections, and muzzle velocity information, are additional considerations when determining the SOP.

e. Target Number. The SOP for this element is normally the next available, as in manual gunnery. The computer may or may not be programmed to automatically assign a target number.

## F-3. Fire Commands

Fire commands for automated gunnery are exactly the same as for manual gunnery.

Depending on the computer systems in use, fire commands may be transmitted by voice or digitally.

## F-4. Establish A Manual Backup For Automated Operations

a. Concept. The manual backup should be set up to allow the automated (BCS and BUCS primary) FDC to continue operations should the computers fail. Manual backup should be established as a form of "position improvement" and should not impede setup or processing with automated means. The manual backup also serves as a basis of rapidly "checking" the automated solution. The basis for the manual backup is that a piece will be designated as the base piece.

The location of this piece is plotted on the firing chart. GFT settings are derived by using this piece and reflect its muzzle velocity and TGPCs. Once the FDC converts from automated to manual operations, all adjustments are conducted with the base piece. All ranges are measured from base piece to the center of the target and all data computed reflects base piece muzzle velocity and location.

When the observer requests fire for effect, the adjusted data from base piece is converted to data for the remaining pieces by applying special corrections, or terrain gun position corrections. These corrections take into account the differences in piece locations
(displacement) and the differences in shooting strength (comparative VEs). TGPCs can be determined by using automated means or the Ml 7 plotting board.

b. Establishment of the Manual Backup. The manual backup is established in five steps as follows:
Select a base piece.

Construct a surveyed firing chart.

Determine and apply GFT settings. Determine comparative velocity errors for the remainder of the guns.

Determine position constants.

Table F-1 elaborates on these steps.

## F-5. Convert A Mission In Progress From Automated To Manual Processing

a. General. Should automated means fail, a battery must continue to process fire missions. With a manual backup established, the FDC continues operations with minimal delay.

b. Procedure. If during the processing of a fire mission the computer fails, the mission is switched to manual processing.

If the observer's total corrections are applied to the firing chart, a significant difference in point of impact in the target area may be noticed because of the difference in automated accuracy.

To make the transition as smooth as possible, the steps in Table F-2 are used.

## F-6. Range K And Fuze K

a. The proportion of correction to range and fuze setting that results from a registration or the solution of a met message is referred to as range K or fuze K. Once determined, range K and fuze K may be used to apply the determined corrections at lesser or greater ranges than that at which the corrections are determined. This procedure allows the application of a "GFT setting" to a TFT.

b. Range K can be determined and applied by using two techniques. These techniques are discussed in Tables F-3 and F-4.

c. Fuze K can be determined and applied by using two techniques. These techniques are discussed in Tables F-5 and F-6.

## Appendix G Determining Data

The purpose of this appendix is to assist in determining data with a GFT.

## G-1. Basic He  Data (155Am2Hemi07 Gft)

The procedures for using the 155AM2HEM107 GFT are discussed in Table G-1.

## G-2. Determine Firing Data From An Ha Gft (Gft Setting Applied)

Table G-2 shows the procedures used to determine firing data from a high-angle GFT
with the GFT setting applied.

## G-3. Dpicm Data (155Am2Hem107 Gft)

The procedures for using the 155AM2HEM107 GFT to determine DPICM data are discussed in Table G-3.

## G-4. M825 Smoke Data (155Am2Hem 107/M825 Gft)

The procedures for using the 155AM2HEM107M4825 GFT to determine smoke data are
-
discussed in Table G-4.

## G-5. Adam And Raams Data (155Anim483A1 Gft)

The procedures for using the 155AN1M483A1 GFT to determine ADAM and RAAMS
are discussed in Table G-5.

## G-6. Construct A Gft Setting From An He Registration On An Illuminating Gft

Table G-6 shows the procedure for constructing a GFT setting from an HE registration on an illum GFT.

## G-7. Determine Firing Data From An Illuminating Gft (Gft Setting Applied)

Table G-7 shows the procedures for determining firing data from an illuminating GFT
with a GFT setting applied.

## G-8. Examples

a. Table G-8 shows the procedures for determining firing data from a low-angle HE
GFT (GFT setting applied) for an HE adjust fire mission with fuze VT in effect. The GFT setting determined from the registration is:
GFT I/A: Chg 4, Lot AG, Rg 4960, El 315, Ti 18.6
Tot Df Corr RIGFT Df Corr R7
Apply the GFT setting to the appropriate GFT. The HCO announces the following chart data:
ONE ALPHA, RANGE 6220, DEFLECTION 3214.

The VCO announces SITE -6.

b. Table G-9 shows the procedures for determining firing data from a low-angle HE
GFT (GFT setting applied) for an HE adjust-fire mission with shell DPICM in effect. The GFT
setting determined from the registration is:
GFT I/A: Chg 4, Lot AG, Rg 4960, El 315, Ti 18.6
Tot Df Corr RI GFT Df Corr R7
Apply the GFT setting to the appropriate GFT. The HCO announces the following chart data:
ONE ALPHA, RANGE 6220, DEFLECTION 3214.

The VCO announces SITE -7.

NOTE: The steps in Table G-9 are for determining DPICM firing data once the HE
rounds have been adjusted. The steps for determining HE firing data are the same as shown earlier.

c. Table G-10 shows the procedures for determining firing data from a high-angle GFT
-
-
(GFT setting applied). The GFT setting determined from the registration is:
GFT I/A: Chg 3, Lot AG, Rg 4960, El 1114
Tot Df Corr L34 GFT Df Corr R18
Apply the GFT setting to the appropriate GFT. The HCO announces the following chart data:
ONE ALPHA, RANGE 4600, DEFLECTION 3310.

The VCO announces ANGLE OF SITE -9.

NOTE: Figure G-3 shows a completed ROF for an HE high-angle FFE mission with fuze VT in effect. Firing data were determined by using a GFT setting.

d. Table G-11 shows the procedures for constructing a GFT setting on an illum GFT
(HE registration). The GFT setting determined from the registration is:
GFT I/A: Chg 7, LOT AW, Rg 12100, El 472, Ti 38.8
Tot Df Corr LO GFT Df Corr L14
Apply the GFT setting to the appropriate illum GFT.

e. Table G-12 shows the procedure for determining firing data from an illum GFT with a GFT setting applied. Use the GFT setting shown in paragraph d to determine firing data. The HCO announces the following chart data:
ONE ALPHA, RANGE 11000, DEFLECTION 3310.

NOTE: Use the 550 HOB scale to determine firing data.

NOTE: Figure G-4 shows a completed ROF for an illum range and lateral spread fire mission. Firing data were determined by using a GFT setting.

## Appendix H Special Situations

This appendix is a supplement to Chapter 13, which details the more common "special situations" missions.

## H-1. Final Protective Fires

A final protective fire is an immediately available prearranged barrier of fire designed to protect friendly troops and installations by impeding enemy movements across defensive lines or areas. The normal use of an FPF is to establish prearranged close-in defensive fires, which include other artillery fires, minefield, obstacles, final protective machine gun lines and small-arms fire, and final protective fire of mortars.

Each battery is assigned one FPF and normally is laid on that FPF when not firing other missions. The FPF may be fired on prearranged signal or on call from the supported unit. The firing of an FPF maybe repeated on call as often as necessary. When time and ammunition permit, the FPF can be adjusted or check rounds fired. A battery FPF may be fired either individually or in coordination with those of other batteries.

a. Width of FPF. The width (or length) of the FPF that can be covered by a single battery without shifting its fire should not exceed the width of an open sheaf for the battery concerned. When necessary, the width (length) of the FPF may be increased by agreement between the commanders of the artillery and the supported unit. However, the effectiveness of fire will be decreased.

b. Preparation of Data. The actual map location of the FPF is reported by the supported unit through the various fire support channels. The FPF is assigned to an artillery unit, which is responsible for computing the firing data. Since the FPF usually is located within a very short distance of positions occupied by friendly troops, precise computational procedures must be employed and all available corrections must be applied.

Special corrections in the form of computations must be made to bring each burst calibration corrections and position corrections, obtained by use of the M17 plotting board, are determined and applied as individual piece corrections. When the axis of the FPF is other than perpendicular to the direction of fire, additional to a desired point on the FPF line.

final protective fires is as outlined in FM 6-30, c. Call for Fire. The call for fire for Chapter 7.

## H-2. Computational Procedures

There are two techniques for determining FPF data: observer-adjusted FPF and nonadjusted FPF.

Both techniques will result in the determination of firing data that are announced to the howitzers and that are used to lay the howitzers when they are not involved in other fire missions.

b. Observer Adjusted FPF. The observer will adjust the burst of each round to its desired location on the FPF sheaf. He starts with the flank round that impacts to the location of the desired sheaf and continues the adjustment until all howitzers have been adjusted. (See Table H-1.)
c. Nonadjusted FPF. When the situation does not permit the adjustment of each burst to its location on the FPF sheaf, the FDC determines firing data by using standard FFE techniques, In the call for fire, the observer should include the altitude of FPF and the length, if different from that of an open sheaf. The FDC will compute special corrections with the M17 for a linear sheaf and determine the FPF firing data. The FPF firing data will be announced to the howitzers and, as in observer adjusted FPFs, the howitzers will lay on the FPF data when not involved in other fire missions.

## H-3. Laser Adjust Missions

a. An observer equipped with a laser can determine accurate target locations if the laser is accurately located. If the observer has directional control and his accurate location has been recorded at the FDC, he should request first-round fire for effect. If the observer does not feel he can achieve first-round fire for effect on the target, he should request an adjust-fire mission, The FDO may also decide to fire an adjustment if the FDC cannot account for some of the requirements for accurate fire. This may occur even if the observer requests first-round fire for effect.

b. Most laser missions, if not fire for effect initially, should require only one adjusting round. Fire for effect should be requested by the observer unless he determines the lasing of the burst is not satisfactory.

Many variables could cause an unsatisfactory lase. For example, an observed burst partially obscured by trees or intermediate hill mass would yield inaccurate land distance to the burst. The **total deviation** between the target and the adjusting burst does not generally determine if fire for effect is requested. Rather, the observer need only determine if an accurate lase to the burst has been obtained.

c. The observer uses the polar method of target location to determine the target location.

He transmits the target location in his call for fire. (See Figure H-1.)
d.  The adjusting round is fired and the observer reports the direction, slant distance, and VA to the burst. (See Figure H-2.)
e. The FDC determines the fire for effect aimpoint from the total corrections necessary to engage the target. (See Figures H-3 and H-4 on page H-4.)
f. If additional adjustment is required, continue to plot the burst locations and compare each to the initial target location.  Apply each correction determined to the previous aimpoint location **not** the initial target location.

g. The M17 plotting board may also be used to determine corrections (see Chapter 12).

## H-4. Laser Adjust-Fire Mission

Table H-2 shows the procedures for a laser adjust-fire mission.

## H-5. Radar Adjust-Fire Missions

a. The AN/TPQ-36 and -37 radars are used as counterbattery radars. They have survey capability, which allows them to determine accurate locations of enemy firing bursts. If used in the friendly mode, the radars are capable of determining burst locations of rounds fired by friendly units.

b. The initial target location for a radar adjust-fire mission can be determined by radar in the case of enemy firing units or by another observer.  Once the initial target location is established and the initial round is fired, the radar will trace the round and report the spotting of the burst by grid coordinates and altitude. (See Figure H-6.)
c. The FDC then determines the corrections needed to move the burst to the target and determines the FFE aimpoint. (See Figure H-7.)
d. Once the FFE aimpoint location is established, FFE fire commands can be determined.

e. If additional adjustment is required, continue to plot the burst locations and compare each to the initial target location. **Apply** each correction determined to the previous aimpoint location, **not** the initial target location. When orienting the target grid for direction, **any** direction will produce the desired results. Each burst location will be reported by using grid coordinates.

The target grid is used only to determine the magnitude of the correction needed and the direction of the corrections relative to the orientation (direction) of the target grid that has been chosen.

f. Another way to determine the corrections would be to mathematically determine the difference between the grid coordinates of the target location and burst location (Table H-3). The corrections would be applied by using a target grid oriented to grid north (0000). Continued adjustment would be performed by determining the difference between each burst location and the initial target location. Each correction would be applied to the previous aimpoint.

## H-6. Destruction Mission

a. General. The purpose of the destruction mission is, as the name implies, to destroy the target. This requires a target hit. The mission is conducted with a single gun and closely parallels precision registration procedures. Given the dispersion suffered by indirect fire weapons and the requirement for a target hit, the great expenditure of ammunition required becomes apparent. This requirement for ammunition and the ensuing possible disclosure of the firing unit make a destruction mission a less desirable method of engaging targets. Whenever possible, other methods or other means of attack should be considered.

b. Conduct of the Destruction Mission. The destruction mission follows the same procedures as a precision registration until the observer establishes a 25-meter bracket. Once it is established, the observer will split the 25-meter bracket by adding or dropping 10 meters and will continue to fire additional rounds. After every third round, additional corrections are announced if necessary. The observer may make corrections after each round. This will continue until the target is destroyed or the observer or FDO chooses to end the mission. At intervals, the observer may request a change of fuze from delay or concrete-piercing to fuze quick to clear rubble and debris around the target.

## H-7. Sweep And Zone

Sweep and zone fires provide a method for the attack of large or irregularly shaped targets. The advantage of sweep and zone fires is the ease with which they may be computed in comparison to attacking the target by using special corrections. The disadvantages are the great quantity of ammunition that must be expended and the time required to do so. The resulting loss of surprise and potential for disclosing the firing unit location make sweep and zone fires a less appealing alternative.

The FDO should weigh these considerations before attacking targets by using sweep and zone techniques.

Possible alternatives are the use of special corrections or dividing the target among a number of firing units.

## A. Computation Of Sweep.

(1) Sweep fires are used to cover a wide target with fire. (Wide target is described as a target whose long axis lies perpendicular or nearly perpendicular to the GT line.) Sweep fire is similar to traversing fire applied with direct fire weapons. The purpose of the sweep is to cause the guns to fire a number of deflections (at the same quadrant elevation) to place a number of sheafs side by side over the target.

(2) Chart data are computed as with any area target.

(3) The number of deflections to fire is determined on the basis of the width of the target and by the sheaf front.

(a) Determination of sheaf front. The sheaf front is the lateral distance between the center of the flank bursts, plus one effective burst width. The size of the sheaf front depends on the type of sheaf fired and the burst width of the projectile. For an open sheaf, the sheaf front is computed as number of bursts multiplied by the burst width for the projectile. The sheaf front for a circular sheaf is the distance across the center of the circle from burst to burst plus one burst width. If special corrections or TGPCs are being used, the size of the sheaf front will correspond with the sheaf front used to determine those corrections. Converged sheaf should not be used as the concentration of fire on a single point. This is contrary to the purpose for sweep fire. The front for a converged sheaf is one burst width. (See Table H-4.)
(b) Determination of the number of deflections to fire. To determine the number of deflections to fire, divide the target width by the sheaf front. If the result is an even number, the result must be expressed UP to the next higher odd number. Because fire commands will be sent to the guns with the center data and special instructions addressing the size and number of shifts, a center sheaf and equal number of sheafs on either side require that an odd number of deflections be fired.

(4) The number of mils by which the guns must change the center deflection in order to fire the sheafs is the deflection shift. The deflection shift is computed as the sheaf front divided by chart range in thousands.

(5) Fire commands are sent as with any area fire mission. The time, deflection and quadrant to the center are announced. The special instruction SWEEP, (the value of the deflection shift) MILS, (the number of deflections) DEFLECTIONS is announced. The number of rounds announced in the method of fire for effect is the number of rounds to be fired at each deflection.

## C. Computation Of Zone.

(1) Zone fires are used to cover a deep target with fire. (Deep target is described as a target whose long axis lies parallel or nearly parallel to the GT line.) Zone fire is similar to searching fire applied with direct fire weapons. The purpose of the zone is to cause the guns to fire a number of quadrants (at the same deflection) to place a number of sheafs "stacked" over the target.

(2) Chart data are computed as with any area target.

by dividing the depth of the
(3) The number of quadrants to fire is determined target by the sheaf depth.

(a) Determination of sheaf depth. The sheaf depth is the distance between the center of the foremost and rearmost burst. The size of the sheaf depth depends on the type of sheaf fired and the burst width of the projectile. For an open sheaf, the sheaf depth is computed as the burst width for the projectile. The sheaf depth for a circular sheaf is the distance across the center of the circle from burst to burst plus one burst width. If special corrections or TGPCs are being used, the size of the sheaf depth will correspond with the sheaf depth used to determine those corrections. Converged sheaf should not be used as the concentration of fire on a single point. This is contrary to the purpose of zone fire. The depth for a converged sheaf is one burst width. (See Table H-5.)
(b) Determination of the number of quadrants to fire. To determine the number of quadrants to fire, divide the target depth by the sheaf depth. If the result is an even number, the result must be expressed **UP**  to the next higher odd number. (Because fire commands will be sent to the guns with the center data and special instructions addressing the size and number of shifts, a center sheaf and equal number of sheafs on either side require that an odd number of quadrants be fired.)
(4) The number of mils by which the guns must change the center quadrant to fire the sheafs is the quadrant shift. The quadrant shift is computed by comparing the elevation corresponding to the range to the center of the target to the elevation corresponding to the center range plus the sheaf depth. The difference is the quadrant shift.

(5) Fire commands are sent as with any area fire mission is announced. The time, deflection, and quadrant to the center are announced. The special instruction ZONE, (the value of the quadrant shift) MILS, (the number of quadrants) QUADRANTS is announced. The number of rounds announced in the method of fire for fire for effect is the number of rounds to be fired at each quadrant.

NOTE: Zone fires are less effective when fired with HE/ti. Since an FS correction is not applied, the chance of graze or high airburst increases as the zone moves from the center. VT is the preferred airburst fuze for shell HE.

d. Sweep and Zone Fires Combined. Sweep and zone fires are used to attack targets that are both wider and deeper than the sheaf covers. The procedures used are the same as when firing sweep or zone fires individually. The special instructions announced in the fire commands are SWEEP, (the value of the deflection shift) MILS, (the number of deflections)
DEFLECTIONS, ZONE, (the value of the quadrant shift) MILS, (the number of quadrants) QUADRANTS. (See Table H-6 on page H-12.)

## H-8. Zone-To-Zone Transformation

a. Zone-to-zone transformation is the technique of converting the coordinates and/or azimuths as expressed in one grid zone to coordinates and/or azimuths of an adjacent grid zone.

When operating near a grid zone boundary, one of the grid zones will be designated as the primary, or base, grid zone. The other will be referred to as a secondary, or adjacent, grid zone.

The decision as to which zone will be primary zone is based on the tactical situation, unit SOP, the directives of the commander, or anticipated location of future operations.

b. Maps printed by the Army Map Service show the differences between universal transverse mercator (UTM) grid zones. Maps that cover an area within 40 kilometers of a UTM
zone junction are printed along the border with two sets of grid line numbers (one set for each zone). One set is printed in black. The other set is printed in blue and corresponds to the adjacent grid zone. Marginal information on the maps also indicates the color that applies to each zone.

c. There are two methods of performing zone-to-zone transformation--the two grid sheets method and the graphic method. The two grid sheets method is considered the fastest and simplest.

(1) Two grid sheets method. For this technique, two grid sheets are prepared and joined to form a large chart (a constructed grid sheet) from which chart data across the zone junction can be determined automatically. (See Figure H-9 on page H-14.)
(a) Preparing the grid sheets. The HCO prepares a piece of chart paper (a grid sheet) for each zone involved. Using a plotting scale and a sharp pencil, the HCO
reproduces on the grid sheets the exact orientation of the zone junction longitudinal and latitudinal lines as they appear on the map of the area of overlap. The HCO marks the edges to be joined with a fine line that is based on accurate measurements taken from the map. He takes care in cutting and taping so that, when the sheets are put together to form one large chart, measurements from the large chart can be made accurately.

(b) Using the constructed grid sheet. No transformation or computation is needed when firing data are determined from a constructed grid sheet. The coordinates are measured and plotted from the grid lines for the respective area. The observer's azimuth is used as announced, and the target grid is emplaced by using grid north of the observer's zone.

(2) Graphic method (battery in primary zone). The procedures for this method are discussed in Table H-7.

## H-9. Aerial Observers

a. Problems Requiring FDC Assistance. Aerial observers may encounter three problems that require special assistance from the fire direction center:
(1) The AO has no fixed direction to the target. Normally, he is moving in relation to the target area. Hence, FDC personnel must be prepared for unusual and changing observer directions or spotting lines.

Each adjustment may have a different observer direction (that is, different magnetic or cardinal direction).

(2) While in the air, the AO may lose his perception of distance and direction. He may request ranging rounds (two rounds impacting 400 meters apart) to help visualize distance and direction in the target area. The observer and FDC personnel must realize that ranging rounds fired along the GT line may disclose to the enemy the general location of the firing unit.

(3) The AO must minimize the time he is exposed to enemy detection. In forward areas, the pilot must fly close to the earth and behind cover as much as possible. Therefore, the AO and his pilot require from the FDC very accurate time of flight, **SHOT,** and **SPLASH** so that the pilot can unmask the aircraft 2 to 3 seconds before the round impacts.

## B. Observer Direction And/Or Spotting Line.

(1) Using GT line adjustment. If the AO knows the location of the firing unit with respect to the target, he may choose to adjust along the GT line. When the AO announces DIRECTION, GUN-TARGET LINE, the HCO plots the target and centers the target grid over the plot with the 0-3200 line (the center arrow) parallel to the GT line.

(2) Using a shift from a known point along the GT line. The AO may announce DIRECTION, GUN-TARGET LINE for a shift from a known point. In this instance, the HCO
plots the known point, centers the target grid, and orients it parallel to the gun-target line. He then plots the observer's shift and determines chart data. He then rotates the target grid around the new pinhole so that the arrow is parallel to the GT line.

(3) Using helicopter instrument readings for direction. When the AO's aircraft is moving in relation to the target area, the AO may use an aircraft instrument reading for his observer direction. As this direction is expressed in degrees, FDC personnel must convert the reading to mils by using the following formula:

## Direction In Degrees X 17.8 = Direction In Mils

For example, if the direction is 250, the direction in mils is 4,450 (250 x 17.8 mils= 4,450 mils).

NOTE: In preparing for AO missions, the VCO (recorder) should mark a target grid in degrees or prepare a conversion chart for quick conversion from degrees to mils.

(4) Using a cardinal direction. The AO may choose to adjust along a cardinal direction (one of the eight principal points of the compass) (Figure H-11, page H-18). When the observer announces a cardinal direction, the HCO converts the direction to mils and orients the target grid to that direction.

For example, FDC personnel would convert direction southwest
(SW) to direction 4,000 mils.

The observer may also shift from a known point by using a cardinal direction. The preferred method for sending direction to the FDC is to send it in degrees if possible.

(5) Using a spotting line. The AO may adjust along a spotting line formed by natural or man-made terrain features, such as roads, railroads, canals, or ridge lines. Before flight, if possible, the AO selects the line, determines the direction, and notifies the fire direction center. While in flight, he may select a line that is more readily identifiable and convenient. The AO may describe the feature in detail and have FDC personnel use a protractor to determine the direction from a map. The HCO
orients the target grid over the target location on this new direction.

## H-10. Ranging Rounds

In his call for fire, the AO may announce **REQUEST RANGING ROUNDS.** This indicates that he wants to see a volley of two rounds that impact 400 meters apart at relatively the same time. Ranging rounds (Figure H-12) are fired only as a last resort, since they reveal the general location of the firing position.

These rounds are fired along the GT line. The HCO
determines initial chart data, and the computer determines initial firing data for the adjusting piece. The computer then adds 400 meters to the announced chart range. Using the new range and the initial chart deflection, the computer determines firing data for the second piece to fire in the volley (usually the other piece in the center platoon).

Ranging rounds are fired at the same time by firing **AT MY COMMAND.** The AO observes the impact of the round and determines the corrections necessary to hit the target. He bases his corrections on the round that lands nearest the target.

He bases his corrections on the round that lands nearest the target. He must specify to the FDC from which round he is adjusting, and the HCO plots the shift accordingly
(Figure H-13).

## H-11. Time Of Flight, Shot, And Splash

In the message to observer, the FDC must specify the time of flight. On all volleys, the FDC must promptly announce **SHOT** and **SPLASH.** The FDC should report changes in the time of flight as the mission progresses.

## H-12. Untrained Observers

a. Calls for fire from untrained personnel acting as ground observers require close attention and initiative from every member of the fire direction center. The FDC personnel must be prepared to assist the untrained observer in his call for fire and adjustment of artillery.

b. FDC personnel must take the initiative if the observer is hesitant or confused in his request for fire support. They must ask leading questions, such as the following:

(1) Where is the target?
(a) What are the grid coordinates of the target? (b) Where is the target in relation to a readily identifiable natural or man-made
feature?

(c) Where are you? How far is the target from you and in what direction is it?
(2) What is the target?
(a) Is the target personnel, vehicles, installations, or equipment?
(b) What is the size of the enemy force? (c) What is the enemy force doing at present?
(d) If the enemy force is moving, in what direction is it moving? How fast is the force moving?

(3) How close is the target to you? If the target is within 600 meters or closer to other friendly troops, the observer may need to "creep" the rounds to the target.

(4) What is your direction to the target?
(a) What is the azimuth to the target in degrees or mils?
(b) What is the cardinal direction to the target (N, NE, E, SE, S, SW, W,
NW)?

(c) Is the direction along a natural or man-made feature?
(5) What effect do you need on target?
(a) Is the target shooting at you? (b) Is it necessary to obscure vision of the target? (c) Do we need to neutralize or destroy the target?
c. The FDC personnel must explain to the observer what artillery fire he is getting. If necessary, the FDC members must educate or inform the observer as follows:
(1) You will see one round that will look like a cloud of dust. You will get more rounds when you move the burst within 50 meters of the target.

(2) The round is now on the way and will impact in (so many) seconds.

d. The FDC personnel must help the observer in making corrections. They must help the observer move the rounds to the target and must be prepared for unusual shifts. To obtain corrections, they should ask leading questions such as the following:

(1) Where did the round land in relation to the target?
(a) Did it land left or right? How far?
(b) Did it land over or short? How far? Ask for distances in meters or in the number of football field lengths.

(2) Did the round land closer than the previous round?
NOTE:  The FDO should consider using shell WP to help the observer locate initial rounds.

e. The FDC personnel must use sound judgment. They must decide whether to require the observer to authenticate. They must watch for possible observer misorientation. Also, FDC
personnel must help the observer determine when satisfactory effects on the target have been achieved. In all cases, the FDC personnel must take the initiative.

## H-13. Example Problems

a. Process a Laser Adjust-Fire Mission. The observer transmits the following call for fire:
H57 THIS IS C19, AF POLAR, OVER. DIRECTION 4950, DISTANCE 6990, VA PLUS 5, OVER. BMP WITH DISMOUNTED INFANTRY, ICM IN EFFECT, OVER.

The procedures for processing a laser adjust-fire mission are discussed in Table H-8.

b. Process a Radar Adjust-Fire Mission. The procedures for processing a radar adjust-fire mission are discussed in Table H-9.

c. Process a Destruction Mission. The observer transmits the following call for fire:
H57 THIS IS T03, ADJUST FIRE, OVER.

GRID 375 257, OVER
CONCRETE BUNKER, DESTRUCTION, CP IN EFFECT, OVER.

The following GFT setting is available:
obtained from the radar registration mission located NOTE:  This GFT setting was in Chapter 10.

12100, El 476, Ti 39.3 (M582)
GFT 1/A, Chg 7, Lot AW, Rg
Total Df Corr = 0
GFT Df Corr = R14

The procedures for processing a destruction mission are discussed in Table H-10. Figure H-18 on page H-28 shows a ROF for a destruction mission.

d. Process a Sweep and Zone Fire Mission. The observer transmits the following all for fire:
H57 THIS IS T03, FIRE FOR EFFECT, OVER.
GRID 359 284, OVER
BATTALION ASSEMBLY AREA, LENGTH 600,
WIDTH 300, ALTITUDE 0800, ICM, OVER.

The following GFT setting is available:

GFT 1/A, Chg 7, Lot A/W, Rg 10,000, El 325, Ti 29.1 (M482)
Tot Df Corr R2
GFT Df Corr R11

The procedures for processing a sweep and zone fire mission are discussed in Table H-11. Figure H-19 on page H-30 shows a ROF for a sweep and zone fire mission.

## Appendix I Smoke Tables

This appendix contains the tables for firing smoke missions.

## Appendix J Extract From An-2 Tabular Firing Table

By Order of the Secretary of the Army:
By Direction of the Commandant of the Marine Corps:
PAUL K. VAN RIPER
Lieutenant General U.S. Marine Corps Commanding General Marine Corps Combat Development Command Quantico, Virginia

## Distribution:

Active Army, USAR, and ARNG: To be distributed in accordance with DA Form
12-11E, requirements for FM 6-40/MCWP 3-1.6.19, Tactics, Techniques, and Procedures for Field Artillery Manual Cannon Gunnery (Qty rqr. block no. 0044).

## Glossary A

A as acquired (attack guidance matrix)
AA artillery airburst (Firefinder mission type) AC aiming circle AD artillery datum plane (Firefinder mission type)
ADA air defense artillery ADAM area denial artillery munitions

add a correction used by an observer or spotter to indicate
that an increase in range along the observer-target
line is desired.
adj adjust
adjust fire command that specifies all howitzer sections to
follow the adjusting phase of a fire mission.
adjusted deflection a deflection based on firing and
computed to place the center of impact of a round on
target. This deflection can differ from chart deflection
because of nonstandard conditions.
adjusted elevation an elevation based on firing and
computed to place the center of impact of a round on
target. This elevation can differ from TFT elevation
because of nonstandard condtions.
adjust fire (1) An order or request to initiate an adjustment.
(2) A method of control transmitted in the call for fire by the observer or spotter that indicates he will control
the adjustment of the rounds to the target.
adjustment (1) A process used in artillery and naval gunfire
to obtain correct direction, range, and height of burst
(if time fuzes are used) in engaging a target with
observed fire. (2) The actual subsequent correction
sent by the forward observer or spotter that is expressed in a LEFT/RIGHT, ADD/DROP, or
UP/DOWN format in relation to the actual impact
versus the desired impact of a round versus the target.

admin administrative AF adjust fire AFDO-AXO assistant fire direction ofiicer-assistant executive officer

AI artillery impact prediction (Firefinder mission type) aimpoint (1) A point or points on the ground in relation to the
target that firing data for munitions are calculated for
in order to achieve the desired effects on target. (2) A
point on the ground where employment of nuclear
weapon(s) achieves the desired target effects without
violating the commander's guidance. (3) A point on the ground where FASCAM projectiles are delivered.
aimpt aimpoint
air a spotting or observation by an observer or spotter
indicating that a burst or group of bursts occurred
before impact.
airburst (1) An explosion of a bomb or projectile above the
surface as distinguished from an explosion on impact
or after penetration of the surface. (2) A nuclear
detonation in the air at a height of burst greater than
the maximum radius of the fireball.

alt altitude AMC at my command ammo ammuniton

ammunition lot number the code number that identifies a
particular quantity of ammunition from one manufacturer. The number is assigned to each lot
when it is manufactured.
SI angle of site
angle of departure the vertical angle between the tangent to
the trajectory at the origin and the horizontal or base
of the trajectory.
angle of elevation the smaller angle at the origin in a vertical
plane from the line of site to the line of elevation.
angle of fall the vertical angle at the level point between the
line of fall and the base of the trajectory.
angle of site the vertical angle between the level base of the
trajectory anchor horizontal and the line of site.
angle T the interior angle formed at the target by the
intersection of the observer-target and the gun-target lines.
ANGLICO air and naval gunfire liaison company
AO aerial observer
AOL azimuth of lay
APERS antipersonnel

APICM antipersonnel improved conventional munitions

approx approximate arg argument
ARTEP Army training and evaluation program
ATACMS Army tactical missile system
AT MY COMMAND (1) Restrictive command used to control
time of delivery of fire that prohibits the battery or
battalion from firing until directed to do so by the fire direction center. (2) Restrictive method of control used by the observer that prohibits the battery or
battalion from firing until directed to do so by the
observer.
avg average

BPAMC by piece at my command BPBRAMC by piece, by round, at my command

axis of tube an imaginary straight line through the center of
the bore at the breech end and the center of the bore
at the muzzle end.

bracketing a method of adjusting fire in which a bracket is

AZIMUTH a command announced to alert the sections to a
large shift in the direction of fire.

BRAMC by round at my command

## B

breechblock a movable steel block that doses the breech of B behind (DA Form 4757)

ballistic density the computed constant air density that

breach ring the breechblock housing that is screwed or

would have the same total effect on a projectile during
its flight as the varying densities actually encountered.
ballistics the science or art that deals with the motion,

btry battery burster an explosive charge used to break open and spread the contents of chemical projectiles, bombs, or mines.

behavior, appearance, or modification of missiles or
other vehicles acted upon by propellants, wind, gravity, temperature, or any other modifying
substance, condition, or force.

BUCS backup computer system

barrel a metal tube through which ammunition is fired, which
controls the initial direction of the projectile.

## 3 Command, Control, And Communications C

base of trajectory a line extending from the muzzle of the
tube that intersects the trajectory at the same altitude
as the muzzle.

CA Canada

BATTERY (PLATOON) ADJUST a fire command given to
alert all elements of a fire unit to follow the mission to participate in the FFE phase of an adjust-fire mission.
battery center a point materialized on the ground at the
approximate geometric center of the battery position;
the chart location of the battery.

BATTERY (PLATOON or TROOP) LEFT (RIGHT) a caliber (1) The inside diameter of the tube as measured between opposite lands. A .45 caliber pistol has a barrel with a diameter of 45/100 of an inch. (2) The diamater of a projectile. (3) An expression of the length of the tube obtained by dividing the length from the breach face to the muzzle by the inside diameter of its bore. A gun tube with a bore 40 feet long (480
inches) and 12 inches in diameter is 40 calibers long.

method of fire in which weapons are discharged from
the flank designated in a 5-second interval.
calibration measuring the muzzle velocity of a weapon and

## Battery (Battalion Or Platoon) 1 (Or More)

call for fire a request for fire containing data necessary for
ROUND(S) a fire order command indicating an FFE
mission and directing all pieces to fire the designated number of rounds at the data announced in the initial
fire command.

BB base bum

cancel when coupled with an order other than quantity or
type of ammunition, rescinds that order.

BCS battery computer system BE base ejection (fuze), Belgium

cannon a complete assembly consisting of an artillery tube, a
breech mechanism, a firing mechanism, and a
sighting system mounted on a carriage.
beehive (ammunition) a type of antipersonnel ammunition
cannoneer a member of an artillery gun or howitzer crew
designed for use in defending a position against massed personnel attack.

BMA battery-minefield angle

boattail the conical section of a ballistic body that
progressively decreases in diameter toward the tail to reduce overall aerodynamic drag through increasing its ballistic coefficient.
CANNOT OBSERVE a method of control in the call for fire
from the observer in which the observer or spotter
believes a target exists at the given location that is important enough to engage; however, the observer is unable to adjust fire onto the target because of
obscuration, mask, and soon.

BOC battery operations center CAS complementary angle of site bourrelet the widest part of the projectile located immediately to the rear of the ogive.

CD compact disk BP base piece CDNL cancel do not load established by obtaining an **OVER** and a SHORT
along the spotting line and then successively splitting this bracket until a target **HIT** or desired bracket is obtained.

a cannon.

shrunk onto the rear of a cannon tube in which the breechblock engages.

## C

then performing a comparison between the muzzle
velocity achieved by a given piece and accepted
standard performance.
obtaining the required fire on a target.
whose primary duty is servicing the piece.

centrifugal force the force acting on a rotating body that
forces its parts outward and away from the center of
rotation.
CEOI communications-electronics operation instructions CF command/fire direction (redo net)
CFF call for fire chap chapter

charge the propellant of semifixed and separate-loading
ammunition.
charge group the charges within the propellant type
associated with a projectile family, within which MVVs
can be transferred.
check firing a command used to cause a temporary halt in
firing.
chemical agent a chemical compound which produces
incapacitating, lethal, or damaging affects on man,
animals, plants, or materials.
chg charge cld cloud CLGP cannon-launched guided projectile COB center of battery col column

cold stick firing data computed from a graphical firing table
with no GFT setting applied.

COLT combat observation/lasing team

comp comparative, complementary complementary angle of site the correction to compensate
for the error made in assuming rigidity of trajectory.

## Corr Correction

complementary range range confections corresponding to
the complementary angle of site. These corrections
are tabulated in the TFT and are a function of chart
range and height above or below the gun.
complete round a term applied to an assemblage of
cos cosine COS center of sector cot cotangent
components designed to perform a specific function at the time and conditions desired to complete the
firing chain. Examples of these rounds are separate
loading, consisting of a primer, a propelling charge, a
projectile, and a fuze; and fixed or semifixed,
consisting of a primer, a propelling charge, a cartridge
case, a projectile, and a fuze.
computer (1) A mechanical or electromechanical device for
solving mathematical problems associated with the
development of the gunnery solution (for example,
BCS). (2) A fire direction center operator who
operates an FDC computer or manually computes
data for laying and firing artiliery.
concurrent met a concurrent mat is solved to separate the
total corrections determined from a registration into
two parts: met corrections and position constants.
CONTINUOUS FIRE a command causing the howitzer crew
to continue firing as rapidly as possible, consistent
with accuracy and the prescribed rate of fire for the
weapon, until the commands CHECK FIRING,
CEASE LOADING, or **END OF MISSION** are given.
continuous illumination (1) A method of fire in which
illumination rounds are fired at specific time intervals
to provide uninterrupted lighting of the target. (2) A
request from the observer in the call for fire for
continuous illumination.
CONVERGED (1) A request from the observer for all rounds
to impact at the center of the target. (2) A command in
the fire order specifying a special sheaf in which all
planes of fire intersect at the same point on the ground (see converged sheaf).
converged sheaf a special sheaf in which each piece fires a
unique time, deflection, and quadrant elevation to
cause the rounds to impact at the same point on the ground.
cook off the functioning of a chambered round initiated by the
heat of the weapon.
coordinated fire line a line beyond which conventional fire
support means (FA, mortars, naval gunfire) may fire
at any time without additional coordination within the
zone of the establishing headquarters. A CFL is
designated to expedite fires across boundaries and speed fire support reaction to targets in those areas.
coordinated illumination (1) The firing of illumination rounds
to illuminate a target only at the time required for
spiting and adjusting HE fires. (2) A request from the
observer in the call for fire for continuous illumination.
coppering metal fouling left in the bore of a weapon by the
rotating band or jacket of a projectile.
Coriolis effect the change in range or azimuth caused by the
rotational effects of the earth.
correcton (1) Any change in firing data to bring the mean
point of impact of a round closer to the target. (2) A
communications proword announcing that an error in
data has been announced and that corrected data will
follow.
COT center of target CP concrete-piercing (fuze) Cphd Copperhead
crest a terrain feature of such altitude that it restricts
observation of an area or fires into an area on either
the ascending or descending branch of the trajectory,
resulting in dead space or limitation to the minimum elevation, or both.

dispersion rectangle a table that shows the probable
CRESTED a report indicating engagement, or observation, of
a target is not possible because of an obstacle or
intervening crest.
CS chlorobenzaimalononitrile (riot control agent)
CSF complementary site factor
displ displacement
CSR controlled supply rate
div arty division artillery
CTGPC cancel terrain gun position correction
DNL do not load
D
D decrease, down (ROF), destroy (attack guidance matrix)

DOWN (1) A term used in a call for fire to indicate that the
target is at a lower altitude than the observation post
or reference point used in locating the target. (2) A
correction used by the observer to indicate a decrease in the height of burst of a round is needed.
DA Denmark DPICM dual-purpose improved conventional munitions dec decrease

drag the resistance of the atmosphere to a projectile moving
defection (1) The setting on the scale of a weapon sight to
place the line of fire in the desired direction. (2) The
horizontal clockwise angle between the axis of the
tube and the line of sight.
drift the lateral deviation of the trajectory from the plane of
deflection index a fine line constructed on a firing chart and
used to measure deflection with the range-deflection protractor.
deflection limits the right and left traverse limits that establish
the lateral limits of a designated impact area.
DROP a correction used by an observer to indicate that a
decrease in range along the observer-target line is
needed.
deflection probable error the directional error caused by
dispersion that will be exceeded as often as not by an
infinite number of rounds fired at the same deflection.
This value is given in the TFT.
droop the algebraic sum of barrel curvature, untrueness of
the breech quadrant seats, and untrueness in
assembling the tube to the breach.
delay action the predetermined delayed explosion of
ammunition after the activation of the fuze.
DS direct support

description of target an element in the call for fire in which
DTG date-time group
the observer describes the personnel, equipment,
activity, or installation to be taken under fire.
E east, easting
destruction fire (1) An element of the method of
engagement potion of the call for fire requesting destruction fire. (2) Fire delivered for the sole purpse
of destroying materiel.
ed edition
EFC equivalent full charge EGL elevatiom gauge line
deviation (1) The distance by which the burst misses the
target. (2) The angular difference between the
magnetic and compass headings.
elevate to raise the muzzle or warhead end of the weapon.

df deflection

elevation the vertical angle between horizontal and the axis

DHD did hit data

did hit data are data fired under nonstandard conditions that
emplacement (1) A prepared position for one or more
will cause the round to impact at a point of known
location.
diff difference
direction a term used by the observer to indicate the bearing
of the observer-target line.
END OF MISSION an order given to terminate firing on a
specific target.
engr engineer
EOL end of orienting line
dispersion pattern the dispersion of a series of rounds fired
from one weapon or group of weapons under
conditions as nearly identical as possible. The points
of bursts or impacts are distributed around a point called the mean point of impact.

distribution of a series of shots fired with the same
firing data. This table is a rectangle made into 64 zones. The table shows the percentage of shots
expected to fall within each zone.
through it. It is directly proportional to the diameter and velocity of the projectile and air density. departure as caused by the rotation of the earth. As a
result, the horizontal projection of trajectory is a
curved, rather than a straight line. The deviation is
always to the right with a projectile having a
right-hand spin.

## E

of the bore or rail of the weapon required for a
projectile to reach a prescribed range.
weapons or pieces of equipment for protection from
hostile fire and from which they can execute their
tasks. (2) The act of fixing a gun in a prepared
position from which it may be fired.

EOM end of mission ERDPICM extended range dual-purpose improved conventional munitions

fire support coordination line a line beyond which all
targets may be attacked by any weapon systems
(including aircraft or special weapons) without
additional coordination with the establishing
headquarters or endangering friendly troops.

erosion the wear in a howitzer tube which is the result of
firing rounds.

fire support team a group of FA observers with the required

ET electronic time (fuze)
ETI elevation to impact

firing data all data necessary for firing an artillery piece eta

exterior ballistics the study of the phenomena associated

firing table a table or chart giving the data needed firing a

with the aerodynamic performance of missiles or
projectiles.

## F

F Fahrenheit, forward (DA Form 4757) FA field artillery fixed ammunition ammunition in which the cartridge case is fac factor FASCAM family of scatterable mines FLOT forward line of own troops

FCI fire control information
FM field manual

FCT firepower control team
FO fire order

FDC fire direction center
FO forward observer

FDO fire direction officer
FFE fire for effect

fork the change in the angle of elevation necessary to
produce a change in range at the level point
equivalent to four probable errors in range.

final protective fire an immediately available, prearranged

forward line of own troops a line that indicates the most

barrier of fire designed to impede enemy movement
across defensive lines.
fins aerodynamic surfaces that are attached to missiles or

forward observer an observer who can observe targets or

projectiles and are designed to provide stability and
control during flight (for example, Copperhead).
FIRE the fire command given to discharge a weapon.

FP firing point

fire control all operations connected with the planning,

FPF final protective fire

preparation, and actual application of fire on a target.
FR France

free fire area an area into which any fire support means may

fire direction (1) The tactical employment of firepower
exercising the tactical command of one or more units in the selection of targets, the concentration and
distribution of fire, and the allocation of ammunition for each mission. (2) The methods and techniques used
to convert target information into the appropriate fire
commands.

fire direction center the element of a commend post
FS fuze setting FS fire support FSCM fire support coordinating measure
consisting of gunnery and/or communications
personnel and equipment which receives target Intelligence and requests for fire and converts it into
appropriate fire direction and by which the commander exercises fire direction or fire control.
FSO fire support officer FT firing tables
FIRE FOR EFFECT (1) A command to indicate that fire for
effect is desired. (2) Fire that is intended to achieve
the desired result on target.
fuze a device used in munitions to initiate detonation.
fuze delay a fuze that has a delay element incorporated into
the fuze train.
FIRE MISSION (1) An order used to sled the weapon or
battery area that the message following is firing data. (2) A specific assignment given to a fire unit as part of
a definite plan.
equipment to plan, request, coordinate, and direct fire
support efforts for a company-sized maneuver force.
given objectve.
particular weapon and ammunition accurately on a
target under standard conditions. It also gives the
corrections needed to compensate for the existence of nonstandard conditions or special conditions such
as variations in temperature.

FIST fire support team

permanently attached to the projectile.
forward location of friendly maneuver forces. The line
is designated from left to right, facing the enemy.
the burst of attillery shells.
deliver fires or aircraft can jettison munitions without additional coordination with the establishing
headquarters. It can be used for an area where neutralization of the enemy by fire support is preferred
over the use of maneuver forces.

fuze superquick a fuze that functions immediately upon
impact of the projectile with the target.
fuze time (fuze mechanical time superquick) a fuze
grid north the northerly or zero direction indicated by the grid
datum of directional reference.
containing a graduated time element which regulates
the time interval after which the fuze will function.
grid system imaginary lines dividing the earth into sectors to
aid in the location of points.
fuze VT see proximity fuze. fz fuze
grooves the spiral channels cut in the bore of a gun making
GSR general support reinforcing GST graphical site table

## G

GT gun to target G/VLLD ground/vehicular laser locator designator

gas check seat on weapons firing separate-loading
gun-target line (GT line) an imaginary straight line from the
gun to the target.
ammunition, the tapered surface in the rear interior of the tube.
GB green bag
GE Germany
H blister agent (mustard)

geometry the control lines, boundaries, and other areas used
HA high angle

to coordinate fire and maneuver (battlefield graphics are sometimes called battlefield geometry).
HB high burst

GFT graphical firing table
HB/MPI high burst/mean point of impact
3 grams per cubic meter gm/m HC hexachlorothane (smoke)
GMET graphical munitions effectiveness table HCO horizontal control operator GMT Greenwich mean time HD blister agent (distilled mustard)

graphical munitions effectiveness table provides guidance
HE high explosive
height of burst (1) The vertical distance from the surface of

for determining the expected fraction of casualities to
personnel targets or damage to material targets in a
graphical format.
graze a spotting by an observer that indicates that a round or
group of rounds detonated upon impact versus in the air.
grid (1) Two sets of parallel lines intersecting at right angles
HEP-T high-explosive plastic-tracer

high-angle fire fire delivered at elevations greater then the
elevation of maximum range of the gun and
ammunition concerned. Range decreases as the angle of elevation increases.
and forming squares. The grid is accurately superimposed on maps, charts, and other similar
representations of the surface of the earth to permit identification of ground locations and permit the
computation of direction and distance to other points.
(2) A term used in giving the location of a geographic
point by grid coordinates. (3) A fire mission in which
target location is sent in grid coordinates.
grid convergence the angular difference in direction
high-burst (mean-point-of-impact) registration a
registration technique used to determine the mean
burnt location of a group of rounds fired with a single
set of firing data.
between grid north and true north measured from
east to west from true north.
high-order detonation complete and instantaneous
grid coordinates numbers and letters of a coordinate system
HIP howitzer improvement program
that designate a point on a gridded map, photograph,
or chart.
HMMWV high-mobility multipurpose wheeled vehicle
grid line one of the lines in the grid system used to divide the
HOB height of burst
map into squares. East-west lines are X lines and north-south lines are Y lines.
HQ headquarters
grid magnetic angle (GM angle) the angular difference in
direction between grid north and magnetic north
ht height
measured east to west from grid north. This is sometimes called the gravitation grid variation.

up part of the rifling.

## H

the earth to the point of burst for a round. (2) The optimum height of burst for a particular target where a nuclear weapon of a specific yield will produce the estimated energy needed to achieve the desired affects on target over the maximum possible area.

explosion.

I increase (DA Form 4200), immediate (attack guidance matrix)
I/E in effect

lateral spread (1) An element of the fire order directing that
firing data be calculated to place the mean point of
impact of two or more guns 1,000 (155 mm) meters apart on a line perpendicular to the gun-target line. (This technique is used with illumination.) (2) An
element of the call for fire requesting that the target be
engaged with a lateral spread sheaf.

IAW in accordance with

lay (1) To direct or adjust the aim of a weapon. (2) Setting of a
weapon for a given range, deflection, or both.

ICAO International Civil Aviation Organization ICM improved conventional munitions

level point point on the descending branch of the trajectory
which is at the same altitude as the origin. This is
sometimes referred to as the point of fall.

IFSAS initial fire support automated system

lb pound

illum illumination

LCU lightweight computer unit
inc increase
LIN line item number
index a scribed mark on an instrument indicating the number
to read.
LINE a spotting used to indicate that the burst occurred along
the observer-target line.
indirect fire (1) Fire delivered at a target not visible to the
firing unit. (2) Fire delivered to a target that is not
used as the point of aim for the weapon or director.
line of departure a line designated to coordinate the jump-off
point for an attack or for scouting elements.
interior ballistics the study of the phenomena associated
line of elevation the axis of the bore prolonged.
with imparting kinetic energy to missiles.
line of sight (1) A straight line joining the origin and a point,
usually the target. (2) Line of vision. (3) A straight line
between two radio antennas.
link general term used to indicate the existence of
communications facilities between two points.
intervening crest a crest tying between the firing point and
the FLOT that is not visible from the firing point that
has the capability of affecting target engagement on
either the ascending or descending branches of the
trajectory. The minimum quadrant elevation needed
to dear this crest is the intermediate or intervening
crest quadrant elevation.
LLHC lower left-hand corner

IS immediate suppression

LMDIRT length (of smokescreen), maneuver target line

IT Italy

direction, direction (of wind), time smoke is required
(duration) (memory aid)
log logarithm
log logistics

JMEM joint munitions effectiveness manual

LOS line of site
joint munitions effectiveness manuals these tables
LOST a spotting used to indicate that the round(s) fired was
not observed.
provide guidance for determining the expected
fraction of casualties to personnel targets or damage
to materiel targets.
low-angle fire fire delivered at or below the elevation of
maximum range for the gun and ammunition
concerned.
jump the displacement of the line of departure from the line of
elevation that exists at the instant the projectile leaves
the tube.
LTD laser target designator
K Kelvin
m/s meters per second
km kilometer
man maneuver (attack guidance matrix)
kn pt known point
maximum ordinate the difference in altitude between the
origin and the summit.
maximum quadrant elevation the greatest vertical angle of
lands the raised portion between grooves in the bore of a gun
the tube for a specific charge which, when fired, will ensure that the rounds impact within the physical
boundaries of a predesignated impact area for safety reasons. This angle is generally limited by the mechanical structure of the piece.
making up part of the rifling.

## Fm 6-40/Mcwp 3-1.6.19

MBL mean burst location MCRES Marine Corps combat readiness evaluation system

mixed graze a spotting used to indicate that the majority of a
group of rounds detonated upon impact versus in the
air.

MD mortar datum plane (Firefinder mission type)

MO maximum ordinate
MDP meteorological datum plane
MOF method of fire
mean height of burst the average of the heights of burst of a
MOS military occupational specialty
group of rounds fired with the same data.
mph miles per hour
mean point of impact the arithmetic average of the point of
MPI mean point of impact
impact of a group of rounds fired with the same data
under a given set of conditions.
msg message
mechanical time fuze a fuze with a clocklike mechanism
MT maneuver target, mechanical time (fuze)
controlling the time the fuze will function.
MTL maneuver target line
met meteorological, meteorology
MTO message to observer
met corrections all measurable nonstandard conditions for
which we can account
MTOE modification tables of organization and equipment
MTSQ mechanical time superquick (fuze)
meteorological data meteorlogical facts pertaining to the
atmosphere, such as wind, temperature, air density,
and so on, that affect military operations.
MULE modular universal laser equipment

METL mission-essential task list

muzzle velocity the velocity of a projectile at the instant the
projectile leaves the muzzle of the weapon.

METT-T mission, enemy, terrain, troops, and time available

muzzle velocity variation the change in muzzle velocity

MGP M gauge point

from the standard muzzle velocity expressed in
meters per second.

MHL manufacturer's hairline

MV muzzle velocity

MI mortar impact prediction (Firefinder mission type)

MVCT muzzle velocity correction tables
mil a unit of measure for angles that is based on the angle
subtended by l/6400 of the circumference of a circle.
MVV muzzle velocity variation
mil relation a gunnery formula expressed as mils = W/R in
N

N north, northing, neutralize (attack guidance matrix) N/CH nuclear and chemical (attack guidance matrix)

which roils is the angular measurement in roils
between two points, W is the lateral distance (width)
in meters between two points, and R is the mean
distance in thousands of meters to the points. This
relation is approximately true for angular
measurements of less than 600 mils.
NATO North Atlantic Treaty Organization
min minute, minimum
NBC nuclear, biological, chemical
minimum quadrant elevation the minimum vertical angle of
NCO noncommissioned officer
NE northeast
the tube for a specific charge which, when fired, ensures the round impacts within the physical
boundaries of a predesignated impact area for safety
reasons.
neutralization this knocks the target out of the baffle
temporarily.
minimum range (1) The least range setting of a gun at which
NL Netherlands NLT not later than
the projectile will dear friendly troops or obstacles
between if and the target. (2) The shortest distance a gun can fire from a given position with a given charge.
NO Norway
misfire (1) Failure of the propellant to ignite when the firing
no-fire area restrictive FSCM in which neither fires or the
effects of fires are permitted.
circuit is complete. (2) Failure to fire or explode properly. (3) Failure of the primer or the propelling charge to function wholly or in part.
northing the northward reading of grid values on a map.
mixed a spotting used to indicate that a group of rounds
equally detonated both in the air and upon impact.
NSN national stock number
number of rounds the part of the fire order or fire command
mixed air a spotting used to indicate that the majority of a
group of rounds detonated in the air versus upon
impact.
that indicates the number of rounds per tube to fire at
a specific target.
NW northwest
O
observation post a position which possesses the
appropriate communications and other equipment to
make military observations and from which fire is
directed and adjusted onto targets.
observed firing chart a chart on which the relative locations
must be established by the adjustment of fire.
observer-target line an imaginary straight line from the
observer to the target.
observer-target range the measured distance of the OT line. obsr observer obturating band a nylon band located below the rotating
band that assists in forward obturation. Current projectiles include the illumination, rocket-assisted,
and Copperhead projectiles.
obturation any process that prevents the escape of gases
from the tube of the weapon during the firing of the
projectile.
OF observed fire
offset registration a registration that is conducted by one
gun from a position away from the rest of the platoon or battery.
ogive the curved forward part up to and including the tip of
the projectile; also called the head.
OIC officer in charge
OL orienting line on-call targets planned targets, other than scheduled
targets, on which fire is delivered when requested.
OP observation post
open sheaf (1) A type of sheaf in which each gun fires a
unique time, deflection, and quadrant to cause the
rounds to impact in a straight line, perpendicular to
the GT line and centered on the target, with bursts
spaced one effective burst width apart. (2) A fire order
commanding that the target be attacked with an open
sheaf.

## Opord Operation Order

origin of the trajectory the center of the muzzle of a gun at
the instant the projectile leaves it.

## Ot Observer To Target

OUT (1) In conduct-of-fire procedure, a proword indicating the
end of a read back or the end of transmission with the
same station expected to transmit. (2) In normal
RATELO procedures, a proword indicating the end of
transmission with no answer required.
OVER (1) A spotting used to indicate that the burnt has
occurred beyond the target along the OT line. (2) In
normal RATELO procedures, a proword that

indicates the end of a transmission with an answer being expected.
P
PAD provisional aiming data
PADS position azimuth determining system
pantel panoramic telescope
PC personal computer
PCR piece-to-crest range
PD point-detonating (fuze) PE probable error
PED probable error in deflection
PEHB probable error in height of burst
PER probable error in range
PERB probable error in range to burnt
PETB probable error in time to burst
plt platoon PMCS preventive maintenance checks and services POC platoon operations center point-detonating fuze a fuze that functions immediately
upon impact.
POL petroleum, oils and lubricants
polar coordinates (1) The direction, distance, and vertical
shift from a known point to another point. (2) The direction, distance, and vertical shift from an observer's location to the target.
polar plot the method of locating a target or point by means
of polar coordinates.
pos position, positive position constants all nonstandard conditions that are
difficult to identify, relatively small in magnitude, and remain relatively constant for which we cannot
account. The purpose of solving a concurrent met is
to isolate the positiom constants.

## Pract Practice

precision registration the determination, by adjustment, of
firing data that will place the MPI of a group of rounds on a point of known location.
predicted fire the delivery technique of applying accurately
computed corrections (not determined by firing) to
standard firing data for all nonstandard conditions
(weather, weapon, ammunition, rotation of the earth)
to deliver accurate, surprise, nuclear, or nonnuclear fire on any known target in any direction from any weapon limited only by the characteristics of the weapon and ammunition used.
preferred charges the charges that are preferred for
range K a correction expressed in meters per 1,000 meters
measuring and transferring muzzle velocities
because of the consistent muzzle velocities produced by these charges.

## Prf Pulse Repetition Frequency

probable error (1) An error that is exceeded as often as it is
range probable error the range error caused by dispersion
that is exceeded as often as not in an infinite number of rounds fired at the same elevation and is a
numerical value given in the TFT. It is one-eighth the
greatest length of the dispersion pattern.
not. (2) The measurement of the impact distribution in
the dispersion pattern around the mean point of
impact resulting in the development of units of measure (PROBABLE ERROR RANGE, PROBABLE ERROR DEFLECTION) used in the solution of the gunnery problem.
range spread (1) An element of the fire order directing that
firing data be calculated to place the mean point of
impact of two or more weapons 1,000(155 mm) meters apart along the gun-target line (This technique
is used with illumination). (2) An element in the call for
fire requesting the target be engaged with a range
spread sheaf.
projectile an object projected by the application of exterior
force and continuing in motion by virtue of its own
inertia such as a bullet, shell, or grenade.
RAP rocket-assisted projectile

projectile family a group of projectiles that have exactor
RATELO radiotelephone operator
very similar ballistic characteristics.
RATT record, apply, transfer, tables (rule)
propellant that which provides the energy required to place a
RDP range-deflection protractor
projectile into motion. Some examples are powder charges and rocket fuel.
REC radio electronic combat

propelling charge a powder charge that is set off in a
repeat an order or request to fire the same number of rounds
weapon to propel a projectile from the weapon through the action of expanding gases in a confined
space produced by the burning of the powder.
propelling increment a distinct portion of a propelling charge
restrictive fire area a restrictive FSCM in which specific
restrictions may not be exceeded or no fires delivered
into this area without prior coordination with the
establishing headquarters.
designed to permit separation of the charge for range adjustment purposes.
restrictive fire line a restrictive FSCM which prohibits fires

prox proximity

proximity fuze a fuze designed to function when activated by
restricted charges those charges within a charge group for
an external influence such as the dose vicinity of the
target.

## Q

RFT rapid fire table Q quick (fuze)
rg range QE quadrant elevation

ROF record of fire

QSTAG quadripartite agreement

rotating band the soft metal band around a projectile that
quadrant elevation the angle between the level base of the
trajectory and the axis of the bore when laid. It is the
algebraic sum of the elevation, angle of site, and the
complementary angle of site.
round (1) All parts that make up the ammunition necessary to

## R

rounds complete a term used to report that the number of
specified FFE rounds have been fired.

R reinforcing, right (ROF)

RSTA reconnaissance, surveillance, and target acquisition

RAAMS remote antiarmor mine system

RTI range to impact
range (1) The distance between any given point and an
object or target. (2) The extent or distance limiting the operation of the gun.
range correction a change in firing data necessary to allow
for deviation because of nonstandard conditions.
S south, southing, suppression (ROF), suppress (attack
range-deflection protractor a device used to measure chart
range and deflection.
SDZ surface danger zone
of range to correct for nonstandard conditions.
again with the same method of fire.
across it without prior coordination with the establishing headquarters.
which it is not preferred to transfer measured MVVs to
or from or for which it is not authorized to fire.
makes it tit tightly in the bore by centering it, thus
preventing the escape of gases and giving the
projectile its spin.
fire one shot (see complete round). (2) One shot
expended by a weapon.

## S

guidance matrix)

SE southeast sh shell SHD should hit data

sheaf planned planes of fire that produce a desired pattern of
bursts with rounds fired by two or more weapons.
SHELL (1) Afire command specifying the type of projectile to
be used in a fire mission. (2) A request for a specific
type of round to be used in a fire mission. (3) A hollow
projectile filled with explosives, chemicals, or other
material as opposed to shot, a solid projectile. (4) To bombard or fire a certain number of rounds on a
target.
shift (1) To transfer fire from one target to another. (2) The
deflection difference from one designated point to
another designated point used in opening or dosing
the sheaf of artillery or mortar units.
SHORT (1) A spotting used to indicate that the round burst
short of the target in relation to the OT line. (2) A
round that strikes or bursts on the nearside of the
target. (3) Around that is fired without sufficient range
to reach the target.
SHOT a report that indicates a gun or guns have been fired.

should hit data are data fired under standard conditions that
will cause the round to impact at a point of known
location.
si site side spray fragments from a bursting shell that are thrown sideways from the line of sight.

sin sine smk smoke SOP standing operating procedures SP self-propelled

special corrections individual piece corrections applied to
time, deflection, and quadrant to place the FFE bursts
in a precise pattern on the target.

special sheaf a type of sheaf in which each weapon fires a
unique time, deflection, and quadrant to cause the rounds to impact in a specific geometric pattern.
SPLASH a proword transmitted to the observer 5 seconds
before the estimated impact of a volley or round of artillery, mortar, or naval gunfire.
spotting the process to determine either visually or
electronically the deviations of artillery or naval gunfire from the target in relation to the OT line and supplying
this information to the FDC for the purpose of
adjustment or analysis of the effects of fire.
spotting line: sea observer-target line.
square a mark or measurement on projectiles used to denote
standard weight or deviation from standard weight.
wt square weight
SR self-registration

ST special text STANAG standardization agreement std standard subcal subcaliber

subsequent met a subsequent met is solved to determine
new met corrections that are applied to the position constants from a previous met to determine new total corrections.

supplemental charge a TNT-filled cylindrical container usually used in deep cavity projectiles to fill the void between the fuze, booster combination, and the booster charge.

suppression this limits the ability of enemy personnel to

perform their mission.

surveyed firing chart a chart on which the location of all

required points are plotted.

sustained rate of **fire** the actual rate of fire that a weapon

can continue to deliver for an indefinite length of time without seriously overheating.

SW southwest sw switch sweep fire a method of fire where weapons fire a constant quadrant elevation with several deflections in direct relation to the direction of fire.

## T

TA target acquisition TAB target acquisition battery TAG target above gun tan tangent target analysis the examination and evaluation of an enemy

target situation to determine the most suitable weapon, ammunition, and method required to defeat,
neutralize, of otherwise disrupt, delay, or limit the
enemy.
target grid a device for convecting the observer's target
locations and corrections in respect to the OT line to
corrections and target locations in respect to the GT
line.

## Tbg Target Below Gun

terrain gun position corrections precomputed individual
piece corrections applied to the gunner's aid on the
panoramic telescope and the correction counter on
the range quadrant of each piece.
TF time of fight (GFT scale)
TFT tabular firing tables
TGL time gauge line TGPC terrain gun position correction
tgt target
US United States
ti time
USAFAS US Army Field Artillery School USDA up, subtract; down, add (memory aid)
time of flight the time in seconds from the time a projectile
leaves the muzzle until it bursts.
USMC United States Marine Corps
time on target a restrictive command that allows the FDO or
UTM universal transverse mercator
FDC to control the time the rounds will impact at the
target.
TLE target location error tml vel terminal velocity
VCO vertical control operator
TNT trinitrotoluene
VE velocity error
TOC tactical operations center
vertical angle the angle measured vertically, up or down,
TOE tables of organization and equipment
TOF time of fight TOT time on target
TRADOC US Army Training and Doctrine Command
vertical clearance the vertical distance by which a projectile
must dear an intervening crest.
trajectory the path traced by a projectile in fight.
vertical interval (1) The difference in altitude between two
specified points or locations, such as the battery and
a target. (2) The difference between the height of the
weapon and the desired burst point.
VI vertical interval
transfer limit the maximum difference in direction and range
from a location or checkpoint within which corrections for the checkpoint are assumed to be sufficiently accurate to warrant application to any target justifying
its attack by a transfer of fire.
VT variable time
transitional ballistics the study of the transition from interior
to exterior ballistics.
VX nerve agent (persistent)

## Tu Turkey

W west, westing
tube wear wearing away of the interface of the bore as a
result of the combined effects of gas, washing,
scoring, and mechanical abrasion, which causes a
reduction in muzzle velocity.
WB white bag
WP white phosphorus
U
WR when ready
U up (ROF)
UBL unit basic load
yaw the angle between the direction of motion of the projectile
and the axis of the projectile-right, down, left, and up.
UCARET unit (that fired registration), charge (fired during the
registration and for which GFT setting applies), ammo lot (used in registration), range ([chart or achieved]
from the howitzer to point of known location),
elevation (adjusted or did hit), time (adjusted or did hit
fuze setting) (memory aid)
UK United Kingdom
zone fire a method of fire where the weapons fire constant
UP (1) A term used to indicate that the target is higher in
attitude than the OP or reference point used to locate
it. (2) A correction used to indicate that an increase in
the height of burst is required.
V
from a horizontal plane of reference and expressed in
plus or minus in roils depending on whether the position is above or below the horizontal plane.
W
Y
Z