DNA-TR-82-15 

ANALYSIS OF RADIATION EXPOSURE FOR 

NAVAL PERSONNEL AT OPERATION 

GREENHOUSE 

Science Applications, Inc. 

P.O. Box 1303 

McLean, Virginia 22102 

30 July 1982 

Technical Report 

CONTRACT No. DNA 001-82-C-0012 

THIS WORK WAS SPONSORED BY THE DEFENSE NUCLEAR AGENCY 

UNDER RMSS CODE B384082466 

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DEFENSE NUCLEAR AGENCY 

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DNA-TR-82-15 

TITLE (and 5 TYPE OF REPORT COVERED 

Technical Report ANALYSIS OF RADIATION EXPOSURE FOR NAVAL 

PERSONNEL AT OPERATION GREENHOUSE PERFORMING ORG. REPORT NUMBER

AU 8. CONTRACT OR GRANT 

C. Thomas R. 

R. Gminder J. Goetz DNA 001-82-C-0012 

J. Stuart J. Klemm PERFORMING ORGANIZATION NAME AND PROGRAM ELEMENT. PROJECT, TASK

Science Applications, Inc AREA 6 WORK UNIT NUMBER5 

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6. SUPPLEMENTARY NOTES 

This work was sponsored by the Defense Nuclear Agency under 

RMSS Code B384082466 

9. KEY WORDS on by block number) 

Operation GREENHOUSE Oceanic Nuclear Tests 

Radiation Exposure Assessment Ship Shielding 

Nuclear Test Personnel Review Task Group 3.3 

Joint Task Force 3 

0. ABSTRACT md by block number) 

The radiological environments are reconstructed for seven ships and the 

residence islands of Enewetak Atoll that received fallout during Operation GREENHOUSE (April-May 1951) as a result of Shots DOG, EASY, and 

ITEM. From the reconstructed operations and radiological environments, 

equivalent personnel film badge doses are calculated and compared with 

actual film badge data available for six of the ships. Considering the 

increased time spent topside by badged personnel as opposed to an average 

crewmember, correlation between calculations and dosimetry is good. 

-- , 1473 EDITION OF NOV 65 OBSOLETE 

UNCLASSIFIED 

SECURITY CLASSIFICATION OF THIS PAGE mr=dJ 
UNCLASSIFIED 

ABSTRACT (Continued) 

Average shipboard doses range from a low of 0.13 rem for the crew of the 

USNS LT. ROEERT CRAIG to a high of 1.14 rem for the crew of the USNS SGT. 

CHARLES E. MOWER. Average doses on the residence islands of Enewetak Atoll 

range from 2.57 rem to 3.10 rem. 

CLASSIFICATION OF THIS 
TABLE OF CONTENTS 

Section Page 

ILLUSTRATIONS 2 

TABLES 4 

1. INTRODUCTION 7 

1.1 BACKGROUND 7 

1.2 NAVALOPERATIONS 9 

1.3 METHODOLOGY 13 

2. SHIPOPERATIONS AND RADIATIONENVIRONMENTS 17 

2.1 18 

2.2 USS 24 

2.3 USS LST-859 30 

2.4 USNS E. 38 

2.5 USS 46 

2.6 USS WALKER (DDE-517) 61 

2.7 USNS LT. ROBERT 69 

2.8 RESIDENCEISLANDSOF ENEWETAKATOLL 73 

2.9 SHIP SHIELDING 82 

3. DOSECALCULATIONS 88 

3.1 PERSONNEL ACTIVITIES 88 

3.2 CALCULATEDPERSONNELFILMBADGEDOSES 89 

4. UNCERTAINTY ANALYSIS 102 

5. FILMBADGE DOSIMETRY 107 

6. CONCLUSIONSANDTOTALDOSESUMMARY II3 

7. REFERENCES 114 

APPENDIX: 117 
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LIST OF ILLUSTRATIONS 

Figure Page 

Operation GREENHOUSE Shot Locations 8 

1-2 Joint Task Force Three Organization 

1-3 Operation GREENHOUSE Dose Reconstruction Methodology 14 

2-l USS CABILDO Anchorage Area Operation GREENHOUSE 19 

2-2 USS CABILDO Ship Intensity Following Shot DOG 21 

2-3 USS CABILDO (LSD-161 Ship Intensity Following Shot EASY 22 

2-4 USS CABILDO (LSD-16) Ship Intensity Following Shot 25 

2-5 USS CURTISS Anchorage Areas Operation GREENHOUSE 28 

2-6 USS CURTISS Ship Intensity Following Shot DOG 31 

2-7 USS CURTISS Ship Intensity Following Shot EASY 32 

2-8 USS CURTISS Ship Intensity Following Shot ITEM 33 

2-9 USS LST-859 Anchorage Areas Operation GREENHOUSE 36 

2-10 USS LST-859 Ship Intensity Following Shot DOG 39 

2-11 USS LST-859 Ship Intensity Following Shot EASY 40 

2-12 USNS SGT. CHARLES E. Anchorage Areas 

Operation GREENHOUSE 43 

2-13 USNS SGT. CHARLES E. MOWER (TAP-186) Ship Intensity 

Following Shot DOG 47 

2-14 USNS SGT. CHARLES E. MOWER (TAP-186) Ship Intensity 

Following Shot EASY 48 

2-15 USS SPROSTON Pre-Shot Positions and Fallout Areas 51 

2-16 USS SPROSTON Patrol Positions 8 April 51 53 

2-17 USS SPROSTON (DDE-577) Ship Intensity Following Shot DOG 54 

2-18 USS SPROSTON (DDE-577) Ship Intensity Following Shot EASY 57 

2-19 USS SPROSTON (DDE-577) Ship Intensity Following Shot ITEM 58 

2-20 USS WALKER Pre-Shot Positions and Fallout Areas 62 

2-21 USS WALKER (DDE-517) Ship Intensity Following Shot DOG 64 

2-22 USS WALKER (DDE-517) Ship Intensity Following Shot EASY 65 

2-23 USS WALKER (DDE-517) Ship Intensity Following Shot ITEM 66 

2 
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LIST OF ILLUSTRATIONS (continued) 

Figure Page 

2-24 USNS LT. ROBERT CRAIG’s Approach to Enewetak Lagoon 

8 April 1951 70 

2-25 USNS LT. ROBERT CRAIG (TAK-252) Ship Intensity 

Following Shot DOG 71 

2-26 Parry and Japtan Island Intensity Following Shot DOG 74 

2-27 Enewetak Island Intensity Following Shot DOG 75 

2-28 Parry and Japtan Island Intensity Following Shot EASY 77 

2-29 Enewetak Island Intensity Following Shot EASY 78 

2-30 Enewetak and Southern Parry Island Intensity Following 

Shot ITEM 

2-31 Japtan and Northern Parry Island Intensity Following 

Shot ITEM 81 

2-32 Ship Shielding Factor vs. Deck Plating Thickness 87 

4-1 Hypothetical Dose Distributions 105 

5-l Shot DOG Dosimetry Data 108 

5-2 Shot EASY Dosimetry Data 109 

5-3 Shot GEOKGE Dosimetry Data 

5-4 Shot ITEM Dosimetry Data 

A-l USS CABILDO Crew Activity Time Lines Operation GREENHOUSE 118 

A-2 USS CURTISS Crew Activity Time Lines Operation GREENHOUSE 119 

A-3 USS LST-859 Crew Activity Time Lines Operation GREENHOUSE 120 

A-4 USNS SGT. C.E. MOWER Crew Activity Time Lines

Operation GREENHOUSE 121 

A-5 USS SPROSTON, USS WALKER, and USNS CRAIG (Shot DOG only) 

Crew Activity Time Lines Operation GREENHOUSE 122 
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LIST OF TABLES 

Table 

l-l 

2-l 

2-2 

2-3 

2-4 

2-5 

2-6 

2-7 

2-8 

2-9 

2-10 

2-l 

2-12 

2-13 

2-14 

2-15 

2-16 

2-17 

2-18 

2-19 

2-20 

2-21 

Page 

Operation GREENHOUSE Shot Data 9 

USS CABILDO Average Radiation Intensity Data 26 

Daily Integrated Free-Field Intensity, USS CABILDO 27 

USS CURTISS Average Radiation Intensity Data 34 

Daily Integrated Free-Field Intensity, USS CURTISS 35 

USS LST-859 Average Radiation Intensity Data 41 

Daily Integrated Free-Field Intensity, USS LST-859 42 

USNS SGT. CHARLES E. Average Radiation 

Intensity Data 49 

Daily Integrated Free-Field Intensity, USNS SGT. 

CHARLES E. 

USS SPROSTON Average Radiation Intensity Data 59 

Daily Integrated Free-Field Intensity, USS SPROSTON 60 

USS WALKER Average Radiation Intensity Data 67 

Daily Integrated Free-Field Intensity, USS WALKER 68 

LT. ROBERT C. CRAIG Average Radiation Intensity Data 69 

Daily Integrated Free-Field Intensity, USNS LT. ROBERT CRAIG 72 

Residence Island Survey Data Shot DOG 73 

Parry Island Survey Data Shot EASY 76 

Enewetak and Parry Island Survey Data Shot ITEM 79 

Daily Integrated Free-Field Intensity, Enewetak Island 83 

Daily Integrated Free-Field Intensity, Parry Island 84 

Daily Integrated Field Intensity, Japtan Island 85 

Ship Shielding Factors 86 

4 
LIST OF TABLES (continued) 

Table Page 

3-1 Calculated Personnel Film Badge Dose, USS CABILDO 92 

3-2 Calculated Personnel Film Badge Dose, USS CURTISS 93 

3-3 Calculated Personnel Film Badge Dose, USS LST-859 94 

3-4 Calculated Personnel Film Badge Dose, 

USNS SGT. CHARLES E. MOWER 95 

3-5 Calculated Personnel Film Badge Dose, USS SPROSTON 96 

3-6 Calculated Personnel Film Badge Dose, USS WALKER 97 

3-7 Calculated Personnel Film Badge Dose,

USNS LT. ROBERT CRAIG 98 

3-8 Calculated Personnel Film Badge Dose, Enewetak Island 99 

3-v Calculated Personnel Film Badge Dose, Parry Island 100 

3-10 Calculated Personnel Film Badge Dose, Japtan Island 101 

4-1 Fractional Standard Deviation for 

Shipboard Radiation Survey Data 103 

6-1 Summary of Calculated Doses 113 

 

Section 

INTRODUCTION 

Operation GREENHOUSE was a series of four atmospheric nuclear tests conducted by the United States at Enewetak (formerly Eniwetok) Atoll in the Pacific 

Ocean in 1951. Civilian and military personnel participated both on land and at sea. 

Radiological safety procedures included the issuance of film badges to selected 

shipboard personnel that were to be worn from D-Day to D-plus-seven days. In 

addition, all personnel and that were operating on D-Day to 

seven days were issued film badges. In the absence of film badge data, personnel doses 

were estimated. The doses assigned in 1951 on the basis of these estimates are 

contained in medical records for most naval personnel, but are of uncertain quality 

because no documentation has been located that describes how the doses were 

estimated. Consequently, where film badge coverage is incomplete, it is necessary to 

reconstruct the radiation dose. This report contains a description of the methodology 

and the results of the reconstruction of radiation doses received by test participants 

aboard seven Naval vessels assigned to support the operation. Because some of the 

task group personnel were assigned to the residence islands of Enewetak Atoll 

(Enewetak, Parry, and Japtan Islands), the radiation environments on these islands are 

also reconstructed. As for other nearby atolls, Bikini Atoll, to the east, was not 

inhabited during operation GREENHOUSE; Kwajalein Atoll, to the southeast, experienced no fallout from any of the detonations. 

1.1 BACKGROUND 

Operation GREENHOUSE was a series of atmospheric nuclear tests performed by 

the United States in April and May of 1951 at Enewetak Atoll in the Pacific Ocean. 

Of five shots authorized, four were conducted: DOG, EASY, GEORGE, and ITEM 

(References 1, are shown in Table 1- 1. The locations of the shots are 

depicted in Figure 1. 

By the direction of the Joint Chiefs of Staff, Joint Task Force Three was formed 

1 November 1949 for the purpose of conducting tests of atomic weapons. This task 
ENGEBI ISLAND 

EBERIRU ISLAND 

NORTHERN 

\ ANCHORAGE 

ENEWETAK ATOLL 

(ENIWETOK) JAPTAN 

0 ISLAND 

STATUTE MILES 

DEEP ENTRANCE 

WIDE PASSAGE 

Source: References 1, 

Figure Operation GREENHOUSE Shot Locations 

8 
---~-

---------------------- ^-- --

force was commanded by Lt. Gen. Edmond R. Quesada, USAF. The organization of 

JTF-3 is shown in Figure l-2 (Reference 1). 

Table 1- Operation GREENHOUSE Shot Data 

DOG EASY GEORGE ITEM - - ---.----I__ 

DATE April 1951 21 April 1951 9 May 1951 25 May 1951 

TIME (Local)* 0634 0627 0930 0617 

ISLAND ENGEBI EBERIRU ENGEBI 

(SITE) (RUBY) (JANET) 

HEIGHT OF 300 ft. 300 200 200 ft. 

BURST 

TYPE TOWER TOWER TOWER TOWER 

PLACEMENT CORAL CORAL CORAL CORAL 

YIELD 47 KT 

*Local was 12 hours behind GMT. Source: Reference 2 

*Yield is 

1.2 NAVAL OPERATIONS 

Military responsibility for the Enewetak area was assigned to Commander JTF-3 

on 1 February 1951, operating directly under the Joint Chiefs of Staff. The Enewetak 

area was defined as the area centered on Enewetak Atoll and bounded by north 

latitudes and and east longitudes and Due to the 

entry of the Chinese Communists into the Korean conflict, the President had declared 

a state of General Emergency. Military assumptions for the conduct of the operations 

were: 

a) War with the USSR and her satellites may begin before or during the 

conduct of the tests. 

b) The USSR will attempt to obtain information of the conduct of the tests 

and the effectiveness of the atomic weapons by all or any means, including 

the use of submarines and aircraft. 

9 
TASK GROUP 

3.2 

ARMY 

BG WALK 

JOINT CHIEFS 

OF 

STAFF 

MANAGER 

SANTA FE 

3 

OPERATIONS 

OFFICE 

COMMANDER 

JOINT TASK 

FORCE 3 

LTG E.R. QUESADA, USAF 

TASK GROUP 

3.1 

SCIENTIFIC 

DR. A.C. GRAVES 

3.3.1 

FLAG 

SHIP 

(CURTISS) 

3.4 

AIR FORCE 

RADM CRUZEN MG LEE 

3.3.2 

CONVOY 

AND ESCORT 

WALKER) 

l-U 3.3.5 

BOA-f 

POOL 

3.3.6 

HARBOR 

CONTROL 

(Enewetak) 

3.3.3 

AIR 

PATROL 

(VP-931) 

Kwajalein) 

*

Figure l-2. Joint Task Force Three Organization 

10 
In order to deny information to unauthorized personnel concerning the conduct of 

the tests, and to support and assist in the tests, Task Group 3.3 was formed and 

specifically directed to: 

Deny entry into the Enewetak area to unauthorized vessels by conducting 

air and surface surveillance patrols to ensure early detection. 

Exercise control of all authorized vessels upon their entry into the 

Enewetak area, during the operational phase; provide harbor entrance 

control and, in coordination with TG 3.2, control harbor facilities at the 

Enewetak Atoll. 

Transport experimental weapons together with assembly personnel of TG 

3.1 and provide necessary shipboard assembly facilities. 

Maintain and operate a boat pool to augment intra-atoll water transportation of personnel and cargo. 

Assist in: establishment and support of weather stations; maintenance of 

Naval aircraft; search and rescue operations. 

The task group consisted of five Naval vessels, two USNS transports, an air unit 

for antisubmarine warfare, and a shore-based harbor control unit. The seven surface 

ships and their crew sizes were: 

Ship Crew Size 

uss CABILDO 16) 378 

USS CURTISS 638 

USS LST-859 113 

USNS SGT. CHARLES E. MOWER (TAP-186) 29 

USS SPROSTON (DDE-577) 283 

USS WALKER (DDE-517) 317 

USNS LT. ROBERT CRAIG (TAK-252) 12 

11 
Personnel aboard these units totaled 1770 officers and men. The boat pool 

consisted of an additional 213 personnel who were embarked in CABILDO, while the 

harbor control unit and other land-based units consisted of 467 personnel assigned to 

the residence islands of Enewetak. The air unit was assigned to Kwajalein and had a 

total strength of approximately 400 personnel. The total Naval participants at 

GREENHOUSE was approximately 3000 and are summarized below: 

Shipboard Personnel 1770 

Boat Pool (on CABILDO) 213 

VP-931 (Air Unit at Kwajalein) 386 

Shore-Based Personnel (at Enewetak) 467 

Total 2836 

The reconstructions and dose calculations in this report apply only to the ship’s 

crews and to personnel assigned to the residence islands of Enewetak Atoll. The 

movements of boat pool personnel and of VP-931 cannot be followed in 

sufficient detail to permit a dose reconstruction for these personnel; however, 

personnel in these units were badged when their missions took them to areas where 

radiation was likely to be encountered. Personnel on Kwajalein were not exposed to 

fallout from any of the detonations. 

A basic operation plan described the general administration arrangements of the 

task group and discussed the general concepts of operation and those operations 

common to all shots. The operation plan assigned the following specific responsibilities to Task Group 3.3 units: 

(a) Receive, transport, and safeguard experimental weapons. Provide shipboard assembly facilities. Base at Enewetak. 

Convoy and Escort Unit proceed in convoy in accordance with separate 

instructions. (CURTISS, SPROSTON, WALKER) 

Surface Patrol Unit conduct surface search and antisubmarine patrol within 

the Enewetak Area. Base at Enewetak. (SPROSTON, WALKER) 

12 
Boat Pool Unit control and provide transportation within Enewetak Lagoon. 

Coordinate scheduling and employment of small craft with TG 3.1. Base at 

Enewetak. 

Unassigned units assist as directed in support of operations, including 

establishing and resupply of outlying stations, POL support and personnel 

housing afloat at Enewetak SGT. C. E. MOWER, LT. R. CRAIG). 

Operation orders (Reference 3) were prepared by Commander Task Group 3.3 for 

each shot. Detailed plans were drawn to control the movements and activities of all 

personnel, not only to support the task force in its mission, but also to provide for 

safety of personnel. A rigid schedule of all ship and boat movements was kept and 

rosters of personnel were maintained for each boat. The liberty boats could take 

parties to Enewetak Island only. For each shot, each unit had pre-assigned tasks that 

were duly checked off by the operation center, in some cases on a minute-by-minute 

basis. 

1.3 METHODOLOGY 

The procedures developed in previous dose reconstruction efforts have been 

adapted to both shipboard and island radiological environments at Operation GREENHOUSE. Figure 1-3 depicts the steps taken in calculating personnel doses. These 

steps are pursued to a level of detail governed by the availability of data. Sufficient 

data were recorded at the time and enough have survived to understand the Naval 

operations and to characterize the radiation environment. Individual ship deck logs 

serve as an authoritative source of ship position and activity. It is assumed that the 

units of Task Group 3.3 adhered to the operation plans as promulgated by Commander 

Task Group 3.3, which serve as guides to ship activities. References 4, 5, and 6 

comprise the official reports of the tests. Each unit prepared radiological contamination and decontamination reports for each test. These reports are available for each 

vessel (Reference although not necessarily for every shot. Supporting documents 

and reports prepared by the Naval Radiological Defense Laboratory (References 

also contain data pertinent to this dose reconstruction. 

13 
SHIP OPERATIONS 

(DECK 

DECONTAMINATION 

REPORTS 

AFTER-ACTION 

REPORTS 

FREE-FIELD 

ISLAND RADIATION 

ENVIRONMENTS 

(WT REPORTS) 

FILM BADGE PERSONNEL 

WIELDING 

DOSE ACTIVITIES 

. 

UNCERTAIMTIES 

FILM BADGE COMPARE DOSIMETRY 

DOSE 

DISTRIBUTIONS RECORDS 

Figure 1-3. Operation GREENHOUSE Dose Reconstruction Methodology 

14 
Radiological data are used to reconstruct the time-dependent radiation environments on the residence islands of Enewetak Atoll and on each of the seven ships at 

Operation GREENHOUSE. Characterization of the radiation environment starts with 

the determination of on-deck intensities from radiological survey data. The periodic 

shipboard surveys, in conjunction with fallout time-of-arrival data and nearby island 

surveys, serve to define the free-field intensity as a function of time. For 

interpolation between shipboard readings, the intensity is assumed to be a power law 

function of time after burst. At times following the last reported shipboard survey, 

decay rates determined from nearby island survey data are utilized. Despite 

significant differences in decay rate between ship and shore due to washdown, 

decontamination, and weathering, the late-time decay, mostly from insoluble particles 

adhering to or soil, is taken to be the same. Specific data regarding the 

development of intensity curves for the ships and islands are presented in Section 2. 

Shipboard radiation surveys indicated a considerable variation in topside intensities because of ship geometry, redistribution of fallout during and 

decontamination, and non-uniform adherence of fallout particles to ship materials. If 

only an average survey reading was reported, this value is used. In other cases, 

readings were taken at many predetermined positions on the ship’s exposed surfaces. 

These readings, taken three feet above the surface, are judged to provide an unbiased 

representation of the topside radiation field. The ship’s crew is presumed to have been 

located at random positions when on deck; thus, the mean survey readings, appropriately decayed, are used to determine the mean intensities encountered by the crew 

when on deck. The distribution of survey readings suggests a distribution in radiation 

exposure to the crew; this matter is considered in the uncertainty analysis (Section 

The analysis of radiation exposure to the crew also requires estimation of 

radiation intensities below deck and the apportionment of crew activities with time 

below and on deck. A ship-shielding factor is defined as the ratio of intensity below to 

the mean intensity topside. This factor, determined for each type of ship in Section 

2.9, is approximately 0.1 and is nearly constant over the usual crew locations within a 

ship. Thus, the radiation dose to the crew is dominated by the topside exposure. 

Specific durations of topside exposure are given in ship logs for shot day (rarely 

15 
thereafter) when the radiological situation altered the normal pattern of duties. For 

other days, and when unspecified, the on-deck intervals are taken to be 0800-1200, 

1330-1700, and 1800-2000 hours, which amount to 40 percent of a day. 

The mean film badge dose to the crew is obtained from time integration of 

intensity for all intervals below (including the shielding factor) and on deck. A 

conversion factor of 0.7 is used to account for body shielding by the badge wearer 

(Reference 12). To facilitate the calculation, the daily fractional topside duration 

rather than the specified intervals is used on the third and subsequent days after burst, 

when the slackening decay rate lessens the need for more precision in timing. Because 

the specified intervals are nearly centered around midday, this approximation is 

suitable by the third day. 

Day-by-day and cumulative film badge doses to the average crewman of each 

ship are calculated and presented in Section 3. Calculations are continued until the 

monthly dose drops below 30 mrem; subsequent dose accrual is negligible compared to 

that previously accrued. An uncertainty analysis of the dose calculations is provided 

in Section 4. In Section 5, the available dosimetry records are analyzed, and their 

comparability to the calculated doses is assessed. 

16 
Section 2 

SHIP OPERATIONS AND RADIATION ENVIRONMENTS 

This section describes the operations of each of the seven ships that participated 

at Operation GREENHOUSE. A complete description of each ship’s movements during 

April and May 1951 while at Enewetak Atoll is obtained from deck logs. Crew 

activities and other anti-contamination measures are also found in deck logs. Shipboard radiological data have been extracted from after-action reports and Material 

Contamination-Decontamination Reports, ‘or inferred from nearby island data as 

detailed in Reference 6. These data have been used to derive shot-specific, 

specific radiation intensity curves, which represent the average topside, free-field 

radiation environment resulting from each detonation where a ship encountered 

fallout. Similar radiation environments are reconstructed for the residence islands of 

Enewetak Atoll. These environments are then time-integrated to determine the daily 

integrated free-field intensities on each of the ships and islands. 

Task Group 3.3 (Reference 1) procedures anticipated that ships would operate in 

a potentially radioactive environment. Personnel doses were to be limited to 

0.1 R/day, thus access to areas where intensities were greater than 12.5 (for an 

assumed eight-hour workday) was controlled. General operating procedures required 

that each ship be brought to a maximum state of readiness at 30 minutes prior to each 

shot, with anchored ships at “short and steam at the throttle. This allowed the 

ship to get underway in a minimum amount of time to maneuver clear of radiological 

fallout. All ships were alerted by Commander Task Group 3.3 at the occurrence of the 

first fallout. All unnecessary personnel were cleared from the weather decks, while 

outside ports, doors, and hatches were closed and the ventilation systems reduced to 

the minimum. Anti-contamination measures were placed into effect. From the onset 

of significant fallout, continuous was maintained over all weather decks to 

minimize the adherence of the fallout particles to the ship’s surfaces (References 4, 

5). This proved to be an extremely effective technique and resulted in reducing the 

radiation environment to levels of approximately half those found on the 

islands in close proximity to the ships. Decontamination procedures that were carried 

out after fallout had ceased, such as scrubbing the bulkheads and weather decks with a 

17 
mixture of lye, soap and water, did not appear to be very effective, except in isolated 

cases. These attempts to decontaminate usually resulted in a further 10 to 20 percent 

reduction in the shipboard intensities (Reference 7). 

With the exception of the SPROSTON, WALKER, and CRAIG, the units of Task 

Group 3.3 spent most of their time in Enewetak Lagoon. At the time of each 

detonation, they were anchored near Parry or Enewetak Islands in the southern 

anchorage area some IO-20 miles from the shot locations. The surface patrol vessels, 

SPROSTON and WALKER, conducted surface and anti-submarine patrols in the 

vicinity of Enewetak Atoll, sweeping with radar and sonar. Patrol areas were 

specified for each shot, and standard search procedures were employed (References 4, 

5). The CRAIG was at Enewetak for five days in April, staying only long enough to 

unload cargo before proceeding to Guam. 

2.1 USS CABILDO (LSD-16) 

When Shot DOG was detonated on 8 April, the USS CABILDO (LSD-16) was 

moored to a telephone buoy in berth N-2, approximately 1700 yards west of Enewetak 

Island and 12 miles south of Shot DOG ground zero (GZ) (see Figure 2-l). A 

radiological survey made at 0830 hours detected no contamination. At 1014 

hours fallout was (apparently) detected because the ventilation systems were closed 

and of the weather decks begun. At 1015 hours all hands, except those 

specifically excepted, were ordered below decks. By 1100 hours the maximum 

intensity reading was 40 and the average intensity was about 25 

At 1300 hours decontamination operations were initiated and a radiological 

survey of the ship was made. The maximum intensity observed was 26 the 

average reading on the foredeck was 13.7 (Reference 7). Reference 5 indicates 

an average of 20 The latter value is used for dose reconstruction. 

Decontamination was accomplished by flushing with high pressure salt water while 

scrubbing the decks with brushes. Application of these measures continued for two 

days during which additional radiological surveys were made at the following times: 

18 
-

ENGEBI ISLAND 

LAND 

EBERIRU ISLAND 

ENEWETAK ATOLL 

(ENIWETOK) JAPTAN 

0 ISLAND 

STATUTE MILES 

DEEP ENTRANCE 

N-2 

WIDE PASSAGE 

Figure 2-l. LJSS CABILDO Anchorage Area Operation GREENHOUSE 

19 
0400 hours, 9 April; 1030 hours, 9 April; 1500 hours, 9 April; 1000 hours, April. By 

1500 hours, 9 April, the average intensity had been reduced to 3.4 mR/hr, with a 

maximum intensity of 10 mR/hr. By 20 April, the day before Shot EASY, the average 

intensity was about 0.15 mR/hr, with a maximum intensity of 0.3 (see 

Figure 

Shot EASY was detonated on 21 April on Engebi Island, approximately 19 miles 

north of the CABILDO (Figure The deck log of the CABILDO makes no mention 

of fallout occurring after Shot EASY and radiological surveys at 0727 hours and 1230 

hours on shot day detected no fallout. However, on Enewetak Island (1700 yards east 

of the CABILDO) and on Parry Island (four miles northeast of the CABILDO), a small 

amount of fallout did occur during the night of 21 April and the early morning of 

22 April. It is assumed that fallout Shot EASY began at 2230 hours, 21 April 

16 hours), and that the peak intensity occurred at about 0630 hours, 22 April 

hours). The maximum intensity of this fallout on Parry Island was reported as two to 

three times the residual radiation from Shot DOG, which had been recently measured 

to be 0.5 mR/hr. Because radiological surveys made after deposition of the Shot EASY 

fallout measured the combined intensities of the residual radiation from both Shots 

DOG and EASY, the intensity to Shot EASY was between 0.5 (two 

tirnes background, minus the Shot DOG contribution) and 1.5 (three times the 

background). Three survey readings for Parry Island are: 0.8 at 0900 hours, 

23 April, 0.6 on 24 April, and 0.6 on 25 April. Because the measured 

intensities were the same on all residence islands, the fallout was sufficiently uniform 

as to be considered the same on the nearby ships. A survey was made aboard the 

CABILDO at 1530 hours, 9 May (GEORGE day), the average intensity of which (0.12 

was due to the combined residual radiation from Shots DOG and EASY (Shot 

GEORGE caused no fallout aboard the CABILDO). The survey data are shown in 

Figure 2 -3. Also shown are the net intensities ascribed to Shot EASY, derived by 

subtracting the calculated intensity of the residual radiation due to Shot DOG from 

the observed data. The data are fitted by a power law. The resultant fit indicates 

-1.1 that Shot EASY fallout decayed as t , and that the intensity at 0630 hours, 22 April 

(the assumed peak) was 1.0 mR/hr, which is within the range of peak intensities 

reported. 

20 
I I I I I 

Average Shipboard 

Measurements (Ref 7) 

Average Shipboard 

Measurements 5) 

••

••Maximum Shipboard •••••

•

Measurements 

-- Intensity 

Z-27) 

inn 1000 -“”

I I I 

I 

I

I

I

I 

I

I 

I

I

I

I

I 

I 

I 

I 

I 

I

I 

I

I 

I 

II 

10 Apr 51 Shot EASY 

21 Apr 51 

Time After Shot DOG (Hours) 

Figure 2-2. CABILDO (LSD-16) Ship Intensity Following 

Shot DOG 

21 
---------~

Time After Shot DOG (Hours) 

322 412 1312 

0 Average Shipboard Measurements 

Average Parry Island 

Measurements 

Derived Shipboard 

Intensities 

Range of Reported

Maximum 

Shot DOG Background 

on Parry Island 

1 

I I I I I I 

on CABILDO 

1 10 100 1000

23 Apr 51 Shot GEORGE 

9 May 51 

Time After Shot EASY (Hours) 

Figure 2-3. CABILDO (LSD-16) Ship Intensity Following 

Shot EASY 

22 
 

The CABILDO remained at in berth N-2 until 0801 hours, 25 April, when 

it got underway to berth P-3 for fuel. It remained in berth P-3 until 0703 

26 April, when it got underway for berth N-2, anchoring there at 0718 hours, 26 Apt-il. 

Shot GEORGE was observed by the crew of the CABILDO from a distance of 16 

miles south of GZ. No fallout from this shot occurred on board the CABILDO. 

The detonation of Shot ITEM on 25 May was observed by the crew of the 

CABILDO from a distance of approximately 20 miles south of GZ (Figure 2-l). At 

1028 hours the ventilation system was shut down, of the weather 

decks was initiated, and all personnel were ordered below decks. At 1045 hours the 

intensity was 4-6 A radiological survey made at 1130 hours indicated 2-26 

with an average intensity of about 12 At 1230 hours decontamination 

operations were initiated. Although decontamination operations continued, the 

ventilation system was again started and personnel were permitted topside at 1245 

hours. A radiological survey made at 1400 hours showed 2-23 with an average 

intensity of about 7.3 

At 1620 hours, 25 May, fallout was again detected aboard the CABILDO and all 

hands wet-e ordered below decks. A radiological survey made at 1630 hours showed 4-

130 with an average intensity of 40 Another radiological survey made 

at 1900 hours showed 4-135 with an average intensity of 33 At 2130 

hours another survey showed intensities of 4-75 with an average of 27 

The decontamination operations begun at 1230 hours were sustained throughout the 

remainder of the day (25 May) and through most of the following day. 

At 0415 hours, 26 May, a radiological survey indicated intensities of 4-50 

with an average of about 20 Three more surveys were made that day, the last 

one, at 1700 hours, indicated intensities of l-22 with an average intensity of 

about 7 At that time only four of the 81 selected survey locations had an 

intensity greater than 12.5 not decontamination was 

radioactive decay would have reduced these intensities to 12.5 less within 24 

hours. 
The CABILDO remained moored in berth N-2 until 1740 hours, 30 May, when it 

got underway for Pearl Harbor. 

The free-field radiation intensities the CABILDO resulting from Shots 

DOG, EASY and are plotted in Figures 2-2, 2-3, and 2-4, respectively. They 

represent the average topside radiation environment resulting from each detonation 

where fallout occurred the ship. When available, both average and maximum 

values of intensity are plotted as a function of time after burst. Because of the 

proximity to Enewetak Island, the average Enewetak Island intensity data 

(Section 2.8) are plotted to demonstrate the effectiveness of the anti-contamination 

procedures carried out the CABILDO after Shots DOG and ITEM (Figures 2-2 

and 2-4). Table 2-1 is a summary of the radiological data for the CABILDO. These 

data are used to calculate the daily integrated free-field intensities the 

CABILDO through 31 May that are presented in Table 2-2. 

2.2 USS CURTISS 

On 8 April, when Shot DOG was detonated, the USS CURTISS was moored to a 

telephone buoy in berth B-l, approximately 1500 yards west of Parry Island and nine 

miles south of Shot DOG GZ Figure 2-5). At 0825 hours the Rad-Safe 

Officer the CURTISS reported contamination levels between 1 and 4 

At that tirne, all ventilation systems were closed and the weather decks were washed 

down. At 1010 hours, a resurvey of the ship led to a reported average radiation 

intensity of 35-40 maximum intensity levels had reached 100 

Fallout again started falling on the CURTISS at 1200 hours and continued for 

appr oxi mate1 y one hour. At 1300 hours, a rad-safe survey indicated average readings 

of 16 with a maximum reading of 57.5 Decontamination, consisting of 

continuously washing down the weather decks and scrubbing with a mixture of lye, 

water, and soap, began at 1300 hours and continued for the next 24 hours. At 1130 

hours, 9 April, a rad-safe survey indicated that all areas of the CURTISS had radiation 

levels at or below 12.5 except for an isolated area of 25 

24 
I I I I I I I I 

I 

I 

I 

I 

I 

I 

I 

I 

0 Average Shipboard 

Measurements 

•• Maximum Shipboard 

Measurements 

--Average Enewetak Intensity 

(See Figure 2-30) 

-

Time After Shot ITEM (Hours) 

Figure 2-4. USS CABILDO (LSD-16) Ship Intensity Following 

Shot ITEM 

25 
TABLE 2-1. USS CABILDO Average Radiation Intensity Data 

Date and Time Time After Shot Intensity 

Shot DOG 

8 April, 1014 3.7 

8 April, 1 100 4.4 25 

8 April, 1300 6.6 20 

9 April, 0400 21.4 5.8 

9 April, 1030 27.9 4.7 

9 April, 1500 32.4 3.4 

10 April, 1000 51.4 1.7 

11 April, 0900 74.4 1.1 

(Enewetak Island survey data indicate decay as t -1.2 thereafter) 

Shot EASY (inferred) 

21 April, 2230 16.0 0.1 

22 April, 0630 24.0 1.0 

(Decay assumed to be as t-1.1 thereafter) 

Shot ITEM 

25 May, 1028 4.2 

25 1130 5.2 11.5 

25 May, 1630 10.2 4.6 

25 May, 1723 11.1 58.6 

25 May, 2130 15.2 26.0 

26 May, 0730 25.2 15.1 

26 May, 0930 27.2 9.1 

26 May, 1700 34.7 7.2 

t -1.1 (Enewetak Island survey data indicate decay as thereafter) 

26 
Table 2-2. Daily Integrated Free-Field Intensity, USS CABILDO 

DATE 

8 

9' 

II 

12 

13 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

May 

2 

3 

4 

5 

6 

7 

8 

9 

II 

13 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

June 

July 

August 

DOG 

180.1 

105.4 

40.6 

26.0 

18.0 

13.9 

11.3 

9.4 

8.0 

7.0 

6.1 

5.6 

5.0 

4.6 

4.1 

3.9 

3.6 

3.3 

3.1 

2.9 

2.7 

2.6 

2.4 

2.3 

2.1 

2.1 

2.0 

1.9 

1.9 

1.7 

1.7 

1.6 

1.6 

1.6 

1.4 

1.4 

1.3 

1.3 

1.3 

1.3 

1.1 

1.1 

1.1 

1.1 

1.0 

1.0 

1.0 

1.0 

1.0 

1.0 

0.9 

0.9 

0.9 

0.9 

19 

13 

9 

EASY 

0.2 

15.4 

9.8 

6.5 

4.8 

3.8 

3.1 

2.6 

2.3 

2.0 

1.8 

1.6 

1.5 

1.4 

1.3 

1.2 

1.1 

1.0 

1.0 

0.9 

0.9 

0.8 

0.8 

0.7 

0.7 

0.7 

0.6 

0.6 

0.6 

0.6 

0.5 

0.5 

0.5 

0.5 

0.4 

0.4 

0.4 

0.4 

0.4 

9 

5 

4 

GEORGE 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

ITEM 

315.7 

257.4 

108.6 

71.4 

52.9 

41.7 

34.4 

330 

106 

61 

27 
DEEP ENTRANCE 

PARRY 

ISLAND 

ENEWETAK ATOLL 

(ENIWETOK) 

0 

STATUTE MILES 

ENEWETAK WIDE PASSAGE ISLAND 

Figure USS CURTISS Anchorage Areas Operation GREENHOUSE 

28 
In the early afternoon of 9 April, the CURTISS got underway from berth B-l 

to berth 768 off Engebi Island, arriving there at 1602 hours (Figure Z-5). It 

remained there until 1410 hours, 20 April, when it returned to berth B-l off Parry 

Island, where the crew observed Shot EASY the following day. 

Shot EASY was detonated on Engebi Island, approximately 16 miles north of the 

CURTISS. There is no mention of fallout occurring aboard the CURTISS in its deck 

log, nor have any Material Contamination-Decontamination Reports been found that 

would indicate shipboard contamination from Shot EASY. On Parry Island, only 1500 

yards east of the CURTISS berth, however, a small amount of fallout did occur during 

the night of 21 April and the early morning of 22 April. It was determined 

insignificant, amounting only to 2 or 3 times the Shot DOG residual radiation. It is 

likely that this same fallout occurred aboard the CURTISS and either went undetected 

or was deemed too insignificant to report. Since Shot EASY fallout on Parry and 

Enewetak Islands was identical, the CURTISS probably received the same fallout that 

occurred the CABILDO and the other ships anchored in the southern 

anchorage area (see Section 2.1). 

The CURTISS remained at anchor in berth B-l until 23 April, when it got 

underway to take on fuel. On 24 April, it shifted berths and moored to a telephone 

buoy near berth 639, approximately 2500 yards south of Eberiru Island, the shot island 

for Shot GEORGE scheduled for 9 May (Figure 2-5). The CURTISS remained there 

until 8 May when it got underway to shift berths. At 1607 hours, 8 May, the CURTISS 

was anchored in berth C-l, approximately 1500 yards off Parry Island, where it 

remained for Shot GEORGE on the following day. 

Shot GEORGE was observed by the crew from a distance of 12% miles south of 

GZ. No fallout occurred on the CURTISS as a result of Shot GEORGE. The ship 

remained in the vicinity of Parry Island until 16 May, when it got underway for the 

northern anchorage area off Engebi Island. It remained moored to a telephone buoy in 

berth 768 off Engebi until 24 May, when it returned to berth B-i off Parry Island, to 

remain for Shot ITEM on 25 May. 

29 
The crew observed Shot ITEM from a position approximately 16 miles south of 

ground zero, At 0940 hours fallout was detected on the CURTISS and by 1030 

hours, average radiation intensities had reached approximately 6.5 with a 

maximum reported intensity of 25 mR/hr. Decontamination, effected at this time, 

consisted of continuously flushing the weather decks with salt water. By 1230 hours, 

decontamination of the ship was halted. At this time intensities had been reduced to 

an average of 1.6 

At 1530 hours, 25 May, fallout was again experienced aboard the CURTISS. 

Average intensities reached 25-30 mR/hr, with maximum (probably isolated) intensities of 70 reported. Fallout continued until approximately 1930 hours, with 

average radiation levels remaining at approximately 30 mR/hr. It was not until noon 

on 26 May that the residual contamination on the weather surfaces of the ship was 

reduced to acceptable levels of 12.5 or less. The CURTISS remained moored in 

berth B-l until 1528 hours, 27 May, when it departed Enewetak Atoll for Pearl Harbor. 

The free-field radiation intensities the CURTISS resulting from Shots 

DOG, EASY and ITEM are plotted in Figures 2-6, 2-7, and 2-8, respectively. They 

represent the average topside radiation environment resulting from each detonation 

where fallout occurred the ship. When available, both average and maximum 

values of intensity are plotted as a function of time after burst. Since the CURTISS 

was always anchored near Parry Island when fallout occurred, the average Parry Island 

intensity data have also been plotted to demonstrate the effectiveness of the 

contamination procedures carried out the CURTISS after Shots DOG and ITEM 

(Figure 2-6 and 2-S). Table 2-3 is a summary of the radiological data used to 

reconstruct the ship intensity curves for the CURTISS. The curves are 

integrated to determine the daily integrated free-fieid intensities on ship through 

31 May, presented in Table 2-4. 

2.3 USS LST-859 

The USS LST-859 was anchored in berth C-2, approximately 2000 yards west of 

Parry Island, when Shot DOG was detonated Figure 2-9). From this vantage point, 

30 
 

I I I I I I I I I I 

Average Shipboard 

Measurements 

Maximum Shipboard 

• Measurements 

--Average Parry Intensity 

(See Figure 2-26) 

10 100 Apr 51 Shot 

21 Apr 51 Time After Shot DOG (Hours) 

Figure 2-6'. USS CURTISS (AV-4) Ship Intensity Following 

Shot DOG 

31 
 

100 

10 

1.0 

0.1 

Time After Shot DOG (Hours) 

322 412 1312 

10 

23 51 

100 

51 

Time After Shot EASY (Hours) 

Figure 2-7. USS CUKTISS (AV-4) Ship Following 

Shot EASY 

32 
- - --

100 

10 

1.0 

0 Average Shipboard 

Measurements 

•• Shipboard 

Measurements 

Average Parry Intensity 

(See Figure 2-31) 

10 100 

Time After Shot ITEM (Hours) 

Figure 2-8. USS CURTISS (AV-4) Ship Intensity Following 

Shot ITEM 

33 
---- - --

TABLE 2-3. USS CURTISS Average Radiation Intensity Data 

Date and Time Time After Shot Intensity 

Shot DOG 

8 April, 0825 1.8 2.5 

8 April, 1010 3.6 40.0 

8 April, 1300 6.4 16.0 

9 April, 1130 29.0 7.0 

(Parry Island decay rate as assumed thereafter) 

Shot EASY (inferred) 

21 April, 2230 16.0 0.1 

22 April, 0630 24.0 1.0 

(Decay assumed to be as t

-1.1 thereafter) 

Shot ITEM 

25 May,0940 3.4 1.0 

25 May, 1030 4.2 6.5 

25 May, 1230 6.2 1.6 

25 May, 1530 9.2 1.1 

25 May, 1630 10.2 30.0 

25 May, 1930 13.2 30.0 

26 May,1130 29.0 7.0 

(Parry Island decay rate as t assumed thereafter) 

34 
 

1TE.M

Table 2-4. Daily Integrated Free-Field Intensity, USS CURTISS 

GEORGE 

10 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

May 

4 

5 

6 

7 

8 

9 

13 

14 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

June 

July 

August 

September 

227.9 

163.9 

88.4 

58.6 

43.6 

34.6 

28.6 

24.3 

21.1 

18.6 

16.7 

15.0 

13.7 

12.6 0.2 

11.6 15.4 

10.9 9.8 

10.1 6.5 

9.4 4.8 

8.9 3.8 

8.4 3.1 

8.0 2.6 

7.6 2.3 

7.1 2.0 

6.9 1.8 

6.6 1.6 

6.3 1.5 

6.0 1.4 

5.7 1.3 

5.6 1.2 

5.3 1.1 

5. I 1.0 

5.0 1.0 

4.9 0.9 

4.6 0.9 

4.4 0.8 

4.3 0.8 

4.3 0.7 

4.1 0.7 

3.7 0.6 

3.7 0.6 

3.6 0.6 

3.4 0.5 

3.4 0.5 

3.3 0.5 

3.3 

3. I 

3. I 0.5 

3.0 0.4 

3.0 0.4 

2.9 0.4 

2.9 0.4 

2.9 0.4 

64 9 

44 6 

33 4 

26 3 

215.3 

198.1 

93.1 

64.1 

49.0 

39.7 

33.4 

357 

131 

81 

57 

35 
'

ENGEBI ISLAND 

EBERIRU ISLAND 

OJOA ISLAND 

- N -

/ 

ENEWETAK ATOLL 

0 

STATUTE MILES N-9 DEEP ENTRANCE 

PARRY 

ISLAND 

WIDE PASSAGE 

Figure 2-9. USS LST-859 Anchorage Areas Operation GREENHOUSE 

36 
the crew observed the detonation on Island, approximately 9 miles to the north. 

At 0735 hours, LST-859 got underway to its assigned anchorage off Rojoa 

Island in the northern portion of the lagoon, taking a station 2500 yards astern of the 

MOWER. LCM-20, a Task Group 3.3 escort boat, preceded the MOWER and the 

859 during their passage north. At 0835 hours LCM-20 reported contamination 

levels of at a position 1000 yards north of buoy N-V in the ship channel 

(Figure 2-V). At that time, the LST-859 and MOWER were ordered to lie to. At 0842 

hours they were ordered to resume their passage to the northern anchorage area. At 

0835 hours, average readings aboard the LST-859 were 25 mR/hr, with a maximum 

reading of 100 mR/hr. Decontamination was begun at 0845 hours. 

Although it is not explicitly stated, it appears that moderate fallout activity 

continued as they steamed north. At approximately 0945 hours, when the LST-859 was 

3.7 miles west of ground zero, it encountered heavy fallout. An attempt to maneuver 

free of the fallout area resulted in exposing the ship for a longer period of time than if 

it had proceeded directly to its assigned berth. By 1100 hours, the LST-859 was 

reporting an average intensity aboard ship of 76 mR/hr, with a maximum reading of 

380 mR/hr. It was not until 1146 hours that the LST finally anchored in its assigned 

berth, 2100 yards west of Rojoa Island, (Figure 2-V). Decontamination continued both 

below and above decks, and by 1630 hours, average intensity levels on the weather 

decks had been reduced to approximately 4 mR/hr, with isolated areas of 10 mR/hr. 

By 1757 hours, 9 April, all weather deck intensities had been reduced below 4.5 

The LST-859 remained anchored in the area off Rojoa until 1649 hours, 20 April, 

when it got underway to shift berths. At 1820 hours, it was anchored in berth C-2 off 

Parry Island, where it remained for Shot EASY on the following day (Figure 2-V). 

Shot EASY was detonated approximately 16 miles north of the LST-859. There is 

no mention of fallout occurring the ship as a result of Shot EASY, but on 

Parry Island, only 2000 yards east, a amount of fallout did occur during the night 

of 21 April and the early morning of 22 April. It was determined insignificant, 

amounting only to 2 or 3 times the Shot DOG residual radiation (Reference 6). It is 

not unreasonable to expect that the same fallout occurred aboard the LST-859 and 

37 
either went undetected or was deemed too insignificant to report. With the 

assumption that the ship did receive this fallout, the average peak intensity 

would have been approximately 1.5 

At 0620 hours, 22 April, the LST-859 got underway to its assigned anchorage off 

Rojoa Island, where it anchored at 0802 hours the same day. Because of the presence 

of underwater telephone cables in this area, it shifted anchorages to berth 646, 2500 

yards southwest of Rojoa, on 24 April (Figure 2-9). It remained in the northern 

anchorage area until 1735 hours, 8 May, when it returned to the southern anchorage 

area. At 2002 hours, 8 May, it dropped anchor in berth P-2, approximately 900 yards 

north of Enewetak Island. 

Shot GEORGE was detonated on Eberiru Island, approximately 16 miles north of 

berth P-2, where the crew observed the detonation. No fallout occurred the 

LST-859 as a result of Shot GEORGE. It remained in berth P-2 until May, when it 

shifted berths to B-2, off Parry Island. On 13 May, the LST-859 departed Enewetak 

to the Caroline Islands, where it arrived on 15 May. It returned to Enewetak 

on 21 May and remained off Enewetak Island until 23 May, when it got underway 

to Kwajalein via Bikini Atoll. No fallout was reported the ship 

following Shot 

The free-field radiation intensities the LST-859 resulting from Shots 

DOG and EASY are depicted in Figures 2-10 and 11, respectively. They represent 

the average topside radiation environment resulting from each detonation where 

fallout occurred ship. Both average and maximum values of intensity are 

plotted with time after burst. Table 2-5 is a summary of the radiological data used to 

derive the ship intensity curves. Daily integrated free-field intensities the 

LST-859 are presented in Table 2-6. 

2.4 SGT. CHARLES E. MOWER (TAP-186) 

The USNS SGT. CHARLES E. MOWER was anchored in berth C-l, approximately 

1500 yards west of Parry Island (see Figure 2-12) when Shot DOG was detonated. The 

38 
 

1000 

Average Shipboard 

Measurements 

Maximum Shipboard 

Measurements 

100 

10 

1.0 

A

1 10 100 1000

10 Apr 51 Shot EASY 

21 Apr 51 Time After Shot DOG (Hours) 

Figure USS LST-859 Ship Intensity Fol owing Shot DOC 

39 
 

Time After Shot DOG (Hours) 

313 322 412 1312 

I I I I I I I I I I 

1 10 100 A 1000 

23 51 Shot GEORGE 

Time After Shot EASY (Hours) May 51 

Figure 2-11. USS LST-859 Ship Intensity Following Shot EASY 

40 
TABLE 2-5. USS LST-859 Average Radiation Intensity Data 

Date and Time Time After Shot Intensity 

Shot DOG 

8 April, 0835 2.0 25.0 

8 April, 1100 4.4 75.6 

8 April, 1630 9.9 3.9 

9 April, 1757 35.4 2.8 

(Parry Island decay rate as assumed thereafter) 

Shot EASY (inferred) 

21 April, 2230 16.0 0.1 

22 April, 0630 24.0 1.0 

(Decay assumed to be as -1.1 thereafter) 

NOTE: LST-859 was to Bikini at the time of Shot ITEM. 

41 
 

ITEM*

Daily Integrated Free-Field Intensity, USS LST-859 

DOG EASY GEOR GE 

8 April 1951 255.4 

9 69.1 

10 43.1 

11 28.5 

12 21.3 

13 16.9 

13.9 

11.9 

16 10.3 

17 9.1 

18 8.1 

19 7.3 

20 6.7 

21 6.1 0.2 

22 5.7 15.4 

23 5.3 9.8 

24 4.9 6.5 

25 4.6 4.8 

26 4.3 3.8 

27 4.1 3.1 

28 3.9 2.6 

29 3.7 2.3 

30 3.4 2.0 

I May 3.3 1.8 

2 3.1 1.6 

3 3.0 1.5 

4 2.9 1.4 

5 2.9 1.3 

6 2.7 1.2 

7 2.6 1.1 

8 2.6 1.0 

9 2.4 1.0 0 

10 2.3 0.9 0 

II 2.3 0.9 0 

12 2.1 0.8 0 

13 2.1 0.8 0 

2.0 0.7 0 

2.0 0.7 0 

16 2.0 0.7 0 

17 1.9 0.6 0 

18 1.9 0.6 0 

19 1.9 0.6 0 

20 1.7 0.6 0 

21 1.7 0.5 0 

22 1.7 0.5 0 

23 1.6 0.5 0 

24 1.6 0.5 0 

25 1.6 0.5 0 

26 1.6 0.5 0 

27 1.4 0.4 0 

28 1.4 0.4 0 

29 I.4 0.4 0 

30 1.4 0.4 0 

31 1.4 0.4 0 

was to Bikini at the time of Shot ITEM. 

42 
- -

EBERIRU ISLAND 

NORTHERN 

\ ANCHORAGE 

D 

NEWETAK 

ENIWETOK) 

SLAND 0 5 

. Buoy STATUTE MILES N-9 

DEEP ENTRANCE 

\ 

PARRY 

ISLAND 

ENEWETAK WIDE PASSAGE ISLAND 

Figure 2-12. USNS SGT. CHARLES E. MOWER Anchorage Areas 

Operation GREENHOUSE 

43 
crew observed the explosion on Island, approximately 9 miles north of their 

anchorage off Parry. At 0737 hours the MOWER weighed anchor and got underway for 

berth 765 in the northern anchorage area off Engebi Island. LCM-20, a Task Group 3.3 

escort boat, preceded the MOWER and the LST-859. At 0835 hours the LCM-20 

reported contamination levels of at a position 1000 yards north of buoy 

N-Y in the ship channel (Figure and both the MOWER and LST-859 were ordered 

to lie to. At 0842 hours, the MOWER was ordered to resume passage to its assigned 

anchorage off Engebi and it steamed up the channel at a speed of approximately 10 

knots. At 0858 hours, when a rad-safe survey was initiated, average intensities 

the MOWER were 15 with maximum readings of 20 At 0937 

hours, when the MOWER was approximately 3.7 miles west of ground zero, it 

encountered heavy fallout. Rather than trying to avoid the fallout area as did the 

LST-859, the MOWER proceeded directly toward its assigned berth. A rad-safe survey 

at 0940 hours indicated average intensity levels aboard the MOWER of approximately 

40 with isolated readings as high as 110 Decontamination was begun at 

09 45 hours. 

By 1037 hours, the MOWER had passed through the fallout area and was anchored 

in berth 765 off Engebi (Figure 2-12). Decontamination of the ship continued, and by 

1215 hours, average levels had been reduced to 20 It was not until approximately 1000 hours, 9 April, that contamination levels were reduced to approximately 

2 with isolated areas as high as 4.1 

The MOWER remained anchored off Engebi until 20 April, when it returned to 

berth C-l in the southern anchorage area off Parry Island, from which the crew would 

observe Shot EASY on the following day. 

Shot EASY was detonated on Engebi, approximately 16 miles north of the 

MOWER. There is no mention of fallout occurring the MOWER as a result of 

Shot EASY, but on Parry Island, only 1500 yards east, a small amount of fallout did 

occur during the night of 21 April and the early morning of 22 April. It is likely that 

this same fallout occurred aboard the MOWER, but either went undetected or was 

deemed too insignificant to report. With the assumption that the MOWER did receive 

44 
this fallout, the average peak intensity would have been approximately 

1.5 mR/hr. 

Except for being refueled on 22 April, the MOWER remained in berth C-l until 

23 April, when it got underway for berth 768 off Engebi. It remained moored off 

Engebi until 1716 hours, 8 May, when it returned to the southern anchorage area and 

anchored in berth M-3, approximately 2500 yards west of the northern tip of Enewetak 

Island (see Figure 2-12). Here, the crew would observe Shot GEORGE on the following 

day. 

Shot GEORGE was detonated on Eberiru Island approximately 15 miles north of 

the MOWER. No fallout occurred as a result of this shot. On 10 May, it 

returned to berth 765 off Engebi, where it remained until 24 May. At 1400 hours, 24 

May, the MOWER got underway for berth O-3 in the southern anchorage area, where, 

at 1605 hours, it anchored 2000 yards off Enewetak Island in close proximity to the 

USS CABILDO (LSD-16). 

On 25 May, the crew observed Shot ITEM, which was approximately 20 miles 

north of the MOWER (see Figure 2-12). Although shipboard rad-safe surveys and 

Material Contamination-Decontamination Reports are not available, a reasonable 

representation of the radiation environment aboard the ship can be inferred from the 

USS CABILDO, only 700 yards to the northeast. 

Fallout from Shot ITEM was deposited on the ships anchored off Enewetak during 

two periods; these were between 1030 and 1230 hours and between 1630 and 

1830 hours. Average intensities the CABILDO reached approximately 12 

during the first period and approximately 60 during the second (see 

Figure 2-4). During each fallout period, the weather decks on the CABILDO were 

being continuously flushed with salt water. It is known that the crew of the MOWER 

followed this procedure during the Shot DOG fallout, and it is probable that they 

effected these same procedures during the Shot ITEM fallout. Thus, it is reasonable to 

infer that average radiation intensities the MOWER would be nearly the same 

as those measured on the CABILDO, at least until the time the fallout stopped. After 

45 
 

the fallout had ceased, all of the ships’ crews normally began decontamination 

procedures to reduce the shipboard radiation intensities. Shipboard intensities, plotted 

in Figure 2-4, indicate that decontamination was quite successful on the CABILDO in 

the first 20 hours after the fallout had stopped. The crew of the MOWER probably 

followed a similar routine, but, because no contamination-decontamination report 

from the MOWER is available to confirm this, it is assumed that they did not effect 

any further decontamination procedures. This assumption tends to high-side the 

subsequent dose calculations for the MOWER crew. The inferred ship intensity curve 

for the [MOWER resulting from Shot ITEM fallout is therefore that of the CABILDO 

(Figure except that, after fallout ceased, radioactive decay acted to reduce 

shipboard intensities. Island data are used to arrive at a rate. 

The free-field radiation intensities the USS MOWER resulting from 

Shots DOG and EASY are depicted in Figures 2-13 and 2-14, respectively. They 

represent the average topside radiation environment resulting from each detonation 

where fallout occurred ship. When available, both average and maximum 

values of intensity are plotted with time after burst. Table 2-7 is a summary of the 

radiological data used to derive ship intensity curves for the MOWER. These data are 

used to calculate the daily integrated free-field intensities the MOWER found 

in Table 2-8. 

2.5 SPROSTON (DDE-577) 

The crew of the USS SPROSTON (DDE-577) observed Shot DOG while patrolling 

the waters 30 miles north of the Island ground zero (see Figure It 

continued patrolling in this area until 0740 hours when it proceeded toward 

DOG ground zero. At 0940, the SPROSTON passed Island 2000 yards abeam 

before heading off on an easterly course to investigate a surface contact. Although it 

passed close to DOG the SPROSTON did not encounter any radioactive fallout at 

this time, although the WALKER had received large particle fallout about two hours 

earlier some 15 nautical miles east of GZ. Apparently, deposition was complete in this 

area by the time the SPROSTON arrived. After identifying the surface contact as the 

46 
 nnn I I II 

I 

I I I I I 

Average Shipboard Average Shipboard 

Measurements Measurements 

Maximum Shipboard Maximum Shipboard 

Measurements Measurements 

- - -

I I I III I I I 

A 1 10 100 1000 

Apr 51 Shot EASY 

2 1 Time After Shot DOG (Hours) 

Figure 2-13. USNS SGT. CHARLES E. (TAP-186) Ship Intensity 

Following Shot DOG 

47 
 

- -

Time After Shot DOG (Hours) 

322 412 1312 

Shot Back 

Shot 

I I . 

10 51 100 Shot GEORGE A 1000

May 51 Time After Shot EASY (Hours) 

Figure 2-14. SGT. CHARLES E. (TAP-186) Ship Intensity 

Following Shot EASY 

48 
TABLE 2-7. USNS SGT. CHARLES E. MOWER Average Radiation Intensity Data 

Date and Time Time After Shot ntensity 

Shot DOG 

8 April, 0858 2.4 15.0 

8 April, 0940 3.1 38.4 

8 April, 1215 5.7 20.0 

9 April, 1000 27.4 2.0 

(Parry Island decay rate as assumed thereafter) 

Shot EASY (inferred) 

21 April, 2230 16.0 0.1 

22 April, 0630 24.0 1.0 

(Decay asssumed to be as thereafter) 

Shot ITEM 

25 May, 1028 4.2 

25 May, 1130 5.2 11.5 

25 May, 1630 10.2 4.6 

25 May, 1723 11.1 58.6 

-1.1 (Enewetak Island decay rate as t assumed thereafter) 

49 
-

Table 2-8. Daily Integrated Free-Field Intensity, USNS SGT. CHARLES E. MOWER 

DATE GEORGE ITEM 

April 1951 

9 

12 

13 

14 

16 

17 

19 

20 

23 

24 

25 

26 

27 

28 

29 

30 

I May 

2 

3 

5 

6 

7 

8 

9 

II 

13 

16 

17 

18 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

June 

July 

August 

September 

October 

188.1 

50.3 

24.0 

15.9 

11.9 

9.3 

7.7 

6.6 

5.7 

5.0 

4.6 

4.1 

3.7 

3.4 

3.1 

2.9 

2.7 

2.6 

2.4 

2.3 

2.1 

2.0 

2.0 

1.9 

1.7 

1.7 

1.6 

1.6 

1.4 

1.4 

1.4 

1.3 

1.3 

1.3 

1.3 

1.1 

1.1 

1.1 

1.1 

1 .o 

1.0 

1.0 

1.0 

1.0 

0.9 

0.9 

0.9 

0.9 

0.9 

0.9 

0.9 

0.9 

0.7 

0.7 

20 

13 

9 

7 

0.2 

15.4 

9.8 

6.5 

4.8 

3.8 

3.1 

2.6 

2.3 

2.0 

1.8 

1.6 

1.5 

1.4 

1.3 

1.2 

1.1 

1.0 

1.0 

0.9 

0.9 

0.8 

0.8 

0.7 

0.7 

0.7 

0.6 

0.6 

0.6 

0.6 

0.5 

0.5 

0.5 

0.5 

0.5 

0.5 

0.4 

0.4 0 

0.4 0 

0.4 0 

0.4 0 

10 

7 

4 

3 

3 

353.1 

508.0 

251.7 

165.6 

122.6 

96.9 

79.7 

764 

244 

143 

97 

77 

50 
uloE PA55AGE

e

Pre-Shot Position

5 1

EASY 

DOG 

LEGEND 

Bearing/Distance From GZ 

Area Where Fallout 

is Encountered 

( Date/Time When Fallout 

is Encountered 

ITEM 

GEORGE 

ENEWETAK ATOLL 

0 

. 

ANCHORAGE 

PASSAGE 

DOG 

Figure 2-15. USS SPROSTON 'ROSTON Pre-Shot Position and Fallout Areas 

51 
 

LT. ROBERT CRAIG, at 1142 hours, the SPROSTON took a southwesterly course, 

where it intercepted the contour off Enewetak Island at approximately 

1230 hours (see Figure 2-16). It then continued along the contour in a 

clockwise direction around the atoll and, at 1300 hours, Wide Passage (South Channel) 

was observed abeam to starboard. It continued patrolling the atoll in this manner until 

approximately 1950 hours, when it reversed direction and began to patrol in a 

counterclockwise direction. 

Between 1230 and 1300 hours, as the SPROSTON was heading in a westerly 

direction along the contour off Enewetak, it began to encounter the 

second period of fallout from the DOG cloud that was passing over the southwestern 

portion of the lagoon. Personnel decontamination was effected at about 1300 hours 

average radiation intensities the SPROSTON, presumably obtained at 

a similar time, were approximately 5 mR/hr, with maximum readings of 10 

The SPROSTON was now heading toward an area of heavier fallout Figure 

and it is probable that it encountered contamination levels greater than 10 

before the fallout ended shortly after 1300 hours. To be conservative, it is assumed 

the ship had proceeded to a point almost due south of Igurin Island (See Figure 

before the fallout ceased, hence, it received fallout similar to that which occurred on 

Parry Island between 1200 and 1300 hours. heavier fallout had occurred to the 

west of this point, but deposition was complete by the time the ship reached this area. 

Figure 2-17 depicts the fallout which occurred on Parry during the two periods of DOG 

fallout. Fallout occurring between 0830 and 1100 is subtracted from the total 

intensity curve to arrive at the 1200 to 1300 fallout intensity the SPROSTON. 

Shipboard decontamination was not begun until approximately 1600 hours, 8 

April. It consisted of washing down the bulkheads with soap and water and cleaning 

the deck areas at a rate of four square feet per minute with a stream of high velocity 

water. About 2% hours were required to reduce the intensities to “normal” (Reference 7). 

The crew of the SPROSTON observed Shot EASY from approximately 30 miles 

north-northwest (bearing 3450T) of the Engebi Island ground zero Figure 2-l 5). 
 

 -

-

r 22 21 

23 

23 29 28 

22 

5 

ENEWETAK LAGOON 

20 

25 

Shot DOG Fallout Contours 

Hour Intensities 

20 

From DASA 1251) 

26 

Hours) 

460 3 600 

600 

(1300 Hours) LEGEND 

630 

0.3 

USS Track 780 

610 

_-- _---~-

700 ---- ••• Approximate positions 

on 8 Apr 51 at (time) 

Figure 2-16. USS SPROSTON Patrol Positions 8 April 1951 
Average Parry Intensity 

(See Figure 2-26) 

o Average Shipboard 

Measurements 

Maximum Shipboard 

Measurements 

100 

10 

Total Intensity (Fallout From 

plus 1200-1300 Fallout) 

I 

I 

I Fallout 

I Fallout on 

I 

I 

I 

I

I

I 

I

I

I 

1.0 

1 10 100 1030 

10 Apr 51 Shot EASY 

21 Apr 51 

Time After Shot DOG (Hours) 

Figure 2-17. USS (DDE-577) Ship Intensity Following 

Shot DOG 

54 
After the detonation, the SPROSTON proceeded toward but approached no closer 

than approximately 15 miles. At hours it began patrolling the area to the north 

and northeast of Engebi Island. At approximately 1300 hours, it took a southwesterly 

course to begin patrolling an area miles east-northeast of Engebi. It continued 

patrolling this area until 1849 hours, when it headed south and began patrolling an 

area to the east of Engebi at 1935 hours. (Shortly after the SPROSTON arrived in this 

area, the WALKER, which had been patrolling these waters since H-hour, departed on 

a clockwise patrol of Enewetak Atoll). SPROSTON remained in an area approximately 

15 miles east of until 1952 hours when it took a northeasterly course. 

While it was on this course radiation levels aboard the SPROSTON began 

to rise and decontamination was begun at 2200 hours, 21 April According to 

the 21 April 1951 Material Contamination-Decontamination Report, all deck surfaces 

were sprayed with a stream of high velocity water. It further states that these 

procedures had virtually no effect on reducing the contamination levels. The 

shipboard radiological survey that accompanies the report shows that the exposed 

surfaces of the ship read virtually the same (15 throughout the ship. It further 

states that: is our opinion that the radiation stayed above us, thus is the reason we 

did not reduce the intensity by decontamination, but withdrawing from the area 

reduced the readings more effectively. Once out of the area our readings dropped to 

normal.” From this same report, intensity levels were not reduced to normal until 18 

hours after decontamination began, or 1600 hours, 22 April. This was about the time 

they departed the area northeast of Engebi Island and began a counterclockwise patrol 

around the atoll. It appears that, al though decontamination was periodically 

attempted during this 18-hour period, “cloud shine” was keeping the intensity 

relatively constant at 15 on all the weather decks. 

On 9 May, the SPROSTON was 15 miles east of the Shot GEORGE on Eberiru 

Island (see Figure 15). After the shot, it took a southwesterly course and, by 1043 

hours, it was conducting a barrier patrol off Wide Passage (South Channel). At no time 

on GEORGE day, or during subsequent days, was the SPROSTON exposed to any fallout 

from the shot. 

55 
Again, during the early morning hours of 25 May, 1951, the SPROSTON took a 

15 miles east of Engebi Island where Shot ITEM was detonated (see Figure 

2-15). After a short rendezvous with the WALKER at approximately 0840 hours, the 

SPROSTON began an independent patrol off the atoll. At this time, an 

gamma intensity meter was indicating radiation levels of 0.03 due to the 

residual contamination from Shot DOG. The 25 May deck log does not yield enough 

navigational data to reconstruct the ship’s movements for the remainder of the day, 

but a memorandum on USS SPROSTON letterhead indicates that the ship did encounter 

minor fallout between approximately 1900 and 2300 hours. The fallout appears to have 

occurred in two closely-spaced periods, the first at 1915 hours with a maximum 

intensity of 0.5 and the second at 2300 hours with a maximum intensity of 4 

The 25 May Material Contamination-Decontamination Report shows that no 

decontamination was effected the ship during this fallout, probably because of 

the relatively low intensities. By 0600 hours, 26 May, the intensity had 

decreased to 0.2 when readings were discontinued and the instrurnent secured. 

This rapid rate of decrease in shipboard intensities is an indication that the 

SPROSTON was again receiving cloud “shine”, in addition to a very small amount of 

fallout. 

The SPROSTON continued patrolling the waters around the atoll until 1254 

hours, 26 May, when it entered the lagoon to take on fuel. After refueling was 

completed at 1540 hours, it anchored in berth L-3, approximately 2500 yards west of 

Enewetak Island. It remained there until 1450 hours, 27 May, when it departed 

to Pearl Harbor. 

The free-field radiation intensities plotted in Figures 2-17, 2-18, and 2-19, 

represent the average topside environment resulting from each detonation where 

fallout occurred the ship. When available, both average and maximum values 

of intensity are plotted as a function of time after burst. Table 2-9 is a summary of 

the shipboard from the radiological data. Daily integrated 

field intensities as determined from the radiological data are presented in Table 2-10. 

56 
Time After Shot DOG (Hours) 

313 322 412 1312 

-

o Average 

Measurements 

Shot DOG 

- - I -

I I I t I I II I I I I 0.1 

1 10 A 100 1090 

Apr 51 Shot GEORGE 

9 May 51 

Time After Shot EASY (Hours) 

Figure 2-18. SPROSTON (DDE-577) Ship Intensity Following 

Shot EASY 

57 
Time After Shot DOG (Hours) 

1129 1138 1228 2128 

L 

0 Average Shipboard 

Shot DOG Background 

\

I I I I I I I 

10 A 

25 May 

0 

I

A 

0 

27 May 51 1 Jun 51 

Time After Shot ITEM (Hours) 

Figure 2-19. USS SPROSTON (DDE-577) Ship Intensity Following 

Shot ITEM 

58 
-- -

TABLE 2-9. USS SPROSTON Average Radiation Intensity Data 

Date and Time Time After Shot Intensity 

Shot DOG 

8 April, 1200 5.4 1.0 

8 April, 1300 6.4 13.7 

8 April, 1700 10.4 8.1 

8 April, 2000 13.4 3.7 

(Parry Island decay rate as assumed thereafter) 

Shot EASY (inferred) 

21 April, 2200 15.5 15.0 

22 April, 1600 33.5 15.0 

22 April, 1630 34.0 

(Decay assumed to be as thereafter) 

Shot ITEM 

25 May, 0717 1.0 

25 May, 1900 12.7 

25 May, 1930 13.2 0.3 

25 May, 1935 13.3 0.5 

25 May, 2200 15.7 0.1 

25 May, 2230 16.2 

25 2300 16.7 4.0 

26 May, 0400 21.7 0.7 

26 May, 0600 23.7 0.2 

(Decay assumed to be as thereafter) 
Table 2-10. Daily Integrated Free-Field Intensity, USS SPROSTON 

DATE 

8 April 51

9 

10 

13 

14 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

I May

2 

3 

4 

5 

6 

7 

8 

9 

10 

II 

12 

13 

16 

17 

18 

19 

20 

21 

24 

25 

26 

27 

28 

29 

30 

31 

DOG EASY 

80.9 

40.1 

20.0 

13.3 

9.9 

7.9 

6.4 

5.6 

4.7 

4.3 

3.7 

3.4 

3.1 

2.9 30.0 

2.6 240.0 

2.4 0 

2.3 0 

2.1 0 

2.0 0 

1.9 0 

1.7 

1.7 0 

1.6 0 

1.6 0 

1.4 0 

I.4 0 

1.3 0 

1.3 0 

1.3 0 

1.1 0 

1.1 0 

0 

0 

1.0 0 

1.0 0 

1.0 0 

1.0 0 

1.0 0 

1.0 0 

0.9 0 

0.9 0 

0.9 0 

0.9 0 

0.7 0 

0 

0 

0.7 0 

0.7 0 

0.7 

0.7 

0.7 0 

0.7 0 

0.7 0 

0.6 0 

6.0 

8.6 

2.0 

1.3 

1.0 

0.7 

0.7 

TOTAL 

60 
2.6 USS WALKER (DDE-517) 

The crew of the USS WALKER (DDE-517) observed Shot DOG from an area 15 

miles east of Island (see Figure 2-20). Immediately after the detonation, the 

WALKER began a security patrol in an area 15-20 miles east of and, at 

approximately 0745 hours the ship began to receive some minor fallout from 

the Shot DOG radioactive cloud. Average shipboard intensities reached approximately 

6 before decontamination was begun at 0830 hours. The Material Contamination-Decontamination Report states that only 5 minutes were spent decontaminating an eight-by-ten foot area on the 01 deck. Although not explicitly stated, 

fallout continued while the crew was trying to decontaminate the ship because by 1010 

hours, average levels had reached 10 There is no mention of any further 

efforts to decontaminate the ship after the Shot DOG fallout had ceased, probably 

because levels were below the maximum permissible intensity of 12.5 set for 

the ships participating in Operation GREENHOUSE. 

The crew observed Shot EASY from an area 15 miles east-northeast (bearing 

070oT) of ground zero (Figure 2-20). After the shot it began to patrol the waters 

15 miles east of Engebi. At 1130 hours the WALKER was approximately 15 

miles east of when a gamma intensity meter began to indicate increased 

levels of Average radiation levels reached 4-5 with a maximum 

of 6 being reported at 1300 hours, 21 April. No decontamination procedures 

were effected by the crew after Shot EASY and by noon the following day, natural 

radioactive decay (using nearby island decay rate according to t had reduced the 

radiation levels the WALKER to less than 1 

On 9 May 1951, the WALKER was 30 miles north (bearing of Eberiru 

Island when Shot GEORGE was detonated (Figure 2-20). Immediately after the shot, it 

steamed on a southerly course and allegedly arrived off Wide Passage (South Channel) 

at 1130 hours. At no tirne on 9 May, or during subsequent days, was the crew of the 

WALKER exposed to any radioactive fallout from Shot GEORGE. 

61 
GEORGE 

LEGEND 

Bearing/Distance From GZ 

Area Where Fallout 

is Encountered 

0 Date/Time When Fallout 

is Encountered 

EASY 

DOG 

ENEWETAK ATOLL 

0 

Figure 2-20. USS WALKER Pre-Shot Positions and Fallout Areas 

62 
The crew of the WALKER observed Shot ITEM from an area 15 miles east of 

Engebi Island (Figure 2-20). After the shot, it continued patrolling the waters east of 

Engebi until 1800 hours when it entered the lagoon through Deep Entrance (East 

Channel). At 1826 the WALKER was lying to in the vicinity of the USS CABILDO (the 

CABILDO was anchored in berth N-2 aproximately 1700 yards west of Enewetak 

Island) to transfer mail and passengers. Two minutes later it got underway and at 1847 

hours departed Enewetak Lagoon through Wide Passage (South Channel) where it 

resumed an irregular counter-clockwise security patrol around the atoll. 

Prior to entering the lagoon at 1800 hours the WALKER had not 

encountered any fallout from the Shot ITEM radioactive cloud. Bet approximately 1600 and 1900 hours a second period of fallout from the ITEM dust cloud did 

occur on the islands of Enewetak Atoll and, as the WALKER entered the lagoon, it 

began to encounter this fallout. A radiation survey the ship at 1900 hours 

(after it had departed the lagoon) noted average intensities of 30 “around the 

bridge deck and on such material as canvas awnings, lines, etc.” Decontamination, 

however, was not begun until 0630 hours the following morning when high pressure salt 

water was used for hours. The decontamination was reported as 95 percent 

effective; it thus reduced intensity levels to approximately 1 mR/hr. 

The WALKER continued to patrol the waters around the atoll until 1208 hours, 

26 May when it reentered the lagoon to take on fuel. After refueling, it proceeded to 

berth M-2, approximately 2000 yards off Enewetak Island where it anchored at 1406 

hours. It remained in berth M-2 overnight and at 1456 hours, 27 May, the WALKER 

got underway for Pearl Harbor. 

The free-field intensities environment the WALKER resulting from shots 

DOG, EASY, and ITEM are plotted in Figures 2-21, 2-22 and 2-23, respectively. They 

represent the average topside radiation environment resulting from each shot where 

fallout occurred ship. When available, both average and maximum values of 

intensity are plotted as a function of time after burst. Table 2-l 1 is a summary of the 

shipboard intensities derived from radiological data; daily integrated free-field intensities on the ship are given in Table 2-12. 

63 
 

o Average Shipboard 

Measurements 

. Maximum Shipboard 

Measurements 

1.0 I I I I I I 

1 10 A 100 A 1000 Apr 51 Shot EASY 

21 Apr 51 Time After Shot DOG (Hours) 

Figure (DDE-517) Ship Following 

t 

64 
Time After Shot DOG (Hours) 

313 322 412 1312 

Total 

10 100 

10 I I I I I I I 

Average Shipboard 

0 Measurements 

L 

Maximum Shipboard 

Measurements 

---

Shot GEORGE 23 51 

9 May 51 Time After Shot EASY (Hours) 

Figure 2-22. (DDE-517) Ship Intensity Following 

Shot EASY 

65 
o Average Shipboard Average Shipboard 

Measurements Measurements 

-- Average Enewetak Intensity -- Average Enewetak Intensity 

(See Figure 2-30) (See Figure 2-30) 

I 

I 

C 

H

I 

I 

I 

I

I 

I

I 

I 

I

I 

I

I I I I I I I I 

-

- . 100 

1.0 

1 10 100 1000 

Time After Shot ITEM (Hours) 

Figure 2-23. USS WALKER (DDE-517) Ship Intensity Following 

Shot ITEM 

66 
- -

TABLE 2-l 1. USS WALKER Average Radiation Intensity Data 

Date and Time Time After Shot Intensity 

Shot DOG 

8 April, 0745 1.2 1.0 

8 April, 0830 1.9 6.0 

8 April, 1010 3.6 10.0 

(Decay assumed to be as thereafter) 

Shot EASY (inferred) 

21 April, 1130 5.0 

22 April, 1399 6.5 5.0 

(Decay assumed to be as thereafter) 

Shot ITEM 

25 May, 1800 11.7 32.5 

26 May, 0630 24.2 15.9 (inferred) 

26 May, 0800 25.7 1.0 (inferred) 

-1.1 (Enewetak Island survey data indicate decay as t thereafter) 

67 
Table 2-12. Daily Integrated Free-Field Intensity, USS WALKER 

DATE 

8 April 1951 

9 

13 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

28 

29 

30 

May 

2 

3 

4 

5 

6 

7 

8 

DOG 

68.3 

25.6 

12.6 

8.3 

6.1 

4.9 

4.0 

3.4 

3.0 

2.6 

2.3 

2.1 

1.9 

1.7 

1.6 

1.4 

1.4 

1.3 

1.3 

1.1 

1.1 

1.0 

1.0 

1.0 

0.9 

0.9 

0.9 

0.9 

0.7 

0.7 

0.7 

EASY GEORGE ITEM 

32.6 

24.3 

12.0 

8.0 

5.9 

4.6 

3.9 

3.3 

2.9 

2.4 

2.1 

2.0 

1.9 

1.7 

1.6 

1.4 

1.3 

1.3 

9 0.7 1.1 

10 0.7 1.1 

II 0.6 1.0 

12 1.0 

0

0

0 

13 1.0 

14 0.6 0.9 

0.6 0.9 

16 0.6 0.9 

17 0.6 0.7 

18 0.6 0.7 

0

0

0

0 

19 0.4 0.7 

20 0.4 0.7 

21 0.4 0.7 

22 0.4 0.7 

23 0.4 0.6 

24 0.4 0.6 

0.6 

0

0

0

0

0

0

0

0

0

0

0

0 

25 0.4 0.6 158.0 

140.6 

11.9 

8.1 

6.3 

5.0 

4.3 

26 0.4 0.6 

27 0.4 0.6 

28 0.4 0.6 

29 0.4 

30 0.4 0.6 

31 0.4 0.4 

June 9 1 0 0 46 

68 
2.7 USNS LT. ROBERT CRAIG 

On 8 April, the USNS LT. ROBERT CRAIG was to Enewetak Atoll from 

Pearl Harbor. At 0634 hours, the crew observed the flash from the Shot DOG 

detonation approximately 100 miles west-southwest of the ship (bearing At 

1214 hours, the CRAIG arrived at the entrance to South Channel (Wide Passage), 

Enewetak Atoll and proceeded to berth C-2, where it anchored at 1420 hours (see 

Figure 2-24). 

Upon arriving at Enewetak, the CRAIG probably encountered the second period 

of Shot DOG fallout that occurred over the southeastern portion of the lagoon between 

1200 and 1300 hours. As it entered the lagoon and during its passage to the anchorage 

off Parry Island, fallout intensities on the ship would have approximated those 

occurring on Parry during this same time period (Figure 2-24). Although shipboard 

contamination levels are not documented, an estimate can be made from island fallout 

data, after subtracting out the fallout that occurred between 0830 and 1100 hours. 

Figure 2-25 depicts the Parry fallout data (dashed curves) and shows the intensity 

contributions from the two periods of Shot DOG fallout. The solid curve is the 

inferred Shot DOG ship intensity curve for the CRAIG and is obtained by subtracting 

the 0830-1100 fallout from the total intensity curve. The difference between the two 

curves is depicted by the shaded region in Figure 2-25. Table 2-13 is a summary of 

the radiological data for the CRAIG as inferred from the island data. 

Table 2-13. USNS LT. ROBERT CRAIG Average Radiation Intensity Data 

Date and Time Time After Shot Intensity 

8 April, 1200 5.4 1 .O (inferred) 

8 April, 1300 6.4 13.7 (inferred) 

(Parry Island decay rate as assumed thereafter) 

The CRAIG remained anchored in the lagoon discharging cargo until 12 April 

when it got underway for Guam via Kwajalein. It returned to Enewetak on 30 April, 

but departed on 6 May, three days prior to Shot GEORGE, to San Francisco via 

Kwajalein and Pearl Harbor. 

69 
 

’

-

-

 0.8 

25 . c-2 

Shot DOG Fallout 

Hour Intensities 

From DASA 1251) 

- -

. 1420 

LEGEND 

USNS LT. ROBERT CRAIG's Track 

Hour;) 

AREA 

Approximate positions on 

8 Apr 51 at 

Figure 2-24. USNS LT. ROBERT CRAIG's Approach to Enewetak Lagoon 8 April 1951 
1 

Average Parry Intensity 

(See Figure 2-26) 

Total Intensity (Fallout From 

Fallout 

plus 1200-1300 Fallout) 

I 

I 

I 

I 

I 

I

 I I 

Fallout on 

10 51 

Apr 

Time After Shot DOG (Hours) 

Figure 2-25. USNS LT. CRAIG Ship Intensity 

Shot DOG 

71 
-

Table 2-14. Daily Integrated Free-Field Intensity, USNS LT. ROBERT CRAIG 

DATE EASY* GEORGE* ITEM* 

8 April 1951 98.4 

9 67.6 

33.7 

II 22.3 

12 16.6 

13 13.1 

14 10.9 

15 9.3 

16 8.0 

17 7.1 

18 6.3 

19 5.7 

20 5.3 

21 4.9 

22 4.4 

23 4.1 

24 3.9 

25 3.6 

26 3.4 

27 3.1 

28 3.0 

29 2.9 

30 2.7 

I May 2.6 

2 2.4 

3 2.4 

4 2.3 

5 2.1 

6 2.1 

7 2.0 

8 2.0 

9 1.9 

1.9 

11 1.7 

12 

13 

1.6 

1.6 

I6 1.6 

17 1.4 

18 I.4 

19 1.4 

20 I 

21 1.3 

22 1.3 

23 1.3 

24 1.3 

25 1.1 

26 1.1 

27 1.1 

28 1.1 

29 1.1 

30 

31 1.0 

*CRAIG did not participate at the remaining GREENHOUSE shots. 

72 
-

The average topside intensity depicted in Figure 2-25 is integrated to determine 

the daily integrated free-field intensity the CRAIG. Calculations are carried 

through 31 May and are presented in Table 2-14. 

2.8 RESIDENCE ISLANDS OF ENEWETAK ATOLL 

As previously noted, fallout was experienced on all the residence islands of 

Enewetak Atoll following Shots DOG, EASY, and ITEM. These islands, Enewetak, 

Parry, and Japtan, received essentially the same fallout as the ships in the southern 

anchorage area (Figure 1-l). Free-field intensities on the islands, however, were 

higher than the shipboard intensities because the ships were equipped with effective 

systems. 

Following Shot DOG, the first survey of the residence islands (at 1500 hours, 

8 April) indicated intensities of 25, 60, and 70 on Enewetak, Parry, and Japtan, 

respectively. This south-to-north gradient of increased fallout intensity is consistent 

with the shipboard data, which showed less fallout occurring on the CABILDO 

(anchored off Enewetak) than on the CURTISS (anchored off Parry). Subsequent 

surveys on 9, I 1, 12, and 13 April revealed that Parry and Japtan Islands had received 

essentially the same fallout, while intensities on Enewetak were approximately 

half to one-third those on the other two islands. Table 2-15 is a summary of the island 

survey data obtained during the five days following Shot DOG. 

Table 2-15. Residence Island Survey Data Shot DOG 

Average Intensity

1500 

8 April 9 April April 12 April 13 April 

Enewetak 25 7 2 2 I 

Parry 60 15 6 5 3 

Japtan 70 12 6 5 3 

The Parry and Japtan intensity data are plotted in Figure 2-26 while the 

Enewetak intensity data are plotted in Figure 2-27. These two figures depict the 

average free-field intensity on the three residence islands resulting from Shot DOG 

73 
1000 

Average Japtan Island 

Measurements 

Average Parry Island 

Measurements 

10 

1.0 

1 10 100 

Time After Shot DOG (hours) 

Figure 2-26. Parry and Japtan Island Intensity Following Shot DOG 
A Average Enewetak Island 

Measurements (Buildup 

inferred from Parry Is. 

intensity rate meter) 

1 10 100 

Time After Shot DOG (Hours) 

Figure 2-27. Enewetak Island Intensity Following Shot DOG 

75 
-

- -

fallout. The buildup and decay of the fallout between 0850 hours, 8 April, and the first 

survey at 1500 hours is inferred from a recording on a gamma intensity rate 

meter outside the radiological safety building on Parry Island (Reference 6). 

Very light fallout occurred on the residence islands following Shot EASY on 

21 April. It began late in the evening and ended during the early morning of 22 April. 

The maximum intensity of this fallout on Parry was reported as two to three times the 

residual radiation from Shot DOG, which had recently been measured to be 0.5 mR/hr. 

It is assumed that fallout from Shot EASY began at 2230 hours and that the 

peak intensity occurred at about 0630 hours, 22 April Table 2-16 is a summary 

of the Parry Island survey data following Shot EASY. Post-shot surveys were not 

obtained on Enewetak or Japtan but it is assumed they received the same fallout. 

Table 2-16. Parry Island Survey Data Shot EASY 

Average Intensity 

0730 

April 21 22 April April April April 23 24 25 

0.5 0.8 0.6 0.6 

These data are plotted in Figure 2-28 to depict the average free-field intensity 

on Parry and Japtan Islands following Shot EASY. The Shot EASY contribution is 

obtained by subtracting the Shot DOG background from the survey data obtained on 

23, 24, and 25 April; these data are also shown in Figure 2-28. A power law fit to 

these three data points, when extrapolated back in time to (the assumed time of 

occurrence of the peak intensity), yields a maximum contribution from Shot EASY of 

approximately 1.0 mR/hr. When added to the Shot DOG residual, the peak intensity on 

Parry following Shot EASY would be approximately 1.5 mR/hr, which is consistent 

with the statement in Reference 6 that the EASY fallout “was insignificant, amounting 

only to 2 or 3 times the background.” In Figure 2-29, the Shot EASY contribution 

calculated on Parry is added to the Shot DOG residual on Enewetak Island to arrive at 

the total free-field intensity on that island. The differences between Figures 2-28 and 

2-29 are slight, due only to small differences between the Shot DOG residual radiation 

on the three residence islands. 

76 
Time After Shot DOG (hours) 

322 412 1312 

I I I I I I I I I I I I 

Shot EASY Contribution 

to Total Fallout 

(Calculated) 

A Average Parry Island 

Measurements 

I -

1 

II I I I I I 11 I I 

10 100 1000 

- -

Shot GEORGE Shot GEORGE 

9 May 51 9 May 51 

Time After Shot EASY (hours) 

Figure 2-28. Parry and Japtan Island Intensity Shot EASY 

77 
Time After Shot DOG (hours) 

313 322 412 1312 

100 I I I I I I I I I I I I 

10 

0.1 II I I

1 10 100 

Shot GEORGE 

9 May 51 

Time After Shot EASY (hours) 

Figure 2-29. Enewetak Island Intensity Shot EASY 

78 
-

Considerable fallout occurred on the residence islands on 25 May following 

Shot ITEM. At approximately 0945 hours a gamma intensity recorder at the 

radiological safety building on the southern end of Parry Island detected a steady rise 

in intensity due to fallout, which lasted approximately 1% hours. After decaying for 

approximately three hours, intensity readings began to rise when fallout started once 

more at approximately eight hours after the detonation; this second “wave” of fallout 

lasted for approximately six hours. The buildup and subsequent decay of the fallout on 

southern Parry Island, as recorded, is reproduced in Figure 2-30. At approximately the 

same time, incomplete but reasonably representative survey of Enewetak Island 

indicated that the fallout situation there was almost identical with that of Parry” 

(Reference 6). Intensity readings obtained on Enewetak on 25-28 May, also depicted in 

Figure 2-30, tend to substantiate this statement. 

At approximately 1800 hours on 25 May, a survey conducted on the northern end 

of Parry Island “established the fact that the intensity there was less by about 50 

percent than that on the southern end of the island and was approximately the same as 

the fallout on Japtan” (Reference 6). The results of the surveys on northern Parry 

during the period 25-28 May are depicted in Figure 2-31. Fallout buildup is inferred 

from the time-intensity recording data obtained at the rad-safe building on the 

southern end of the island. This is also the same fallout that was reported to have 

occurred on Japtan. Table 2-17 summarizes the intensity data obtained on Enewetak 

and Parry islands during the period 25-28 May. Radiation intensities on Japtan are 

assumed to be the same as those on Northern Parry. 

Table Z-17. Enewetak and Parry Survey Data Shot ITEM 

Average Intensity 

1030 

25 May 26 May May May 27 2 8

tak and 

Southern Parry 45 40 28 30 

Northern Parry 

and Japtan 6 30 18 

The island intensity curves in Figures 2-26 through 2-31 are time-integrated, by 

day, from 8 April through 31 May to obtain the daily integrated free-field 

intensities on each of the residence islands resulting from fallout from Shots DOG, 

79 
 

I I I I I I I 

cl Average Enewetak Island 

Measurements 

A Intensities From 

Intensity Rate Meter on 

Southern Parry Island 

(Ref. 6) 

1 

10 

1 I I I I I I I

10 100 1000 

Time After Shot (Hours) 

Figure 2-30. Enewetak and Southern Parry Island Intensity Following 

Shot 

80 
 I I I I I 

A Average Parry Island 

Measurements 

(Northern end of the 

Island) 

1 

Time After Shot ITEM (Hours) 

Figure -31. Japtan and Northern Parry Island Intensity Following 

Shot ITEM 

81 
 

EASY, and ITEM. The results are presented in Tables Z-18, 2-19, and for 

Enewetak, Parry, and Japtan Islands, respectively. The integrated free-field intensities 

on Parry following Shot ITEM are obtained by averaging the integrated intensity on the 

southern portion of Parry (or Enewetak) with that on the northern part of Parry (or 

Japtan). This is done under the assumption that anyone assigned to Parry would spend 

equal amounts of time on each half of the island. 

2.9 SHIP SHIELDING 

Dose estimates for crewmembers require consideration of the shielding provided 

by the ship structure for radioactive fallout deposited on the weather surfaces of the 

ships. A ship shielding factor, defined as the ratio of radiation intensity at an interior 

location to an intensity topside, depends on several variables: time after detonation, 

distribution of fallout on the weather surface, amount of intervening material 

(decking, bulkheads, piping, etc.) from weather surface to point of interest, and 

distance from weather surface. Consequently, while ship shielding effects have been 

experimentally and theoretically studied by the Navy since Operation CROSSROADS 

values of shielding factors remain uncertain. Readings taken on target ships 

during Operation CROSSROADS, and on two test ships (YAG-39 and YAG-40) during 

Operations CASTLE and REDWING gave preliminary estimates of 

shielding factors (References 8, 9, 10). However, a significant fraction of the 

radiation penetrating to the interior of these ships, especially at the lower depths, 

apparently came from radioactive materials in the water and on the hulls of the ships. 

Thus, these shielding factors are not directly applicable to the present problem. 

Experimental results reported by W.F. Waldorf (Reference 11) on radiation from 

Cobalt-60 and Cesium-137 sources on the flight deck penetrating the interior of a light 

aircraft carrier indicated that an average shielding factor could be 

correlated with the thickness of deck plating directly above the point of interest in the 

ship. He further showed that the effects of bulkheads, piping, and other miscellaneous 

intervening material could be approximated (somewhat high-sided) by doubling the 

deck plating thickness in shielding calculations. Results from British experiments on a 

carrier, destroyer, and light cruiser, referenced by Waldorf, verified these conclusions 

and indicated that this factor of two may apply to most ship types. C.F. Ksanda 

82 
Table 2-18. Daily Integrated Free-Field Intensity, Enewetak Island 

EASY GEORGE ITEM 

8 April 51 363.7 

9 159.2 

76.3 

II 49.4 

36.1 

13 28.2 

23.1 

19.5 

16 16.8 

17 14.7 

18 13.1 

19 11.7 

20 10.6 

21 9.7 0.2 

22 9.0 15.4 

23 8.3 9.8 

24 7.7 6.5 

25 7.2 4.8 

26 6.7 

27 6.3 

28 6.0 2.6 

29 5.7 2.3 

30 5.4 2.0 

May 5.1 1.8 

4.9 1.6 

4.6 1.5 

4 4.4 1.4 

5 4.3 1.3 

6 4.1 1.2 

7 3.9 1.1 

8 3.8 1.0 

9 3.6 1.0 

3.5 0.9 

II 3.4 0.9 

12 3.3 0.8 

13 3.2 0.8 

3.1 0.7 

15 3.0 0.7 

16 2.9 0.7 

17 2.8 0.6 

18 2.7 0.6 

19 2.6 0.6 

20 2.6 0.6 

21 2.5 0.5 0 

22 2.4 0.5 0 

23 2.4 0.5 

24 2.3 0.5 

25 2.3 0.5 

26 2.2 0.5 1293.9 

27 2.2 0.4 642.7 

28 2.1 0.4 423.6 

29 2.1 0.4 313.8 

30 2.0 0.4 248.1 

2.0 0.4 204.5 

0

0

0

0

0

0

0

0

0

0

0

0 

83 
Table 2-19. Daily 

DOG 

8 51 363.7 

159.2 

76.3 

II 49.4 

36.1 

13 28.2 

14 23.1 

19.5 

16 16.8 

17 14.7 

18 13.1 

19 11.7 

20 10.6 

21 9.7 

22 9.0 

23 8.3 

24 7.7 

25 7.2 

26 6.7 

27 6.3 

28 6.0 

29 5.7 

30 5.4 

2 

5.1 

4.9 

3 4.6 

4.4 

5 4.3 

6 4.1 

7 3.9 

8 3.8 

9 3.6 

3.5 

3.4 

12 3.3 

13 3.2 

14 3.1 

15 3.0 

16 2.9 

17 2.8 

18 2.7 

19 2.6 

20 2.6 

21 2.5 

22 2.4 

23 2.4 

24 2.3 

25 2.3 

26 2.2 

27 2.2 

28 2.1 

29 2.1 

30 2.0 

31 2.0 

0

0 

0

0

0

0

0

0

0

0

0

0

0

0 

Integrated Free-Field intensity, Parry Island 

EASY GEORGE ITEM 

0.2 

15.4 

9.8 

6.5 

4.8 

3.8 

3.1 

2.6 

2.3 

2.0 

1.8 

1.6 

1.5 

I.4 

1.3 

1.2 

1.1 

1.0 

1.0 

0.9 

0.9 

0.8 

0.8 

0.7 

0.7 

0.7 

0.6 

0.6 

0.6 

0.6 

0.5 

0.5 

0.5 

0.5 

0.5 

0.5 

0.4 

0.4 

0.4 

0.4 

0.4 

723.5 

1007.5 

514.4 

344.8 

258.5 

206.4 

171.5 

84 
Table 2-20. Daily Integrated Free-Field Intensity, Japtan 

DATE DOG 

8 April 51 791.2 

407.3 

203.3 

II 134.6 

12 100.1 

13 79.4 

65.6 

15 55.8 

16 48.5 

17 42.8 

18 38.3 

19 34.6 

20 12.9 

21 11.8 

22 10.9 

23 10.1 

24 9.5 

25 8.9 

26 8.3 

27 7.9 

28 7.5 

29 7.1 

30 6.7 

May

2 

6.4 

6.1 

3 5.9 

4 5.6 

5 5.4 

6 5.2 

7 5.0 

8 4.8 

9 4.7 

4.5 

II 4.4 

12 4.2 

13 4.1 

14 4.0 

15 3.9 

16 3.7 

17 3.6 

18 3.5 

19 3.4 

20 3.4 

21 3.3 

22 3.2 

23 3.1 

24 3.0 

25 3.0 

26 2.9 

27 2.8 

28 2.8 

29 2.7 

30 2.7 

31 2.6 

EASY GEORGE ITEM 

0.2 

15.4 

9.8 

6.5 

4.8 

3.8 

3.1 

2.6 

2.3 

2.0 

1.8 

1.6 

1.5 

1.4 

1.3 

I.2 

1.1 

1.0 

1.0 

0.9 

0.9 

0.8 

0.8 

0.7 

0.7 

0.7 

0.6 

0.6 

0.6 

0.6 

0.5 

0.5 

0.5 

0.5 

0.5 403.9 

0.5 721.1 

0.4 386.1 

0.4 265.9 

0.4 203.2 

0.4 164.6 

0.4 138.5 

0 

0

0

0

0

0

0

0

0 

0

0

0

0

0

0

0

0

0

0 

0 

85 
(References 13) performed detailed calculations on an aircraft carrier (USS 

RANGER), presenting the shielding factors graphically as functions of deck plating 

thickness for various times after detonation. Following Waldorf, he accounted for 

miscellaneous shielding materials by doubling the deck plating thickness when performing the calculations. The results of the Waldorf experiment and the geometric 

means of Ksanda’s upper and lower limit shielding factors for unfractionated U-235 

fission products at one day after detonation are displayed in Figure 2-32. Due to 

geometric attenuation, these curves approach values less than one as deck plating 

thickness becomes small. Comparison indicates that Ksanda’s mean values represent a 

somewhat high-sided estimate of the shielding factor, since the average gamma energy 

for the times of interest (several hours to days after detonation) is similar to the 0.66 

from the cesium source. Because of the detailed nature of Ksanda’s effort, and 

the general agreement with experiment, the Ksanda mean value for shielding factor 

versus deck plating thickness is used in the present calculations. 

In applying Ksanda’s results to the present analysis, it is assumed that, when 

topside, personnel experienced the average external topside intensity, and any 

shielding provided by the superstructure is neglected. Large variations in personnel 

activities and shielding factors preclude a more accurate assessment of this factor, It 

is further assumed that, when below decks, personnel were located on the second deck, 

with only the thickness of the main deck to provide radiation shielding. Personnel 

below the second deck, and in those portions of the second deck under the superstructure, were afforded additional radiation shielding not included in these calculations. 

The main deck thicknesses and the shielding factors used for the seven ships are given 

in Table 2-21. 

Table 2-2 1. Ship Shielding Factors 

Ship 

Main 

Thickness 

Deck 

(inches) Shielding Factor 

CABILDO 

CURTISS 

LST-859 

MOWER (TAP-186) 

SPROSTON (DDE-5 17) 

WALKER (DDE-577) 

CRAIG (YAK-2521 

86 
1 

I I I I I I I I I I I I 

.J 

Waldorf Co-60 (1.25 

.OJ 

I I I I I . I I I I I I 

.a 1.0 1.2 1.4 

Total Deck Plating Thickness (in.) 

Figure 2-32. Ship Shielding Factor vs. Deck Plating Thickness 

87 
 

Section 3 

DOSE CALCULATIONS 

To determine the dose to personnel, consideration is given to the time spent 

topside (outside) and below decks (inside) and the radiation protection afforded by a 

ship or building. The daily, free-field integrated intensities from Section 2 are 

adjusted to account for personnel activities, either documented or assumed. The 

adjusted exposures are then multipled by a film badge conversion factor to 

determine a daily film badge dose as described in Reference 12. Results are 

presented as a daily cumulative dose to personnel through 31 May 1951, when the 

GREENHOUSE roll-up phase was nearly complete. For shipboard personnel, dose 

calculations are continued on a monthly basis until the dose is 30 mrem per month or 

less, i.e., less than 1 mrem per day. At the end of May, heavy rains set in and 

apparently washed away rnost of the radioactive material from the inhabited islands 

(Reference 6). This statement is supported by the observation of a former member of 

the rad-safe unit at GREENHOUSE who states that June 1 heavy rains 

again occurred reducing the fallout dose rate from ITEM shot to background values” 

(Reference Based on these statements, dose calculations for the island-based 

personnel are terminated on 32 May. 

3.1 PERSONNEL ACTIVITIES 

An estimate of personnel movements is critical in determining the film badge 

dose, especially during fallout deposition and at early times when intensities are 

relatively high and intensity levels are changing through decay and decontamination. 

As inferred from deck logs, normal crew activities were somewhat altered during the 

day that fallout occurred and during the following day when decontamination was 

underway. On the morning of the second day after fallout, normal crew duties were 

generally resumed. 

With the exception of 8-V April (Shot DOG fallout), 21-22 April (Shot EASY 

fallout), and 25-26 May (Shot ITEM fallout), when actual times topside and below are 

used, the free-field integrated intensities are multiplied by a time-averaged shielding 
factor to account for the time spent topside (outside) and below (inside) during a 

“typical” work day. It is estimated that the typical crew on each ship was on deck at 

the following times: 1200, 1330-1700, and 1800-2000 hours. This amounts to 40 

percent of the day hours) topside and 60 percent hours) below. While below, 

the crew was offered shielding provided by the ship’s structure. In Section 2.9, it is 

estimated that ship-shielding factors vary from approximately 0.08 to 0.15, depending 

on the main deck thickness. A time-averaged shielding factor is computed as (0.4 + 

0.6 x ship-shielding factor), where the 0.4 and 0.6 represent the fraction of the day 

spent above and below the deck, respectively. The time-averaged shielding factors 

vary from approximately 0.45 to 0.49. A similar argument is used to obtain a 

averaged shielding factor of 0.8 for the land-based personnel. This assumes that 

60 percent of the day is spent outside and 40 percent inside. While inside, personnel 

are afforded a protection factor of 2, i.e., a shielding factor of 0.5. 

3.2 CALCULATED PERSONNEL FILM BADGE DOSES 

Dose calculations for shipboard personnel are complicated by the fact that on 

D-Day and the magnitude of the fallout required normal crew routines to be 

altered. On even though normal crew routines were generally adhered to, 

intensity levels were still such that specific periods above and below deck must be 

determined. For all other days, the ship-specific, time-averaged shielding factor is 

applied to the daily free-field intensities to account for ship shielding. These adjusted 

exposures are then converted to an equivalent film badge dose using a conversion 

factor of 0.7 mrem/mR. 

In order to demonstrate the effect of crew activities on the calculated personnel 

film badge dose, an example of the calculations is shown below. The Shot DOG fallout 

on the USS CURTISS is selected as typical. First, a crew activity time-line is inferred 

from the CURTISS deck log for the 9th and 10th of April (See Figure A-2, 

Appendix A). This figure indicates the times during these three days that an average 

crewmember would have been above and below deck. For those periods when the crew 

would have been topside, the integrated free-field intensity (from Section 2) is used. 

For those time periods spent below, the integrated intensity is adjusted to account for 

89 
 

 

 

-

-

= =

-

=

- - -

the shielding provided by the ship’s structure (see Section 2.9). The contributions from 

each period are added to determine an adjusted exposure for the average crewmember. 

These adjusted exposures are then converted to a film badge dose. For personnel 

aboard the CURTISS after Shot DOG, the film badge dose on 8 and 9 April is 

calculated as follows: 

USS CURTISS Shot DOG (0634 hours, April) 

Integrated Ship-Shielding Adjusted 

April I(t) DOG Intensity x Factor = Exposure 

0825-0900 2.9 1.0 2.9 

0900-1010” 25.0 2.0 

1010-1300” 307.6 70.4 5.6 

44.2 7.9 0.6 

1330-1700 44.2 47.8 1.0 47.8 

1700-1800” 44.2 12.0 1.0 

1800-2000 44.2 22.2 1.0 22.2 

2000-2400” 44.2 39.7 3.2 

227.9 (Table 2-4) 85.3 

8 April film badge dose (85.3 59.7 mrem (Table 3-2) 

9 April 

0000-0800” 44.2 66.7 5.3 

0800-L 130 44.2 25.4 1.0 25.4 

1130-1200 268.5 3.4 1.0 3.4 

1200-1330” 268.5 t -1.083 10.0 0.8 

1330-1700 268.5 t -1.083 21.6 1.0 21.6 

1700-1800” 268.5 5.7 0.5

1800-2000 268.5 11.0 1.0 11.0 

2000-2400” 268.5 t -1.083 20.1 1.6 

163.9 (Table 2-4) 69.6 

April film badge dose (69.6 48.7 mrem (Table 3-2) 

“Denotes time periods below deck (from Figure A-2) 
 

Starting on the crews on all ships are estimated to have spent approximately 40 

percent of the day above deck and 60 percent below; therefore on and subsequent 

days, a time-averaged shielding factor is used to calculate the adjusted exposure. On 

10 April and the following days, the time-averaged shielding factor for the CURTISS is 

0.4 + 0.45, as described in Section 3.1, where is the ship-shielding factor 

for the CURTISS. Similar calculations are made for the crews of the other six ships 

for each of the detonations where occurred on the ships. The results of these 

calculations are given in Tables 1 through 3-7. The calculations are continued until 

the total monthly accumulated dose to the crew is less than 30 mrem. 

When Shot DOG fallout began on the residence islands, rad-safe personnel at 

Parry evaluated the situation and concluded that personnel activities could continue as 

usual; there would be no disruption of the routine (Reference Thus, for the 

based personnel, normal routines were not altered by the occurrence of fallout. 

Personnel film badge doses are calculated by multiplying the free-field integrated 

intensities by the appropriate time-averaged shielding factor and by the film badge 

conversion factor. Results of these calculations are given in Tables 3-8, 3-9, and 3-10 

for Enewetak, Parry, and Japtan Islands, respectively. 

91 
- - - -

Table 3-1. Calculated Personnel Film Badge Dose, CABILDO 

DATE 

8 April 1951

9 

II 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

I May 1951 

2 

3 

4 

5 

6 

7 

8 

DOG EASY GEORGE ITEM CUMULATIVE 

10.1 mrem 

29 

12.4 42 

8.2 50 

5.6 55 

4.4 60 

3.5 63 

3.0 66 

2.5 69 

2.2 71 

1.9 73 

1.7 75 

1.6 76 

I.4 0.0 mrem 78 

1.3 5.4 84 

I 3.1 89 

1.1 2.0 92 

1 1.5 94 

1.0 1.2 96 

0.9 1.0 98 

0.9 0.9 100 

0.8 0.7 102 

0.8 0.6 103 

0.7 0.6 104 

0.7 0.5 106 

0.7 0.5 107 

0.6 0.5 108 

0.6 0.4 109 

0.6 0.4 110 

0.5 0.4 111 

0.5 0.3 112 

9 0.5 0.3 

0.5 0.3 

II 0.5 0.3 

12 0.5 0.3 

13 0.4 0.2 

0

0

0

0

0 

112 

113 

114 

115 

115 

0.4 0.2 116 

15 0.4 0.2 117 

16 0.4 0.2 

17 0.4 0.2 

18 0.4 0.2 

19 0.4 0.2 

20 0.4 0.2 

21 0.3 0.2 

22 0.3 0.2 

23 0.3 0.2 

24 0.3 0.1 

25 0.3 0.1 

26 0.3 0.1 

27 0.3 0.1 

28 0.3 0.1 

29 0.3 0.1 

30 0.3 0.1 

31 0.3 0.1 

June 51 6 3 

July 51 4 2 

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0

0 

0

0

0 

0 

117 

118 

118 

118 

119 

I 20 

121 

121 

32.3 mrem 154 

60.5 215 

34.0 249 

22.4 272 

16.6 289 

13.1 303 

10.8 314 

104.0 427 

33.0 466 

19.0 489 

345.7 489 mrem 

August 51 3 

TOTAL 112.9 30.3 

92 
-

- -

Table 3-2. 

DATE 

8 April 1951

9 

10 

13 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

May

2 

3 

4 

5 

6 

7 

8 

9 

12 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

31 

July

August

September 

TOTAL 

Calculated 

DOG 

59.7 mrem 48.7 

27.9 

18.5 

13.7 

10.9 

9.0 

7.7 

6.7 

5.9 

5.3 

4.7 

4.3 

4.0 

3.6 

3.4 

3.2 

3.0 

2.8 

2.7 

2.5 

2.4 

2.3 

2.2 

2.1 

2.0 

1.9 

1.8 

1.8 

1.7 

1.6 

1.6 

1.5 

I.4 

I.4 

1.4 

1.4 

1.3 

1.3 

1.2 

1.2 

1.1 

1.1 

1.1 

1.0 

1.0 

1.0 

1.0 

0.9 

0.9 

0.9 

0.9 

0.9 

20 

14 

10 

8 

346.2 

Personnel 

EASY 

0 mrem 

5.4 

3.1 

2.0 

1.5 

I 

1.0 

0.9 

0.7 

0.6 

0.6 

0.5 

0.5 

0.5 

0.4 

0.4 

0.4 

0.3 

0.3 

0.3 

0.3 

0.3 

0.2 

0.2 

0.2 

0.2 

0.2 

0.2 

0.2 

0.2 

0.2 

0.2 

0.2 

0.1 

0.1 

0.1 

0.1 

0.1 

0.1 

0.1 

0.1 

3 

2 

31.3 

Film Badge Dose, USS CURTISS 

GEORGE ITEM CUMULATIVE 

60 

108 

136 

15.5 

169 

179 

188 

196 

203 

209 

214 

219 

223 

227 

236 

243 

248 

252 

256 

260 

263 

266 

269 

272 

275 

277 

280 

282 

284 

286 

288 

0 290 

0 292 

0 293 

0 295 

297 

298 

0 300 

0 301 

0 303 

0 304 

0 306 

0 307 

0 308 

0 309 

0 311 

0 312 

0 73.5 mrem 386 

0 51.9 439 

0 29.3 470 

0 20.2 491 

0 15.4 507 

0 12.5 521 

0 10.5 532 

113 668 

725 

26 762 

789 

411.4 789 mrem 

93 
- - -

Table 3-3. Calculated Personnel Film Badge Dose, USS 

DATE DOG EASY GEORGE ITEM* 

8 April 1951 147.8 mrem 

9 23.4 

14.8 

II 9.8 

12 7.3 

13 5.8 

4.8 

15 4.1 

16 3.5 

17 3.1 

18 2.8 

19 2.5 

20 2.3 

21 2.1 0 mrem 

22 2.0 5.8 

23 1.8 3.4 

24 1.7 2.2 

25 1.6 1.7 

26 1.5 1.3 

27 1.4 1.1 

28 1.3 0.9 

29 1.3 0.8 

30 1.2 0.7 

I May 0.6 

2 1.1 0.5 

3 1.0 0.5 

4 1.0 0.5 

5 1.0 0.4 

6 0.9 0.4 

7 0.9 0.4 

0.9 0.3 

9 0.8 0.3 0 

0.8 0.3 0 

11 0.8 0.3 0 

12 0.7 0.3 0 

13 0.7 0.2 0 

0.7 0.2 0 

0.7 0.2 0 

16 0.7 0.2 0 

17 0.6 0.2 0 

18 0.6 0.2 0 

19 0.6 0.2 0 

20 0.6 0.2 0 

21 0.6 0.2 

22 0.6 0.2 

23 0.5 0.2 0 

24 0.5 0.1 0 

25 0.5 0.1 0 

26 0.5 0.1 0 

27 0.5 0.1 

28 0.5 0.1 

29 0.5 0.1 0 

30 0.5 0.1 0 

31 0.5 0.1 

TOTAL 269.8 26.3 0 

CUMULATIVE 

148 

171 

186 

196 

203 

209 

214 

218 

221 

224 

227 

230 

232 

234 

242 

247 

251 

254 

257 

260 

262 

264 

266 

268 

269 

271 

272 

274 

275 

276 

277 

278 

280 

281 

282 

283 

283 

284 

285 

286 

287 

288 

288 

289 

290 

291 

291 

292 

293 

293 

294 

294 

295 

296 

296 mrem 

••LST-859 was to Bikini at the time of Shot ITEM. 

94 
-

-

 3-4. Calculated Personnel Film Badge Dose, USNS SGT. CHARLES E. MOWER 

DATE DOG 

8 April 1951 96.9 mrem 

9 . 

13 

14 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

May 

2 

3 

4 

5 

6 

7 

8 

14.3 

7.7 

5.1 

3.8 

3.0 

2.5 

2.1 

1.8 

1.6 

1.5 

1.3 

1.2 

1.1 

1.0 

0.9 

0.9 

0.8 

0.8 

0.7 

0.7 

0.6 

0.6 

0.6 

0.6 

0.6 

0.5 

0.5 

0.5 

0.5 

0.5 

EASY GEORGE ITEM 

0 mrem 

5.5 

3.2 

2.1 

1.6 

1.2 

1.0 

0.9 

0.7 

0.6 

0.6 

0.5 

0.5 

0.5 

0.4 

0.4 

0.4 

0.3 

CUMULATIVE 

97 

111 

119 

124 

128 

131 

133 

135 

137 

139 

140 

142 

143 

144 

150 

155 

158 

160 

162 

164 

165 

167 

168 

169 

170 

171 

172 

173 

174 

175 

176 

9 0.4 0.3 

0.4 0.3 

0.4 0.3 

0

0

0

0

0

0

0

0

0

0 

0

0

0

0

0

0

0

0

0

0 

176 

177 

178 

178 

179 

179 

180 

181 

181 

182 

182 

183 

183 

184 

184 

185 

116.2 mrem 302 

148.2 450 

81.1 532 

53.3 585 

12 0.4 

13 0.4 

14 0.4 

15 0.4 

16 0.4 

17 0.3 

18 0.3 

19 0.3 

20 0.3 

21 0.3 

0.3 

0.3 

24 0.3 

25 0.3 

26 0.3 

27 0.3 

28 0.3 

29 0.3 39.5 625 

30 0.2 31.2 657 

31 0.2 

June 6 

July 4 

August 3 

0 

0

0

0

0 

25.7 683 

246 938 

79 1023 

1074 

September 3 1109

October 25 1137 

TOTAL 180.6 33.8 0 922.2 1137 mrem 

95 
- - -

Table 3-5. Calculated 

DOG__ 

8 April 51 38.9 mrem 

9 12.3 

6.7 

II 4.4 

3.3 

13 2.6 

14 2.2 

15 1.9 

16 1.6 

17 1.4 

18 1.3 

19 1.1 

20 l.L 

21 1.0 

22 0.9 

23 0.8 

24 0.8 

25 0.7 

26 0.7 

27 0.6 

28 0.6 

29 0.6 

30 0.5 

May 0.5 

2 0.5 

3 0.5 

4 0.5 

5 0.4 

6 0.4 

7 0.4 

0.4 

9 0.4 

0.4 

If 0.3 

12 0.3 

13 0.3 

14 0.3 

15 0.3 

16 0.3 

17 0.3 

18 0.3 

19 0.3 

Personnel Film Badge Dose, 

EASY GEORGE ITEM 

2.9 mrem 

82.2 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 

0 0 

0 0 

SPROSTON 

CUMULATIVE 

39 

51 

58 

62 

66 

68 

70 

72 

74 

75 

77 

78 

79 

83 

166 

167 

167 

168 

169 

169 

170 

171 

172 

172 

173 

173 

174 

174 

174 

175 

175 

176 

176 

176 

177 

177 

177 

178 

178 

178 

20 0.3 0 

21 0.3 0 

22 0.3 0 

2 3 0.3 0 

24 0.3 0 

25 0.2 0 

26 0.2 0 

27 0.2 0 

28 0.2 0 

29 0.2 0 

30 0.2 0 

0

0

0

0

0

0

0

0

0

0

0 

179 

179 

179 

180 

0.6 mrem 181 

0.8 182 

0.7 182 

0.4 183 

0.3 184 

0.2 184 

31 0.2 0.2 184 

TOTAL 96.0 85.1 0 3.2 184 mrem 

96 
-

Table 3-6. Calculated Personnel Film Badge Dose, USS WALKER 

DATE DOG EASY GEORGE ITEM CUMULATIVE 

8 April1951 35.9 mrem 36 

9 7.9 44 

4.2 48 

2.8 51 

12 2.1 53 

13 1.6 55 

14 1.3 56 

15 1.2 57 

16 1.0 58 

17 0.9 59 

18 0.8 60 

19 0.7 60 

20 0.6 61 

21 0.6 13.9 mrem 76 

22 0.5 7.6 84 

23 0.5 4.0 88 

24 0.5 2.7 91 

25 0.4 2.0 94 

26 0.4 1.5 96 

27 0.4 1.3 97 

28 0.4 1.1 99 

29 0.3 1.0 100 

30 0.3 0.8 101 

I May 0.3 0.7 102 

2 0.3 0.7 103 

3 0.3 0.6 

4 0.3 0.6 105 

5 0.3 0.5 106 

6 0.2 0.5 107 

7 0.2 0.4 107 

8 0.2 0.4 108 

9 0.2 0.4 0 108 

0.2 0.4 0 109 

II 0.2 0.3 0 109 

12 0.2 0.3 0 110 

13 0.2 0.3 0 110 

14 0.2 0.3 0 111 

15 0.2 0.3 111 

16 0.2 0.3 112 

17 0.2 0.2 0 112 

18 0.2 0.2 0 113 

19 0.1 0.2 0 113 

20 0.1 0.2 0 113 

2 1 0.1 0 114 

22 0.1 0 

23 0.1 0 114 

24 0.1 0 115 

25 0 51.7 mrem 167 

26 0.1 0 18.6 185 

27 0.1 0 4.0 190 

28 0.1 0 2.7 193 

29 0.1 0 2.1 195 

0.1 1.7 197 

0.1 I.4 199 

June 220 

TOTAL 74.4 0 97.2 220 mrem 

97 
195’

EASY+ ITEM*

-

Table 3-7. Calculated Personnel Film Badge Dose, USNS LT. ROBERT CRAIG 

DATE 

13 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

I May 

2 

3 

4 

5 

6 

7 

8 

9 

II 

13 

15 

16 

i7 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

31 

TOTAL 

• CRAIG did 

GEOR GE* 

37.5 mrem 

19.7 

10.9 

7.2 

5.3 

4.2 

3.5 

3.0 

2.6 

2.3 

2.0 

1.7 

1.5 

1.4 

I 

1.2 

1.2 

1.1 

I.0 

I.0 

0.9 

0.9 

0.8 

0.8 

0.8 

0.7 

0.7 

0.7 

0.7 

0.6 

0.6 

0.6 

0.6 

0.6 

0.5 

0.5 

0.5 

0.5 

0.5 

0.5 

0.5 

0.4 

0.4 

0.4 

0.4 

0.4 

0.4 

0.4 

0.4 

0.4 

0.4 

0.3 

0.3 

129.5 

not participate at the remaining GREENHOUSE shots. 

CUMULATIVE 

38 

57 

68 

75 

81 

85 

88 

91 

94 

96 

98 

100 

102 

103 

105 

106 

107 

108 

109 

110 

111 

112 

113 

115 

116 

116 

117 

118 

119 

120 

122 

122 

123 

123 

124 

124 

125 

125 

126 

126 

127 

127 

128 

128 

129 

129 

129 

130 

130 mrem 

98 
-

- - -

Table 3-8. 

DATE 

8 April 51

9 

13 

14 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

I May

2 

3 

4 

5 

6 

7 

8 

9 

Calculated 

DOG 

203.7 mrem 

89.2 

42.7 

27.7 

20.2 

15.8 

12.9 

10.9 

9.4 

8.2 

7.3 

6.6 

5.9 

5.4 

5.0 

4.6 

4.3 

4.0 

3.8 

3.5 

3.4 

3.2 

3.0 

2.9 

2.7 

2.6 

2.5 

2.4 

2.3 

2.2 

2.1 

Personnel Film Badge Dose, 

EASY GEORGE ITEM 

0.1 mrem 

8.6 

5.5 

3.6 

2.7 

2.1 

1.7 

1.5 

1.3 

1.1 

1.0 

0.9 

0.8 

0.7 

0.6 

0.6 

Enewetak Island 

CUMULATIVE 

204 

293 

336 

363 

383 

399 

412 

423 

433 

441 

448 

455 

461 

466 

480 

490 

498 

504 

510 

515 

520 

525 

529 

533 

536 

540 

543 

546 

549 

552 

555 

557 

560 

562 

564 

567 

569 

571 

573 

575 

577 

578 

580 

582 

583 

0

0

0

0

0

0

0

0

0

0

0

0

0 

11 1.9 0.5 

13 

14 1.7 0.4 

1.7 0.4 

1.6 0.4 

17 1.6 0.3 

18 1.5 0.3 

19 1.5 0.3 

20 1.5 0.3 

21 1.4 0.3 

22 1.3 0.3 

23 1.3 585 

24 1.3 587 

25 1.3 0.3 584.1 mrem 1172 

26 1.2 0.3 8 724.6 1898

8

0

0 

27 1.2 0.2 359.9 2260 

28 1.2 0.2 

1.2 0.2 

30 1.1 0.2 

237.2 2498 

175.7 2675 

138.9 2816 

31 1.1 0.2 114.5 2932 

TOTAL 554.8 42.2 0 2334.9 2932 

99 

29 
- -

Table 3-9. Calculated Personnel Film Badge Dose, Parry Island 

DATE DOG EASY GEORGE ITEM CUMULATIVE

8 April 51 443.1 mrem 443 

9 228.1 671 

113.8 785 

II 75.4 860 

12 56.1 916 

13 44.5 961 

36.7 998 

31.2 1029 

16 27.2 1056 

17 24.0 1080 

18 21.4 

19 19.4 1121 

20 7.2 1128 

21 6.6 0.1 mrem 1135 

22 6.1 8.6 1150 

23 5.7 5.5 1161 

24 5.3 3.6 1170 

25 5.0 2.7 1177 

26 4.6 2.1 1184 

27 4.4 1.7 1190 

28 4.2 1.5 1196 

29 4.0 1.3 1201 

30 3.8 1.1 1206 

1 May 3.6 1.0 1211 

2 3.4 0.9 1215 

3 3.3 0.8 1219 

4 3.1 0.8 1223 

5 3.0 0.7 1227 

6 2.9 0.7 1230 

7 2.8 0.6 1234 

8 2.7 0.6 1237 

9 2.6 0.6 0 1240 

2.5 0.5 0 1243 

II 2.5 0.5 0 1246 

12 2.4 0.4 0 1249 

13 2.3 0.4 0 1252 

2.2 0.4 0 1254 

15 2.2 0.4 0 1257 

16 2.1 0.4 0 1259 

17 2.0 0.3 0 1262 

18 2.0 0.3 0 1264 

19 1.9 0.3 0 1266 

20 1.9 0.3 0 1268 

21 1.8 0.3 0 1270 

22 1.8 0.3 0 1273 

23 1.7 0.3 0 1275 

24 1.7 0.3 0 1277 

25 1.7 0.3 0 405.2 mrem 1684 

26 1.6 0.3 0 564.2 2250 

27 1.6 0.2 0 288.1 2540 

28 1.6 0.2 0 193.1 2735 

29 1.5 0.2 0 144.8 2882 

30 1.5 0.2 0 115.6 2999 

31 1.5 0.2 96.0 3096 

TOTAL 1247.2 42.2 0 1807.0 3096 mrem 
-

Table 3-10. 

DATE 

8 April 51 

9 

10 

II 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

1 May 

2 

3 

5 

6 

7 

8 

9 

11 

12 

13 

15 

16 

19 

20 

21 

22 

23 

24 

25 

26 

27 

28 

29 

30 

TOTAL 

Calculated 

DOG 

443.1 mrem 

228.1 

113.8 

75.4 

56.1 

44.5 

36.7 

31.2 

27.2 

24.0 

21.4 

19.4 

7.2 

6.6 

6.1 

5.7 

5.3 

5.0 

4.6 

4.4 

4.2 

4.0 

3.8 

3.6 

3.1 

3.0 

2.9 

2.8 

2.7 

2.6 

2.5 

2.5 

2.4 

2.3 

2.2 

2.2 

2.1 

2.0 

2.0 

1.9 

1.9 

1.8 

1.8 

1.7 

1.7 

1.7 

1.6 

1.6 

1.6 

1.5 

1.5 

1.5 

1247.2 

Personnel 

EASY 

0.1 mrem 

8.6 

5.5 

3.6 

2.7 

2.1 

1.7 

1.5 

1.3 

1.1 

1.0 

0.9 

0.8 

0.8 

0.7 

0.7 

0.6 

0.5 

0.5 

0.4 

0.4 

0.4 

0.4 

0.4 

0.3 

0.3 

0.3 

0.3 

0.3 

0.3 

0.3 

0.3 

0.3 

0.3 

0.2 

0.2 

0.2 

42.2 

Film Badge Dose, Japtan Island 

GEORGE ITEM CUMULATIVE 

443 

671 

785 

860 

916 

961 

998 

1029 

1056 

1080 

1101 

1128 

1135 

1161 

1170 

1177 

1184 

1190 

1196 

1201 

1206 

1211 

1215 

1219 

1223 

1227 

1230 

1234 

1237 

0 1240 

0 1243 

0 1246 

0 1249 

0 1252 

1254 

1257 

0 1259 

0 1262 

0 1264 

0 1266 

0 1268 

0 1270 

0 1273 

0 1275 

0 1277 

0 226.2 mrem 1505 

0 403.8 1910 

0 216.2 2128 

148.9 2279 

113.8 2395 

0 92.2 2489 

77.6 2568 

0 1278.7 2568 mrem 

101 
Section 4 

UNCERTAINTY ANALYSIS 

The uncertainty in calculated film badge doses is estimated from the underlying 

parameters. Not only is the uncertainty in the mean film badge dose determined, but 

also the distribution in dose about the mean is estimated for typical personnel. The 

basic uncertainties include radiation intensities on deck, the positions of personnel 

(hence their exposure) on deck, the time spent on deck, and the shielding afforded to 

those below. 

Intensity levels on deck are determined from shipboard radiological survey data, 

supplemented at late times by decay rates measured on nearby islands. Individual 

meter readings on deck, where available, are taken as accurate, their inherent error 

having a negligible influence on the overall uncertainty in dose. Average on-deck 

intensity as a function of time is taken as accurate; the power law interpolation in 

time between surveys closely approximates fission product decay at the times after 

burst considered. Power law fitting is less accurate during fallout deposition and 

decontamination; however, the influence of this uncertainty is minimized because the 

typical crewmember was below during these intervals. Overall, error in on-deck 

intensity is small compared to the uncertainty associated with crew position in the 

non-uniform radiation environment. 

The significant variation in on-deck intensities for each survey focuses attention 

on the positioning of the crew relative to those intensities. The specific locations of 

each survey reading are reported in some instances; from these it is judged that the 

readings adequately define the topside radiation environment. Specific data on crew 

positioning are lacking; however, the crew size and the variety of duties performed 

suggest that the crew was, on the average, randomly positioned on deck and therefore 

randomly exposed to each reported intensity. The uncertainty in dose resulting from 

these assumptions cannot be directly quantified, except by considering unrealistic 

extremes. However, an indication of the magnitude is obtained by assuming that, for 

each interval topside, personnel remained in the same general deck area but were 

randomly repositioned for each subsequent interval. A distribution around the mean 

102 
 

 

 

-

-

-

film badge reading is calculated by assuming a random position, corresponding to an 

intensity reading, each time a crewman comes on deck. The tails of this distribution 

indicate, in a general way, the possible error of the mean dose if crew positioning were 

significantly biased toward the extremes of intensity readings. It should be noted that, 

for personnel moving continuously about the deck, their dose approaches the calculated mean. 

In order to arrive at dose distributions, the intensity readings of each radiation 

survey are taken to represent a normal distribution, characterized by the mean 

and standard deviation Where more than one set of survey data is available for a 

given shot and ship, the average fractional (of mean) standard deviation is used, for 

simplicity, at all times on deck. The fractional standard deviations obtained, or 

inferred, from the ship survey data and used in the uncertainty analysis are given in 

Table 1. 

Table 1. Fractional Standard Deviation for 

Shipboard Radiation Survey Data 

DOG EASY ITEM 

CABILDO 0.821 1.277 0.543 

CURTISS 0.625 1.277”” 0.585 

LST-859 0.858 

MOWER 0.555 0.531”“” 

SPROSTON 0.547 0.547” 0.547” 

WALKER 0.547” 0.547” 0.547” 

CRAIG 0.547” 

No Survey Data inferred from SPROSTON, Shot DOG 

No Survey Data inferred from CABILDO, Shot EASY 

No Survey Data inferred from CABILDO, Shot ITEM (before

decontamination) 

The normal distribution around the average intensity is integrated throughout each 

interval on deck to obtain the corresponding distribution in dose. When the dose 

distributions from all intervals are combined, the square of the standard deviation of 

the resultant normal distribution is equal to the sum of the squares of the standard 

103 
deviations of the contributing distributions. As contributions from more intervals are 

added, the fractional standard deviation of the combined distribution decreases. 

Because the calculated dose in reality approaches a limit with time, a finite 

distribution remains around the mean total dose. Distributions for each ship and each 

shot (where survey data are available) are reported at the 90-percent level, i.e., 

(5th to 95th percentile). Although exposure below deck makes some contribution to the mean total dose, it is not used in generating a dose distribution because its 

minor contribution involves an averaging of topside readings (for geometrical reasons). 

Despite the simplified calculation of mean dose starting on the third day after burst, 

the uncertainty analysis continues to reflect three intervals (taken equal) per day of 

on-deck exposure at random positions. For the island survey data, only average 

intensities are reported. Since the ships were anchored in close proximity to the 

islands when fallout was experienced, it is reasonable to assume the distribution of 

island intensities can be approximated utilizing the shipboard data. The distribution of 

island intensities around the reported mean is inferred by averaging the fractional 

standard deviation of the shot-specific, shipboard survey data. 

Because the distribution of survey readings typically shows deviations from 

normality (either with ostensible outliers or a lognormal appearance), a combined 

distribution is generated numerically to gauge the applicability of normal analysis. 

One of the most significantly skewed distributions is a set of 30 survey readings from 

the LST-859, with a maximum of five times the mean and a fractional standard 

deviation of about unity. These readings are taken to apply to a hypothetical exposure 

in six intervals of uniform duration and no radiological decay. Such a construct of 

day exposure simulates a longer exposure of ever-decreasing intensity. As all readings 

are weighted equally, each possible sum of readings over the six intervals makes an 

equal contribution to the total dose distribution. The complete, computer-generated 

distribution, although markedly skewed, is essentially continuous and can be described 

in terms of percentiles of the maximum possible value. Figure 4-l depicts this 

distribution and compares it with that obtained through normal analysis. At the level 

of one standard deviation are the 12th and 27th percentiles; at the 90-percent level 

are the 10th and 33rd percentiles. These compare favorably with those obtained from 

the assumption of normality in the survey readings, which are the 12th and and 

104 
-- - -

&Numerically-Generated Distribution 

Normal Distribution 

. 

Percentage of Possible Maximum 

Figure 4-l. Hypothetical Dose Distributions 

105 
-

-

7th and 34th percentiles, respectively. On this basis, the assumption of normality of 

the survey distributions is considered to be generally satisfactory as utilized. 

The value for the fraction of time spent on deck is estimated to be accurate 

within a factor of 1.2 with 90-percent confidence. For the typical (non-shot) day, this 

to 8 to hours on deck. The systematic uncertainty in the time on deck 

is considered to be greater than its random variation from day to day and ship to ship. 

The uncertainty in mean total dose is reasonably high-sided by treating the uncertainty 

in time on deck as a systematic error; as such, the factor of 1.2 applies to the on-deck 

contribution to the mean total dose as well. Not only the means, but also the 

distributions as discussed above (minus the below-deck contribution) are directly 

proportional to the time spent on deck. The below-deck contribution introduces a 

small, ship-dependent perturbation to the factor of 1.2. 

The ship-shielding factor reduces the below-deck crew exposure to a minor 

contribution to dose, thus any realistic error in that parameter has only a few-percent 

effect on the total dose. For example, for a typical day percent below deck) and a 

ship-shielding factor of 0.10, with an error generously assumed to be 50.05, the 

fractional error introduced is 0.065. Such values negligibly . ilJ 

increase the uncertainty in dose resulting from uncertainty in time spent topside. 

106 
Section 5 

FILM BADGE DOSIMETRY 

Calculated personnel film badge doses are compared with the available 

dosimetry data. Film badges were issued to selected personnel aboard the ships “in 

order to obtain a record of exposure to radiation in various parts of the ship at the 

time of, and subsequent to, the detonation” (Reference Film badge readings are 

available for 231 personnel exposures (Reference 16) aboard six of the ships for which 

dose calculations were made. This data is summarized by ship and shot-related time 

period in Figures 5-l through 5-4. The circles in the figures represent the actual film 

badge data while the triangles depict the calculated average film badge dose (from 

Section 

With the exception of the badged periods for Shot GEORGE (Figure where 

agreement between calculated doses and dosimetry data from all ships is very good, 

the calculated average dose generally underestimates the exposures indicated by the 

dosimetry data. In spite of this, there appears to be a very good correlation between 

the calculated doses and dosimetry data on a ship-to-ship basis, i.e., if the dosimetry 

data suggests Ship A received more fallout than Ship B, calculated doses for both ships 

support this observation. This correlation suggests that the difference between the 

calculated average dose and average of the dosimetry data on each ship is a 

systematic underestimation (i.e., the calculated doses are all low by percent). 

A closer look at the personnel who were badged for each shot explains, for the 

most part, why the calculated average doses are lower than the dosimetry data. 

Virtually all of the film badges were worn by personnel whose duties required them to 

be on deck a greater percentage of the day than assumed for the average 

member. These include personnel assigned to the signal bridge, coxswains and 

boatswain’s mates assigned to the weather decks, members of damage control and 

repair parties, and rad-safe monitors. This observation alone could account for a 20 

percent increase in the calculated dose (see Section 4). Further, most of the badged 

107 
-

0 0 

108 
0 

0 

0 
17 "ZEROS" USS CURTISS 

May) 

USS LST-859 NO BADGE DATA AVAILABLE , 

USNS C.E. MOWER 6 "ZEROS" 0 

(8-15 May) 

USS SPROSTON "ZEROS" 

(9-15 May) 

USS WALKER 0 0 15 "ZEROS" 

(9-14 May) 

0 100 200 300 400 500 600 

FILM BADGE DOSE 

Figure 5-3. Shot GEORGE Dosimetry Data 

USS CABILDO 13 "ZEROS" 

(8-16 May) 
USNS C.E. MOWER 

May) 

USS SPROSTON 

May) 

USS WALKER 

USS LST-859 4 "ZEROS"

May) 

00 00 

0 0 

NO FILM BADGE DATA AVAILABLE 

I I I I I 

0 100 200 300 400 500 600 700 800 900 1000 1100 1200 

FILM BADGE DOSE 

Figure 5-4. Shot ITEM Dosimetry Data 
personnel, especially the rad-safe monitors and the damage control and repair parties, 

would have been required to be topside in spite of or even because of fallout 

deposition. These personnel were exposed during periods of early fallout deposition 

when the dose calculations assume the average crewmember was below deck. It has 

been noted in previous dose reconstructions for shipboard personnel (Reference 17) 

that, on the day fallout occurs, personnel involved with monitoring and decontamination can easily receive 50-60 percent of the daily topside dose. As an 

example, the average integrated free-field intensity on the CURTISS on 8 April was 

228 (Table 2-4). Sixty percent of this would be 137 and, when converted to an 

equivalent film badge dose, would result in a calculated film badge dose of 96 mrem. 

On 9 and 10 April, an additional 77 mrem was accrued by the average crew; assuming a 

20 percent increase due to time spent topside, the high exposure personnel would have 

received 92 mrem. The total dose received by these personnel during the 7-10 April 

badged period would be 188 mrem, compared to 136 mrem calculated for the average 

crew (Table 3-2). This compares quite favorably with a dose of 220 mrem obtained by 

averaging the actual film badge readings. Similar calculations can be made for the 

other ships and shots with generally good agreement between the dosimetry data and 

the calculated film badge doses for these high exposure personnel. 

112 
Section 6 

CONCLUSIONS AND TOTAL DOSE SUMMARY 

In Section 5, a comparison between calculated doses and dosimetry data for the 

crews of six ships indicated a systematic underestimation by the calculated doses in 

portraying the actual doses received by the badge wearers during most badged periods. 

When the shipboard duties of the badged personnel are accounted for in the dose 

calculations (by considering extended periods of time topside), agreement between the 

calculated doses and the dosimetry data is significantly improved. 

Table 6-l summarizes, by shot, the calculated dose due to fallout for the seven 

ships considered in this report and for the residence islands of Enewetak Atoll. The 

total dose (with bounds) is tabulated and, in the absence of dosimetry data, should be 

used for dose determination. The uncertainity in dose due to assumed time topside is 

not reflected in the mean or bounds (see Section 4); the inclusion of this uncertainity 

will increase (or decrease) the mean and bounds by 20 percent depending on the 

assumed or documented personnel activity scenario. 

Table 6-1. Summary of Calculated Doses 

Dose Contribution From Shot Total 

Shipboard Personnel DOG EASY GEORGE ITEM Dose 

CABILDO 0 

USS CURTISS 0 

USS LST-859 0 

USNS SGT. C.E. MOWER 0 

USS SPROSTON 0 5 

USS WALKER 0 0.22 

USNS LT. ROBERT CRAIG 0.13 

Island-Based Personnel 

Enewetak 0 

Parry 0 181 

Japtan 0 

Values are rounded to the nearest 0.01 rem. 
-

Section 7 

REFERENCES 

1. Joint Task Force Three, Task Group 3.3 Operation Plan l-51, 31 January 1951. 

2. “Compilation of Local Fallout Data from Nuclear Test Detonations, 

Volume II Oceanic U.S. Tests, DNA Defense Nuclear Agency, 

1 May 1979. 

3. Joint Task Force Three, Task Group 3.3, Operation Order 1-52, dated 27 March 

1951, Operation Order 2-51, dated 14 April 195 1, Operation Order 3-5 1, dated 3 

May 1951, Operation Order 4-51, dated 20 May 1951. 

4. Commander Task Group 3.3 letter, “Report of Participation in Operation 

GREENHOUSE,” 16 June 1951. 

5. Commander Task Group 3.3 letter dated 27 May 1951, Subject, “History of Task 

Group 3.3,” National Archives, Record Group 374. 

6. Operation GREENHOUSE, Scientific Director’s Report, Annex 9.3, Radiological 

Safety, WT-89, Los Scientific Laboratory, July 1951. 

7. Radiological Contamination-Decontamination Reports for USS CABILDO, USS 

CURTISS, USS LST-859, USNS SGT. C.E. MOWER, USS SPROSTON, and USS 

WALKER, 1951. 

8. “Proceedings of Tripartite Symposium on Technical Status of Radiological 

Defense in the Fleets,” Volume I, Reviews and Lectures No. 103, U.S. Naval 

Radiological Defense Laboratory, May 1960. 

9. “Proof Testing of Atomic Weapons Ship Countermeasures,” Project 6.4, Operation CASTLE, Pacific Proving Grounds, WT-927, U.S. Naval Radiological Defense 

Laboratory, October 1957. 

114 
10. “Ship-Shielding Studies,” Project 2.7 1, Operation Redwing, Pacific Proving 

Grounds, WT-1321, U.S. Naval Radiological Defense Laboratory, July 1959. 

Correlation Between Theory and Experiment in Ship Shielding Studies,” 

USNRDL-TR-373, U.S. Naval Radiological Defense Laboratory, October 1959. 

12. “Analysis of Radiation Exposure for Task Force WARRIOR, Shot Smoky,” 

Exercise Desert Rock VII-VIII, Operation Plumbbob, DNA Defense 

Nuclear Agency, May 1979. 

13. Supplemental material supplied by C.F. Ksanda to Reference 8, September 1960. 

14. “Information on GREENHOUSE,” letter from Payne Harris, M.D. to 

Navy NTPR, June 1981. 

15. “Film Badges, Procurement, Distribution, and Processing: Information 

Concerning,” letter from CTG 3.3 to TG 3.3, 22 March 1951. 

16. “Film Badge Summaries for Six GREENHOUSE Ships,” enclosure (2) to letter 

from Navy NTPR to DNA, 14 June 1983. 

17. “Estimate of Radiation Dose to Shipboard Personnel, Shot BRAVO, Operation 

CASTLE,” memorandum from Science Applications, Inc. to NNTPR, 

28 June 1982. 

115 
-

116 
Appendix 

SHIPBOARD CREW ACTIVITIES 

In order to transform the average topside dose into a more meaningful 

crewmember dose, as is shown in Section 3 of this report, it is necessary to determine 

the amount of time spent on and below deck by an average crewmember. For 

whatever day fallout occurred a ship and on the following day, when radiation 

intensities were still relatively high, not only the total time on deck, but also the 

actual time of day spent on deck, becomes significant. The reason is that a 

crewmember on deck has virtually no protection, while a crewmember below deck is 

afforded varying degrees of shielding depending on the material between him and the 

source of the gamma rays--usually the weather deck surfaces (see Section 2.9). 

For the seven ships participating in Operation GREENHOUSE, crew activity time 

are derived or inferred from each deck log. These time lines depict when normal 

crew activities occurred topside and when these were suspended due to fallout 

deposition on the ships and during subsequent attempts at decontamination. Generally, 

on the second day after fallout, normal crew activities were resumed. With the 

knowledge of when and for how long a crewmember was topside or below deck, the 

appropriate shielding factor is applied to the average free-field integrated intensity 

for that same period (corrected for film badge equivalence) to arrive at the calculated 

film badge dose to crew personnel. 

The crew activity time lines depicted in Figures A-l through A-5 are used in the 

dose calculations of Section 3. It is apparent from these figures that, when fallout was 

heavy, variations in the normal crew activities occurred during the first two days. 

After two days, all crews had returned to their normal work routine, spending 

approximately hours on deck each day. At these later times, when shipboard 

radiation intensities were significantly reduced, the time of day when a crewmember 

was on deck becomes relatively unimportant, and only the daily time topside is needed 

to estimate an average shielding factor. This is applied to the integrated intensities 

derived in Section 2 as described in Section 3. 

117 
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