Torpedo countermeasures

A device which is deployable in the ocean environment to defeat an active torpedo comprises a mesh net structure constructed of a plurality of flat ribbons oriented in a particular geometric orientation with uniform spacings between adjacent ribbons, the ribbons being comprised of synthetic materials and more particularly of SPECTRA yarns in combination with yarns taken from the group comprising nylon, polyester, aramid, and KEVLAR. The net structure has stitched interconnections of the ribbons and a diameter of at least ten feet and exhibits a packing density of about 45 lbs/ft.sup.3 and a substantial neutral buoyancy in salt water.

FIELD OF THE INVENTION 
This invention generally pertains to torpedo countermeasures, that is, to 
anti-torpedo devices. 
More particularly, the present invention pertains to an anti-torpedo device 
which may be deployed into the water environment to intercept an active 
torpedo and to interact with the torpedo in such a manner as to defeat it 
so that it cannot complete the intended mission. 
Specifically, the present invention provides a passive anti-torpedo net 
structure which exhibits a high packing density for storage and deployment 
from an aircraft, a surface ship, and/or a submarine while also exhibiting 
structural strength and integrity to defeat an active torpedo in the water 
environment. 
BACKGROUND OF THE INVENTION 
Net structures which are intended to stop a torpedo have been used in 
coastal waters with a high degree of effectiveness as harbor and/or dam 
protection devices. Generally, these prior art nets have been fabricated 
from high strength metal cables and have been deployed as static 
structures in the water environment with anchorages to the ocean floor. 
Various of these prior art devices are described and illustrated in the 
patent art as exemplified by U.S. Pat. No. 2,383,095 (D. A. Wallace); U.S. 
Pat. No. 2,170,481 (J. J. Morrison et al); and U.S. Pat. No. 2,388,459 (C. 
S. Allen, Jr.). These known net structures are costly to manufacture and, 
because of the method of construction and their significant weight, do not 
lend well to a high packing density for storage onboard light aircraft 
and/or in the limited spaces of a submarine. 
Another known net structure is described and illustrated in U.S. Pat. No. 
4,768,417 (J. E. Wright). This net is in the configuration of an active 
detonator weapon and it is comprised of lengths of nylon rope interwoven 
with detonator cord. The purpose of the net is to disable a target by way 
of the explosive detonator cord which is ignited by control packages 
carried on the net structure. The control packages include initiators for 
igniting the explosive detonator cord. 
With the introduction of smart weapons, ie., acoustic homing torpedos and 
the like, a need exists for an anti-torpedo device which cannot be 
detected by these type smart weapons. The anti-torpedo device, therefore, 
must be passive and comprised of materials which are not ordinarily 
detectable by conventional methods. The anti-torpedo device must also be 
economical to manufacture in large quantities and lightweight enough to be 
carried onboard light aircraft. Furthermore, the anti-torpedo device must 
exhibit a high packing density for storage onboard aircraft as well as 
onboard a submarine where space is at a premium. 
Therefore, it is in accordance with one aspect of the present invention an 
object to provide a lightweight, highly packageable, and economically 
produced passive anti-torpedo device. 
In accordance with another aspect of the invention it is an object to 
provide a passive anti-torpedo net structure comprised of parachute type 
ribbon materials which exhibit a high structural integrity and the total 
net structure exhibits a substantially neutral buoyancy when it is 
deployed into a salt water environment. 
In accordance with still another aspect of the invention it is an object to 
provide an anti-torpedo net comprised of ribbon materials, the ribbon 
materials being taken from a synthetic group comprising nylon, polyester, 
aramid, KEVLAR (KEVLAR is a registered trademark of the E. I. Du Pont de 
Nemours Company of Wilmington, Delaware) and SPECTRA (SPECTRA is a 
registered trademark of the Allied Chemical Corporation of Norristown, 
N.J.). 
SUMMARY OF THE INVENTION 
The foregoing aspects and other aspects and advantages of the present 
invention are provided in a device deployable into a salt water 
environment to defeat an active torpedo, the device comprising in 
combination: a plurality of flat ribbon materials in a geometric 
orientation at uniform spacings with stitched interconnections to form an 
integral net structure, the ribbon materials being taken from a group of 
synthetic materials comprising nylon, polyester, aramid, KEVLAR and 
SPECTRA and the particular combination of materials is such that the total 
net structure exhibits a substantial neutral buoyancy in a salt water 
environment.

DETAILED DESCRIPTION OF THE INVENTION 
Referring to the drawings, FIG. 1 pictorially illustrates an ocean 
environment generally indicated by reference numeral 10 in which various 
military scenarios are depicted and these may include a surface ship 12, 
an aircraft 14, and a submarine 16. 
In accordance with a first scenario as it pertains to the present 
invention, a torpedo 50 is illustrated as it may have been launched by an 
enemy submarine (not shown) to pose a threat to the surface ship 12. Of 
course, the ship 12 will carry some type of sonar detection equipment 18 
onboard and its personnel will be appraised of the torpedo threat 50. 
While the ship 12 may carry various type of active self-protect devices 
which may be used against a torpedo threat, the particular ship 12 
illustrated in the drawing also carries anti-torpedo nets 100 in 
accordance with this invention. 
An anti-torpedo net 100 may be deployed from the ship 12 using various 
techniques and/or methods and one of these may comprise a dispensing 
device 20 which shoots a frangible canister 22 away from the ship for 
deployment of the anti-torpedo net 100. As illustrated in the drawing, the 
net 100 is deployed in a manner to intercept the track of the torpedo 
threat 50 such that it entangles the torpedo within its net structure. The 
net 100 may entangle the control functions of the torpedo such that its 
internal guidance system is defeated and/or the mass of the net structure 
will provide sufficient drag forces to the torpedo which cannot be 
overcome by its propulsion system. In either case, the torpedo is defeated 
from carrying out its intended function. 
As further illustrated in a second scenario, the surface ship 12 may also 
carry a helicopter 14 onboard for ASW purposes and such helicopter may be 
used to deploy the anti-torpedo net 100. Again, various techniques and 
methods may be used to accomplish the deployment of the net 100 including 
a frangible canister 22 which may be dropped or otherwise launched from 
the helicopter such that a net 100 is positioned appropriately within the 
pathway track of the torpedo 50. Thus, the torpedo threat 50 is 
intercepted by the net 100 and it is entangled within the mesh of the net 
structure and defeated in the manner described above. 
As further illustrated in a third scenario of FIG. 1, a net 100 may also be 
deployed from a submarine 16 as a self-protect or countermeasures device 
to defeat a torpedo threat 52. The net 100 may be deployed via a frangible 
canister 22 which is launched from the submarine 16 by way of its 
countermeasures dispenser (not shown) which may be located near the rear 
of the boat. Countermeasures dispensers of the type alluded to are known 
in the art and such will not be specifically described here suffice to say 
that a frangible canister 22 is launchable from such dispenser. In any 
event, a frangible canister 22 may be broken up by the forces imposed on 
it as it exits the submarine and/or various other means may be used to 
extricate the net 100 from within the canister. For example, a tether line 
102 may be used to draw the net 100 free from within the canister 22 and 
to deploy it in its intended full-form configuration. Upon being deployed, 
the tether 102 will break away from the submarine when the tensile forces 
on it reach a predetermined break strength. In this manner, the net 
deployment is totally passive and will not aid an enemy in locating the 
submarine 16 which may now take other evasive actions. 
FIG. 2 of the drawings illustrates a particular mode of deploying an 
anti-torpedo net 100 from a submarine 16 to defeat a torpedo threat 52. 
The drawing illustrates the approximate sizes of the submarine 16, the 
torpedo 52, and the deployed condition of a net 100. For example, a net 
100 may be configured to have a diameter D.sub.n within the range of 
10-100 feet (3.05-30.5 meters) while the diameter D.sub.t of a 
conventional torpedo 52 will be about 2 feet (0.6 meters). Thus, the area 
coverage of a net 100 will be at least five times the frontal area 
exposure of a torpedo 52 and may be as much as ten times the frontal 
exposure of such torpedo. Anti-torpedo nets 100 exhibiting greater 
diameters D.sub.n may, of course, be made but this will be determined by 
the volume capacity of the deployment canister 22 and the achievable 
packing density of the net. For example, it has been determined that a net 
100 having a diameter D.sub.n of about 80 feet (24.4 meters) may be made 
in accordance with this invention as will be described hereinafter and 
such net will exhibit a packing density to meet the constraints imposed by 
the known and available countermeasures dispenser canister 22. A net 100 
having a diameter greater than 80 feet may be made but then the dispenser 
canister 22 will have to be of greater volume capacity to stow such net. 
This constraint is not considered to be a limiting facter in the practice 
of the present invention. 
Referring now to FIG. 3 of the drawings, a portion of a net 100 is shown in 
plan view as the net comprises a plurality of textile ribbons 110 and 120. 
The ribbons 110 and 120 are flat ribbons comprised of synthetic yarns 
taken from the group comprising nylon, polyester, aramid, KEVLAR, and 
SPECTRA (KEVLAR a trademark of the E. I. Du Pont de Nemours Company; 
SPECTRA a trademark of the Allied Chemical Corporation). More preferably, 
the ribbons 110,120 will be comprised of SPECTRA yarns in combination with 
nylon, polyester, aramid, or KEVLAR yarns in an 80-to-20 percent ratio by 
volume in favor of SPECTRA. This combination of yarns exhibits a high 
strength-to-weight ratio and substantially neutral buoyancy in salt water. 
For example, an 80-to-20 percent mix of yarns of SPECTRA and KEVLAR will 
produce ribbons which exhibit substantially neutral buoyancy in salt water 
inasmuch as SPECTRA yarns exhibit a specific gravity of about 0.97 while 
KEVLAR yarns exhibit a specific gravity of about 1.44. Both of these yarns 
exhibit comparable stiffness and elongation specifications and when the 
ribbons 110 and 120 are comprised of this combination of yarns they will 
share any loading forces imposed on a net 100. A SPECTRA-KEVLAR ribbon 
capable of accepting a 1,000 pound tensile load will exhibit a weight of 
about 0.20 oz/yd. Ribbons 110,120 of this combination of yarns which are 
0.25 inches (6.35 mm) wide will construct a net having a diameter D.sub.n 
of 80 feet (24.4 meters) which will weigh approximately 140 pounds (63.5 
kilograms). 
As illustrated in FIG. 3 of the drawings, the ribbons 110,120 may be 
oriented in a square woven pattern with intersections at 115. The ribbons 
are woven in warp and weft orientation and the intersections 115 are sewed 
using a box-X or box-Z stitching pattern using KEVLAR threads. 
Intersections which are made in accordance with the above will insure 
failure of any ribbon 110 or 120 only outside of the intersection and this 
is necessary to insure capture of an active torpedo. 
The net mesh spacing indicated at "d" in FIG. 3 is also an important 
consideration in the construction of a net 100. Inasmuch as the ribbons 
110,120 must accept the loading produced during engagement with a torpedo 
as the net collapses about the nose of the torpedo, the spacings "d" must 
be such that any hole produced due to breakage of any ribbon 110 or 120 
will be still small enough to contain a torpedo. For example and as 
illustrated in FIG. 3, a net comprised of 1.0 inch (2.54 cm) wide ribbons 
110,120 having spacings "d" on 4.0 inch (10.6 cm) centers is shown as it 
may be engaged by a conventional torpedo 50 indicated by the dot-dash 
ghost lines. Failure of one of the intersections, if such would occur, 
will result in an allowable spacing of about 7 inches (17.78 cm), and 
this, to contain a 21 inch (53.34 cm) diameter torpedo. Accordingly, it 
has been determined that the spacings "d" may be within the range of 4-12 
inches (10.16-30.48 cm) when the ribbons 110,120 have widths within the 
range of 0.25-1.5 inches (6.35-38.1 mm) respectively. 
Referring to FIG. 4 of the drawings an alternative ribbon orientation is 
illustrated and generally indicated by reference numeral 200. The net 
structure 200 comprises a plurality of flat ribbons 210 which are oriented 
to form a plurality of interconnected hexogonals which are formed when the 
ribbons 210 are stitched together in a particular manner. 
A hexagon, of course, is a polygon having six equal length sides and the 
area of a hexagon is determined by the length of its sides. In FIG. 4, a 
side length is indicated at "L" and all sides of a desired hexagon will 
have a length equal to "L". As further illustrated in the drawing, a first 
ribbon 212 is stitched to a second ribbon 214, the stitched length 215 
being equal to a hexagon side length "L". The stitching is stopped as 
between ribbons 212 and 214 for a length "L" and resumed again but, the 
ribbon 212 is now stitched to a third ribbon 216 for a length 217 which is 
also equal to "L". Again, stitching is stopped as between ribbons 212 and 
216 and, after a length "L", is resumed again as between ribbons 212 and 
214. Thus, the stitching alternates as between ribbon 212 and adjacent 
ribbons 214 and 216 and it also alternates with side lengths "L" which are 
not stitched. This stitching pattern is continued in the direction of 
arrow A.sub.1 until the desired length of net structure is achieved in 
that direction. Concurrently, additional ribbons 210 may be added in the 
same stitching pattern until a complete net is realized in the direction 
of arrow A.sub.2. 
It will be recognized and as indicated in FIG. 4, that the maximum length 
of opening in a net structure having the hexagon pattern will be equal to 
"2L". Accordingly, and to insure that the net structure captures an active 
torpedo, the length "2L" will be within the range of 4-8 inches 
(10.16-20.32 cm). It will also be recognized that the hexagon pattern 
offers an advantage in that, when the net structure is completely 
collapsed for stowage, the packing density is enhanced by the very nature 
of its construction. 
Finally, the packing density of a net 100 and/or 200 is an important 
consideration inasmuch as such net may be carried onboard light aircraft 
or onboard a submarine where it may be used as a self-protect 
countermeasure against a homing torpedo. Accordingly, it has been found 
that flat ribbons 110, 120, and/or 210 may achieve a packing density of 
about 45 pounds per cubic foot (730 kgms/m.sup.3). At this level of 
packing density, a net structure 100 and/or 200 exhibits a volumetric 
loading capacity which is approximately equal to forty percent that of 
high explosive type countermeasures as presently known and used in this 
art and these exhibit a packing density of about 114 lbs/ft.sup.3 (1828.5 
kgms/m.sup.3). The advantages of the present invention should be clearly 
obvious! 
From the foregoing, it will be recognized that various modifications may be 
made to the ribbon geometric pattern without departing from the spirit or 
scope of the invention. For example, the ribbons 110 and 120 may be 
oriented at a bias angle which may vary within the range of 0-90 degrees. 
Of course, the pattern of FIG. 3 is at an angle of 90 degrees. The actual 
geometric orientation of the ribbons will, therefore, be dictated by the 
volume capacity of a stowage container 22 and/or by the diameter dimension 
of the torpedo to be captured by the net structure. Obviously, the shorter 
the dimensions "d" and/or "L" may be, the larger the volume of stowage 
capacity needed for a particular diameter net structure 100 and/or 200.