BHARAT RAKSHAK MONITOR - Volume 3(4) January-February 2001

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Modern Torpedoes And Countermeasures

Austin Joseph

The Torpedo is one of the oldest weapons in the Naval Inventory ,Having been invented over 130 years ago, But at the same time it remains one of the deadliest anti-ship and anti-submarine weapon ,It is far more lethal to submarines and surface ship than any other conventional weapon. Torpedoes fall in two main categories: Heavy Weights that are mainly confined to submarines (with a few notable exception) and Light Weights that are used both as offensive weapons in anti-submarine warfare or as defensive anti-submarine weapons by surface warship. Although a number of elderly weapons still rely on gyroscopic guidance (Straight –or Pattern runners), The majority of Modern Torpedoes rely on Active or Passive acoustic homing or Wake homing .The fashion for Passive rather than Active homing passed when silencing of submarine’s noise signatures made it very hard for passive seekers to detect them, and today active seekers offers the best way of attacking submerged submarines. Before looking at the different kinds of torpedoes adopted & used by various countries, I would like to brief the members on the kind of guidance system used in Torpedoes.

Guidance

Although sound travels very great distances through water, its erratic path makes underwater warfare very difficult. Water is in fact a hostile medium, the surface of the sea acts as a mirror and in shallow water seabed can also reflect sound. Active Torpedoes seekers operating near the surface or in shallow waters must therefore be designed to counter such effects. As active detection relies on the Doppler effect to distinguish the real target from surrounding clutter, it follows that a hovering submarine may almost be impossible to detect. A submarine that detects the active "Pinging" of a torpedo seeker will normally try to escape at top speed, but increasing the speed of the torpedo causes noisy water flow over the acoustic head. One way to get around this is to run a heavyweight torpedo out to the vicinity of the target at high speed (transit speed) and then carry out the final-attack phase at a speed low enough to make the active seeker effective. This solution was chosen for the US Navy’s Mk 48 and the Royal Navy Spearfish. As these HWT are wire guided the seeker can transmit target data back down the wire to the parents submarine fire control system. In effect it becomes an off board sensor, and incase the wire breaks the torpedo can be programmed to switch to home on seeker-data only. The maximum speed at which the sonar is usable has improved in recent years as a result of better signal processing and Dome shaping. A Torpedo acquisition range is set largely by its ping rate, while the aspect angle of the seeker defines the band depth which it "sees" at any moment.
Torpedoes with narrow depth-bands usually follows helical search path/patterns whereas those with broader depth bands will seek a greater volume at any fixed depth, usually following a Sinuous (snake like) pattern. Against surface targets passive seekers can be used, because the ship emit considerable noise from propellers and bow-waves, but is no longer considered good enough to home onto modern diesel-electric submarines (SSK) even when they are snorkeling and therefore making maximum noise. To improve detection it would be necessary to go to lower frequencies with long wavelengths, too long for torpedoes seeker, This reason led the US navy to believe that active seeking was the only way to counter SSK. Both active and passive seekers are limited to the higher frequencies and so have relative short ranges. Wire guidance is therefore necessary to extend the effective range by providing midcourse guidance .In its simplest form the wire provides a one way link to allow the torpedo to be corrected, but most modern torpedoes uses a two way wire to allow the torpedo to feed back its own data to the fire control system. This allows the operator to defeat countermeasures such as bubble screens or noisemakers.

Wake Homing and Nibbling

Wake Homing discovered over fifty years ago is still very effective against surface ship. In effect the Torpedo seeker looks Upward and the Rudder is set automatically to turn the torpedo through a Fixed Angle each time the torpedo crosses the wake of its target. This enables a torpedo to follow a sinuous track towards the ship (provided it enters the wake at an acute angle). It is relative simple for the seeker to determine the boundaries of the wake, which extends many lengths behind the target. A wake is difficult to simulate, so countermeasures relying on seduction are ineffective, this is the reason for the Navies showing so much interest in Hard Kill defense (which would be discussed later) against Torpedoes. "Wake-Nibbling" differs in that the seeker detects and follows the boundaries of the wake. It is claimed to be more efficient than Wake Homing because the torpedo expends less time and energy criss-crossing the wake. This technique is much difficult to achieve. Although comparatively old fashioned in technological terms. Pattern running is still used in some torpedoes as a means of attacking ships in a tight formation or in anchorage .The torpedo is turned to an adjustable Gyro Angle after leaving the tube allowing it to cross and re-cross among potential targets, but hit probability still depends on seeker performance (an older generation depends on random probability).
Let us examine the various Torpedoes [lightweight & Heavy Weights] manufactured by various Countries and used by the Navies around the world.

LWT (Light Weight Torpedoes)

Lightweight torpedoes require a change of emphasis in seeker design. To keep the weight down dimension must be restricted, so the seeker head must function in a narrower diameter. Most of the western Navies have followed the US navies lead in keeping the 324 mm diameter introduced with the Mk 44, which has been the standard for many years for many NATO countries. For e.g. South Africa have produced the A44 which is 324 mm in diameter.

Britain: As with heavyweights, the British produced their own light weight torpedoes the successor to the Mk 46, is the Stingray, Like the Mk50 {USA} its seeker selects the most vulnerable point of attack, The onboard computer selects the search mode (sinus or helical depending on the circumstances) and a continuous –wave or FM sonar pulse. Macron Underwater has extended the life of the Torpedo adding a digital corrector and a new processor to keep the Stingray Mod 1 effective until 2020. The Stingray is claimed to be particularly effective in shallow water and besides Britain has been bought by country like Thailand and Norway.

France: France initiated its own program to replace the US made Mk46 which happens to be the most widely used Torpedo including most Notably by the Pakistan Navy. France started development of LW Torpedo "Mourn" but this was aborted and was absorbed into the "MU 90 Impact" to meet the German and Italian requirement as well as for export.

Sweden: Lightweight developed & used by Sweden happens to be very different from that used by other Navies, in being wire-guided to defeat the very difficult acoustic condition in the Baltic and being 400mm in Diameter. The original Tap 42 series was replaced by the modular Tap 43 series, including the Tap 431/432 and the export variant Tp43XO. It introduced data programming at transmission an autopilot and a three-speed motor. The latest Tap 46 Grampus is capable of attacking deeper-diving submarines than previous marks. Development cost is being shared with Denmark.

United States: The successor to the Mk 44 was Honeywell’s Mk 46, designed to counter the higher performance of the then Soviet submarines. The major production version was the Mod 1,an active/passive weapon using a fixed-programming digital computer with an auto pilot, which could be reset with homing modes, initial search and ceiling-depths, search-patterns and course-heading. Initial depth was one of six options, depending on target course and speed. When launched by a surface ship the search ceiling was set at about 16 meters to prevent the Mk 46 from attacking its own ship. The Mk 46 Near-Term Improvement Program (Neartip), now known as Mod 5, involved so much upgrading that it is virtually a new torpedo. The upgrade included a new Sonar Transducer, Transmitter and Receiver, needed to detect submarines hulls coated with Anechoic tiles, It was given a slower but quieter approach-speed of 30 knots, giving it a range of about 15 Km, and the sonar transmitted coded pulses to improve the Signal-to-Noise ratio. Reverberation in shallow water has been reduced and signal processing improved to allow the Mod 5 to reject false targets. Alliant now offers Kits for converting older Mk46 to Mod 5 standard configuration. Which cost less than one-third of a new torpedo. The Mk 50 "Barracuda" lightweight was developed specifically to counter the threat from the "Alpha" class SSN, and hence its emphasis is on speed and deep diving. But it is Known to search at "Reduced" speed, suggesting it is a dual –speed weapon, and it homes actively at a claimed range twice that of the Mk 46. Unofficially its seeker is credited with frequency-modulated (FM) pulses and an output of 25 kHz from two digital signal-processors. It has the same envelope as the Mk 46 (324 diameter), but can be programmed to attack the most vulnerable part of the target, the control room.

India: India uses both Western and Russian built LWT in its submarines and ships, while the Whitehead A244 which is used by the Indian Navy on the Godavari class Frigate as well as other Ships of its Class .An Air Launched variant of A244 is used by ASW planes. The A244 is an entirely Italian built concept. There is also an advanced variant of A244 called A244/S uses the Elsag AG70 Ciacio –S programmable triple frequency active/passive seeker with what are believed to be pre-formed beams and variable search-patterns. As such the A244S is the first such torpedo in its class to have a credible shallow water capability, It has a range of some 8Km at 33-35Knots and carries a shaped charge 33kg warhead. Shyena: It is the first indigenously designed Torpedo designed and built by the Naval Scientific & Technology Laboratory (NSTL). Though its design is heavily based on the Whitehead A244S but it is a new generation Torpedo and India being only the fifth country in the world to be capable of building such advanced Torpedo. It is a highly advanced State of the art processor based torpedo. It incorporates solid state electronics, digital technology and has been equipped with an integrated Active/Passive sensor package for homing, Named after the bird Shyena which is Known for its swift dive into waters to catch its prey, these Torpedoes can either be launched form Air or from the Ship. NSTL has faced an uphill task of developing a torpedo that could sustain its efficiency, in particularly the maneuverability and structural integrity while traveling from air medium to water medium.

HWT (Heavy Weight Torpedoes)

Britain : The Spearfish Mod 1 has similar performance to Mk 48 Adcap(20 Km at 65 knots and over 40 Km at 29 knots ) but a compound of Hydrogen Ammonium Perchlorate(HAP) and Otto II( HAP-Otto)was chosen as the fuel ,with a Sundstrand turbine driving a shrouded pump-jet. The Spearfish like the Adacp is required to have an under-ice capability ,but ironically the first torpedo in NATO with such capability was the Spearfish’s elderly predecessor , the Tigerfish Mk 24 Mod 2 . Some years a trial involving a US Navy SSN and one from Royal Navy at the North Pole showed that the Tigerfish could function under the Polar icecap , where as the Adcap failed .

Germany :STN Atlas Elektronik has its own range of advanced heavy weights . The DM2A3 Seehecht is an upgrade of older-generation seal and Seeschlange weapons with an improved seeker and reduced self-noise. It uses an Alenia three dimensional seeker , a new two way wire guidance system and a new course-attitude reference Gyro (maintaining depth by means of pressure cell).Its export variant is Known as Seahake. The successor is DM2A4 also known as Seahake Mod 1 with upgraded propulsion and probably wake Homing . It will arm the Type 212 submarines and is being promoted as a basis for a new "Euro" heavyweight to replace the current weapons in the French ,Germany and Italian Navies ,Certainly the development cost of modern Torpedo rival those of missiles.

Sweden : Bofors Underwater system remains faithful to HTP as thermal fuel ,claming over more than 15,000 runs without accident but the Tp 61 series is being replaced by the Tp 62,also known as the Tp 2000 or T96 . This uses an Advanced 7-cylinder axial piston semi-closed cycle swash plate engine with twin sinusoidal cam, driving a pump jet . The Tp 62 is in production and it is estimated that the Royal Swedish Navy alone will require 600 by 2003,while Denmark and Norway are likely customers. There is one school of thought that argues that the battery technology has advanced to the point where it produces performance rivaling that of thermal propulsion system . The French F17 Mod 2 uses a Saft Battery to drive it to 20Km at 40 Knots ,using a more powerful 85Kw motor .The German heavyweight also uses electric propulsion.

United States : The US Navy Mk 48 was the standard heavyweight from the early 1970 using a Gould (formerly Clevite) swashplate piston engine running on Otto II . To cope with Fast Deep Diving Soviet SSN an Advanced Capability(Adcap) was initiated at the end of the 1970 using a faster fuel rate to boost speed .Advances in electronics reduced the internal volume of the seeker sub-system and the space gained was used to provide more fuel , The Mk 48 Adcap has undergone constant improvement and 5 years ago its performance was claimed to be 65 Knots over a distance of 20Km although unofficial estimates credit it with a range of 30Km at 65knots or 50Km at 40 Knots . The US Navy has inventory of more than 2000 Mk 48 Adcaps ; Other users of Mk48 are Australia , Canada , the Netherlands and Turkey.

Russia : Even after the fall of Soviet Union ,little hard information has been released about the Russian Heavyweights , The Best Known and the Most feared once is the 65cm super-heavyweight ,a Wake Homer with a 500Kg warhead , sufficient to sink a large carrier ,Two version are known to exist the 65 to 73 and the 65 to 76 kit , both credited with a range of 50Km at a speed of 50 Knots or 100 Km at a speed of 30 Knots , The Russian also talk of the gas turbine driven DT model the DST-90,DST-92 and DST-96 with some what different characteristics but very little is Known about them. The Disadvantage of such a large Torpedoes ( estimated between 9 to 11 meters in length) is that they can be used in large submarines and require special handling ,For that reason the Russian Navy still uses the 53 cm weapon; the Project 671 RTM Victor III for example is armed with four 65 cm tubes and two 53cm tubes outboard, For Years the Russian claim of a rocket propelled torpedo were generally ridiculed in the West but it is now recognized that the VA-111 Shkval is a reality . It is a cone shaped rocket using some of its exhaust gas to form Super Cavitating bubble in which it runs . Originally designed for Nuclear warhead it is now offered in a variety of Non Nuclear form , capable of 200 Knots speed and range over about 10Km .Research is claimed to be underway to increase speed to 500 Knots ,but a follow on system is also reported, capable of searching at 60 Knots and having a transits speed of 300 Knots .

India : India is known to use HWT in all its Destroyers(Delhi, Rajput class ) as well as in its Kilo class Submarine , The Standard Wire Guided heavy weight used by the Russian and Indian Navy is the Test-71 and its Test-96( Test = Teleupravlyayannaya Torpedo or tele guided torpedo ) . The current version is the Test-71M and the Export version sold with Project 887 Kilo Type SSK is the Test-71ME, It searches at 24 Knots accelerating at 40 Knots in the Attack Phase and has a range of 15 to 20 km .Its seeker can be shut down to evade decoys . The Utest –71E is the Test-71ME with the Wake Homing added . The successor to the Test-71 is called the Ugst or Udwt and has a thermal engine running on a monopropellant ,similar to Mk 48 or Spearfish. India is also Know to be in the Process or Already has reverse engineered the Type-53cm Wake Homer Torpedoes with Ukranian/Russian help , The Type –53 cm is known to have a speed of more than 50 Knots and a range between 20-25Km .

Warheads

Older generation Torpedoes Acoustic Seekers homed on propeller cavitations and the relative small charge was calculated to be sufficient to disable a submarine . With SSBN it became clear that a crippled submarine must be able to launch her nuclear armed ballistic missile , and so the designers were told to investigate ways of sinking a submarine with a single shot or a total Mission Kill. The Soviet SSN and SSBN were also double hulled and there was a fear that conventional light charges would not be able to penetrate both sets of titanium.  For heavyweight’s the answer is to increase the weight of the charge(the Spearfish for example has a 300Kg charge),but the warhead must also hit in a lethal spot ;as a consequences guidance system program the Torpedo to hit Amidships; where it would be certain to destroy the command team ability to give any last minute orders. Lightweight are very sensitive to weight increase so a heavier charge is not an option, instead a shaped charge can do the job quite effectively if it hits the right spot.

Propulsion

For many years electric propulsion was favored for antisubmarine torpedoes - it generated very little noise and the technology was mature, although there was weight penalty. But the need for much higher speed forced designers to turn to thermal propulsion, High-Test Peroxide (HTP), Otto II fuel (nitrogen ester plus an Oxidant) and HAP-Otto being the most successful examples, For many years it was not known that the Swedish Torpedoes was of a very high performance. The Tp 61 series of wire guided heavyweights were a good 15 to 20 Knots faster than the contemporary US and British Torpedoes. The Mk 46 lightweight introduced a 5-cylinder swash plate engine running on Otto monopropellant, but the Mk 50 needed a much powerful propulsion unit to reach the higher speed required. The Stored Chemical Energy Power System (Sceps) uses a solid Block of lithium and a tank of sulphur hexaflouride which generates heat to create steam. Because the residue of solid ash occupies less volume than the reagents, it does not have to be jettisoned during the torpedo’s run. The displacement remains constant, so the engine does not have to fight increasing pressure while running at maximum depth. The Stingray was intended to have a Sceps plant as well, but this was cancelled in 1991 and it runs on a sea water battery .The Swedish Tp 45 and Tp 46 weapons are driven by a three-speed electric motor, whereas Eurotrop’s MU 90 Impact uses a variable speed motor designed by STN Atlas Elektronik.

Electric propulsion was favored by the designers due to the Maturity of Technology but had some drawbacks Like Weight penalty and the speed achieved too was not enough to defeat a Modern SSN or a Diesel Electric Submarine(SSN) so designers started to investigate the possibility of using a Thermal Propulsion(High-test peroxide(HTP) ,Otto II fuel (nitrogen ester plus an Oxidant) and HAP-Otto) . The main advantage of thermal Propulsion being able to provide the highest energy conversion Rates necessary for Long Endurance Mission and Increased Speed. Propulsion system based on Electro Chemical power sources such as Batteries ,Fuel Cell and Semi Fuel cells are likely to be less expensive to manufacture, Mechanically Recharge Batteries employing a Water reduction cathode reaction or a water augmented flowing Catholyte(semi fuel cells) could provide exceptional specific energy densities if high electrochemical efficiencies are realized. Besides the US the only other users of Thermal Propulsion are the British who have adopted a variant of the Otto-fuel concept for the Spear Fish , While Thermal Propulsion schemes still offer unmatched energy density levels, significant improvements being introduced in the sector of Electric Propulsion may change the overall future Panorama, Particularly important in this regard is the availability of new brushless electric motors that allow for steeples speed variation ,or of Thrystors- Controlled motors that offer the instantaneous choice between three different rotation speed , The first solution ( which also allow to get rid of the reduction gear , Thus Saving/Space weight and eliminating a major source of Noise) has been selected for the Italian A-184 while the second scheme has been adopted for the Swedish 43X2(Tp 45).More ever today’s technology offer previously unheard of power outputs. The new Ago/Zn( Silver Oxide/Zinc) batteries with circulation electrolyte cooling system can supply up to 40kWh( corresponding to a maximum speed of 45 Knots) i.e. nearly twice the figure for a traditional battery section of the same length (25kWh) ,while the latest Al/Ago( Aluminum/Silver Oxide) models offer some 70kWh that would allow speed of around 60 knots. The Mg/AgCl(Magnesium/Silver Chloride) batteries as adopted for the STINGRAY Mod 1 produce slightly lower but still highly attractive energy densities.   Thus the Modern Batteries and in particular Al/Ago models ,would thus seem to offer the best of both the world, combining as they do performance comparable with the Thermal Engines and many other advantages of their own. They also have a distinct advantage over Thermal Models in terms of Storage Risk and Life Cycle Cost , Finally in operational Terms thermal torpedoes always tend to leave a more or less noticeable wake which an alerted Target may detect.

As regard the Propulsion mechanisms, the Pump jet is nowadays the standard solution for LightWeight Torpedoes(LWT) while for Heavy Weight Torpedoes(HWT) the choice is between the Pump Jet and Counter Rotating Propellers. For example, the new 40 Knots A-184Mod3 is fitted with two counter rotating propellers with six and seven composite material skewed blades, respectively. This solution replaces the previous models more traditional scheme with two four blade propellers offer a Drastic reduction in noise level , A further derived version with 9 + 11 Blade propellers, is being studied for advance variant of the A-184 model, Advanced torpedoes is expected to allow for a speed of 50-55knots while maintaining sound within acceptable levels., Lower Noise levels and increased performance are also being obtained through the adoption of optimized Hydrodynamic profiles for both the front section and aft cones as well as introduction of special outer materials ( including the adoption of the so called "mammal skin" polymers ) that provide a form of control of the boundary layers and prevent and at least delay the onset of turbulence and micro-cavitation phenomena.

TORPEDO COUNTERMEASURES:

The World of Torpedo Countermeasures are more Sophisticated and Complex and has bought forward unimaginable Challenges and Complexity for defense against Torpedoes(for Submarines & Surface Vessel)
The Fact that very few countries has decent capability to develop an effective Torpedo defense( as compared to number of countries who have developed State of the art Torpedoes) and till date there is no single effective system deployed(both Hard Kill & Soft Kill) which can claim to be highly Effective, Compact & Integrated , against broad range of Torpedoes( Wake Homer, Active/Passive Homing, Straight Runners) gives weight to this argument. The primary means in any Anti-Torpedo defense measures is understandably enough to ascertain that ones own ship (surface vessel or submarine) is under torpedo attack ,This definitely demands 360* coverage, extremely low false alarm rate , highly automated function and a search range sufficiently large as to provide enough time for countermeasures to be implemented , Range is however ,dependent not only on the system characteristics but also on highly variable and often unpredictable factors such as ambient condition (particularly as regard to sound propagation ),ship speed and the torpedo radiated noise level. Torpedo search is normally carried out in passive mode ,listening for both highly characteristics noise of the torpedoes fast propellers( or pump-jet) and /or the emission of its active sonar(assuming that the torpedo is an active homer)

Submarine & Ship’s Threat Characteristics

Straight Runners: These HWT have no homing sensors ,are launched at Short to Medium ranges run in pre-designed patterns and don’t have re-attack capability. In terms of acoustic signatures ,they produce high level of radiated noise and are comparatively easy to attack ,Due to lack of intelligence in them they can only be countered by maneuvers or hard-kill defense.

Wake Homers(HWT): These torpedoes are intended to follow the wake of the target vessel and use this information for their closing-in procedures .Depending on detection ranges they are typically launched at medium range distances and can only be countered by course/speed changes ,loss of wake ,or by a hard-kill defense.

Acoustically Homing Torpedoes(HWT,LWT): These represent the majority of today’s modern torpedoes ,They are quite and difficult to detect when passive. Depending on the degree of sophistication they can utilize their own target information and easily overcome false target situation; they are capable of re-attack . When wire guided (which in essence is the case for HWT) they can be assisted by the launching platform in order to enhance attack performance .Torpedoes defense requires Soft-kill and or/ Hard-kill measures.

Submarine’s Defense Scenario Against Torpedoes:

Modern Light Weight Torpedoes like the MU-90, Stingray & Mk 50 are usually dropped from air platform like ASW Helicopter & Aircraft(MPA) in the vicinity of submarine usually some 100-150 meters away, Immediately after the drop the Torpedoes start their 3D search using active sonar and start commencing of the attack thereafter ,Upon target acquisition the LWT approaches the target at very high speed , and incase of the target loss ,has on board sophisticated signal processing algorithms and logic to reacquire the submarine . The Sub in order to avoid getting detected will sail at low speed and use its Passive sensors , Therefore Torpedo detection will be dependent on the relative Noise of the weapon and the active pulse of its attack sonar., Although the Sub will detect the Torpedo at splash the torpedo will not allow a reaction time of more than a minute , As far as HWT is concerned the Torpedo will be launched by another submarine at considerable large distance and will mostly approach in a silent passive mode , The Torpedo will switch to active mode only upon remotely controlled(for wire guided) or preset command or upon target acquisition ,Detection is once again difficult and will mostly occur at short distances ,Like any modern LWT the modern HWT can run at very high speed , has long endurance , is equipped with target acquisition/detection sensors that can operate in Passive/Active or in combined modes and even in wake homing modes and can use multi frequency beams for target classification and multi beam seekers for spatial discrimination . In addition many HWT are wire guided giving advantage in case the Target Sub tries to take defensive action or use countermeasures .

Decoys For Submarine:

Anti-Torpedoes defense for submarines is a substantial different problem . To start with the submarine ability to carry out evasive man oeuvres is sharply limited when compared to surface vessel; further and more fundamentally ,water viscosity prevents the use of long-range decoys for immediate deployment. Submarines can use decoys and jammers while no "Hard Kill" submarine launched anti-torpedo system appears to be under consideration . Some of the Available Decoys & Jammers are mentioned below ,without any pretension of completeness and mostly in order to provide of the technology involved .

a) WASS offer two different model of submarine launched anti-torpedo system, the C-303/S(127mm dia) and the 303(76mm dia) .The C-303 use a range of semi-stationary device (very low sinking) including both decoys(target simulator) and Jammers this has been developed in parallel to the already –mentioned C-309 system for surface vessel .The C-303/S adds a mobile target emulator based on the A200 mini torpedo design. Each decoy/jammed is accommodated inside an individual launch tube with compressed air bottle , and can be launched in either a manual or automatic mode.

b) The Royal Navy uses the SSDE (Submerged Signal and Decoy Ejector) system ,available in the Mk56(Swiftsure class) ,Mk8(Trafalgar class) and the Mk10(Vanguard class) version .Each boat has two reloadable ,multiple tube launchers that fire Type 2066(76 mm dia) and Type 2071(127mm dia) decoys also known as AMULET.

c) The standard US navy system ,installed on virtually all the submarine is based on Librascope 127mm dia. CSA Mk2 launchers ,which fire a large variety of Torpedo and anti-Sonar decoys. The range includes for instance the ADC Mk2 ,operational since late 70’s( this is a powered anti-torpedo decoy ,able to remain hovering at a pre-established depth while emitting signals) or the more advanced Mk3 version ,The Sea-Wolf class boats are schedule to have a much larger WLY-1 system capable of launching 16 Decoys. The Heavy Weights among US submarine launched decoys is indisputably the MOSS(Mobile Submarine Simulator).This is a full size (254mm dia) torpedo ,able to generate a strong underwater signature extremely similar to that of the submarine . The MOSS which first entered service in 1976 and has been progressively improved ,is deployed by both the SSBN(which have two dedicated launch tubes and 6 decoys)and the SSN .The latter normally carries four MOSS which are launched either through the Standard Torpedo Tubes or a Single Dedicated Tubes .

d) The Israeli SCUTTER self propelled torpedo decoy is also compatible with submarine use being launched through the standard signal ejector.

e) The Most Advanced Torpedo Countermeasures to be ever deployed on a conventional submarine will be onboard the Type 212 next generation submarine program for the German Navy is the TAU(Torpedo Abwehr Uboote),It will be based on the concept of a coordinated use of all countermeasures as available to the submarines namely Low Signatures features ,evasive maneuvers ,jammers and Decoys as well as on the principle that in order for the decoys to work properly ,the Torpedo sonar contact must be broken before hand through the use of jammers ,Further more ,given that multiple jammers/decoys are necessary to counter a torpedo’s re-attack capability small size and weight are mandatory. According ,TAU will use small underwater vehicles that can be pre-programmed immediately before launch to act either as jammers or decoys ,or even to change their working mode during the run .

f) Thomson-CSF of France produces two Target simulator under the names of TOSCA (a towed source/target) and CALAS(a torpedo like self-propelled target) both of which can also be used as anti-torpedo decoy.

Surface Vessel Defense Scenario Against Torpedoes:

The torpedo threat for surface vessel are HWT of all kind ,be they simple straight runners or the latest hi-tech products-some of them are wire guided such as the US torpedo Mk 48 ADCAP , the Italian torpedo A 184, the UK torpedo Spearfish , the German torpedo DM2 A3/A4 and of course the Russian torpedo USET 80(even used by the IN) , In recent years an addition type of torpedoes have caused concern- the "Wake Homing Torpedoes" it is a torpedo which approaches from astern by using the wake information ,it may also attack in salvos .HWT are typically launched from submarines at a large distance ( 10,000-15000 m) and if equipped with acoustic sensors –approach the Target ‘silently’ i.e. using sensors in passive mode , Upon detection modern HWT can and will make use of large variety of sensors and logic means to set up a very effective homing procedures which are also designed to defeat or overcome countermeasures .
Modern torpedoes are quite and radiate little noise , therefore ASW forces have to use active sonar for torpedo detection .Torpedo detection is difficult in general due to :
1) Large launching distance. 2) unfavorable sound propagation conditions in particular in littoral waters ,yielding torpedo detection ranges from ‘very large’ to ‘very short’ and high false alarm rates, 3) low torpedo detection probability.

As a torpedo defense system for surface ship has to cope with both long range as well as short range situations it is evident that there is not just one single defense solution but that a spectrum of defensive means are required , The situation calls for tiered-defense concept where a soft-kill approach is applied against long distance attacks and a hard kill solution takes care of the rest, But such layered defense system has its merits and demerits merits if the Soft Kill measure work effectively ,but there are many tactical situations where starting the defense with soft kill may prevent the initiation of a required hard Kill action in case the soft kill measures do not work .The reason is "Information Confusion" on board the monitoring platform which is directly linked to the fact that the soft-kill procedures make it extremely difficult for the evaluator to keep track of scenario ,in such case it would have been effective to ignore the soft kill option and just go for the Hard-Kill .

Surface Vessel Torpedo Countermeasures Requirement And Available Option’s.

The important factors for a torpedo defense from surface vessels are:

Early Torpedo Detection:
As the launching platform are submarines at large distance ,this translates into development of far reaching sensors that are designed to operate in the frequency domain in which the typical torpedoes noises is being observed ,Also 360* coverage is required which calls for sensor suit consisting of hull mounted sonar ,flank or/and towed arrays ,similar to submarine low acoustic signatures may be helpful .

A Fast And Qualified Threat Evaluator:
Utilization of available information , multi sensor integration is the key to early torpedo warning and subsequent torpedo alarm .The resulting actions –maneuvers and/or effector deployment are dependent on the knowledge of threat characteristics .In contrast to the submarine scenario ,in many cases a surface vessel has a chance to deploy more than one round of effectors ,this of course depends on range .At large detection ranges ,jammers positioned in the line of sight ,will break the acoustic contact with corresponding approaching torpedoes ;however incase of wire guided torpedoes or just straight runners they are of little value and the only chance for the vessel is to speed up and try to outrun the torpedo , If detected at shorter ranges the soft kill is of little value and only hard kill effectors can help out ,as of now no such effectors are available .

Soft Kill Option:

a) As regard Anti-Torpedo decoy ,the most wide spread Western system is by far the ubiquitous AN/SLQ-25 NIXIE ,NIXIE is a small noise making towed body and it works only against passive homing torpedoes by presenting them a false target more "attractive" than the true one was first deployed back in 70’s to replace the previous FANFARE, and has been progressively improved over the years, US carriers have the SLQ –36 system which in the current phase I configuration includes an Improved NIXE body and a magnetic countermeasures device that causes a torpedo’s proximity fuse to activate prematurely. The Phase II version is expected to add a dedicated jammed to counter a wake homing torpedoes as well as a towed torpedo alarm sensor,

b) The Royal Navy deploys its on system the Grasbey Type 182 .This is relatively large(533mm dia) towed decoy/jammed body ,which works both by simulating the ship-generation noise (in order to decoy passive homing torpedoes ) and by emitting sound signals very similar to those by a torpedo active homing heads, in order to saturate and jam it. The two modes can also operate simultaneously

c) Rafael of Israel has recently lifted the veil of secrecy around the indigenous ATC-1 system which has been operational for some time .The operating principle is described similar to NIXIE’S a towed body that transmits strong acoustic signals to create a false target for the Torpedo ;yet ATC-1 is officially presented by Rafael as being able to counter both passive and active acoustic Homing torpedoes ,which suggest that a jammed mode is present.

d) Russian ships are known to use a towed decoy system conceptually similar to NIXIE system although very little information is available about the system.

e)Surface vessel can further use a series of passive acoustic anti-torpedo countermeasures such as the well known MASKER and PRAIRIE system . These work by insufflating air through either a belt all along the quickwork (MASKER) or around the propellers (PRAIRIE) in order to create a gaseous curtain that will absorb and dampen the ship’s self generated noise , Such system must be used with prudence though because while they are very efficient in degrading the performance of passive sonar ( be they torpedo mounted or onboard the submarine) they are highly counter productive when facing an attack by active homers in that the air bubbles act as a powerful noise reflectors further increasing the strength of the signals reaching the active sonar .

f ) Thomson –CSF of France and Whitehead-Alenia has developed a sophisticated torpedo countermeasures system which was to be originally deployed on board the Horizon class frigate now will be deployed on the French Frigate is the SALT system (Systeme de Lutte Anti-Torpille) which is a France Italian co-operation .Salt includes three main modules ,namely a search module(ALERT),a threat evaluation module(RATO) and a counter measures module(CMAT), the system will be deployed on board the air-craft carrier(Charles De Gualle) and other major surface combatant of Italian and French navy . The Alert module includes a dedicated towed array as well as a standard hull-mounted cylindrical array, Its signals are passed down to RATO module, which decides whether or not they indicate the presence of attacking torpedoes and if necessary automatically activates countermeasures and evasive maneuvers. A fundamental tenant of the system is that the decoy positioning and evasive maneuvers should be carried out in a coordinated and integrated manner, not unlike the standard approach for seduction (centroid effect) in the field of anti-missile ECM, The CMAT modules is to include several different effectors families , In particular electro-acoustic decoys ,this family consist of the C-309 range of stationary jammers and stationary target simulators as well as the C-310 range of stationary jammers and mobile target simulators ,both developed by WASS. Also under development are a family of bubble decoys, it could be used to decoy or saturate wake homers ,It should be mentioned that the Russians are not alone in deploying wake homers( Type 65 and Type 53-65); France has now also started marketing a modified F-17 Torpedoes( also to be deployed on the PN new Agosta class sub) with Wake Homing circuits, As of now there is no counter measures against Wake Homers.

Hard Kill Option:

Hard Kill option are currently at sea only on Russian Ship, Currently the Russian Navy HWT hard kill capability is illustrated by two system ,the UDAV-1 and RBU-1000,Both the system tend to divert and destroy the incoming torpedo. The ASW team on board the Russian Destroyer would take acoustic information , determine the weapon position through triangulation and conduct a quick target motion analysis(TMA) ,They would then launch their Depth Bombs from the RBU-1000 into the path of the torpedo ,The goal being destruction ,but at least causing the torpedo to break homing lock thus allowing the ship time to escape before the torpedoes reacquire their target , A much more robust capability to destroy attacking weapons has been deployed with the UDAV-1 MLRS, The UDAV-1 has several payloads that are fired from a 10 barreled launcher with a maximum range of 3000 m. It launches acoustic decoys that seduces the incoming weapons away from the target and break its homing lock, . The acoustic decoys then draw the incoming weapon towards a drifting barrage of acoustically fused programmable depth bombs. These depth bombs would then detonate in an attempt to destroy the HWT. The UDAV-1 is integrated with the ship ASW system to determine the optimum placement of the decoys and hard kill weapons .The Russian system does has its drawback ,including command & control situational awareness ,and ship impact ,The footprint required for the UDAV-1 its rocket magazine and associated infrastructure would be considerable and at best could be deployed aboard large Surface Combatant, But is addressed partially by its inherent multipurpose capability in a 300mm rocket that can deploy ASW munitions if desired ,It does have some capability to defeat Straight Runners and even Wake Homers depending on its location and firing arc.

 

Currently Used Heavy Weight Torpedoes At A Glance:

Country : United States ; Torpedo : Mk48 Adcap ; Propulsion : Thermal ; Range/Speed(Knots) :30Km(65kts)/ 50Km(40Kts) ; Guidance: Wire Guided & Active/Passive Acoustic Homing .

Country : United Kingdom ; Torpedo : Spearfish ; Propulsion : Thermal ; Range/Speed(Knots) : 65Km(60Kts) ; Guidance: Wire Guided with Active/Passive Homing Head ;

Country : Sweden ; Torpedo : Tp 62(Torpedo-2000) ; Propulsion : Thermal ; Range/Speed(Knots) : 50Km+(45+Kts) ; Guidance: Wire Guided with Active/Passive Homing Head .

Country : Russia ; Torpedo :SET-65KE ; Propulsion : Thermal;
Range/Speed(Knots) : 50Km(60Kts)/ 100Km(30Kts) ; Guidance: Wake Homer.

Country : Republic OF Korea ; Torpedo : White Shark ; Propulsion : Battery/ Electric ; Range/Speed(Knots) : 30Km(40Kts) ; Guidance: Active/Passive Acoustic Homing.

Country : India ; Torpedo : Type 53cm(Reverse Engineered) ; Propulsion: Electric &/ Thermal ; Range/Speed(Knots) : 25Km(50Kts) ; Guidance: Wake Homer.

Country : Japan ; Torpedo : Type 89 ; Propulsion: Electric/ Battery(Ag/Zn) ; Range/Speed(Knots) : 30Km(70Kts) ; Guidance: Active/Passive ;

Country : Italy ; Torpedo : A 184 ; Propulsion: Battery/ Electrical(AgO/ Al) ; Range/Speed(Knots) : 50Km+(50 Kts+) ; Guidance: Active Passive Homing +Optic Fiber Wire Guidance .

Country : Germany ; Torpedo : DM2A4(Seehecht) ; Propulsion: Electric(Ag/Zn) ; Range/Speed(Knots) : 50Km(50Kts) ; Guidance: Wake Homer.

Country : France ; Torpedo : F 17P Mod 2 ; Propulsion: Electric/Battery ; Range/Speed(Knots) : 20Km(40Kts) ; Guidance: Wake Homer .


Currently Used Light Weight Torpedoes At A Glance:

Country : International ; Torpedo : MU 90 ; Propulsion: Battery(AgO/Al)( Pump Jet Propulsar) ; Range/Speed(Knots) : 15Km+(50Kts) ; Guidance: Active/Passive.

Country : Italy ; Torpedo : A/244S ; Propulsion: Battery ; Range/Speed(Knots) : 7Km+(33Kts) ; Guidance: Active/Passive.

Country : India ; Torpedo : Shyena ; Propulsion: Battery/ Electric ; Range/Speed(Knots) : 9-12Km(40Kts+) ; Guidance: Active/Passive.

Country : United States ; Torpedo : Mk 50(Barracudda) ; Propulsion: SCEPS ; Range/Speed(Knots) : 20Km+(40Kts+) ; Guidance: Active.

Country : United Kingdom ; Torpedo : Stingray Mod 1 ; Propulsion: Battery(Sea Water) ; Range/Speed(Knots) : N/K ; Guidance: Active/Passive.

Country : Sweden ; Torpedo : Tp 45 ; Propulsion: Battery ; Range/Speed(Knots) : N/K ; Guidance: Wire Guided(Active/Passive).

 

Copyright Bharat Rakshak