Acoustic torpedo
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An acoustic torpedo is a
torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, and with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, su ...
that aims itself by listening for characteristic sounds of its target or by searching for it using
sonar Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigation, navigate, measure distances (ranging), communicate with or detect o ...
(
acoustic homing Acoustic homing is a system which uses the acoustic signature (sound) of a target to guide a moving object, such as a torpedo. Acoustic homing can be either passive or active in nature. Using passive homing, the system is designed to move either ...
). Acoustic torpedoes are usually designed for medium-range use, and often fired from a
submarine A submarine (or sub) is a watercraft capable of independent operation underwater. It differs from a submersible, which has more limited underwater capability. The term is also sometimes used historically or colloquially to refer to remotely op ...
. The first passive acoustic torpedoes were developed nearly simultaneously by the United States Navy and the Germans during
World War II World War II or the Second World War, often abbreviated as WWII or WW2, was a world war that lasted from 1939 to 1945. It involved the vast majority of the world's countries—including all of the great powers—forming two opposin ...
. The Germans developed the G7e/T4 Falke, which was first deployed by the submarines , and in March 1943. Few of these torpedoes were actually used and quickly phased out of service in favor of the T4's successor, the G7es T5 ''Zaunkönig'' torpedo in August 1943. The T5 first saw widespread use in September 1943 against North Atlantic escort vessels and
merchant ships A merchant ship, merchant vessel, trading vessel, or merchantman is a watercraft that transports cargo or carries passengers for hire. This is in contrast to pleasure craft, which are used for personal recreation, and naval ships, which are us ...
in convoys. On the Allied side, the
US Navy The United States Navy (USN) is the maritime service branch of the United States Armed Forces and one of the eight uniformed services of the United States. It is the largest and most powerful navy in the world, with the estimated tonnage of ...
developed the
Mark 24 mine The Mark 24 mine (also known as FIDO or Fido) is an air-dropped anti-submarine warfare weapon (ASW) incorporating passive acoustic homing system and torpedo integration. It was used by the United States, the British and Canadian forces during the ...
, which was actually an aircraft launched, anti-submarine passive acoustic homing torpedo. The first production Mk. 24s were delivered to the U.S. Navy in March 1943, and it scored its first verified combat kills in May 1943. About 204 torpedoes were launched against submarine targets, with 37
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submarines being sunk and a further 18 damaged. Since its introduction, the acoustic torpedo has proven to be an effective weapon against surface ships as well as serving as an
anti-submarine weapon An anti-submarine weapon (ASW) is any one of a number of devices that are intended to act against a submarine and its crew, to destroy (sink) the vessel or reduce its capability as a weapon of war. In its simplest sense, an anti-submarine weapo ...
. Today, ''acoustic torpedoes'' are mostly used against submarines.


Overview

Acoustic homing torpedoes are equipped with a pattern of acoustic transducers on the nose of the weapon. By a process of phase delaying the signals from these transducers a series of "acoustic beams" (i.e. a variation of acoustic signal sensitivity dependent on the incident angle of the noise energy). In early homing torpedoes the "beam patterns" were fixed whereas in more modern weapons the patterns were modifiable under on-board computer control. These sensor systems are capable of either detecting sound originating from the target itself i.e. engine and machinery noise, propeller cavitation, etc., known as passive sonar, or responding to noise energy reflections as a result of "illuminating" the target with sonar pulses, known as active sonar. Acoustic torpedoes can be compared to modern
fire-and-forget Fire-and-forget is a type of missile guidance which does not require further external intervention after launch such as illumination of the target or wire guidance, and can hit its target without the launcher being in line-of-sight of the targe ...
guided missiles In military terminology, a missile is a guided airborne ranged weapon capable of self-propelled flight usually by a jet engine or rocket motor. Missiles are thus also called guided missiles or guided rockets (when a previously unguided rocket i ...
. What this means is the enemy (most likely a submarine) will be detected by sonar in any direction it goes. The torpedo will start with passive sonar, simply trying to detect the submarine. Once the torpedo's passive sonar has detected something, it will switch over to an active sonar and will begin to track the target. At this point, the submarine has probably started evasive maneuvers and may have even deployed a noisemaker. The torpedo's logic circuitry, if not fooled by the noise maker, will home in on the noise signature of the target submarine. Before a torpedo is launched, the target must be "boxed in". A fire control system on the firing platform will set an initial search depth range which is passed to the weapon's microprocessor. The search parameters cover the expected depth of the target.


Operational use

The initial impact of the acoustic torpedo in the
Battle of the Atlantic The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the naval history of World War II. At its core was the Allied naval blockade ...
prior to the widespread deployment of counter-measures cannot be overstated. The German U-boats now had an effective "fire and forget" weapon capable of homing-in on attacking escorts and merchant ships and doing so in close quarters of only three or four hundred yards. By summer of 1943, the German U-boat campaign was experiencing severe setbacks in the face of massive anti-submarine efforts integrating Coastal Command attacks in the
Bay of Biscay The Bay of Biscay (), known in Spain as the Gulf of Biscay ( es, Golfo de Vizcaya, eu, Bizkaiko Golkoa), and in France and some border regions as the Gulf of Gascony (french: Golfe de Gascogne, oc, Golf de Gasconha, br, Pleg-mor Gwaskogn), ...
, the deployment of merchant aircraft carriers in convoys, new anti-submarine technologies such as
hedgehog A hedgehog is a spiny mammal of the subfamily Erinaceinae, in the eulipotyphlan family Erinaceidae. There are seventeen species of hedgehog in five genera found throughout parts of Europe, Asia, and Africa, and in New Zealand by introducti ...
and improved radar, and the use of dedicated hunter-killer escort groups. The Allies' improved escorts had greater range, and the use of fuelling at sea added hundreds of miles to the escort groups' radius of action. From June through August, 1943 the number of merchant ships sunk in the Atlantic was almost insignificant, while the number of U-boat kills rose disproportionally and caused a general withdrawal from the Bay of Biscay. For a time, the acoustic torpedo again put the escorts and convoys on the defensive, starting with the attacks in September, 1943 on
Convoys ONS 18/ON 202 ONS 18 and ON 202 were North Atlantic convoys of the ONS/ON series which ran during the battle of the Atlantic in World War II. They were the subject of a major U-boat attack in September 1943, the first battle in the ''Kriegsmarine''s autumn ...
.


Countermeasures


World War 2

The German T5 torpedoes were countered by Allied introduction of the
Foxer Foxer was the code name for a British built acoustic decoy used to confuse German acoustic homing torpedoes like the G7 torpedo during the Second World War. A US version codenamed FXR was deployed at the end of September 1943 on all transatlant ...
noise maker. ''Foxer'' was the code name for a
British British may refer to: Peoples, culture, and language * British people, nationals or natives of the United Kingdom, British Overseas Territories, and Crown Dependencies. ** Britishness, the British identity and common culture * British English, ...
built acoustic decoy used to confuse
German German(s) may refer to: * Germany (of or related to) ** Germania (historical use) * Germans, citizens of Germany, people of German ancestry, or native speakers of the German language ** For citizens of Germany, see also German nationality law **Ge ...
acoustic homing
torpedo A modern torpedo is an underwater ranged weapon launched above or below the water surface, self-propelled towards a target, and with an explosive warhead designed to detonate either on contact with or in proximity to the target. Historically, su ...
es. A US version codenamed FXR was deployed at the end of September 1943 on all transatlantic escort vessels but was soon replaced by the more effective
Fanfare A fanfare (or fanfarade or flourish) is a short musical flourish which is typically played by trumpets, French horns or other brass instruments, often accompanied by percussion. It is a "brief improvised introduction to an instrumental perfo ...
noisemaker. The device consisted of one or two noise-making devices towed several hundred metres astern of the ship. The noise makers mechanically generated a far louder
cavitation Cavitation is a phenomenon in which the static pressure of a liquid reduces to below the liquid's vapour pressure, leading to the formation of small vapor-filled cavities in the liquid. When subjected to higher pressure, these cavities, cal ...
noise than the ships propellers. This noise distracted the acoustic torpedoes away from the rear of the ship into a circling pattern around the noise maker until the torpedo ran out of fuel. The downside of the ''Foxer'' was that it also rendered the ship's own
ASDIC Sonar (sound navigation and ranging or sonic navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigate, measure distances (ranging), communicate with or detect objects on or ...
ineffective and concealed any other U-boat nearby that could home in on the convoy. Nevertheless, the FXR countermeasure proved to be highly effective in decoying German acoustic torpedoes. Of the c. 700 fired
G7es The G7es (T5) ''"Zaunkönig"'' ("wren") was a passive acoustic torpedo employed by German U-boats during World War II. It was called the GNAT (German Navy Acoustic Torpedo) by the British. Description The forerunner of the ''Zaunkönig'' was t ...
torpedoes about only 77 had found their aim. Aside from decoys, British analysts developed a maneuver known as "Step-Aside" in which a ship, upon spotting a U-boat, would trick the U-boat into firing its acoustic torpedo early, and then make a hard turn to put itself out of the torpedo's detection arc, after which it could then bear down on the U-boat to attack.


Postwar

The
AN/SLQ-25 Nixie The AN/SLQ-25 Nixie and its variants are towed torpedo decoys used on US and allied warships. It consists of a towed decoy device (TB-14A) and a shipboard signal generator. The decoy emits signals to draw a torpedo away from its intended targe ...
(and AN/SLQ-25A and variants) is a towed decoy deployed on USN and allied surface ships for defending against passive acoustic homing torpedoes. Another, more modern, such system is the AN/SLQ-61 Lightweight Tow (LWT) Torpedo Defense Mission Module (TDMM).


Captured technology

The capture of of 4 June 1944 marked the first time that allied forces gained access to this technology. In September 1944,
Russian commando frogmen The Russian commando frogmen (russian: Морской спецназ, Morskoy spetsnaz), informally called "frogmen" in civilian media, are a Russian Naval Spetsnaz unit under operational subordination to the Main Intelligence Directorate (GRU). ...
discovered T5 torpedoes aboard the German submarine '' U-250 , ''which had been sunk in shallow waters by the depth charges of the Soviet submarine chasers Mo 103 and Mo 105 off
Beryozovye Islands Beryozovye Islands (russian: Берёзовые острова, Finnish: Koivisto, Swedish: Björkö; literally: "Birch Islands"), alternatively spelled Berezovye Islands, is an island group in Leningrad Oblast, Russia. The islands are situated at ...
. Torpedoes were safely delivered to surface ships.The Type VIIIC boat U-250
List of All U-boats, uboat.net Key components of the G7es T-5 ''Zaunkönig'' torpedo were later ordered by
Joseph Stalin Joseph Vissarionovich Stalin (born Ioseb Besarionis dze Jughashvili; – 5 March 1953) was a Georgian revolutionary and Soviet political leader who led the Soviet Union from 1924 until his death in 1953. He held power as General Secreta ...
to be given to British naval specialists. However, after a protracted journey to
Kronstadt Kronstadt (russian: Кроншта́дт, Kronshtadt ), also spelled Kronshtadt, Cronstadt or Kronštádt (from german: link=no, Krone for "crown" and ''Stadt'' for "city") is a Russian port city in Kronshtadtsky District of the federal city of ...
the two
Royal Navy The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against F ...
officers were not allowed access to the submarine and returned home empty handed.


Military examples

;United States: *
RUR-5 ASROC The RUR-5 ASROC (for "Anti-Submarine Rocket") is an all-weather, all sea-conditions anti-submarine missile system. Developed by the United States Navy in the 1950s, it was deployed in the 1960s, updated in the 1990s, and eventually installed ...
- Ship-launched anti-submarine missile *
MK 48 The Mark 48 and its improved Advanced Capability (ADCAP) variant are American heavyweight submarine-launched torpedoes. They were designed to sink deep-diving nuclear-powered submarines and high-performance surface ships. History The Mark 48 w ...
- ADCAP submersion launch torpedo * MK 24 / MK 27 - Passive homing surface / submersible fire torpedo * MK 32 - Active homing surface / submersible / air fire torpedo


References


Bibliography

*Cutler, Thomas J. ''The Battle of Leyte Gulf''. New York: Simon and Schuster, 1996 *Clancy, Tom. ''Red Storm Rising''. New York: Penguin and Putnam, 1986 * * * * *{{cite book, last=Williamson, first=Gordon, title=U-boat Tactics in World War II, location=London, UK, publisher=Bloomsbury Publishing, year=2012, isbn=978-1849081740
ADM 199/2022 analysis of u-boat operations in the vicinity of convoys ONS 18 and ON 202


External links



German inventions of the Nazi period German inventions