Anti-submarine weapon

Anti-submarine weapon

Overview


An anti-submarine weapon is any one of a range of devices that are intended to act against a submarine, and its crew, to destroy (sink) the vessel or to destroy or reduce its capability as a weapon of war. In its simplest sense an anti-submarine weapon is a projectile
Projectile
A projectile is any object projected into space by the exertion of a force. Although a thrown baseball is technically a projectile too, the term more commonly refers to a weapon....

, missile
Missile
Though a missile may be any thrown or launched object, it colloquially almost always refers to a self-propelled guided weapon system.-Etymology:The word missile comes from the Latin verb mittere, meaning "to send"...

 or bomb
Bomb
A bomb is any of a range of explosive weapons that only rely on the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy...

 that is optimized to destroy submarines
Anti-submarine warfare
Anti-submarine warfare is a branch of naval warfare that uses surface warships, aircraft, or other submarines to find, track and deter, damage or destroy enemy submarines....

.

Prior to about 1890, naval weapons were used only against surface shipping.
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An anti-submarine weapon is any one of a range of devices that are intended to act against a submarine, and its crew, to destroy (sink) the vessel or to destroy or reduce its capability as a weapon of war. In its simplest sense an anti-submarine weapon is a projectile
Projectile
A projectile is any object projected into space by the exertion of a force. Although a thrown baseball is technically a projectile too, the term more commonly refers to a weapon....

, missile
Missile
Though a missile may be any thrown or launched object, it colloquially almost always refers to a self-propelled guided weapon system.-Etymology:The word missile comes from the Latin verb mittere, meaning "to send"...

 or bomb
Bomb
A bomb is any of a range of explosive weapons that only rely on the exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy...

 that is optimized to destroy submarines
Anti-submarine warfare
Anti-submarine warfare is a branch of naval warfare that uses surface warships, aircraft, or other submarines to find, track and deter, damage or destroy enemy submarines....

.

Before World War I


Prior to about 1890, naval weapons were used only against surface shipping. With the rise of the military submarine
Submarine
A submarine is a watercraft capable of independent operation below the surface of the water. It differs from a submersible, which has more limited underwater capability...

 after this time, countermeasures were considered for use against them. The first submarine installation of torpedo tubes was in 1885 and the first ship was sunk by a submarine-launched torpedo in 1887. There were only two ways of countering the military submarine initially, ramming them or sinking them with gunfire. However once they were submerged they were largely immune until they had to surface again. By the start of the First World War there were nearly 300 submarines in service with another 80 in the pipeline.

World War I


World War I
World War I
World War I , which was predominantly called the World War or the Great War from its occurrence until 1939, and the First World War or World War I thereafter, was a major war centred in Europe that began on 28 July 1914 and lasted until 11 November 1918...

 marked the first earnest conflict involving significant use of submarines and consequently marked the beginning of major efforts to counter that threat. In particular, the United Kingdom
United Kingdom
The United Kingdom of Great Britain and Northern IrelandIn the United Kingdom and Dependencies, other languages have been officially recognised as legitimate autochthonous languages under the European Charter for Regional or Minority Languages...

 was desperate to defeat the German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 U-Boat
U-boat
U-boat is the anglicized version of the German word U-Boot , itself an abbreviation of Unterseeboot , and refers to military submarines operated by Germany, particularly in World War I and World War II...

 threat against British merchant shipping. When the bombs that it employed were found to be ineffective it began equipping its destroyer
Destroyer
In naval terminology, a destroyer is a fast and maneuverable yet long-endurance warship intended to escort larger vessels in a fleet, convoy or battle group and defend them against smaller, powerful, short-range attackers. Destroyers, originally called torpedo-boat destroyers in 1892, evolved from...

s with simple depth charge
Depth charge
A depth charge is an anti-submarine warfare weapon intended to destroy or cripple a target submarine by the shock of exploding near it. Most use explosives and a fuze set to go off at a preselected depth in the ocean. Depth charges can be dropped by either surface ships, patrol aircraft, or from...

s
that could be dropped into the water around a suspected submarine's location. During this period it was found that explosions of these charges were more efficient if the charges were set to explode below or above the submarine. However many other techniques were used, including minefields, barrages and Q-ship
Q-ship
Q-ships, also known as Q-boats, Decoy Vessels, Special Service Ships, or Mystery Ships, were heavily armed merchant ships with concealed weaponry, designed to lure submarines into making surface attacks. This gave Q-ships the chance to open fire and sink them...

s and the use of cryptanalysis
Cryptanalysis
Cryptanalysis is the study of methods for obtaining the meaning of encrypted information, without access to the secret information that is normally required to do so. Typically, this involves knowing how the system works and finding a secret key...

 against intercepted radio messages. The airship
SS class blimp
SS class blimps were simple, cheap and easily assembled small non-rigid airships that were developed as a matter of some urgency to counter the German U-boat threat to British shipping during World War I...

 ("blimp") was used to drop bombs but fixed-wing aircraft were mostly used for reconnaissance. However the most effective countermeasure was the convoy
Convoy
A convoy is a group of vehicles, typically motor vehicles or ships, traveling together for mutual support and protection. Often, a convoy is organized with armed defensive support, though it may also be used in a non-military sense, for example when driving through remote areas.-Age of Sail:Naval...

. In 1918 U-boat losses became unbearably high. During the war a total of 178 U-boats were sunk :-

Mines 58,
Depth charges 30,
Gunfire 20,
Submarine torpedoes 20,
Ramming 19,
Unknown 19,
Accidents 7,
Other (including bombs) 2

British submarines operated in the Baltic, North Sea and Atlantic as well as the Mediterranean and Black Sea. Most of the losses were due to mines but two were torpedoed. French, Italian and Russian submarines were also destroyed.

Before the war ended, the need for forward-throwing weapons had been recognized by the British and trials began. Hydrophone
Hydrophone
A hydrophone is a microphone designed to be used underwater for recording or listening to underwater sound. Most hydrophones are based on a piezoelectric transducer that generates electricity when subjected to a pressure change...

s had been developed and were becoming effective as detection and location devices. Also, aircraft and airships had flown with depth bombs (aerial depth charges), albeit quite small ones with poor explosives. In addition, the specialist hunter-killer submarine had appeared, HMS R-1
British R class submarine
The R-class submarines were a class of 12 small British diesel-electric submarines built for the Royal Navy during World War I, and were forerunners of the modern hunter-killer submarines, in that they were designed specifically to attack and sink enemy submarines, their battery capacity and hull...

.

Inter-war


The main developments in this period were in detection, with both active sonar (ASDIC) and radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

 becoming effective. The British integrated the sonar with fire control and weapons to form an integrated system for warships. Germany was banned from having a submarine fleet but began construction in secret during the 1930s. When war broke out it had 21 submarines at sea.

In the inter-war period Britain and France had experimented with several novel types of submarine. New sonars and weapons were developed for them.

Atlantic/Mediterranean Theatre


By the time of World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

, anti-submarine weapons had been developed somewhat, but during that war, there was a renewal of all-out submarine warfare by Germany
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 as well as widespread use of submarines by most of the other combatants. The effective use of depth charges required the combined resources and skills of many individuals during an attack. Sonar information, helmsmen, depth charge crews and the movement of other ships had to be carefully coordinated in order to deliver a successful depth charge attack. As the Battle of the Atlantic wore on, British and Commonwealth forces in particular proved particularly adept at depth charge tactics, and formed some of the first destroyer hunter-killer groups to actively seek out and destroy German U-boats.
Air-dropped depth bombs were normally set to explode at a shallow depth, while the submarine was crash-diving to escape attack. Aircraft were very successful in not only attacking U-boats, but also in disrupting U-boats from carrying out attacks against ships. Some were fitted with a searchlight
Leigh light
The Leigh Light was a British World War II era anti-submarine device used in the Second Battle of the Atlantic.It was a powerful carbon arc searchlight of 24 inches diameter fitted to a number of the British Royal Air Force's Coastal Command patrol bombers to help them spot surfaced...

 as well as bombs.

A host of new anti-submarine weapons were developed. Forward-throwing anti-submarine mortars were introduced in 1942 to prevent loss of sonar contact. These mortars, the first being Hedgehog
Hedgehog (weapon)
The Hedgehog was an anti-submarine weapon developed by the Royal Navy during World War II, that was deployed on convoy escort warships such as destroyers to supplement the depth charge. The weapon worked by firing a number of small spigot mortar bombs from spiked fittings...

 fired a pattern of small depth charges. One type of charge was used to create entire patterns of explosions underwater
Underwater explosion
An underwater explosion, also known as an UNDEX, is an explosion beneath the surface of water. The type of explosion may be chemical or nuclear...

 around a potential enemy, while the second type was of round was fitted with contact detonators, meaning the warhead exploded only upon contact with the submarine. A later design enabled a pursuing destroyer or destroyer escort to maintain continual sonar contact until a definite 'hit' was achieved. Additionally, new weapons were designed for use by aircraft
Aircraft
An aircraft is a vehicle that is able to fly by gaining support from the air, or, in general, the atmosphere of a planet. An aircraft counters the force of gravity by using either static lift or by using the dynamic lift of an airfoil, or in a few cases the downward thrust from jet engines.Although...

, rapidly increasing their importance in fighting submarines. The development of the FIDO (Mk 24 mine)
Mark 24 FIDO Torpedo
The Mark 24 Mine was a US air-dropped passive acoustic homing anti-submarine torpedo used during the Second World War against German and Japanese submarines. It entered service in March 1943 and continued in service with the US Navy until 1948...

 anti-submarine homing torpedo in 1943 (which could be dropped from aircraft) was a significant contributor to the rising number of German sub sinkings.

Pacific Theater


Japan, the United States, Great Britain, The Netherlands, and Australia all employed anti-submarine forces in the Pacific Theater during World War II. Because the Japanese Navy tended to utilize its submarines against capital ships such as cruisers, battleships and aircraft carriers, U.S. and Allied anti-submarine efforts concentrated their work in support of fleet defense.

Early Japanese submarines were not very maneuverable under water, could not dive very deep, and lacked radar. Later in the war, Japanese submarines were fitted with radar scanning equipment for improved hunting while surfaced. However, these radar-equipped submarines were in some instances sunk due to the ability of U.S. radar receivers to detect their tell-tale scanning emissions. For example, sank three Japanese radar-equipped submarines in the span of four days. In 1944, U.S. anti-submarine forces began to employ the FIDO (Mk 24 mine) air-dropped homing torpedo against submerged Japanese subs with considerable success.

In contrast, Allied submarines were largely committed against Japanese merchant shipping. As a consequence, Japanese anti-submarine forces were forced to spread their efforts to defend the entirety of their merchant shipping lanes, not only to resupply their forces, but also to continue the necessary importation of war material to the Japanese home islands.

At first, Japanese anti-submarine defenses proved less than effective against U.S. submarines. Japanese sub detection gear was not as advanced as that of some other nations. The primary Japanese anti-submarine weapon for most of WWII was the depth charge, and Japanese depth charge attacks by its surface forces initially proved fairly unsuccessful against U.S. fleet submarines. Unless caught in shallow water, a U.S. submarine commander could normally dive to a deeper depth in order to escape destruction, sometimes using temperature gradient barriers to escape pursuit. Additionally, during the first part of the war, the Japanese tended to set their depth charges too shallow, unaware that U.S. submarines possessed the ability to dive beyond 150 feet.

Unfortunately, the deficiencies of Japanese depth-charge tactics were revealed in a June 1943 press conference held by U.S. Congressman Andrew J. May
Andrew J. May
Andrew Jackson May was a Kentucky attorney and influential New Deal-era politician, best known for his chairmanship of the House Military Affairs Committee during World War II, and his subsequent conviction for bribery...

, a member of the House Military Affairs Committee who had visited the Pacific theater and received many confidential intelligence and operational briefings. At the press conference, May revealed that American submarines had a high survivability because Japanese depth charges were fused to explode at too shallow a depth, typically 100 feet (because Japanese forces believed U.S. subs did not normally exceed this depth). Various press associations sent this story over their wires, and many newspapers, including one in Honolulu, thoughtlessly published it. Soon enemy depth charges were rearmed to explode at a more effective depth of 250 feet. Vice Admiral Charles A. Lockwood
Charles A. Lockwood
Charles Andrews Lockwood was an admiral of the United States Navy. He is known in submarine history as the legendary commander of Submarine Force Pacific Fleet during World War II...

, commander of the U.S. submarine fleet in the Pacific, later estimated that May's revelation cost the navy as many as ten submarines and 800 crewmen.

In addition to resetting their depth charges to deeper depths, Japanese anti-submarine forces also began employing autogyro
Autogyro
An autogyro , also known as gyroplane, gyrocopter, or rotaplane, is a type of rotorcraft which uses an unpowered rotor in autorotation to develop lift, and an engine-powered propeller, similar to that of a fixed-wing aircraft, to provide thrust...

 aircraft and Magnetic Anomaly Detection
Magnetic anomaly detector
A magnetic anomaly detector is an instrument used to detect minute variations in the Earth's magnetic field. The term refers specifically to magnetometers used by military forces to detect submarines ; the military MAD gear is a descendent of geomagnetic survey instruments used to search for...

 (MAD) equipment to sink U.S. subs, particularly those plying major shipping channels or operating near the home islands. Despite this onslaught, U.S. sub sinkings of Japanese shipping continued to increase at a furious rate as more U.S. subs deployed each month to the Pacific. By the end of the war, U.S. submarines had destroyed more Japanese shipping than all other weapons combined, including aircraft.

Post-war developments



The Cold War
Cold War
The Cold War was the continuing state from roughly 1946 to 1991 of political conflict, military tension, proxy wars, and economic competition between the Communist World—primarily the Soviet Union and its satellite states and allies—and the powers of the Western world, primarily the United States...

 brought a new kind of conflict to submarine warfare. This war of development had both the United States
United States
The United States of America is a federal constitutional republic comprising fifty states and a federal district...

 and Soviet Union
Soviet Union
The Soviet Union , officially the Union of Soviet Socialist Republics , was a constitutionally socialist state that existed in Eurasia between 1922 and 1991....

 racing to develop better, stealthier and more potent submarines while consequently developing better and more accurate anti-submarine weapons and new delivery platforms, including the helicopter
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...

.

Attack submarines (SSKs and SSNs) were developed to include faster, longer range and more discriminating torpedoes. This, coupled with improvements to sonar systems, made ballistic missile submarines more vulnerable to attack submarines and also increased the Anti-Surface Warfare
Anti-Surface Warfare
Anti-surface warfare is a type of naval warfare directed against surface combatants. More generally, it is any weapons, sensors, or operations intended to attack or limit the effectiveness of an adversary's surface ships....

 (ASuW) capabilities of attack subs. SSBNs themselves as well as cruise-missile submarines (SSGNs) were fitted with increasingly more accurate and longer range missiles and received the greatest noise reduction technology.
To counter this increasing threat torpedo
Torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...

es
were honed to target submarines more effectively and new anti-submarine missile
Anti-submarine missile
An anti-submarine missile is a standoff weapon including a rocket designed to rapidly deliver an explosive warhead or homing torpedo from the launch platform to the vicinity of a submarine.-History:...

s and rockets were developed to give ships a longer-range anti-submarine capability. Ships, submarines and Maritime Patrol Aircraft (MPA) also received increasingly effective technology for locating submarines, e.g. Magnetic Anomaly Detectors (MAD) and improved sonar.

Anti-Submarine Technology


Many concepts have been tried to come up with ways of attacking submarines. The first component of an Anti-submarine attack is detection: anti-sub weapons cannot be successfully employed without first locating the enemy submarine.

Optical Detection


The "Mark I Eyeball" was the first submarine detection method, and remains an important method of target confirmation. This may now be supplemented by thermal techniques. However, the low "indiscretion rate" of modern submarines means that optical detection is now less successful.

Radio Intercept


The use of the "wolf pack" by submarines in both the first and second World Wars allowed interception of radio signals. Though these were encrypted, they were broken by the British at "Room 40
Room 40
In the history of Cryptanalysis, Room 40 was the section in the Admiralty most identified with the British cryptoanalysis effort during the First World War.Room 40 was formed in October 1914, shortly after the start of the war...

" in the First World War and by Bletchley Park
Bletchley Park
Bletchley Park is an estate located in the town of Bletchley, in Buckinghamshire, England, which currently houses the National Museum of Computing...

 during the second. This allowed convoys to be diverted and hunter-killer groups to be targeted on the pack. Submarines now transmit using methods that are less susceptible to intercept.

Radar


Radar
Radar
Radar is an object-detection system which uses radio waves to determine the range, altitude, direction, or speed of objects. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, weather formations, and terrain. The radar dish or antenna transmits pulses of radio...

 was a prime tool in World War II for locating surfaced submarines. After development of the snorkel, and then of nuclear-powered submarines, submarines rarely surfaced outside their home port, rendering direct radar detection largely useless. However, it is possible that radar can detect the surface effects produced by a submarine.

Sonar


Since World War II, sonar
Sonar
Sonar is a technique that uses sound propagation to navigate, communicate with or detect other vessels...

 has emerged as the primary method of underwater detection of submarines. The most effective type has varied between active and passive, depending on the countermeasures taken by the submarine. Its versatility has increased with the development of air-dropped sonobuoys, which relay sonar signals to overhead aircraft, dipping sonar from helicopters and fixed long range systems.

Magnetic Anomaly Detection


A Magnetic Anomaly Detector
Magnetic anomaly detector
A magnetic anomaly detector is an instrument used to detect minute variations in the Earth's magnetic field. The term refers specifically to magnetometers used by military forces to detect submarines ; the military MAD gear is a descendent of geomagnetic survey instruments used to search for...

 (MAD) is an electronic magnetometer designed to measure magnetic field variations caused by large metal objects, such as the steel hull of a submarine. Before the development of sonar buoys, MAD gear was often installed in aircraft to pick up shallow-submerged submarines. It is still used today.

Other non-acoustic methods


Submarine detector loops were one of the first ways of finding the presence of an underwater submarine. The "sniffer" for detecting diesel exhausts was developed in the Second World War. More recently indirect methods of submarine detection have been tried, mainly via its wake.

Anti-submarine Weapons


Anti-submarine weapons can be divided into three categories according to their mode of operation: Guided weapons, Non-guided weapons and Rocket- and Mortar weapons.

Guided anti-submarine weapons, such as torpedoes, seek out the submarine, either via its own sensors or from the launching platform's sensors. The advantage with this type of weapon is that it requires a relatively small payload since it detonates in direct contact or within a very close proximity of the submarine. The disadvantage is that this type of weapon can be decoyed and is adversely affected by stealth features of the submarine.

Non-guided anti-submarine weapons, such as mines and depth charges, are "dumb" weapons that has to be carried to the submarine or that the submarine has to come in close proximity of. This is to some degree compensated by a heavy payload, in some mines exceeding half a metric ton, but since the effect of an underwater explosion decreases with a factor of the distance cubed, an increase in payload of a depth charge from 100 to 200 kg would not result in more than a few meters in killing radius.

Rocket- and mortar weapons, such as anti-submarine grenades and anti-submarine rockets, main advantage is the rapid response time since they are carried through the air to the target. Once dropped on top of the target, they also have the advantage of not being sensitive to decoys or stealth features. A hybrid of this category is the rocket launched torpedo, which is carried to the proximity of the target via a rocket and therefore reduces the response time and gives the submarine less time to undertake countermeasures or evasive maneuvers.

Finally, a submarine can of course also be destroyed by means of artillery fire and missiles in the rare case that a modern submarine surfaces, but these weapons are not specifically designed for submarines and their importance in modern anti-submarine warfare is very limited.

Guns/Missiles


Gunfire has been used to disable submarines from the First World War onwards, while a helicopter missile attack was used to disable the "Santa Fé" in the Falklands War.

Depth charge


Perhaps the simplest of the anti-submarine weapons, the depth charge
Depth charge
A depth charge is an anti-submarine warfare weapon intended to destroy or cripple a target submarine by the shock of exploding near it. Most use explosives and a fuze set to go off at a preselected depth in the ocean. Depth charges can be dropped by either surface ships, patrol aircraft, or from...

, is a large canister filled with explosives and set to explode at a predetermined depth. The concussive effects of the explosion could damage a submarine from a distance, though a depth charge explosion had to be very close to break the submarine's hull. Air-dropped depth charges were referred to as 'depth bombs'; these were sometimes fitted with an aerodynamic casing.

Surface-launched depth charges are typically used in a barrage
Barrage (artillery)
A barrage is a line or barrier of exploding artillery shells, created by the co-ordinated aiming of a large number of guns firing continuously. Its purpose is to deny or hamper enemy passage through the line of the barrage, to attack a linear position such as a line of trenches or to neutralize...

 manner in order to cause significant damage through continually battering the submarine with concussive blasts. Depth charges improved considerably since their first employment in World War I. To match improvements in submarine design, pressure-sensing mechanisms and explosives were improved during World War II to provide greater shock power and a charge that would reliably explode over a wide range of depth settings.

Aerial-launched depth bombs are dropped in twos and threes in pre-computed patterns, either from airplanes, helicopters, or blimps. Since aerial attacks normally resulted from surprising the submarine on the surface, air-dropped depth bombs were usually timed to explode at a shallow depth, while the sub was in the process of making a crash dive. In many cases destruction was not achieved, but the submarine was nonetheless forced to retire for repairs.

Early depth charges were designed to be rolled into the water off of the stern of a fast ship. The ship had to be moving fast enough to avoid the concussion of the depth charge blast. Later designs allowed the depth charge to be hurled some distance from the ship, allowing slower ships to operate them and for larger areas to be covered.

Today, depth charges not only can be dropped by aircraft or surface ships, but can also be carried by missiles to their target.

Anti-submarine mortar


With the discovery that depth charges rarely scored a kill by hitting a submarine, but instead were most effective in barrages, it was found that similar or better effects could be obtained by larger numbers of smaller explosions. The anti-submarine mortar
Anti-submarine mortar
Anti-submarine mortars are artillery pieces deployed on ships for the purpose of sinking submarines by a direct hit with a small explosive charge. They are often larger versions of the mortar used by infantry and fire a projectile in relatively the same manner...

 is actually an array of spigot mortars, designed to fire off a number of small explosives simultaneously and create an array of explosions around a submarine's position. These were often called Hedgehogs
Hedgehog (weapon)
The Hedgehog was an anti-submarine weapon developed by the Royal Navy during World War II, that was deployed on convoy escort warships such as destroyers to supplement the depth charge. The weapon worked by firing a number of small spigot mortar bombs from spiked fittings...

after the name given a World War II
World War II
World War II, or the Second World War , was a global conflict lasting from 1939 to 1945, involving most of the world's nations—including all of the great powers—eventually forming two opposing military alliances: the Allies and the Axis...

 British design. Later ASW mortar shells were fitted with impact detonators that fired only after actual contact with the hull of the submarine, allowing sonar crews to maintain a constant sound track until a hit was achieved.

The Hedgehog fired twenty four 14.5 kg charges whereas a later development called the "Squid
Squid (weapon)
Squid was a British World War II ship-mounted anti-submarine weapon. It consisted of a three-barrelled mortar which launched depth charges. It replaced the Hedgehog system, and was in turn replaced by the Limbo system....

" fired three full-sized depth charges. A further development called "Limbo
Limbo (weapon)
Limbo, or Anti Submarine Mortar Mark 10 , was the final British development of a forward-throwing anti-submarine weapon originally designed during the Second World War. Limbo, a three-barreled mortar similar to the earlier Squid that it superseded, was developed by the Admiralty Underwater Weapons...

" was used into the 1960s, and this used 94 kg charges.

A development of the Anti-submarine mortar, designed primarily for the exceptionally challenging task of littoral anti-submarine operations, utilizes a shaped charge warhead. An example of this is the Saab Dynamics ASW-600 and the upgraded ASW-601.

Torpedo



The early anti-submarine torpedo
Torpedo
The modern torpedo is a self-propelled missile weapon with an explosive warhead, launched above or below the water surface, propelled underwater towards a target, and designed to detonate either on contact with it or in proximity to it.The term torpedo was originally employed for...

es were straight-running types and usually a group was fired in case the target manoeuvred. They can be divided into two main types, the heavyweight, fired from submarines, and the lightweight which are fired from ships, dropped from aircraft (both fixed wing and helicopters) and delivered by rocket. Later ones used active/passive sonar homing and wire-guidance. Pattern running and wake-homing torpedoes have also been developed.

The first successful homing torpedo was introduced by the German Navy for use by its U-boat arm against Allied shipping. After capturing several of these weapons, along with independent research, the United States introduced the FIDO air-dropped homing torpedo (also called the Mark 24 'mine' as a cover) in 1943. FIDO was designed to breach the steel pressure hull of a submarine but not necessarily cause a catastrophic implosion, forcing the now-crippled submarine to surface where the submarine and crew might possibly be captured. After World War II, homing torpedoes became one of the primary anti-submarine weapons, used by most of the world's naval powers. Aircraft continued to be a primary launching platform, including the newly available helicopter
Helicopter
A helicopter is a type of rotorcraft in which lift and thrust are supplied by one or more engine-driven rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forwards, backwards, and laterally...

, though homing torpedoes can also be launched from surface ships or submarines. However, the torpedo's inherent limitations in speed of attack and detection by the target have led to the development of missile-borne anti-submarine weapons that can be delivered practically on top of the enemy submarine, such as ASROC
ASROC
ASROC 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 on over 200 USN surface ships, specifically cruisers, destroyers, and frigates...

.

On ships the torpedoes are generally launched from a triple-barreled launcher by compressed air. These may be mounted on deck or below. On submarines torpedoes have been carried externally as well as internally. The latter have been launched in the past by stern tubes as well as by the more normal forward ones.

Aircraft delivery platforms have included both unmanned helicopters, such as the US DASH, and manned ones such as British Westland Wasp
Westland Wasp
The Westland Wasp was a British small first-generation, gas-turbine powered, shipboard anti-submarine helicopter. Produced by Westland Helicopters, it came from the same P.531 programme as the British Army Westland Scout, and was based on the earlier piston-engined Saunders-Roe Skeeter...

. The helicopter may be solely a weapons carrier or it can have submarine detection capabilities.

Mine


Similar to those designed to defeat surface ships, mines can be laid to wait for an enemy submarine to pass by and then explode to cause concussive damage to the submarine. Some are mobile and upon detection they can move towards the submarine until within lethal range. There has even been development of mines that have the ability to launch an encapsulated torpedo at a detected submarine. Mines can be laid by submarines, ships, or aircraft.

Anti-submarine Rocket



One of the latest anti-submarine weapons, Anti-Submarine ROCkets (ASROCs), SUBROC, the Ikara
Ikara (missile)
The Ikara missile was an Australian ship-launched anti-submarine missile, named after an Australian Aboriginal word for "throwing stick". It launched an acoustic torpedo to a range of , allowing fast-reaction attacks against submarines at ranges that would otherwise require the launching ship to...

, the French Malafon
Malafon
Malafon was a French ship-launched anti-submarine missile system. Developed in the 1950s and 60s, the weapon was intended to take advantage of the greater detection ranges possible with towed sonar arrays. The missile entered service in 1966 and was manufactured by Groupe LatécoèreThe weapon is...

, and the Italian MILAS differ from other types of missiles in that instead of having a warhead which the missiles delivers to the target directly and explodes, they carry another anti-submarine weapon to a point of the surface where that weapon is dropped in the water to complete the attack. The missile itself launches from its platform and travels to the designated delivery point.

The major advantages of a missile are range and speed of attack. Torpedoes are not very fast compared to a missile, nor as long-ranged, and are much easier for a submarine to detect. Anti-sub missiles are usually delivered from surface vessels, offering the surface escort an all-weather, all-sea-conditions instant readiness weapon to attack time-urgent targets that no other delivery system can match for speed of response. They have the added advantage that they are under the direct control of the escort vessel's commander, and unlike air-delivered weapons cannot be diverted to other taskings, or be dependent on weather or maintenance availability. Aircraft-delivery can be further compromised by low-fuel-state, or an expended weapon load. The missile is always available, and at instant readiness. It allows the torpedo or Nuclear Depth Bomb
Nuclear Depth Bomb
A Nuclear Depth Bomb is the nuclear equivalent of the conventional depth charge and can be used in Anti-Submarine Warfare for attacking submerged submarines...

to enter the water practically on top of the submarine's position, minimizing the submarine's ability to detect and evade the attack. Missiles are also more rapid and accurate in many cases than helicopters or aircraft for dropping torpedoes and depth charges, with a typical interval of 1 to 1.5 minutes from a launch decision to torpedo splashdown. Helicopters frequently take much longer to just get off the escort's deck.

Weapon Control Systems


The readiness of weapons was at first determined manually. Early fire control consisted of range measurements and calculation of the submarines course and speed. The aiming point was then manually determined by rule. Later, mechanical computers were used to solve the fire control problem with electrical indication of weapon readiness. Today the weapon firing process is carried out by digital computer with elaborate displays of all relevant parameters.

ASW Countermeasures


The main countermeasure the submarine has is stealth, that it tries not to be detected. Against the ASW weapon itself, both active and passive countermeasures are used. The former may be a noise making jammer or a decoy providing a signal that looks like a submarine. Passive countermeasures may consist of coatings to minimise a torpedo's sonar reflections or an outer hull to provide a stand-off from its explosion. The Anti-submarine weapon has to overcome these countermeasures.

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