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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 weapon is usually a
projectile A projectile is an object that is propelled by the application of an external force and then moves freely under the influence of gravity and air resistance. Although any objects in motion through space are projectiles, they are commonly found in ...
,
missile 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 ...
or
bomb A bomb is an explosive weapon that uses the Exothermic process, exothermic reaction of an explosive material to provide an extremely sudden and violent release of energy. Detonations inflict damage principally through ground- and atmosphere-t ...
that is optimized to destroy submarines.


History


Before World War I

Prior to about 1890, naval weapons were only used against surface shipping. With the rise of the military
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 ...
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 production.


World War I

World War I World War I (28 July 1914 11 November 1918), often abbreviated as WWI, was one of the deadliest global conflicts in history. Belligerents included much of Europe, the Russian Empire, the United States, and the Ottoman Empire, with fightin ...
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 The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain, is a country in Europe, off the north-western coast of the continental mainland. It comprises England, Scotland, Wales and North ...
was desperate to defeat the
U-boat U-boats were naval submarines operated by Germany, particularly in the First and Second World Wars. Although at times they were efficient fleet weapons against enemy naval warships, they were most effectively used in an economic warfare role ...
threat against British
merchant shipping Maritime transport (or ocean transport) and hydraulic effluvial transport, or more generally waterborne transport, is the transport of people (passengers) or goods (cargo) via waterways. Freight transport by sea has been widely used throug ...
. When the bombs that it employed were found to be ineffective it began equipping its
destroyer In naval terminology, a destroyer is a fast, manoeuvrable, long-endurance warship intended to escort larger vessels in a fleet, convoy or battle group and defend them against powerful short range attackers. They were originally developed in ...
s with simple
depth charge A depth charge is an anti-submarine warfare (ASW) weapon. It is intended to destroy a submarine by being dropped into the water nearby and detonating, subjecting the target to a powerful and destructive Shock factor, hydraulic shock. Most depth ...
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-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 f ...
s and the use of
cryptanalysis Cryptanalysis (from the Greek ''kryptós'', "hidden", and ''analýein'', "to analyze") refers to the process of analyzing information systems in order to understand hidden aspects of the systems. Cryptanalysis is used to breach cryptographic sec ...
against intercepted radio messages. The
airship An airship or dirigible balloon is a type of aerostat or lighter-than-air aircraft that can navigate through the air under its own power. Aerostats gain their lift from a lifting gas that is less dense than the surrounding air. In early ...
("blimp") was used to drop bombs but fixed-wing aircraft were mostly used for reconnaissance. However, the most effective countermeasure was the
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 and can help maintain cohesion within a unit. It may also be used ...
. In 1918 U-boat losses became unbearably high. During the war a total of 178 U-boats were sunk, by the following causes: *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 A hydrophone ( grc, ὕδωρ + φωνή, , water + sound) 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 an electric potenti ...
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''.


Inter-war

The main developments in this period were in detection, with both
active 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 navigate, measure distances (ranging), communicate with or detect objects on or ...
(ASDIC) and
radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
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.


World War II


Atlantic/Mediterranean Theatre

By the time of
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 ...
, anti-submarine weapons had been developed somewhat, but during that war, there was a renewal of all-out submarine warfare by
Germany Germany,, officially the Federal Republic of Germany, is a country in Central Europe. It is the second most populous country in Europe after Russia, and the most populous member state of the European Union. Germany is situated betwe ...
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 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 ...
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 A searchlight (or spotlight) is an apparatus that combines an extremely bright source (traditionally a carbon arc lamp) with a mirrored parabolic reflector to project a powerful beam of light of approximately parallel rays in a particular direc ...
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 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 ...
, fired a pattern of small depth charges. One type of charge was used to create entire patterns of explosions underwater around a potential enemy, while the second type 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 An aircraft is a vehicle that is able to fly by gaining support from the air. It 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 ...
, rapidly increasing their importance in fighting submarines. The development of the FIDO (Mk 24 mine) 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 Jackson May (June 24, 1875 – September 6, 1959) was a Kentucky attorney, an influential New Deal-era politician, and chairman of the House Military Affairs Committee during World War II, infamous for his rash disclosure of classified nav ...
, 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 Andrews Lockwood (May 6, 1890 – June 6, 1967) was a vice-admiral and flag officer of the United States Navy. He is known in submarine history as the commander of ComSubPac, Submarine Force Pacific Fleet during World War II. He devised ...
, 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.. Lanning, Michael Lee (Lt. Col.), "Senseless Secrets: the failures of U.S. Military Intelligence, from George Washington to the present", Carol Publishing Group, 1995 In addition to resetting their depth charges to deeper depths, Japanese anti-submarine forces also began employing
autogyro An autogyro (from Greek and , "self-turning"), also known as a ''gyroplane'', is a type of rotorcraft that uses an unpowered rotor in free autorotation to develop lift. Forward thrust is provided independently, by an engine-driven propeller. Whi ...
aircraft and
Magnetic Anomaly Detection A magnetic anomaly detector (MAD) 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 (a mass of ferromagnetic material cr ...
(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 The Cold War is a term commonly used to refer to a period of geopolitical tension between the United States and the Soviet Union and their respective allies, the Western Bloc and the Eastern Bloc. The term '' cold war'' is used because the ...
brought a new kind of conflict to submarine warfare. This war of development had both the
United States The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country primarily located in North America. It consists of 50 states, a federal district, five major unincorporated territorie ...
and
Soviet Union The Soviet Union,. officially the Union of Soviet Socialist Republics. (USSR),. was a transcontinental country that spanned much of Eurasia from 1922 to 1991. A flagship communist state, it was nominally a federal union of fifteen national ...
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 A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...
. 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 (ASuW or ASUW) is the branch of naval warfare concerned with the suppression of surface combatants. More generally, it is any weapons, sensors, or operations intended to attack or limit the effectiveness of an adversary's su ...
(ASuW) capabilities of attack subs.
SSBN A ballistic missile submarine is a submarine capable of deploying submarine-launched ballistic missiles (SLBMs) with nuclear warheads. The United States Navy's hull classification symbols for ballistic missile submarines are SSB and SSBN – ...
s 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 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 were honed to target submarines more effectively and new
anti-submarine missile An anti-submarine missile is a standoff anti-submarine weapon. Often a variant of anti-ship missile designs, an anti-submarine systems typically use a jet or rocket engine, to deliver an explosive warhead aimed directly at a submarine, a depth ch ...
s and rockets were developed to give ships a longer-range anti-submarine capability. Ships, submarines and
maritime patrol aircraft A maritime patrol aircraft (MPA), also known as a patrol aircraft, maritime reconnaissance aircraft, or by the older American term patrol bomber, is a fixed-wing aircraft designed to operate for long durations over water in maritime patrol roles ...
(MPA) also received increasingly effective technology for locating submarines, e.g. magnetic anomaly detectors (MAD) and improved sonar.


Anti-submarine technology

The first component of an anti-submarine attack is detection: anti-sub weapons cannot be successfully employed without first locating the enemy submarine.


Detection equipment


Optical detection

Initial methods involved making visual contact with the submarine, 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, also known as 40 O.B. (old building; officially part of NID25), was the cryptanalysis section of the British Admiralty during the First World War. The group, which was formed in October 1914, began when Rear-Admiral Henry Oliver, the ...
" in the First World War and by
Bletchley Park Bletchley Park is an English country house and estate in Bletchley, Milton Keynes ( Buckinghamshire) that became the principal centre of Allied code-breaking during the Second World War. The mansion was constructed during the years following ...
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. In World War II, high frequency direction finding (HF/DF or "Huff-duff) was used by Allied escort vessels to detect submarines making position or sighting reports. The direction finding technology was not thought feasible for installation on a warship by the Kriegsmarine and they attributed successes of Huff-duff to radar technology of a performance that did not exist at the time. The standard escort tactic was to steer at speed in the direction of an HF/DF bearing until the target submarine was sighted (often visually, but sometimes on radar) and open fire before the submarine dived. If the submarine dived before being shelled, it could be hunted on sonar.


Radar

Radar Radar is a detection system that uses radio waves to determine the distance (''ranging''), angle, and radial velocity of objects relative to the site. It can be used to detect aircraft, ships, spacecraft, guided missiles, motor vehicles, w ...
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 (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 ...
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 A magnetic anomaly detector (MAD) 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 (a mass of ferromagnetic material crea ...
(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 Wake or The Wake may refer to: Culture *Wake (ceremony), a ritual which takes place during some funeral ceremonies *Wakes week, an English holiday tradition * Parish Wake, another name of the Welsh ', the fairs held on the local parish's patron s ...
.


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 as 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. The main advantage of rockets and mortar weapons, such as anti-submarine grenades and anti-submarine rockets, is their rapid response time as 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; this then reduces the response time and gives the submarine less time to undertake countermeasures or evasive maneuvers. Finally, a submarine can 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 Anti-submarine warfare (ASW, or in older form A/S) is a branch of underwater warfare that uses surface warships, aircraft, submarines, or other platforms, to find, track, and deter, damage, or destroy enemy submarines. Such operations are t ...
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. After the First World War, special ASW shells were developed for medium calibre naval guns.


Depth charge

Perhaps the simplest of the anti-submarine weapons, the
depth charge A depth charge is an anti-submarine warfare (ASW) weapon. It is intended to destroy a submarine by being dropped into the water nearby and detonating, subjecting the target to a powerful and destructive Shock factor, hydraulic shock. Most depth ...
, 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 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 submarine 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 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 t ...
is actually an array of
spigot mortar A mortar is usually a simple, lightweight, man-portable, muzzle-loaded weapon, consisting of a smooth-bore (although some models use a rifled barrel) metal tube fixed to a base plate (to spread out the recoil) with a lightweight bipod mount and a ...
s, 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 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 introduction ...
'' after the name given to a
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 ...
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 True squid are molluscs with an elongated soft body, large eyes, eight arms, and two tentacles in the superorder Decapodiformes, though many other molluscs within the broader Neocoleoidea are also called squid despite not strictly fitting t ...
" fired three full-sized depth charges. A further development called "
Limbo In Catholic theology, Limbo (Latin '' limbus'', edge or boundary, referring to the edge of Hell) is the afterlife condition of those who die in original sin without being assigned to the Hell of the Damned. Medieval theologians of Western Euro ...
" was used into the 1960s, and this used 94 kg charges. A development of the
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 t ...
, designed primarily for the exceptionally challenging task of
littoral The littoral zone or nearshore is the part of a sea, lake, or river that is close to the shore. In coastal ecology, the littoral zone includes the intertidal zone extending from the high water mark (which is rarely inundated), to coastal areas ...
anti-submarine operations, utilizes a shaped charge warhead. An example of this is the Saab Dynamics
Elma ASW-600 The Elma ASW-600 is an anti-submarine warfare system designed by the Saab Group and used by the Royal Swedish Navy. It is designated in Antiubåts-granatkastarsystemen 83 in Sweden, and was previously called the Elma LLS-920. History The ASW-600 ...
and the upgraded .


Torpedo

The early anti-submarine
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 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 Wake homing is a torpedo guidance technique based on the wake trajectory left behind a moving target. The torpedo is fired to cross behind the stern of the target ship, through the wake. As it does so, it uses sonar to look for changes in the ...
torpedoes have also been developed. The first successful homing torpedo was introduced by Nazi Germany's ''
Kriegsmarine The (, ) was the navy of Germany from 1935 to 1945. It superseded the Imperial German Navy of the German Empire (1871–1918) and the inter-war (1919–1935) of the Weimar Republic. The was one of three official branches, along with the a ...
'' for use by its
U-boat arm The (, ) was the navy of Germany from 1935 to 1945. It superseded the Imperial German Navy of the German Empire (1871–1918) and the inter-war (1919–1935) of the Weimar Republic. The was one of three official branches, along with the an ...
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 A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...
, 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 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 ...
. 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 The dash is a punctuation mark consisting of a long horizontal line. It is similar in appearance to the hyphen but is longer and sometimes higher from the baseline. The most common versions are the endash , generally longer than the hyphen b ...
, and manned ones such as British
Westland Wasp The Westland Wasp is a small 1960s British 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 is based on the earlier piston-e ...
. The helicopter may be solely a weapons carrier or it can have submarine detection capabilities.


Mine

Similar to
naval mine A naval mine is a self-contained explosive device placed in water to damage or destroy surface ships or submarines. Unlike depth charges, mines are deposited and left to wait until they are triggered by the approach of, or contact with, any ...
s 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 rockets and missiles

One of the latest anti-submarine weapons, Anti-Submarine ROCkets (ASROCs),
SUBROC The UUM-44 SUBROC (SUBmarine ROCket) was a type of submarine-launched rocket deployed by the United States Navy as an anti-submarine weapon. It carried a 250 kiloton thermonuclear warhead configured as a nuclear depth bomb. Development SUBROC ...
, the
Ikara Ikara is a town in Kaduna State, northern Nigeria, located around 75 kilometres north-east away from the city of Zaria. Ikara as a district consist of five towns which are Ikara, Tudun - wada, Nasarawa, Sabon - Gari, Jamfalan, Kurmin - Kogi, Hay ...
, the French
Malafon Malafon (MArine LAtécoère FONds) was a French ship-launched anti-submarine missile system. Developed in the 1950s and 1960s, the weapon was intended to take advantage of the greater detection ranges possible with towed sonar arrays. The missil ...
, and the Italian
MILAS Milas ( grc, Μύλασα, Mylasa) is an ancient city and the seat of the district of the same name in Muğla Province in southwestern Turkey. The city commands a region with an active economy and very rich in history and ancient remains, the ter ...
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
anti-submarine missile An anti-submarine missile is a standoff anti-submarine weapon. Often a variant of anti-ship missile designs, an anti-submarine systems typically use a jet or rocket engine, to deliver an explosive warhead aimed directly at a submarine, a depth ch ...
s 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 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. The Royal Navy, Soviet Navy, and United States Navy had nuclear depth bombs in their ...
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 submarine's 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; 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 minimize 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.


See also

*
Anti-submarine net An anti-submarine net or anti-submarine boom is a boom placed across the mouth of a harbour or a strait for protection against submarines. Examples of anti-submarine nets * Lake Macquarie anti-submarine boom *Indicator net * Naval operations in ...
*
Magnetic anomaly detector A magnetic anomaly detector (MAD) 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 (a mass of ferromagnetic material crea ...


References

{{reflist


Bibliography

*Blair, Clay, ''Silent Victory'' (Vol.1), The Naval Institute Press, 2001 *Lanning, Michael Lee (Lt. Col.), ''Senseless Secrets: The Failures of U.S. Military Intelligence from George Washington to the Present'', Carol Publishing Group, 1995 *Preston, Anthony, ''The World's Greatest Submarines", Greenwich Editions, 2005.


External links


Early British torpedoes

US Naval Weapons
Naval warfare Projectiles