Anti - submarine weapon An anti - submarine weapon 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 , missile or bomb that is optimized to destroy submarines . History . Before World War I . Prior to about 1890 , naval weapons were used only against surface shipping . With the rise of the military submarine 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 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 was desperate to defeat the German U - Boat threat against British merchant shipping . When the bombs that it employed were found to be ineffective it began equipping its destroyer s with simple depth charge 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 s and the use of cryptanalysis against intercepted radio messages . The airship ( " blimp " ) was used to drop bombs but fixed - wing aircraft were mostly used for reconnaissance . However the most effective countermeasure was the convoy . 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 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 ( ASDIC ) and radar 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 , anti - submarine weapons had been developed somewhat , but during that war , there was a renewal of all - out submarine warfare by Germany 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 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 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 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 , 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 , 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 , 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 aircraft and Magnetic Anomaly Detection ( 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 brought a new kind of conflict to submarine warfare . This war of development had both the United States and Soviet Union 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 . 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 ( ASuW ) capabilities of attack subs . 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 es were honed to target submarines more effectively and new anti - submarine missile 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 . Detection Equipment . 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 " in the First World War and by Bletchley Park 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 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 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 ( 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 . 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 , 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 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 is actually an array of spigot mortar 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 " after the name given a World War II 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 " fired three full - sized depth charges . A further development called " Limbo " 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 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 , 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 . 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 . 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 , the French Malafon , 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 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 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 .