Depth charge Mark IX Depth Charge used by the U . S . Navy late in World War II . Unlike the cylindrical , barrel - shaped depth charge used earlier , the Mark IX is streamlined and equipped with canted fins to impart rotation on the depth charge , allowing it to fall in a straight trajectory with less chance of drifting off target . This type of depth charge contained 200 pounds ( 90 kg ) of Torpex . ] ] The depth charge is an anti - submarine warfare ( ASW ) weapon intended to destroy or cripple its 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 could be dropped by either surface ships , patrol planes , or from helicopter s . However , in modern times , the depth charge has been nearly replaced by anti - submarine homing torpedo es . Some depth charges had been designed to use nuclear warhead s - either dropped from a patrol plane or fired on a rocket from a surface ship or another submarine ( See the ASROC weapon ) . This was necessary because of the extreme danger that a nuclear explosion presented to the warship that fired the nuclear depth charge . The explosion had to be many miles away from the ship that fired it - and also from any friendly ship . However , all nuclear anti - submarine weapons were withdrawn from service by the navies of the United States , the United Kingdom , France , Russia , and China in about 1990 . Nuclear weapons were supplanted in this role by conventional weapons with their ever - increasing accuracy and range as ASW technology improved . Hence , the subject of nuclear depth charges is of historical interest only , and none of these was ever used in warfare , either . History . The concept of a " dropping mine " was first discussed in 1910 , and the idea was developed into practicality when the British Royal Navy ’ s Commander - in - Chief of the Home Fleets , Admiral Sir George Callaghan , requested its production in 1914 . The design work was carried out by Herbert Taylor at HMS " Vernon " Torpedo and Mine School in Portsmouth , England . The first effective depth charge , the " Type D " , became available in January 1916 . These were barrel - like casings containing a high explosive , usually TNT or amatol . There were initially two sizes — a 300 - pound ( 140 kg ) charge for fast ships and a 120 - pound ( 55 kg ) charge for ships too slow to clear the danger area of the more powerful charge . A hydrostatic pistol actuated by water pressure at a pre - selected depth detonate d the charge . Initial depth settings were 40 feet and 80 feet ( 12 and 24 meters . ) Anti - submarine vessels initially carried only two depth charges to be released from a chute at the stern of the ship . The first success was the sinking of SM U - 68 off Kerry , Ireland , on 22 March 1916 by the Q - ship " Farnborough . " Germany became aware of the depth charge following unsuccessful attacks on U - 67 on 15 April 1916 and U - 69 on 20 April 1916 . UC - 19 and UB - 29 were the only other submarines sunk by depth charge during 1916 . Numbers of depth charges carried per ship increased to 4 in June 1917 , to 6 in August , and to 30 or 40 by 1918 . Improved pistols allowed greater depth settings in 50 - foot ( 15 - meter ) increments to 200 feet ( 60 meters . ) Even the slower ships could safely use the 300 - pound depth charge at the greater depths , so the relatively ineffective 120 - pound depth charge was withdrawn from service . Monthly use of depth charges increased from 100 to 300 per month during 1917 to an average of 1745 per month during the last 6 months of World War I . The “ Type D ” could be detonated as deep as 300 feet ( 91 . 44 metres ) by that date . The depth charge was such a successful device that it attracted the attention of the United States , who requested full working drawings of the devices in March 1917 . Having received them , Commander Fullinwider of the U . S . Bureau of Naval Ordnance and U . S . Navy engineer Minkler made some modifications and then patented it in the U . S . It has been argued this was done to avoid paying the original inventor . The Royal Navy Type D depth charge was designated the Mark VII by 1939 . Initial sinking speed was 7 feet per second ( 2 . 1 m / s ) with a terminal velocity of 9 . 9 feet per second ( 3 m / s ) reached at a depth of 250 feet ( 76 m ) if rolled off the stern , or upon water contact from a depth charge thrower . Cast iron weights of 150 pounds ( 70 kg ) were attached to the Mark VII at the end of 1940 to increase sinking velocity to 16 . 8 feet per second ( 5 . 1 m / s ) . New hydrostatic fuzes increased the maximum detonation depth to 900 feet . The Mark VII ' s 290 pound ( 130 kg ) Amatol charge was estimated capable of splitting a 7 / 8 - inch ( 22 mm ) submarine pressure hull at a distance of 20 feet ( 6 . 1 m ) , and forcing the submarine to surface at twice that distance . Change of explosive to Torpex ( or Minol ) at the end of 1942 was estimated to increase those distances to 26 feet and 52 feet ( 7 . 9 m and 15 . 8 m ) . The British Mark X depth charge weighed 3000 pounds ( 1400 kg ) and was launched from 21 - inch ( 53 cm ) torpedo tube s of older destroyers to achieve a sinking velocity of 21 feet per second ( 6 . 4 m / s ) . The launching ship needed to clear the area at 11 knots to avoid damage , and the charge was seldom used . The tear - drop - shaped United States Mark 9 depth charge entered service in the spring of 1943 . The charge was 200 pounds ( 91 kg ) Torpex with a sinking speed of 14 . 4 feet per second ( 4 . 4 m / s ) and depth settings up to 600 feet . Later versions increased depth to 1000 feet ( 300 m ) and sinking speed was increased to 22 . 7 feet per second ( 6 . 9 m / s ) with increased weight and improved streamlining . Although the explosions of the standard United States 600 - pound ( 270 kg ) Mark 4 or Mark 7 depth charge used in World War II were nerve - wracking to the target , an undamaged U - boat ’ s pressure hull would not rupture unless the charge detonated closer than about five meters . Placing the weapon within this range was entirely a matter of chance and quite unlikely as the target maneuvered evasively during the attack . Most U - boats sunk by depth charges were destroyed by damage accumulated from a long barrage rather than by a single carefully - aimed attack . Many survived hundreds of depth charge detonations over a period of many hours ; U - 427 survived 678 depth charge blasts aimed at her in April 1945 , though many may have detonated a considerable distance from the target . Delivery mechanisms . The first delivery mechanism was to simply roll the " ashcans " off racks at the stern of the attacking vessel . Originally depth charges were simply placed at the top of a ramp and allowed to let roll . Improved racks , which could hold several depth charges and release them remotely with a trigger , were developed towards the end of the First World War . These racks remained in use throughout World War II , because they were simple and easy to reload . Some Royal Navy trawlers used for anti - submarine work during 1917 – 1918 had a thrower on the forecastle for a single depth charge , but there do not seem to be any records of it being used in action . Specialized depth charge projectors were developed to generate a wider dispersal pattern when used in conjunction with rack - deployed charges . The first of these projectors could throw a charge 40 yards ( 40 m ) and became operational in August 1917 . Projectors called Y - guns ( in reference to their basic shape ) became available in 1918 . Mounted on the centerline of the ship with the arms of the " Y " pointing towards the sides of the ship , a depth charge was cradled on a shuttle inserted into each arm . An explosive propellant charge was detonated in the vertical column of the Y - gun to propel a depth charge about 150 feet ( 50 meters ) over each side of the ship . The main disadvantage of the Y - gun is that it must be mounted on the centerline of a ship ' s deck , which may otherwise be occupied by superstructure , masts , or gun turrets . The K - gun , made standard in 1942 , replaced the Y - gun as the primary depth charge projector . K - guns could be mounted on the periphery of a ship ' s deck , thus freeing up valuable centerline space . The K - guns were often used together with stern racks to create patterns of six to ten charges . In all cases , the attacking ship needed to be moving above a certain speed or it would be damaged by the force of its own weapons . Depth - charges can also be dropped from an attacking aircraft against submarines . At the start of World War II , Britain ' s aerial anti - submarine weapon was the 100 lb ( 45 kg ) anti - submarine bomb . This weapon was too light and ultimately , a failure . Indeed , on September 5 , 1939 , a Royal Air Force Avro Anson of 233 squadron was destroyed when its own A / S bomb skipped off the surface of the water and detonated under the aircraft . To remedy the failure of this weapon , the Royal Navy ' s 450 lb ( 200 kg ) Mark VII depth charge was modified for aerial use by the addition of a streamlined nose fairing and stabilising fins on the tail . The first to use depth charges on airplanes in actual combat were the Finns , though . Experiencing the same problems as RAF with insufficient charges on anti - submarine bombs , Captain Birger Ek of Finnish Air Force squadron LeLv 6 contacted one of his Navy friends and suggested testing of using aerial use of standard Finnish Navy depth charges . The tests proved successful , and the Tupolev SB bombers of LeLv 6 were modified in early 1942 to carry depth charges . The success of the anti - submarine missions reached also the RAF Coastal Command , which promptly began modifying depth charges for aerial use . Later depth charges would be developed specifically for aerial use . Such weapons still have utility today and are in limited use , particularly for shallow - water situations where a homing torpedo may not be suitable . Depth charges are especially useful for " flushing the prey " in the event of a diesel submarine lying on the bottom or otherwise hiding , with all machinery shut down . Homing torpedoes can be used for the same purpose , but the cost is prohibitive and aircraft and shipboard inventories limited . An example of such a weapon is the BAE Systems Mark 11 , deployed by the British Fleet Air Arm . Effectiveness . The effective use of depth charges required the combined resources and skills of many individuals during an attack . Sonar , helm , depth charge crews and the movement of other ships had to be carefully coordinated . Aircraft depth charge tactics depended on the aircraft using it ' s speed to rapidly appear from over the horizon and surprising the sub on the surface ( where it spent most of its time ) during the day or night ( using radar to detect the target and a Leigh Light to illuminate just prior to the attack ) , then quickly attacking once it had been located , as the sub would normally crash dive to escape attack . As the Battle of the Atlantic wore on , British and Commonwealth forces became 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 . The shortcoming of the depth charge as deployed by surface ships was not the weapon itself , but how it was delivered . An attacking vessel would usually detect a submerged contact using its sonar ( or in British parlance , " ASDIC " ) . However , to drop its depth charges it had to pass over the contact to drop them over the stern . As such , sonar contact would be lost immediately prior to attack , thus rendering the hunter blind at the crucial moment . A skillful submarine commander therefore had an opportunity to take successful evasive action . This situation would be remedied by the adoption of the ahead - throwing weapon , allowing contacts to be engaged at a stand - off distance while still in sonar contact . Pacific theater . In the Pacific , Japanese depth charge attacks initially proved fairly unsuccessful against U . S . and British submarines . Unless caught in shallow water , a U . S . submarine commander could normally dive to a deeper depth in order to escape destruction . The deficiencies of Japanese depth - charge tactics were revealed in a 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 intelligence and operational briefings . Incredibly , May mentioned the highly sensitive fact that American submarines had a high survivability rate because Japanese depth charges were fuze d to explode at too shallow a depth . Various press associations sent this leaked news story over their wires , compounding the danger , and many newspapers ( including one in Honolulu , Hawaii ) published it . Soon , Japanese forces were resetting their depth charges to explode at a more effective average depth of 75 m ( 250 feet ) , to the detriment of American submariners . Vice Admiral Charles A . Lockwood , commander of the U . S . submarine fleet in the Pacific , later estimated that May ' s revelation cost the United States Navy as many as ten submarines and 800 seamen killed in action . Later developments . For the reasons expressed above , the depth charge was generally replaced as an anti - submarine weapon . Initially , this was by ahead - throwing weapons such as the British - developed Hedgehog and later Squid . These weapons threw a pattern of warheads ahead of the attacking vessel to bracket a submerged contact . Hedgehog was contact fuze d , while Squid fired a pattern of three large ( 200 kg ) depth - charges with clockwork detonators . Later developments included the Mark 24 " Fido " acoustic homing torpedo ( and later such weapons ) or the SUBROC , which was armed with a nuclear depth charge . The USSR , United States and United Kingdom developed anti - submarine weapons using nuclear warheads and these are sometimes referred to as Nuclear Depth Bomb s ( NDB ) . Underwater explosions . The high explosive in a depth charge undergoes a rapid chemical reaction at an approximate rate of 8 , 000 meters per second ( 25 , 000 ft / s ) . The gaseous products of that reaction momentarily occupy the volume previously occupied by the solid explosive , but at very high pressure . This pressure is the source of the damage and is proportional to the explosive density and the square of the detonation velocity . A depth charge gas bubble expands to reach the pressure of the surrounding water . This gas expansion propagates a shock wave . The density difference of the expanding gas bubble from the surrounding water causes the bubble to rise toward the surface . Unless the explosion is shallow enough to vent the gas bubble to the atmosphere during its initial expansion , the momentum of water moving away from the gas bubble will create a gaseous void of lower pressure than the surrounding water . Surrounding water pressure then collapses the gas bubble with inward momentum causing excess pressure within the gas bubble . Re - expansion of the gas bubble then propagates another potentially damaging shock wave . Cyclical expansion and contraction continues until the gas bubble vents to the atmosphere . Consequently , explosions where the depth charge is detonated at a shallow depth and the gas bubble vents into the atmosphere very soon after the detonation are quite ineffective , even though they are more dramatic and therefore preferred in movies . A sign of an effective detonation depth is that the surface just slightly rises and only after a while vents into a water burst . Very large depth charges , including nuclear weapons , may be detonated at sufficient depth to create multiple damaging shock waves . Very large depth charges may produce damage at distance where reflected shock waves from the ocean floor and / or ocean surface converge to amplify radial shock waves . Submarines or surface ships may be damaged if operating in convergence zones of their own depth charge detonations . The damage that an underwater explosion inflicts on a submarine comes from a primary and a secondary shock wave . The primary shock wave is the initial shock wave from the depth charge , and will cause damage to personnel and equipment inside the submarine if detonated close enough . The secondary shock wave is a result from the cyclical expansion and contraction of the gas bubble and will bend the submarine back and forth and cause catastrophic hull breach , in a way that can be best described as bending a plastic ruler back and forth until it snaps . Up to sixteen cycles of the secondary shock wave have been recorded in tests . The effect of the secondary shock wave can be reinforced if another depth charge detonates on the other side of the hull in a close proximity in time of the first detonation , which is why depth charges normally are launched in pairs with different pre - set detonation depths . The killing radius of a depth charge depends on the payload of the depth charge and the size and strength of the submarine hull . A depth charge of approximately 100 kg of TNT ( 4 MJ ) would normally have a killing radius ( hull breach ) of only against a conventional submarine , while the disablement radius ( where the submarine is not sunk but put out of commission ) would be approximately . A higher payload only increases the radius by a few meters due to the fact that the effect of an underwater explosion decreases with the distance cubed . The killing range would be greater against a larger submarine and shorter against a smaller submarine . It is doubtful if the hull of a midget submarine with a titanium hull could be sunk by a depth charge by anything less than a direct hit , even though it could be decommissioned with less .