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Depth charge

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US World War II Mark IX depth charge. Streamlined and equipped with fins to impart rotation, allowing it to fall in a straight trajectory with less chance of drifting off target. This depth charge contained 200 lb (91 kg) of Torpex.
US World War II Mark IX depth charge. Streamlined and equipped with fins to impart rotation, allowing it to fall in a straight trajectory with less chance of drifting off target. This depth charge contained 200 lb (91 kg) of Torpex.

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 hydraulic shock. Most depth charges use high explosive charges and a fuze set to detonate the charge, typically at a specific depth. Depth charges can be dropped by ships, patrol aircraft, and helicopters.

Depth charges were developed during World War I, and were one of the first viable methods of attacking a submarine underwater. They were widely used in World War I and World War II, and remained part of the anti-submarine arsenals of many navies during the Cold War, during which they were supplemented, and later largely replaced, by anti-submarine homing torpedoes.

The Mk 101 Lulu was a US nuclear depth bomb operational from 1958-1972
The Mk 101 Lulu was a US nuclear depth bomb operational from 1958-1972

A depth charge fitted with a nuclear warhead is also known as a "nuclear depth bomb". These were designed to be dropped from a patrol plane or deployed by an anti-submarine missile from a surface ship, or another submarine, located a safe distance away. By the late 1990s all nuclear anti-submarine weapons had been withdrawn from service by the United States, the United Kingdom, France, Russia and China. They have been replaced by conventional weapons whose accuracy and range had improved greatly as ASW technology improved.

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Anti-submarine warfare

Anti-submarine warfare

Anti-submarine warfare 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 typically carried out to protect friendly shipping and coastal facilities from submarine attacks and to overcome blockades.

Shock factor

Shock factor

Shock factor is a commonly used figure of merit for estimating the amount of shock experienced by a naval target from an underwater explosion as a function of explosive charge weight, slant range, and depression angle.

Explosive

Explosive

An explosive is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An explosive charge is a measured quantity of explosive material, which may either be composed solely of one ingredient or be a mixture containing at least two substances.

Fuze

Fuze

In military munitions, a fuze is the part of the device that initiates function. In some applications, such as torpedoes, a fuze may be identified by function as the exploder. The relative complexity of even the earliest fuze designs can be seen in cutaway diagrams.

Ship

Ship

A ship is a large watercraft that travels the world's oceans and other sufficiently deep waterways, carrying cargo or passengers, or in support of specialized missions, such as defense, research and fishing. Ships are generally distinguished from boats, based on size, shape, load capacity and purpose. Ships have supported exploration, trade, warfare, migration, colonization, and science. After the 15th century, new crops that had come from and to the Americas via the European seafarers significantly contributed to world population growth. Ship transport is responsible for the largest portion of world commerce.

Helicopter

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 allow helicopters to be used in congested or isolated areas where fixed-wing aircraft and many forms of short take-off and landing (STOL) or short take-off and vertical landing (STOVL) aircraft cannot perform without a runway.

Cold War

Cold War

The Cold War was 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 there was no large-scale fighting directly between the two superpowers, but they each supported opposing sides in major regional conflicts known as proxy wars. The conflict was based on the ideological and geopolitical struggle for global influence by these two superpowers, following their temporary alliance and victory against Nazi Germany and Imperial Japan in 1945. Aside from the nuclear arsenal development and conventional military deployment, the struggle for dominance was expressed via indirect means such as psychological warfare, propaganda campaigns, espionage, far-reaching embargoes, rivalry at sports events, and technological competitions such as the Space Race.

Nuclear depth bomb

Nuclear depth bomb

A nuclear depth bomb is the nuclear equivalent of a 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 arsenals at one point.

Anti-submarine missile

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 charge, or a homing torpedo that is carried from a launch ship, or other platform, to the vicinity of a target.

France

France

France, officially the French Republic, is a country located primarily in Western Europe. It also includes overseas regions and territories in the Americas and the Atlantic, Pacific and Indian Oceans, giving it one of the largest discontiguous exclusive economic zones in the world. Its metropolitan area extends from the Rhine to the Atlantic Ocean and from the Mediterranean Sea to the English Channel and the North Sea; overseas territories include French Guiana in South America, Saint Pierre and Miquelon in the North Atlantic, the French West Indies, and many islands in Oceania and the Indian Ocean. Its eighteen integral regions span a combined area of 643,801 km2 (248,573 sq mi) and had a total population of over 68 million as of January 2023. France is a unitary semi-presidential republic with its capital in Paris, the country's largest city and main cultural and commercial centre; other major urban areas include Marseille, Lyon, Toulouse, Lille, Bordeaux, and Nice.

Russia

Russia

Russia, or the Russian Federation, is a transcontinental country spanning Eastern Europe and Northern Asia. It is the largest country in the world encompassing one-eighth of Earth's inhabitable landmass. Russia extends across eleven time zones and shares land boundaries with fourteen countries. It is the world's ninth-most populous country and Europe's most populous country, with a population of over 147 million people. The country's capital and largest city is Moscow. Saint Petersburg is Russia's cultural centre and second-largest city. Other major urban areas include Novosibirsk, Yekaterinburg, Nizhny Novgorod, and Kazan.

China

China

China, officially the People's Republic of China (PRC), is a country in East Asia. It is the world's most populous country, with a population exceeding 1.4 billion, slightly ahead of India. China spans the equivalent of five time zones and borders fourteen countries by land, the most of any country in the world, tied with Russia. With an area of approximately 9.6 million square kilometres (3,700,000 sq mi), it is the world's third largest country by total land area. The country consists of 22 provinces, five autonomous regions, four municipalities, and two special administrative regions. The national capital is Beijing, and the most populous city and largest financial center is Shanghai.

History

Depth charges on USS Cassin Young (DD-793)

The first attempt to fire charges against submerged targets was with aircraft bombs attached to lanyards which triggered them. A similar idea was a 16 lb (7.3 kg) guncotton charge in a lanyarded can. Two of these lashed together became known as the "depth charge Type A".[1] Problems with the lanyards tangling and failing to function led to the development of a chemical pellet trigger as the "Type B".[2] These were effective at a distance of around 20 ft (6.1 m).[2]

A 1913 Royal Navy Torpedo School report described a device intended for countermining, a "dropping mine". At Admiral John Jellicoe's request, the standard Mark II mine was fitted with a hydrostatic pistol (developed in 1914 by Thomas Firth and Sons of Sheffield) preset for 45 ft (14 m) firing, to be launched from a stern platform. Weighing 1,150 lb (520 kg), and effective at 100 ft (30 m), the "cruiser mine" was a potential hazard to the dropping ship.[2] The design work was carried out by Herbert Taylor at the RN Torpedo and Mine School, HMS Vernon. The first effective depth charge, the Type D, became available in January 1916. It was a barrel-like casing containing a high explosive (usually TNT, but amatol was also used when TNT became scarce).[2] There were initially two sizes—Type D, with a 300 lb (140 kg) charge for fast ships, and Type D* with a 120 lb (54 kg) charge for ships too slow to leave the danger area before the more powerful charge detonated.[2][3]

A hydrostatic pistol actuated by water pressure at a pre-selected depth detonated the charge.[3] Initial depth settings were 40 or 80 ft (12 or 24 m).[3] Because production could not keep up with demand,[4] anti-submarine vessels initially carried only two depth charges, to be released from a chute at the stern of the ship.[3] The first success was the sinking of U-68 off Kerry, Ireland, on 22 March 1916, by the Q-ship Farnborough.[3] Germany became aware of the depth charge following unsuccessful attacks on U-67 on 15 April 1916, and U-69 on 20 April 1916.[3] The only other submarines sunk by depth charge during 1916 were UC-19 and UB-29.[3]

Numbers of depth charges carried per ship increased to four in June 1917, to six in August, and 30-50 by 1918.[4] The weight of charges and racks caused ship instability unless heavy guns and torpedo tubes were removed to compensate.[4] Improved pistols allowed greater depth settings in 50 ft (15 m) increments, from 50 to 200 ft (15 to 61 m).[2][5] Even slower ships could safely use the Type D at below 100 ft (30 m) and at 10 kn (19 km/h; 12 mph) or more,[4] so the relatively ineffective Type D* was withdrawn.[5] Monthly use of depth charges increased from 100 to 300 per month during 1917 to an average of 1745 per month during the last six months of World War I.[5] The Type D could be detonated as deep as 300 ft (91 m) by that date. By the war's end, 74,441 depth charges had been issued by the RN, and 16,451 fired, scoring 38 kills in all, and aiding in 140 more.[4]

Depth charge exploding after being released by HMS Ceylon
Depth charge exploding after being released by HMS Ceylon

The United States requested full working drawings of the device 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.[6] It has been argued that this was done to avoid paying the original inventor.[7][8]

The Royal Navy Type D depth charge was designated the "Mark VII" in 1939.[9] Initial sinking speed was 7 ft/s (2.1 m/s) with a terminal velocity of 9.9 ft/s (3.0 m/s) at a depth of 250 ft (76 m) if rolled off the stern, or upon water contact from a depth charge thrower.[9] Cast iron weights of 150 lb (68 kg) were attached to the Mark VII at the end of 1940 to increase sinking velocity to 16.8 ft/s (5.1 m/s).[9] New hydrostatic pistols increased the maximum detonation depth to 900 ft (270 m).[9] The Mark VII's 290 lb (130 kg) amatol charge was estimated to be capable of splitting a 78 in (22 mm) submarine pressure hull at a distance of 20 ft (6.1 m), and forcing the submarine to surface at twice that.[9] The change of explosive to Torpex (or Minol) at the end of 1942 was estimated to increase those distances to 26 and 52 ft (7.9 and 15.8 m).[9]

The British Mark X depth charge weighed 3,000 lb (1,400 kg) and was launched from the 21 in (530 mm) torpedo tubes of older destroyers to achieve a sinking velocity of 21 ft/s (6.4 m/s).[9] The launching ship needed to clear the area at 11 knots to avoid damage, and the charge was seldom used.[9] Only 32 were actually fired, and they were known to be troublesome.[10]

The teardrop-shaped United States Mark 9 depth charge entered service in the spring of 1943.[11] The charge was 200 lb (91 kg) of Torpex with a sinking speed of 14.4 ft/s (4.4 m/s) and depth settings of up to 600 ft (180 m).[11] Later versions increased depth to 1,000 ft (300 m) and sinking speed to 22.7 ft/s (6.9 m/s) with increased weight and improved streamlining.[11]

Although the explosions of the standard United States 600 lb (270 kg) Mark 4 and Mark 7 depth charge used in World War II were nerve-wracking to the target, a U-boat's pressure hull would not rupture unless the charge detonated within about 15 ft (4.6 m). Getting the weapon within this range was a matter of luck and quite unlikely as the target took evasive action. Most U-boats sunk by depth charges were destroyed by damage accumulated from an extended barrage rather than by a single charge and many survived hundreds of depth charges over a period of many hours, such as U-427 which survived 678 depth charges fired against it in April 1945.

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Demining

Demining

Demining or mine clearance is the process of removing land mines from an area. In military operations, the object is to rapidly clear a path through a minefield, and this is often done with devices such as mine plows and blast waves. By contrast, the goal of humanitarian demining is to remove all of the landmines to a given depth and make the land safe for human use. Specially trained dogs are also used to narrow down the search and verify that an area is cleared. Mechanical devices such as flails and excavators are sometimes used to clear mines.

HMS Vernon (shore establishment)

HMS Vernon (shore establishment)

HMS Vernon was a shore establishment or "stone frigate" of the Royal Navy in Portsmouth. Vernon was established on 26 April 1876 as the Royal Navy's Torpedo Branch also known as the Torpedo School, named after the ship HMS Vernon which served as part of its floating base. After the First World War, HMS Vernon moved ashore, taking over the Gunwharf site, where it continued to operate until 1 April 1996, when the various elements comprising the establishment were split up and moved to different commands.

Explosive

Explosive

An explosive is a reactive substance that contains a great amount of potential energy that can produce an explosion if released suddenly, usually accompanied by the production of light, heat, sound, and pressure. An explosive charge is a measured quantity of explosive material, which may either be composed solely of one ingredient or be a mixture containing at least two substances.

Amatol

Amatol

Amatol is a highly explosive material made from a mixture of TNT and ammonium nitrate. The British name originates from the words ammonium and toluene. Similar mixtures were known as Schneiderite in France. Amatol was used extensively during World War I and World War II, typically as an explosive in military weapons such as aircraft bombs, shells, depth charges, and naval mines. It was eventually replaced with alternative explosives such as Composition B, Torpex, and Tritonal.

SM U-68

SM U-68

SM U-68 was a Type U 66 submarine or U-boat for the German Imperial Navy during the First World War. She had been laid down in December 1913 as U-9 of the U-7 class for the Austro-Hungarian Navy but was sold to Germany, along with the others in her class, in November 1914. Under German control, the class became known as the U 66 type and the boats were renumbered; U-9 became U-68, and was redesigned and reconstructed to German specifications. She was launched in June 1915 and commissioned in August.

County Kerry

County Kerry

County Kerry is a county in Ireland. It is located in the South-West Region and forms part of the province of Munster. It is named after the Ciarraige who lived in part of the present county. The population of the county was 155,258 at the 2022 census,

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. The use of Q-ships contributed to the abandonment of cruiser rules restricting attacks on unarmed merchant ships and to the shift to unrestricted submarine warfare in the 20th century.

HMS Farnborough

HMS Farnborough

HMS Farnborough, also known as (Q-5), was a Q-ship of the British Royal Navy that saw service in the First World War. Farnborough was a heavily armed merchant ship with concealed weaponry that was designed to lure submarines into making surface attacks. Farnborough sank two submarines in her service in the First World War. The first submarine was SM U-68 which involved the first successful use of depth charges. The second submarine was SM U-83, which was sunk on 17 February 1917 in an action for which Captain Gordon Campbell of Farnborough received the Victoria Cross. HMS Farnborough was severely damaged in the action and was beached the same day.

SM U-67

SM U-67

SM U-67 was a Type U 66 submarine or U-boat for the German Imperial Navy during the First World War. She had been laid down in November 1913 as U-8 the second boat of the U-7 class for the Austro-Hungarian Navy but was sold to Germany, along with the others in her class, in November 1914.

SM U-69

SM U-69

SM U-69 was a Type U 66 submarine or U-boat for the German Imperial Navy during the First World War. She had been laid down in February 1914 as U-10 the fourth boat of the U-7 class for the Austro-Hungarian Navy but was sold to Germany, along with the others in her class, in November 1914.

SM UB-29

SM UB-29

SM UB-29 was a German Type UB II submarine or U-boat in the German Imperial Navy during World War I. The U-boat was ordered on 30 April 1915 and launched on 31 December 1915. She was commissioned into the German Imperial Navy on 18 January 1916 as SM UB-29.

HMS Ceylon (30)

HMS Ceylon (30)

HMS Ceylon was a Fiji-class light cruiser of the Royal Navy. She was of the Ceylon sub class, named after the island and British colony of Ceylon. The cruiser saw service in the Atlantic and Pacific theatres during the Second World War. In the postwar era, she participated in actions in Egypt and the Korean War. In 1960 she transferred to the navy of Peru and renamed Coronel Bolognesi. The cruiser was scrapped in 1985.

Delivery mechanisms

Loading a drum-type Mark VII depth charge onto a Flower-class corvette's K-gun
Loading a drum-type Mark VII depth charge onto a Flower-class corvette's K-gun
Y-gun depth charge thrower
Y-gun depth charge thrower

The first delivery mechanism was to simply roll the "ashcans" off racks at the stern of the moving attacking vessel. Originally depth charges were simply placed at the top of a ramp and allowed to 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 and 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.[5] Specialized depth charge throwers were developed to generate a wider dispersal pattern when used in conjunction with rack-deployed charges.[5] The first of these was developed from a British Army trench mortar,[12] 1277 were issued, 174 installed in auxiliaries during 1917 and 1918.[13][14] The bombs they launched were too light to be truly effective; only one U-boat is known to have been sunk by them.[13]

Thornycroft created an improved version able to throw a charge 40 yd (37 m).[13] The first was fitted in July 1917[13] and became operational in August.[5] In all, 351 torpedo boat destroyers and 100 other craft were equipped.[13] Projectors called "Y-guns" (in reference to their basic shape), developed by the U.S. Navy's Bureau of Ordnance from the Thornycroft thrower,[13] became available in 1918. Mounted on the centerline of the ship with the arms of the Y pointing outboard, two depth charges[13] were cradled on shuttles inserted into each arm. An explosive propellant charge was detonated in the vertical column of the Y-gun to propel a depth charge about 45 yd (41 m)[13] over each side of the ship. The main disadvantage of the Y-gun was that it had to be mounted on the centerline of a ship's deck, which could otherwise be occupied by superstructure, masts, or guns. The first were built by New London Ship and Engine Company beginning on 24 November 1917.[13]

The K-gun, standardized in 1942, replaced the Y-gun as the primary depth charge projector. The K-guns fired one depth charge at a time and could be mounted on the periphery of a ship's deck, thus freeing valuable centerline space. Four to eight K-guns were typically mounted per ship. 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 bombs hung under the wings of an RAF Short Sunderland flying boat
Depth bombs hung under the wings of an RAF Short Sunderland flying boat

Depth charges could also be dropped from an aircraft against submarines. At the start of World War II, Britain's primary aerial anti-submarine weapon was the 100 lb (45 kg) anti-submarine bomb but this was too light to be effective. To replace it, 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, which then entered service in 1941 as the Mark VII Airborne DC. Other designs would follow in 1942.

Experiencing the same problems as the RAF with ineffective anti-submarine bombs, Captain Birger Ek of Finnish Air Force squadron LeLv 6 contacted a navy friend to use Finnish Navy depth charges from aircraft which led to his unit's Tupolev SB bombers being modified in early 1942 to carry depth charges.[15]

Later depth charges would be developed specifically for aerial use. These are still useful today and remain in use, particularly for shallow-water situations where a homing torpedo may not be effective. Depth charges are especially useful for "flushing the prey" in the event of a diesel submarine hiding on the bottom.

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Flower-class corvette

Flower-class corvette

The Flower-class corvette was a British class of 294 corvettes used during World War II by the Allied navies particularly as anti-submarine convoy escorts in the Battle of the Atlantic. Royal Navy ships of this class were named after flowers.

Naval trawler

Naval trawler

Naval trawlers are vessels built along the lines of a fishing trawler but fitted out for naval purposes; they were widely used during the First and Second World Wars. Some—known in the Royal Navy as "Admiralty trawlers"— were purpose-built to naval specifications, others adapted from civilian use. Fishing trawlers were particularly suited for many naval requirements because they were robust vessels designed to work heavy trawls in all types of weather, and had large clear working decks. A minesweeper could be created by replacing the trawl with a mine sweep. Adding depth charge racks on the deck, ASDIC sonar below, and a 3-inch (76 mm) or 4-inch (102 mm) gun in the bow equipped the trawler for anti-submarine duties.

Forecastle

Forecastle

The forecastle is the upper deck of a sailing ship forward of the foremast, or, historically, the forward part of a ship with the sailors' living quarters. Related to the latter meaning is the phrase "before the mast" which denotes anything related to ordinary sailors, as opposed to a ship's officers.

British Army

British Army

The British Army is the principal land warfare force of the United Kingdom, a part of the British Armed Forces along with the Royal Navy and the Royal Air Force. As of 2022, the British Army comprises 79,380 regular full-time personnel, 4,090 Gurkhas, and 28,330 volunteer reserve personnel.

Thornycroft

Thornycroft

Thornycroft was an English vehicle manufacturer which built coaches, buses, and trucks from 1896 until 1977.

Bureau of Ordnance

Bureau of Ordnance

The Bureau of Ordnance (BuOrd) was a United States Navy organization, which was responsible for the procurement, storage, and deployment of all naval weapons, between the years 1862 and 1959.

New London Ship and Engine Company

New London Ship and Engine Company

The New London Ship and Engine Company (NELSECO) was established in Groton, Connecticut as a subsidiary of the Electric Boat Company to manufacture diesel engines.

Short Sunderland

Short Sunderland

The Short S.25 Sunderland is a British flying boat patrol bomber, developed and constructed by Short Brothers for the Royal Air Force (RAF). The aircraft took its service name from the town and port of Sunderland in North East England.

Birger Ek

Birger Ek

Rolf Birger Ek was a Finnish pilot and Mannerheim Cross Knight.

Finnish Air Force

Finnish Air Force

The Finnish Air Force is one of the branches of the Finnish Defence Forces. Its peacetime tasks are airspace surveillance, identification flights, and production of readiness formations for wartime conditions. The Finnish Air Force was founded on 6 March 1918.

Tupolev SB

Tupolev SB

The Tupolev ANT-40, also known by its service name Tupolev SB and development co-name TsAGI-40, was a high speed twin-engined three-seat monoplane bomber, first flown in 1934. The Tupolev design was advanced but lacked refinement, much to the dismay of crews, maintenance personnel, and Stalin, who pointed out that "there are no trivialities in aviation".

Torpedo

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, such a device was called an automotive, automobile, locomotive, or fish torpedo; colloquially a fish. The term torpedo originally applied to a variety of devices, most of which would today be called mines. From about 1900, torpedo has been used strictly to designate a self-propelled underwater explosive device.

Effectiveness

To be effective depth charges had to be set to the correct depth. To ensure this, a pattern of charges set to different depths would be laid atop the submarine's suspected position.
To be effective depth charges had to be set to the correct depth. To ensure this, a pattern of charges set to different depths would be laid atop the submarine's suspected position.

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 its speed to rapidly appear from over the horizon and surprising the submarine 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 submarine 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.

Surface ships usually used ASDIC (sonar) to detect submerged submarines. However, to deliver its depth charges a ship had to pass over the contact to drop them over the stern; sonar contact would be lost just before attack, rendering the hunter blind at the crucial moment. This gave a skillful submarine commander an opportunity to take evasive action. In 1942 the forward-throwing "hedgehog" mortar, which fired a spread salvo of bombs with contact fuzes at a "stand-off" distance while still in sonar contact, was introduced and proved to be effective.

Pacific theater and the May Incident

In the Pacific Theater during World War II, Japanese depth charge attacks were initially unsuccessful. Unless caught in shallow water, a submarine could dive below the Japanese depth charge attack. The Japanese were unaware that the submarines could dive so deep. The old United States S-class submarines (1918–1925) had a test depth of 200 ft (61 m) but the more modern Balao-class submarines (1943) could reach 400 ft (120 m).

In June 1943, the deficiencies of Japanese depth-charge tactics were revealed in a press conference held by U.S. Congressman Andrew J. May of the House Military Affairs Committee, who had visited the Pacific theater and received intelligence and operational briefings.[16][17]

Various press associations reported the depth issue. Soon, the Japanese were setting their depth charges to explode at a more effective average depth of 246 ft (75 m). 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.[18] The leak became known as The May Incident.

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Crash dive

Crash dive

A crash dive is a maneuver by a submarine in which the vessel submerges as quickly as possible to avoid attack. Crash diving from the surface to avoid attack has been largely rendered obsolete with the advent of nuclear-powered submarines, as they normally operate submerged. However, the crash dive is also a standard maneuver to avoid a collision.

Battle of the Atlantic

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 of Germany, announced the day after the declaration of war, and Germany's subsequent counter-blockade. The campaign peaked from mid-1940 through to the end of 1943.

Commonwealth of Nations

Commonwealth of Nations

The Commonwealth of Nations, simply referred to as the Commonwealth, is a political association of 56 member states, the vast majority of which are former territories of the British Empire. The chief institutions of the organisation are the Commonwealth Secretariat, which focuses on intergovernmental aspects, and the Commonwealth Foundation, which focuses on non-governmental relations among member states. Numerous organisations are associated with and operate within the Commonwealth.

Sonar

Sonar

Sonar is a technique that uses sound propagation to navigate, measure distances (ranging), communicate with or detect objects on or under the surface of the water, such as other vessels.

Hedgehog (weapon)

Hedgehog (weapon)

The Hedgehog was a forward-throwing anti-submarine weapon that was used primarily during the Second World War. The device, which was developed by the Royal Navy, fired up to 24 spigot mortars ahead of a ship when attacking a U-boat. It was deployed on convoy escort warships such as destroyers and corvettes to supplement the depth charges.

Pacific War

Pacific War

The Pacific War, sometimes called the Asia–Pacific War, was the theater of World War II that was fought in eastern Asia, the Pacific Ocean, the Indian Ocean, and Oceania. It was geographically the largest theater of the war, including the vast Pacific Ocean theater, the South West Pacific theater, the Second Sino-Japanese War, and the Soviet–Japanese War.

Submarine depth ratings

Submarine depth ratings

Depth ratings are primary design parameters and measures of a submarine's ability to operate underwater. The depths to which submarines can dive are limited by the strengths of their hulls.

Balao-class submarine

Balao-class submarine

The Balao class was a successful design of United States Navy submarine used during World War II, and with 120 boats completed, the largest class of submarines in the United States Navy. An improvement on the earlier Gato class, the boats had slight internal differences. The most significant improvement was the use of thicker, higher yield strength steel in the pressure hull skins and frames, which increased their test depth to 400 feet (120 m). Tang actually achieved a depth of 612 ft (187 m) during a test dive, and exceeded that test depth when taking on water in the forward torpedo room while evading a destroyer.

Andrew J. May

Andrew J. May

Andrew Jackson May 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 naval information that may have resulted in the loss of 10 American submarines and 800 sailors, and his subsequent unrelated conviction for bribery. May was a Democratic member of United States House of Representatives from Kentucky during the 72nd to 79th sessions of Congress.

United States House Committee on Armed Services

United States House Committee on Armed Services

The U.S. House Committee on Armed Services, commonly known as the House Armed Services Committee or HASC, is a standing committee of the United States House of Representatives. It is responsible for funding and oversight of the Department of Defense (DoD) and the United States Armed Forces, as well as substantial portions of the Department of Energy. Its regular legislative product is the National Defense Authorization Act, which has been passed by Congress and signed into law each year since 1962.

Charles A. Lockwood

Charles A. Lockwood

Charles Andrews Lockwood was a vice-admiral and flag officer of the United States Navy. He is known in submarine history as the commander of Submarine Force Pacific Fleet during World War II. He devised tactics for the effective use of submarines, making the members and elements of "silent service" key players in the Pacific victory.

Killed in action

Killed in action

Killed in action (KIA) is a casualty classification generally used by militaries to describe the deaths of their own personnel at the hands of enemy or hostile forces at the moment of action. The United States Department of Defense, for example, says that those declared KIA did not need to have fired their weapons, but only to have been killed due to hostile attack. KIAs include those killed by friendly fire in the midst of combat, but not from incidents such as accidental vehicle crashes, murder or other non-hostile events or terrorism. KIA can be applied both to front-line combat troops and to naval, air and support troops.

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 mortars. These weapons threw a pattern of warheads ahead of the attacking vessel to bracket a submerged contact. The Hedgehog was contact fuzed, while the 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), and the SUBROC, which was armed with a nuclear depth charge. The USSR, United States and United Kingdom developed nuclear depth bombs. As of 2018, the Royal Navy retains a depth charge labelled as Mk11 Mod 3, which can be deployed from its AgustaWestland Wildcat and Merlin HM.2 helicopters.[19][20]

Signaling

During the Cold War when it was necessary to inform submarines of the other side that they had been detected but without actually launching an attack, low-power "signalling depth charges" (also called "practice depth charges") were sometimes used, powerful enough to be detected when no other means of communication was possible, but not destructive.[21]

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Hedgehog (weapon)

Hedgehog (weapon)

The Hedgehog was a forward-throwing anti-submarine weapon that was used primarily during the Second World War. The device, which was developed by the Royal Navy, fired up to 24 spigot mortars ahead of a ship when attacking a U-boat. It was deployed on convoy escort warships such as destroyers and corvettes to supplement the depth charges.

Squid (weapon)

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.

Soviet Union

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 republics; in practice, both its government and its economy were highly centralized until its final years. It was a one-party state governed by the Communist Party of the Soviet Union, with the city of Moscow serving as its capital as well as that of its largest and most populous republic: the Russian SFSR. Other major cities included Leningrad, Kiev, Minsk, Tashkent, Alma-Ata, and Novosibirsk. It was the largest country in the world, covering over 22,402,200 square kilometres (8,649,500 sq mi) and spanning eleven time zones.

Nuclear depth bomb

Nuclear depth bomb

A nuclear depth bomb is the nuclear equivalent of a 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 arsenals at one point.

Royal Navy

Royal Navy

The Royal Navy (RN) is the United Kingdom's naval warfare force. Although warships were used by English and Scottish kings from the early medieval period, the first major maritime engagements were fought in the Hundred Years' War against France. The modern Royal Navy traces its origins to the early 16th century; the oldest of the UK's armed services, it is consequently known as the Senior Service.

AgustaWestland AW159 Wildcat

AgustaWestland AW159 Wildcat

The AgustaWestland AW159 Wildcat is a British military helicopter. It is an improved version of the Westland Super Lynx designed to serve in the battlefield utility, search and rescue and anti-surface warfare roles. In British service, common variants are being operated by both the Royal Navy and British Army, having replaced their Lynx Mk.7/8/9 predecessors. The AW159 has also been offered to several export customers, and has been ordered by the Republic of Korea Navy and the Philippine Navy.

AgustaWestland AW101

AgustaWestland AW101

The AgustaWestland AW101 is a medium-lift helicopter in military and civil use. First flown in 1987, it was developed by a joint venture between Westland Helicopters in the United Kingdom and Agusta in Italy in response to national requirements for a modern naval utility helicopter. Several operators, including the armed forces of Britain, Denmark, and Portugal, use the name Merlin for their AW101 aircraft. It is manufactured at factories in Yeovil, England, and Vergiate, Italy. Licensed assembly work has also taken place in Japan and the United States.

Cold War

Cold War

The Cold War was 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 there was no large-scale fighting directly between the two superpowers, but they each supported opposing sides in major regional conflicts known as proxy wars. The conflict was based on the ideological and geopolitical struggle for global influence by these two superpowers, following their temporary alliance and victory against Nazi Germany and Imperial Japan in 1945. Aside from the nuclear arsenal development and conventional military deployment, the struggle for dominance was expressed via indirect means such as psychological warfare, propaganda campaigns, espionage, far-reaching embargoes, rivalry at sports events, and technological competitions such as the Space Race.

Underwater explosions

USS Agerholm (DD-826) launches an ASROC anti-submarine rocket, armed with a nuclear depth bomb, during Dominic Swordfish (1962)
USS Agerholm (DD-826) launches an ASROC anti-submarine rocket, armed with a nuclear depth bomb, during Dominic Swordfish (1962)

The high explosive in a depth charge undergoes a rapid chemical reaction at an approximate rate of 8,000 m/s (26,000 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 equalize with the pressure of the surrounding water.[22]

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 can continue for several seconds until the gas bubble vents to the atmosphere.[22]

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. Such depth charges can also cause damage at longer distances, if reflected shock waves from the ocean floor or surface converge to amplify radial shock waves. Submarines or surface ships may be damaged if operating in the convergence zones of their own depth charge detonations.[22]

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 of 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 of 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 likened to bending a plastic ruler rapidly back and forth until it snaps. Up to sixteen cycles of secondary shock waves 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 close time proximity to the first detonation, which is why depth charges are normally launched in pairs with different pre-set detonation depths.

The killing radius of a depth charge depends on the depth of detonation, the payload of the depth charge and the size and strength of the submarine hull. A depth charge of approximately 220 lb (100 kg) of TNT (400 MJ) would normally have a killing radius (resulting in a hull breach) of only 9.8–13.1 ft (3–4 m) against a conventional 1000-ton submarine, while the disablement radius (where the submarine is not sunk but is put out of commission) would be approximately 26–33 ft (8–10 m). A larger payload increases the radius only slightly because the effect of an underwater explosion decreases as the cube of the distance to the target.

Source: "Depth charge", Wikipedia, Wikimedia Foundation, (2023, January 29th), https://en.wikipedia.org/wiki/Depth_charge.

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See also
Notes
  1. ^ McKee 1993, p. 46
  2. ^ a b c d e f McKee 1993, p. 49
  3. ^ a b c d e f g Tarrant 1989, p. 27
  4. ^ a b c d e McKee 1993, p. 50
  5. ^ a b c d e f Tarrant 1989, p. 40
  6. ^ US 1321428, Fullinwider, Simon P. & Minkler, Chester T., "Horn Mine", published 1919-11-17, assigned to United States Government 
  7. ^ Museum Discovers Unknown Inventor, Explosion – Museum of Naval Firepower, retrieved 29 September 2012
  8. ^ Prudames, David (20 August 2003), Inventor Of The Depth Charge Discovered At Explosion!, Brighton, UK: Culture24, archived from the original on 29 September 2012, retrieved 29 September 2012
  9. ^ a b c d e f g h Campbell 1985, p. 89
  10. ^ McKee 1993, p. 53
  11. ^ a b c Campbell 1985, p. 163
  12. ^ McKee 1993, p. 51
  13. ^ a b c d e f g h i McKee 1993, p. 52
  14. ^ McKee 1993, pp. 51–52
  15. ^ Karhunen 1980
  16. ^ Blair 2001, p. 397 May stated publicly that American submarines had a high survival rate in combat with Japanese destroyers because Japanese depth charges were fuzed to explode at too shallow a depth. To Admiral Edwards Lockwood wrote, "I hear ... Congressman May ... said the Jap depth charges ... are not set deep enough. ... He would be pleased to know the Japs set'em deeper now."
  17. ^ Kershaw 2008, p. 22
  18. ^ Blair 2001, p. 397
  19. ^ "815 NAVAL AIR SQUADRON" (PDF). Fleet Air Arm Association. 21 June 2018. Retrieved 21 June 2018.
  20. ^ Ministry of Defence (9 October 2014), Written answer 4.5.2.5 (Type 26 Frigate) to Defence Select Committee (PDF), parliament.uk, retrieved 21 June 2018
  21. ^ Grint, Keith (2005-01-20). Leadership: Limits and Possibilities. p. 43. ISBN 9781137070586.
  22. ^ a b c Jones 1978, pp. 50–55
References
External links
  • in re Hermans, 48 F.2d 386, 388 (Court of Customs and Patent Appeals April 15, 1931) ("Meanwhile, however, the Naval Torpedo Station at Newport had developed a type of hydrostatically operated depth charge, which appeared at least the equal of even the latest British design. This firing mechanism was mainly the work of the Bureau's engineer of mines and explosives, Mr. C. T. Minkler. ... The American and British depth charges differ in several main particulars. Ours fires by means of hydrostatic pressure, while the British utilize the seepage principle also.").
  • Depth Charges, Mark 6, Mark 6 Mod. 1, Mark 7, Mark 7, Mod. 1 - PART 2 illustration and operation of the pistol

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