Depth Charges

A depth charge is an anti-submarine warfare 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 effective methods of attacking a submarine underwater. They were widely used in World War I and World War II. They remained part of the anti-submarine arsenals of many navies during the Cold War. Depth charges have now largely been replaced by anti-submarine homing torpedoes.

A depth charge fitted with a nuclear warhead is 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. All nuclear anti-submarine weapons were withdrawn from service by the United States, the United Kingdom, France, Russia, and China in or around 1990. They were replaced by conventional weapons whose accuracy and range had improved greatly as ASW technology improved.

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". Problems with the lanyards tangling and failing to function led to the development of a chemical pellet trigger as the "Type B". These were effective at a distance of around 20 ft (6.1 m).

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. 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). 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.

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