A depth charge is an anti-submarine warfare (ASW) weapon intended to destroy or cripple a 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 helicopters. In recent times, however, the depth charge has been nearly replaced by anti-submarine homing torpedoes.
Some depth charges have been fitted with nuclear warheads. These varieties of depth charge were designed to be dropped from a patrol plane or launched on a rocket from a surface ship, or perhaps another submarine, located a safe distance away. (See the ASROC weapon). This distance factor was necessary because of the extreme danger that a nuclear explosion, with its wide fall-out zone, presented.
However, all nuclear anti-submarine weapons were withdrawn from service by the navies of the United States, the United Kingdom, France, Russia, and China in or around 1990. They were supplanted by conventional weapons that boasted ever-increasing accuracy and range as ASW technology improved. Consequently, the subject of nuclear depth charges is now of mere historical interest.
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 the production of such a device 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 detonated 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.
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