Depth charge
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The depth charge is the oldest anti-submarine weapon. It is usually a cylindrically-shaped object packed with explosives and a fuse set to go off at a pre-determined depth. It was primarily used to destroy submerged submarines. Depth charges could be deployed by both ships and aircraft.
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[edit] History
The concept of a “dropping mine” was first discussed in 1910, and the idea was developed into practicality when the Royal Navy’s Commander in Chief, Admiral of the Fleet 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. The first effective depth charge, the “Type D”, developed in 1916, was a 300-pound (140 kg) barrel-like casing containing a high explosive, usually TNT. A “pistol” actuated by water pressure at a pre-selected depth detonated the charge. The “Type D” could be detonated as deep as 300 feet (100 meters).
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 US Bureau of Naval Ordnance and US Navy engineer Minkler made some modifications and then patented it in the US. It has been argued this was done to avoid paying the original inventor.
In 1943, Torpex, an explosive 50% more powerful than TNT, was introduced along with a more streamlined depth charge casing that sank faster. Although the explosions of the standard 600-pound 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 (if not all) of these may have actually detonated nowhere near the target.
[edit] 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.
Later, special depth-charge projectors called “Y-guns” were developed, which used an explosive propellant charge to hurl charges about 150 feet (50 meters) to the sides of the attacker. 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. The first depth charge “projectors” were called Y-guns; these were first produced in 1918. Y-guns allowed for a wider “spread” of depth charges to be deployed by ships. Y-guns were replaced by K-guns, which became the standard in 1942. The K-guns were often used together with stern racks to create patterns of six to ten charges. The attacking ship needed to be moving above a certain speed or it would be damaged by 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 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 Mark VII depth charge was modified for aerial use by the addition of a streamlined nose fairing and stabilising fins on the tail. 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 a diesel submarine is 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.
[edit] 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 upon location of the sub during the day and at night, 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 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.
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 avoiding 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.
[edit] Pacific Theatre
In the Pacific, Japanese depth charge attacks initially proved fairly unsuccessful against U.S. and Russian subs. 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. At the press conference, May revealed that American submarines had a high survivability rate because Japanese depth charges were fused 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), thoughtlessly published it. Soon, Japanese forces were resetting their depth charges to explode at a more effective average 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 United States Navy as many as ten submarines and 800 crewmen lost in action.[1]
[edit] 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 throw a pattern of warheads ahead of the attacking vessel to bracket a submerged contact. Hedgehog was contact fused, but Squid fired small depth-charges with hydrostatic arming. 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 Bombs (NDB).
[edit] See also
[edit] References
- ^ Blair Jr., Clay, Silent Victory: The US Submarine War against Japan, Annapolis, MD: Naval Institute Press, 2001
