Depth Charge - Delivery Mechanisms

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 was developed from a British Army trench mortar, 1277 were issued, 174 installed in auxiliaries during 1917 and 1918. The bombs they launched were too light to be truly effective; only one U-boat is known to have been sunk by them.

Thornycroft created an improved version able to throw a charge 40 yd (37 m). The first was fitted in July 1917 and became operational in August. In all, 351 TBDs and 100 other craft were equipped. Projectors called Y-guns (in reference to their basic shape), developed by the U.S. Navy's Bureau of Ordnance from the Thornycroft thrower, became available in 1918. Mounted on the centerline of the ship with the arms of the "Y" pointing outboard, two depth charges 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) over each side of the ship. The main disadvantage of the Y-gun is needed 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 24 November 1917.

The K-gun, standardized 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, 5 September 1939, a Royal Air Force Avro Anson of No. 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 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 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.