Editing Depth charge (section)

==Effectiveness==
[[File:Depthcharge.gif|thumb|upright|To be effective depth charges had to explode at 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 (at night using radar to detect the target and a [[Leigh light]] to illuminate it immediately before  attacking), 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 of Nations|Commonwealth]] forces became particularly adept at depth charge tactics, and formed some of the first 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 skilful submarine commander an opportunity to take evasive action. In 1942 the forward-throwing [[Hedgehog (weapon)|"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 War|Pacific Theater]] during [[World War II]], Japanese depth charge attacks were initially unsuccessful because they were unaware that the latest United States Navy submarines could dive so deep. Unless caught in shallow water, an American submarine could dive below the Japanese depth charge attack. The Japanese had used attack patterns based on the older [[United States S-class submarine]]s (1918–1925) that had a [[Submarine depth ratings|test depth]] of {{cvt|200|ft}}; while the WWII [[Balao-class submarine]]s (1943) could reach {{cvt|400|ft}}.

This changed in June 1943 when [[United States House of Representatives|U.S. Congressman]] [[Andrew J. May]] of the [[United States House Committee on Armed Services|House Military Affairs Committee]] caused [[Andrew J. May#The May Incident|The May Incident]]. The congressman, who had just returned from the Pacific theater where he had received confidential intelligence and operational briefings from the US Navy, revealed at a press conference that there were deficiencies in Japanese depth-charge tactics.<ref>{{harvnb|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. 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."</ref><ref>{{harvnb|Kershaw|2008|p=22}}</ref> After various press associations reported the depth issue, the [[Japanese Imperial Navy]] began setting their depth charges to explode at a more effective average depth of {{cvt|75|m|order=flip}}. Vice Admiral [[Charles A. Lockwood]], commander of the U.S. submarine fleet in the Pacific, later estimated that May's ill-advised comments cost the US Navy as many as ten submarines and 800 seamen [[killed in action]].<ref>{{harvnb|Blair|2001|p=397}}</ref>