page_title: Anti-submarine warfare
section_title: Battle of the Atlantic
hierarchical_section_title: Anti-submarine warfare / History / World War II / Battle of the Atlantic
caption_attribution_description: English: Anti-Submarine Weapons: Leigh Light used for spotting U-boats on the surface at night fitted to a Liberator aircraft of Royal Air Force Coastal Command.
context_page_description: Anti-submarine warfare is a branch of underwater warfare that uses surface warships, aircraft, or other submarines to find, track, and deter, damage, or destroy enemy submarines.
  Successful anti-submarine warfare depends on a mix of sensor and weapon technology, training, and experience. Sophisticated sonar equipment for first detecting, then classifying, locating, and tracking the target submarine is a key element of ASW. To destroy submarines, both torpedoes and naval mines are used, launched from air, surface, and underwater platforms. ASW also involves protecting friendly ships.
context_section_description: During the Second World War, the submarine menace revived, threatening the survival of island nations like Britain and Japan which were particularly vulnerable because of their dependence on imports of food, oil, and other vital war materials. Despite this vulnerability, little had been done to prepare sufficient anti-submarine forces or develop suitable new weapons. Other navies were similarly unprepared, even though every major navy had a large, modern submarine fleet, because all had fallen in the grip of Mahanian doctrine which held guerre de course could not win a war.
  At the beginning of the war, most navies had few ideas how to combat submarines beyond locating them with sonar and then dropping depth charges on them. Sonar proved much less effective than expected, and was no use at all against submarines operating on the surface, as U-boats routinely did at night. The Royal Navy had continued to develop indicator loops between the wars but this was a passive form of harbour defense that depended on detecting the magnetic field of submarines by the use of long lengths of cable lain on the floor of the harbour. Indicator loop technology was quickly developed further and deployed by the US Navy in 1942. By then there were dozens of loop stations around the world. Sonar was far more effective and loop technology died straight after the war.
  The use and improvement of radar technology was one of the most important proponents in the fight against submarines.  Locating submarines was the first step in being able to defend against and destroy them.  Throughout the war, Allied radar technology was much better than their German counterparts.  German U-Boats struggled to have proper radar detection capabilities and keep up with the successive generations of Allied airborne radar.  The first generation of Allied airborne radar used a 1.7 meter wavelength and had a limited range.  By the second half of 1942 the "Metox" radar detector was used by U-boats to give some warning from airborne attack.  In 1943 the Allies began to deploy aircraft equipped with new cavity magnetron-based 10-centimeter wavelength radar (ASV III), which was undetectable by "Metox", in sufficient numbers to yield good results.  Eventually the "Naxos" radar detector was fielded that could detect 10-cm wavelength radar, but it had a very short range and only gave a U-Boat limited time to dive.  From 1943–1945 radar equipped aircraft would account for the bulk of Allied kills against U-Boats.  Allied anti-submarine tactics developed to defend convoys (the Royal Navy's preferred method), aggressively hunt down U-boats (the U.S. Navy approach), and to divert vulnerable or valuable ships away from known U-boat concentrations.
  During the Second World War, the Allies developed a huge range of new technologies, weapons and tactics to counter the submarine danger. These included:
  Vessels
  Allocating ships to convoys according to speed, so faster ships were less exposed.
  Adjusting the convoy cycle.  Using operations research techniques, analysis of convoy losses over the first three years of the war showed that the overall size of a convoy was less important than the size of its escorting force.  Therefore, escorts could better protect a few large convoys than many small ones.
  Huge construction programmes to mass-produce the small warships needed for convoy defense, such as corvettes, frigates, and destroyer escorts.  These were more economical than using destroyers, which were needed for fleet duties.  Corvettes were small enough to be built in merchant shipyards and used triple expansion engines.  They could be built without using up scarce turbine engines and reduction gears, thus not interfering with larger warship production.
  Ships that could carry aircraft, such as the CAM ships, the merchant aircraft carrier, and eventually the purpose-built escort carriers.
  Support groups of escort ships that could be sent to reinforce the defense of convoys under attack. Free from the obligation to remain with the convoys, support groups could continue hunting a submerged s
caption: A Leigh Light fitted to a Liberator of Royal Air Force Coastal Command, 26 February 1944.
exif: {}