Editing Sonar (section)

=== ASDIC ===
[[File:ASDIC.png|thumb|right|ASDIC display unit from around 1944]]
In 1916, under the British [[Board of Invention and Research]], Canadian physicist [[Robert William Boyle]] took on the active sound detection project with [[Albert Beaumont Wood|A. B. Wood]], producing a prototype for testing in mid-1917. This work for the Anti-Submarine Division of the British Naval Staff was undertaken in utmost secrecy, and used quartz piezoelectric crystals to produce the world's first practical underwater active sound detection apparatus. To maintain secrecy, no mention of sound experimentation or quartz was made – the word used to describe the early work ("supersonics") was changed to "ASD"ics, and the quartz material to {{not a typo|"ASD"ivite}}: "ASD" for "Anti-Submarine Division", hence the British acronym ''ASDIC''. In 1939, in response to a question from the ''[[Oxford English Dictionary]]'', the [[British Admiralty|Admiralty]] made up the story that it stood for "Allied Submarine Detection Investigation Committee", and this is still widely believed,<ref name="Abbot">{{cite web |url=http://abbot.us/DD629/dictionary/ |title=World War II Naval Dictionary |website=USS Abbot (DD-629) |access-date=12 November 2019 |archive-date=12 December 2013 |archive-url=https://web.archive.org/web/20131212091457/http://abbot.us/DD629/dictionary/ |url-status=dead }}</ref> though no committee bearing this name has been found in the Admiralty archives.<ref name="Hackmann">W. Hackmann, ''Seek & Strike: Sonar, anti-submarine warfare and the Royal Navy 1914–54'' (HMSO, London, 1984).</ref>

By 1918, Britain and France had built prototype active systems. The British tested their ASDIC on {{HMS|Antrim|1903|6}} in 1920 and started production in 1922. The 6th Destroyer Flotilla had ASDIC-equipped vessels in 1923. An anti-submarine school [[RNAS Portland (HMS Osprey)|HMS ''Osprey'']] and a training [[flotilla]] of four vessels were established on [[Isle of Portland|Portland]] in 1924.

By the outbreak of [[World War II]], the [[Royal Navy]] had five sets for different surface ship classes, and others for submarines, incorporated into a complete anti-submarine system. The effectiveness of early ASDIC was hampered by the use of the [[depth charge]] as an anti-submarine weapon. This required an attacking vessel to pass over a submerged contact before dropping charges over the stern, resulting in a loss of ASDIC contact in the moments leading up to attack. The hunter was effectively firing blind, during which time a submarine commander could take evasive action. This situation was remedied with new tactics and new weapons.

The tactical improvements developed by [[Frederic John Walker]] included the creeping attack. Two anti-submarine ships were needed for this (usually sloops or corvettes). The "directing ship" tracked the target submarine on ASDIC from a position about 1500 to 2000 yards behind the submarine. The second ship, with her ASDIC turned off and running at 5 knots, started an attack from a position between the directing ship and the target. This attack was controlled by radio telephone from the directing ship, based on their ASDIC and the range (by rangefinder) and bearing of the attacking ship. As soon as the depth charges had been released, the attacking ship left the immediate area at full speed. The directing ship then entered the target area and also released a pattern of depth charges. The low speed of the approach meant the submarine could not predict when depth charges were going to be released. Any evasive action was detected by the directing ship and steering orders to the attacking ship given accordingly. The low speed of the attack had the advantage that the [[G7es torpedo|German acoustic torpedo]] was not effective against a warship travelling so slowly. A variation of the creeping attack was the "plaster" attack, in which three attacking ships working in a close line abreast were directed over the target by the directing ship.<ref name="Burn">{{cite book |last1=Burn |first1=Alan |title=The Fighting Captain: Frederic John Walker RN and the Battle of the Atlantic |date=1993 |publisher=Pen and Sword |location=Barnsley |isbn=978-1-84415-439-5 |edition=2006, Kindle|chapter=Appendix 6}}</ref>

The new weapons to deal with the ASDIC blind spot were "ahead-throwing weapons", such as [[Hedgehog (weapon)|Hedgehogs]] and later [[Squid (weapon)|Squids]], which projected warheads at a target ahead of the attacker and still in ASDIC contact. These allowed a single escort to make better aimed attacks on submarines. Developments during the war resulted in British ASDIC sets that used several different shapes of beam, continuously covering blind spots. Later, [[acoustic torpedo]]es were used.

Early in World War II (September 1940), British ASDIC technology was [[Tizard Mission|transferred for free]] to the United States. Research on ASDIC and underwater sound was expanded in the UK and in the US. Many new types of military sound detection were developed. These included [[sonobuoy]]s, first developed by the British in 1944 under the [[codename]] ''High Tea'', dipping/dunking sonar and [[naval mine|mine]]-detection sonar. This work formed the basis for post-war developments related to countering the [[nuclear submarine]].