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Sonar (ASDIC)
1917–18 (France and Britain)· Invention or discovery· Technology, codes & intelligence
Well documentedSolid records, physical evidence or scientific consensus.
Finding submarines by sound: a ship sends out sound pulses and listens for echoes, a technique developed in France and Britain in 1917–18.
See it on the Battles & Wars map →What happened
After the Titanic sank in 1912, inventors tried using sound to detect icebergs. U-boats made the need urgent. In France, physicist Paul Langevin and Constantin Chilowsky used vibrating quartz crystals to send high-pitched pulses and time their echoes. Britain's version, ASDIC, was ready just after the war. Its range was a mile or two, and it could not find a submarine on the surface. In World War II the US Navy's name, sonar, for 'sound navigation and ranging,' spread.
Why it matters
Sonar gave escorts their main way to find a submerged submarine. Every later anti-submarine war, and submarines' own navigation, has depended on it.
Think of it like
Like a bat in the dark: send a sound, listen for the echo, and the delay tells how far away the target is.
How we know
Langevin and Chilowsky's 1916 patent, Admiralty research records, naval trial reports, and postwar studies matching U-boat sinkings to their causes.
Still debated
The origin of the name ASDIC is unclear; the often-quoted 'Allied Submarine Detection Investigation Committee' seems never to have existed.
Connections (3)
▸Battle of the Atlantic pitted U-boats against escorts using Sonar (ASDIC)Well documented
The connection
Britain entered the war trusting ASDIC, but U-boats often attacked on the surface at night, where sonar could not find them, and contact was lost as an escort ran over its target to drop depth charges. Forward-firing Hedgehog mortars, radar, aircraft and broken codes filled the gaps, and the U-boats were decisively beaten in May 1943.
When and how
North Atlantic convoy routes, 1939–45; British, Canadian and US escorts, such as Captain Frederic 'Johnnie' Walker's group, against Admiral Karl Dönitz's U-boats.
How we know
Naval action reports, U-boat logs and postwar studies matching each sinking to its cause, which show sonar played a part in many kills.
Debates and open questions
How to divide the credit among sonar, radar, codebreaking, aircraft and sheer numbers of escorts is still debated.
▸Sonar (ASDIC) was developed to hunt the U-boats and unrestricted submarine warfareWell documented
The connection
U-boats sank thousands of Allied ships in World War I. Listening hydrophones could hear a submarine but not pinpoint it, so France and Britain raced to develop echo-ranging, sending sound pulses and timing their echoes. It came too late for that war, where convoys beat the U-boats, but it was standard on escorts by 1939.
When and how
France (Paul Langevin and Constantin Chilowsky) and Britain's Admiralty Board of Invention and Research, 1915–18.
How we know
Patents, Admiralty research records, and test reports describing the first echoes from submarines in 1918.
Debates and open questions
Credit is shared and disputed among Langevin, the British team, and Canadian-born Reginald Fessenden, whose 1914 sound oscillator detected an iceberg.
▸Sonar (ASDIC) is the main sense of the Nuclear and missile submarines (Nautilus, Polaris)Well documented
The connection
Underwater, light and radio barely travel, so submarines depend on sound. Nuclear submarines carry large passive sonar arrays that listen for other vessels, and designers make them as quiet as possible to avoid being heard. Cold War cat-and-mouse between US and Soviet submarines was largely a contest of sonar against quieting.
When and how
North Atlantic and Pacific from the 1950s, along with the US SOSUS network of seabed listening arrays.
How we know
Declassified Navy histories and accounts such as 'Blind Man's Bluff' (1998) describe sonar's central role in submarine operations.
Debates and open questions
Current sonar performance and submarine quieting are classified; how close some Cold War encounters came to collisions or worse is partly unknown.