Sonar

Sonar is a technique that uses the propagation of sound, usually underwater, to navigate, measure distance, communicate with or detect objects on or beneath the surface of the water, either passively by listening for sound made by a vessel or actively by emitting a pulse and listening for its echo. The earliest recorded use of the underlying idea dates to 1490, when Leonardo da Vinci described inserting a tube into the water to detect vessels by ear. The first patent for an underwater echo-ranging device was filed with the British Patent Office by the meteorologist Lewis Fry Richardson a month after the sinking of the Titanic in 1912, and working active and passive sonar systems were built by Britain and France during the First World War, entering operational use by 1918.