Leonardo listened underwater with a tube in 1490
Sonar—sound navigation and ranging—uses underwater sound to navigate, range, and detect objects. Passive modes only listen; active modes ping and hear echoes. Leonardo da Vinci recorded a tube-in-water listening trick in 1490, and the sinking of the Titanic spurred the first patent for underwater echo ranging.
Sonar, short for sound navigation and ranging, uses sound travelling through water to navigate, measure distances, communicate, and find objects such as other vessels. Passive sonar simply listens for noises a ship makes, while active sonar sends out pulses and listens for the echoes. Dolphins, bats, and some shrews have located things by sound for millions of years; the first recorded human use came in 1490, when Leonardo da Vinci described putting an ear to a tube dipped into the water to hear distant ships.
In the late nineteenth century underwater bells supplemented lighthouses and lightships as hazard warnings. The Titanic disaster of 1912 seems to have prompted echo location: a month after the sinking, the English meteorologist Lewis Fry Richardson filed the first patent for an underwater echo-ranging device. The Canadian engineer Reginald Fessenden, working for the Submarine Signal Company in Boston, built an experimental system from 1912 and in 1914 tested it from the cutter Miami on the Grand Banks off Newfoundland, measuring depth.
The First World War's submarine threat drove rapid progress. Britain relied on hydrophones, the French physicist Paul Langevin and the engineer Constantin Chilowsky worked on active devices, and from 1916 Robert William Boyle and A. B. Wood built a secret British prototype using quartz. To hide the work, it was named for the Anti-Submarine Division, giving the acronym ASDIC. A passive system was working by 1918, ASDIC was tested on HMS Antrim in 1920 and entered production in 1922, and a training school opened at Portland in 1924.
Early ASDIC lost contact just as a ship passed over a submarine to drop depth charges, so Frederic John Walker devised the creeping attack, with one ship tracking while another crept in silently, and ahead-throwing weapons like the Hedgehog and Squid fired while contact held. Britain gave the technology to the United States free in September 1940. American engineers of the 1930s had discovered how thermoclines bend sound, and Frederick Hunt coined the word SONAR as a counterpart to RADAR.
Source: Sonar
