The word 'sonar' is an abbreviation of which phrase?

The word 'sonar' was created during the Second World War as an acronym for Sound Navigation and Ranging. Sonar is a machine that uses sound waves to detect and locate underwater objects. It was first used in 1917 by Paul Langevin to detect icebergs, before it was adopted in the First World War to aid submarine warfare. It was known as ASDIC (Anti-Submarine Detection Investigation Committee) until the 1940s.

Since submarines and other military vessels do not usually have windows, sonar acts as the eyes of the ship. There are two types of sonar: active and passive. The latter listens to the sounds of the water and picks up any noises made by nearby marine life or ships. Active sonar, on the other hand, sends out pulses of sound and records how long they take to return. The sonar sound waves rebound off of a target and relay the frequency back to its sender. The faster the relay, the nearer the object.

A sonar machine emits a ping that can reach as loud as 235 decibels. This is far higher than the level human eardrums can withstand, which is around 160 decibels. Water carries sound differently to airwaves, making the sound too high-pitched for humans to hear. This prevents targets from realising they have been detected by a sonar device.

The earliest form of sonar was used in 1490 by Leonardo da Vinci, who placed a tube into water and listened through it. Modern sonar machines consist of a transmitter, which creates sound waves, and a listening device.