The underwater detection system that uses sound to locate and track objects around a submarine is sonar. The name comes from “sound navigation and ranging,” describing the system’s basic purpose.
Active sonar sends out an acoustic pulse and analyzes returning echoes. Passive sonar does not transmit; it listens for sounds made by ships, submarines, marine animals, or machinery. A submarine can use passive sonar while remaining comparatively difficult to detect.
Sound travels through seawater much more effectively than radio waves, which is why sonar is central to underwater navigation and warfare. Temperature, salinity, and pressure affect the speed and path of sound, creating layers and channels that operators must understand.
Sonar is not identical to radar. Radar uses radio waves and is primarily useful in air or on the surface, while sonar is adapted to the acoustic conditions of water.