The speed of sound waves in the ocean ranges from 4,800 to 5,100 feet per second, depending on water temperature, salinity, and depth. This speed is about 4 and ? times the average speed of sound waves in the air. Sound waves can travel great distances in regions of minimum velocity called sound channels. In 1960 the sound from depth charges exploded by a Columbia University research ship off southwestern Australia was detected in a sound channel by hydrophones off Bermuda, 12,000 miles away.
In addition to determining the shape of the ocean floor, sonar equipment is used for navigation, to locate submerged submarines, and to locate schools of fish. Porpoises and certain species of sea lions have a natural form of sonar. They emit high- frequency sound pulses, which they use to avoid collisions and to search for food. A fully submerged submarine can communicate with a nearby submarine or surface ship by means of an underwater telephone. This device transmits voice signals directly through water. Reference: 1. Blair, Carvel. (1986). Exploring the Sea: Oceanography Today. Random House Publishing.