In 1943, Maurice Ewing detonated a pound of TNT in the waters of the Bahamas. When the sound was picked up on the west coast of Africa, his theory of a "deep sound channel" was confirmed. Dubbed the sound fixing and ranging, or SOFAR, channel, this region of water takes advantage of the laws of refraction to allow sound waves to travel great distances.

As the temperature of water decreases, so does the speed of the sound waves travelling through it. Increase water pressure, and that speed will increase. At an average depth of 1 km, these two effects meet creating a region of minimum sound velocity.

Sound waves tend to bend downward as the speed of sound decreases, and bend upward again as the speed of sound increases. Sound waves introduced at the depth where the speed of sound is slowest will be trapped by this effect, allowing them to travel thousands of miles with minimal loss of signal.