In oceanography, a sofar bomb (SOund Fixing And Ranging bomb), occasionally also referred to as a sofar disc, is a long-range position-fixing system that uses explosive sounds in the deep sound channel of the ocean to pinpoint the location of ships or crashed planes. The depth of water at the deep sound channel is ideal for the device, as the minimal speed of sound helps with the positioning calculations and improves the signal's traveling ability. A position is determined from the differences in arrival times at receiving stations of known geographic locations. The useful range from the signal sources to the receiver can exceed .