Mark 37 torpedo

American acoustic torpedo
Due to its electric propulsion, the torpedo swam smoothly out of the launch tube, instead of having to be ejected by pressurized air, therefore significantly reducing its acoustic launch signature. To allow for water flow around the torpedo while swimming out, several 1" thick guide studs were attached to the torpedo, which although 19" in diameter was designed to be used only from 21" torpedo tubes. The guidance of a Mk37 mod 0 torpedo was done by a gyroscope control during the initial part of its trajectory, where the gyro control achieved a straight run, a passive sonar homing system, and at the last by a Doppler enabled active sonar homing, with magnetostrictive transducers operating at 60 kHz. The electronics was based on miniature vacuum tubes, later on solid state semiconductor devices.

The mod 1 torpedoes were longer, slower and heavier than mod 0, but offered better target acquisition capabilities and higher ability to intercept agile submarines. They used wire guidance. The efficiency of Mk37 torpedoes was high for targets with speed lower than and depth less than 1000 feet (305 m). As submarines with higher speeds and operating depths appeared, new torpedoes were developed. Of them, NT37C, D, E, and F are based on the Mk37 design. In 1967, the mod 0s started being refurbished as mod 3, and mod 1 as mod 2. These modifications involved many changes including replacement of magnetostrictive transducers with piezoelectric ones, and resulted in target acquisition range increased from to without loss of sensitivity with increasing depth. The torpedoes used Mark 46 silver zinc batteries. These had a known tendency to overheat, occasionally igniting or exploding. Training torpedoes used rechargeable secondary batteries. For a long time, the Mark 37 was a primary U. S. submarine launched ASW torpedo. It was replaced by the Mark 48 starting in 1972. The remaining inventory was then rebuilt and sold to several countries, including Israel, as the NT 37C after the vacuum tube guidance systems were replaced by solid state electronics and the electric propulsion was replaced with a liquid monopropellant.

The Mk 67 submarine launched mobile mine is based on a Mark 37 torpedo body. It entered service in 1983 and is capable of swimming as far as 10 miles through or into a channel, harbor, shallow water area and other zones which would normally be inaccessible to the vessel laying it. After reaching the target area it sinks to the sea bed and acts like a conventionally laid influence mine. The exploder in the Mk 67 warhead is computerised and incorporates magnetic, acoustic and pressure sensors.