| Mark 37 torpedo | |
| Origin: | United States |
| Type: | Acoustic torpedo[1] |
| Is Ranged: | yes |
| Is Explosive: | yes |
| Is Missile: | yes |
| Service: | 1956-1972 |
| Used By: | United States Navy Israeli Navy Royal Netherlands Navy |
| Designer: | Westinghouse Electric Underwater Sound Laboratory, Harvard University Ordnance Research Laboratory, Pennsylvania State University |
| Manufacturer: | Naval Ordnance Station Forest Park |
| Design Date: | 1946 |
| Variants: | Mark 37 Mod 1 Mark 37 Mod 2 Mark 37 Mod 3 NT37C NT37D NT37E NT37F |
| Weight: | 1430lb |
| Length: | 135inch |
| Diameter: | 19inch (21-inch guide rails) |
| Range: | 23000yards at 17 knots, 10000yards at 26 knots |
| Filling: | Mk 37 Mod 0, HBX-3 |
| Filling Weight: | 330 pounds |
| Detonation: | Mk 19 contact exploder |
| Engine: | Electric |
| Speed: | 17knots, 26knots |
| Guidance: | Gyroscope (initial), passive sonar (cruise) and Doppler active sonar homing (terminal) |
| Launch Platform: | Submarines |
The Mark 37 torpedo is a torpedo with electrical propulsion, developed for the US Navy after World War II. It entered service with the US Navy in the early 1950s, with over 3,300 produced. It was phased out of service with the US Navy during the 1970s, and the stockpiles were sold to foreign navies.
Its engineering development began in 1946 by Westinghouse. It was largely based on the concept of the passive homing Mark 27,[2] with added active homing system tested on modified Mark 18s, and a new torpedo body. Between 1955 and 1956, thirty torpedoes were produced for development testing, with large-scale production commenced shortly afterwards.[3]
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.[4]
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 20knots and depth less than 1000feet. 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 700yd to 1000yd 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.[5]
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.[6]