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Mark 18, U.S. Torpedo


Schematic of Mark 18 torpedo
U.S. Navy. Via hnsa.org


Specifications:

Dimensions     
21" by 20'5"
53.3cm by 6.223m
Weight
3154 lbs
1431 kg
Range 4000 yards (3650m) at 29 knots
Warhead 575 lbs Torpex
261 kg Torpex
Propulsion       Electric
Production
About 8500


The Mark 18 was an electric torpedo based on the German G7e, examples of which were captured by the British in August 1941. The U.S. Navy had been experimenting with electric torpedoes since 1915, but at a very leisurely pace until examples of the G7e were provided to the Navy by their British counterparts. With the Navy's Torpedo Station already working at full capacity to remedy the shortage of wet-heater torpedoes, the project was turned over to Westinghouse. A reluctant partner at first, Westinghouse was initially instructed to make the closest possible copy of the G7e in order to put the new torpedo into production as soon as possible. However, German engineering and manufacturing techniques could not be economically duplicated, and Westinghouse redesigned the torpedo to use a new thin-plate battery produced by Exide and to use the same control mechanisms used in other American torpedoes. The initial design had numerous bugs and the first production Mark 18s did not reach the fleet until September 1943. 

A significant design challenge was designing an electric motor both compact enough to fit in the torpedo case and powerful enough to produce an acceptable speed. Westinghouse solved the problem by relaxing the usual quality controls on an electric motor, and the Mark 18 motor was prone to both overheating and sparking commutators. Since the motor only had to last long enough for the run to the target, this was considered acceptable, as was the corollary that the motors would have to be refurbished after each practice run.

Like other electric torpedoes, the Mark 18 left no wake and was easier to construct than a wet-heater torpedo. It became very popular with submarine commanders convinced that its lack of wake gave a significant tactical advantage. Postwar studies failed to bear this out, finding that conventional wet-heater torpedoes were 17% more likely to hit a merchantman and 250% more likely to hit an escort. The overall hit percentage for the Mark 18 was 28%. It was a noisy torpedo posing a significant risk of a hydrogen explosion, and a hydrogen fire on Flying Fish heated a Mark 18 to the point where the Torpex melted and ran out of the warhead. As a result, the Mark 18 it was retired from service in 1950.

References

Branfill-Cook (2014)

Campbell (1985)

Wildenberg and Polmar (2010)


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