Propulsion
The first of Whitehead's torpedoes had a single propeller and needed a large vane to stop it turning in a circle. Not long afterward the idea of contra-rotating propellers was introduced (at Woolwich), to avoid the need for the vane. The three-bladed propeller came in 1893 and the four-bladed one in 1897. To minimise noise, today's torpedoes often use pump-jets.
Some torpedoes, such as the Russian VA-111 Shkval, the Iranian Hoot and the German Unterwasserlaufkörper/ Barracuda, use supercavitation to increase their speed to over 200 knots (370 km/h); the maximum speed of torpedoes which do not use supercavitation, such as the American Mark 48 and British Spearfish, is well under 100 kn (120 mph; 190 km/h), although figures are not always supplied.
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