G7a torpedo

The G7a (T1) was the standard issue Kriegsmarine torpedo during the early years of World War II.

The G7a(TI) torpedo was 533.4 mm (21 in) in diameter, 7163 mm (23 ft 6 in) in length (with a type Ka or Kb warhead and Pi1 or Pi2 pistol), the warhead holding a charge of approximately 280 kg (617lbs) of so called Schießwolle 36. It was the standard issue torpedo for all German U-boats and surface torpedo-bearing vessels of the war.

The torpedo was of a straight-running unguided design, controlled by a gyroscope. The G7a(TI) was of variable speed, running a distance of 5,000 m at 81 km/h (5,500 yd at 44kt), 7,500 m at 74 km/h (8,250 yd at 40 kt), and 12,000 m at 55.6 km/h (13,200 yd at 30 kt). The 44 kt setting was used only by torpedo boats like the Schnellboote on torpedoes with reinforced engine.

The G7a(TI) was the last naval torpedo of German design to use a wet heat method of propulsion. The torpedo was powered by a steam-engine fed by a mixture of compressed air and steam. Fuel kerosene was burning in a combustion-chamber, creating steam from fresh water. The torpedo's speed was determined by the level of pressure (three settings for 30/40/44 kn) from the low-pressure regulator feeding air to the bottom of the combustion-chamber. The resulting superheated steam powered a four cylinder reciprocating engine, in turn powering a pair of contra-rotating propellers.

Though this system of propulsion gave the G7a(TI) great speed and endurance – the greatest of any production model German torpedo of World War II – it had the distinct disadvantage of being very noisy and leaving a long wake of bubbles, common to most torpedoes of the period, with the exception of the Japanese Type 93 and submarine Type 95, which were fuelled by enriched oxygen. For U-boats, this relegated the G7a(TI) for use mainly at night, when its wake was least noticeable, so as to not give away the element of surprise and the location of the submarine that fired it.

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Wikipedia