Acoustic torpedo

An acoustic torpedo is a torpedo that aims itself by listening for characteristic sounds of its target or by searching for it using sonar (acoustic homing). Acoustic torpedoes are usually designed for medium-range use, and often fired from a submarine.

The first passive acoustic torpedoes were developed independently and nearly simultaneously by the Allies and the Germans during World War II. The Germans developed the G7e/T4 Falke, which was first deployed in March 1943. However, this early model was actually used in combat by only three German U-Boats. It was not until after the deployment of the T-4's successor, the G7es T-5 Zaunkönig torpedo in August 1943 that Germany began to use passive acoustic torpedoes in substantial numbers; the T-5 first saw widespread use in September 1943. This weapon was developed to attack escort vessels and merchant ships in convoys.

The initial impact of the acoustic torpedo in the Battle of the Atlantic prior to the widespread deployment of counter-measures cannot be overstated. The U-boats now had an effective "fire and forget" weapon capable of homing-in on attacking escorts and merchant ships and doing so in close quarters of only three or four hundred yards. By Summer of 1943, the German U-boat campaign was experiencing severe setbacks in the face of massive anti-submarine efforts integrating Coastal Command attacks in the Bay of Biscay, the deployment of merchant aircraft carriers in convoys, new anti-submarine technologies such as hedgehog and improved radar, and the use of dedicated hunter-killer escort groups. The Allies' improved escorts had greater range, and the use of fuelling at sea added hundreds of miles to the escort groups' radius of action. From June through August, 1943 the number of merchant ships sunk in the Atlantic was almost insignificant, while the number of U-boat kills rose dramatically and caused a general withdrawal from battle as the submarines could hardly make it through the Bay of Biscay to engage the convoys. For a time, the acoustic torpedo again put the escorts and convoys on the defensive, starting with the attacks in September, 1943 on Convoys ONS-18/ON-202.

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