These days, all navies use guided torpedoes against their targets (submarines and surface vessels). Not surprisingly (as submarine warfare was always its strongest suite), the first navy to use guided (homing) torpedo on a large scale was the Kriegsmarine of Nazi Germany.
The G7es (T5) “Zaunkönig” (“wren”) was the passive acoustic torpedo that guided itself by homing onto sounds emitted by propellers of enemy surface ships. The homing mechanism consisted of two hydrophone receivers which sensed the sound waves of ship propellers and altered the direction of the torpedo rudder via an electropneumatic device.
T5 was electric and had an effective range of 5700 meters traveling at a speed of 24 knots (44 km/h). It became active after a straight run of 400 meters (employed for safety reasons in order not to hit the sub that launched the torpedo).
However, there were at least two unconfirmed instances of U-boats (U-972 in December 1943 and U-377 in January 1944) sinking after being hit by their own torpedoes. This risk was later mitigated by requiring submarines to dive to 60 meters and go completely silent after launching acoustic torpedoes.
T5 was first deployed in August of 1943 and first saw widespread use in September 1943. 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 German 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.
For a time, the acoustic torpedo again put the escorts and convoys on the defensive. However, the Zaunkönig was countered by the introduction by the Allies of the Foxer noise maker. Which was so efficient that it rendered the T5 essentially useless.
Besides, the T5 often detonated behind the enemy ship because the acoustic steering was very imprecise. This was particularly evident at its first large-scale use from 20 to 24 September 1943 in the attacks on convoy ON-202.
The U-boat commanders reported a number of torpedo strikes and recorded the sinking of nine commercial steamers and 12 escort ships after the battle. In fact, only six merchant ships and three escort vessels were sunk. A total of 640 TVs were fired in combat, sinking 45 ships – hardly an impressive result.