The forerunner of the Zaunkönig was the G7e/T4 Falke, codename "Falcon," which was introduced in March 1943, but only fired by three U-boats by September of that year when the G7es (which was faster, had more range, possessed a magnetic exploder and could also be equipped with a percussion pistol) became available.
The torpedo was electric and had an effective range of 5700 metres at a speed of 24 knots (44 km/h). This torpedo employed passive acoustic homing to find its target, becoming active after a straight run of 400 metres. The homing mechanism consisted of two hydrophone receivers which sensed the sound waves of ship propellers and altered the direction of the rudder via an electropneumatic device.
There were three variants:
- Two flat-nosed versions which contained four sets of magnetostriction hydrophones.
- A round-nosed version which contained two magnetostriction hydrophones inside a funnel-shaped baffle.
The 400 metres (1,300 ft) limit was employed for safety reasons. 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 torpedo. This risk was later mitigated by requiring submarines to dive to 60 metres (200 ft) and go completely silent after launching acoustic torpedoes.
The first 80 TVs were delivered on 1 August 1943, and the weapon was first used in September. Despite some success, in particular sinking destroyers and corvettes, the Zaunkönig 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 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, a destroyer, a frigate and a corvette were sunk. A total of 640 TVs were fired in combat, sinking 45 ships. The Zaunkönig was countered by the introduction by the Allies of the Foxer noise maker.
The Zaunkönig was nicknamed Zerstörerknacker (destroyer cracker) by the German submariners, as it was especially used against convoy escorts.
- Campbell, John (2002). Naval Weapons of World War Two. Annapolis, MD: Naval Institute Press. ISBN 0-87021-459-4.
- Hellions of the Deep, Robert Gannon, ISBN 0-271-01508-X
- Padfield, Peter, War Beneath the Sea Submarine Conflict 1939-1945, Pimlico 1997. ISBN 0-7126-7381-4
- Valentin Pikool, a Soviet Novelist talked about Gn7es torpedo in one of his historic novels.
- Alan Burn frequently refers to the Gn7es "gnat" torpedoes as a major threat to the convoy escorts in his book The Fighting Captain the story of Frederic Walker RN CB DSO & the Battle of the Atlantic
- Helgason, Guðmundur. "A brief synopsis of German torpedo evolution during World War II". German U-boats of WWII - uboat.net.
- More indepth details of G7es (TV) Acoustic Homing Torpedo at uboataces.com