proximity fuze

proximity fuze, generic term for radio devices which detonated projectiles within lethal range of their targets.

An early version was fitted to British rocket weapons in 1940 and British research into the fuze was passed by the Tizard committee to the USA for development the same year. The Oslo report revealed that the Germans were also working on a similar device but, it seems, they never used any operationally. The Americans called it the VT fuze—VT was just a codename and did not stand for variable time or anything else. It was placed in the nose of a projectile—which had to be 75 mm. (2.9 in.) calibre or more—and emitted signals which were received back after being reflected from the target. When these reached the right strength the projectile exploded.

The proximity fuze was one of the war's most closely guarded secrets. Its operational use was controlled by the Combined Chiefs of Staff Committee which initially authorized only its use at sea to minimize the possibility of its being compromised. It was first employed operationally in June 1943 when the US cruiser Helena shot down a Japanese aircraft during the Pacific war. British anti-aircraft guns defending London were permitted to use it against the German V-1 (see V-weapons) from June 1944 and during the last week of these attacks it was responsible for their destruction of 79% of their targets. The Ardennes campaign, which started on 16 December 1944, brought forward the date for its use in north-west Europe by nine days and it contributed decisively to the defeat of this German offensive, artillery air bursts having a particularly devastating effect. It was first employed against land targets in the Pacific during the pre-landing saturation bombardment of Iwo Jima's defences in February 1945.