Proximity fuse

From Academic Kids

A proximity fuse (sometimes spelled "fuze") is a fuse that is designed to detonate an explosive automatically when close enough to the target to destroy it. By sending out radio waves that are reflected by the target and comparing the frequency of the outgoing waves to the incoming waves, a radio proximity fuse uses the Doppler effect to determine its proximity to a target. When the incoming waves sharply decrease in frequency, the target is at the closest proximity that can be determined using this method. (The sharp decrease in frequency means that the projectile has just passed the target. Think of the sound a train whistle makes as the train approaches you. The long blast of the whistle changes as it just passes your location.)

Before their invention, detonation had to be induced either by direct contact, time since launch, or height. All of these have significant disadvantages. Getting direct contact with a relatively small moving target is hard (even ignoring the effect of wind); to set a time- or height-triggered fuse one must measure the height of the target (or even predict the height of the target at the time one will be able to get a missile in its neighbourhood).

With a proximity fuse, all one has to worry about is getting a shell or missile on a trajectory that, at some time, will pass close by the target (that still is a significant problem).

Use of timing to produce air bursts against ground targets requires observers to provide information for adjusting the timing. This is not practical in all situations and is slow in any event. Proximity fuses remove these problems.

The proximity fuse was developed through a U.S. and British collaboration during World War II. Vannevar Bush, head of the U.S. Office of Scientific Research and Development (OSRD) during this war, credits it with three significant effects. It was important in defense from Japanese Kamikaze attacks in the Pacific. It was an important part of the radar-controlled anti-aircraft batteries that finally neutralized the German V1 bomb attacks on England. Third, it was released for use in land warfare just in time for use in the Battle of the Bulge, where it decimated German divisions caught in the open. The Germans felt safe from timed fire because the weather prevented accurate observation. Bush cites an estimated 7 times increase in the effect of artillery with this innovation.

Proximity fuses were also used on the first atomic bombs.


  • Pieces of the Action by Vannevar Bush, William Morrow and Co., inc. 1970
  • An account of the development and initial introduction of proximity fuses is given in The Deadly Fuze by Ralph B Baldwin (UK Edition published by Janes, 1980. ISBN 0 354 01234 6). Dr Baldwin was a member of the Johns Hopkins University team headed by Merle A Tuve that did most of the work.

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