Tuesday, December 16, 2008

The True Origins of the Proximity Fuze - Part 1

Below: 1935 Shell with Proximity Fuze
Quite a bit has been written about the proximity fuze, over 20 million of which were produced in the Crosley Corporation's Cincinnati factory during World War II. However, there's more than a little of the fuze's history that has not been made available to the general public.

To complete the missing info in Crosley, this and ensuing installments will describe the origins and development of the fuze. This includes the details of experiments with the proximity fuze in pre-war England as a "bomb to bomb bombers."

The most-publicized information to date has had to do with the proximity fuze's applications in four different anti-aircraft shells in the Pacific, against Japanese aircraft. Lesser-known are the original aerial types of the proximity fuze, and the use made of it in place of ground-burst shells.

The first proximity fuzes grew out of a British Air Ministry "bomb the bomber" program in 1938, when it was discovered that the only way Britain's obsolescent biplane fighters could successfully attack fast monoplane bombers was to get above them and drop contact-fused bombs. This meant that drops had to made connect with with the target--a rare occurrence. It was decided then that it would be worthwhile to develop other kinds of detonators, able to set off bombs when they reached close-enough proximity to do damage to an aircraft.

Two kinds of proximity fuzes were initially developed: acoustic and photoelectric. The acoustic fuzes were engineered in both high-frequency and low-frequency models. The challenge of course was to create a fuze that would not detonate a bomb because of the ambient noise created by being dropped. Many trials and errors resulted in a bomb with a piezoelectric(PE) microphone in its nose. Sounds at a certain frequency--as created by a large monoplane--would activate the fuze, which would close a circuit to a relay and electrically detonate the bomb. Both high- and low-frequency models were built.

The acoustic fuzes were a bit sensitive to nearby (up to 2,000 feet) airbursts, as well as vibration from their own arming. So work was done on a photoelectric fuze that would detonate in response to a change in ambient light, nearly always the result of the presence of an aircraft.

The photoelectric proximity fuze been developed before the British Air Ministry began its fuze program. In 1935 a Swiss engineer developed and later patented a concept for an antiaircraft shell fuze that would be detonated by sensing the presence of an aerial target through a change in ambient light. Hence, the fuze was far from being an American invention, and was in fact in use in Britain before American authorities knew of it.
--To be continued in a later post--

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