Proximity fuze
Proximity fuzes fitted to such weapons as artillery and mortar shells solve this problem by having a range of set burst heights [e.g. 2, 4 or 10 m (7, 13 or 33 ft)] above ground that are selected by gun crews.
Several ideas had been considered, including optical systems that shone a light, sometimes infrared, and triggered when the reflection reached a certain threshold, various ground-triggered means using radio signals, and capacitive or inductive methods similar to a metal detector.
Work on the radio shell fuze was completed by Tuve's group, known as Section T, at The Johns Hopkins University Applied Physics Lab (APL).
While no one invention won the war, the proximity fuze must be listed among the very small group of developments, such as radar, upon which victory very largely depended.
In mid-November 1939, a German neon lamp tube and a design of a prototype proximity fuze based on capacitive effects was received by British Intelligence as part of the Oslo Report.
In the post-World War II era, a number of new proximity fuze systems were developed, using radio, optical, and other detection methods.
[21][22] In 1936, the Air Ministry took over Bawdsey Manor in Suffolk to further develop their prototype radar systems that emerged the next year as Chain Home.
Early field testing connected the circuit to a thyratron trigger operating a tower-mounted camera which photographed passing aircraft to determine distance of fuze function.
Prototype fuzes were then constructed in June 1940, and installed in "unrotated projectiles", the British cover name for solid-fueled rockets, and fired at targets supported by balloons.
[26][27] Looking for a short-term solution to the valve problem, in 1940 the British ordered 20,000 miniature electron tubes intended for use in hearing aids from Western Electric Company and Radio Corporation of America.
An American team under Admiral Harold G. Bowen, Sr. correctly deduced that they were meant for experiments with proximity fuzes for bombs and rockets.
[9][33][34] In just two days, Diamond was able to come up with a new fuze design and managed to demonstrate its feasibility through extensive testing at the Naval Proving Ground at Dahlgren, Virginia.
[41] In addition to extreme acceleration, artillery shells were spun by the rifling of the gun barrels to close to 30,000 rpm, creating immense centrifugal force.
Gun batteries aboard cruiser USS Cleveland (CL-55) tested proximity-fuzed ammunition against radio-controlled drone aircraft targets over Chesapeake Bay.
[9][42] A particularly successful application was the 90 mm shell with VT fuze with the SCR-584 automatic tracking radar and the M9 Gun Director fire control computer.
The combination of these three inventions was successful in shooting down many V-1 flying bombs aimed at London and Antwerp, otherwise difficult targets for anti-aircraft guns due to their small size and high speed.
If the amplified beat frequency signal's amplitude was large enough, indicating a nearby object, then it triggered the fourth tube – a gas-filled thyratron.
In order to be used with gun projectiles, which experience extremely high acceleration and centrifugal forces, the fuze design also needed to utilize many shock-hardening techniques.
[citation needed] To prevent premature detonation, the inbuilt battery that armed the shell had a several millisecond delay before its electrolytes were activated, giving the projectile time to clear the area of the gun.
US Navy development and early production was outsourced to the Wurlitzer company, at their barrel organ factory in North Tonawanda, New York.
[54] Vannevar Bush, head of the U.S. Office of Scientific Research and Development (OSRD) during the war, credited the proximity fuze with three significant effects.
As most of the British heavy anti-aircraft guns were deployed in a long, thin coastal strip (leaving inland free for fighter interceptors), dud shells fell into the sea, safely out of reach of capture.
[57] The Pentagon refused to allow the Allied field artillery use of the fuzes in 1944, although the United States Navy fired proximity-fuzed anti-aircraft shells in the July 1943 Battle of Gela during the invasion of Sicily.
[60] German divisions were caught out in open as they had felt safe from timed fire because it was thought that the bad weather would prevent accurate observation.
U.S. General George S. Patton credited the introduction of proximity fuzes with saving Liège and stated that their use required a revision of the tactics of land warfare.
[citation needed] Optical sensing was developed in 1935, and patented in the United Kingdom in 1936, by a Swedish inventor, probably Edward W. Brandt, using a petoscope.
Actuation can be either through an electronic circuit coupled to a microphone, or hydrophone, or mechanically using a resonating vibratory reed connected to diaphragm tone filter.
[64] [66] During WW2, the National Defense Research Committee (NDRC) investigated the use of acoustic proximity fuzes for anti-aircraft weapons but concluded that there were more promising technological approaches.
The NDRC research highlighted the speed of sound as a major limitation in the design and use of acoustic fuzes, particularly in relation to missiles and high-speed aircraft.
Fuzes of this type can be defeated by degaussing, using non-metal hulls for ships (especially minesweepers) or by magnetic induction loops fitted to aircraft or towed buoys.
