Proximity Fuses: The VT Fuze ~ 1945 US Army Signal Corps Training Film; World War II

more at http://quickfound.net/

Originally a public domain film from the US Army, slightly cropped to remove uneven edges, with the aspect ratio corrected, and one-pass brightness-contrast-color correction & mild video noise reduction applied.

The soundtrack was also processed with volume normalization, noise reduction, clipping reduction, and/or equalization (the resulting sound, though not perfect, is far less noisy than the original).

https://en.wikipedia.org/wiki/Proximity_fuze

Wikipedia license: http://creativecommons.org/licenses/by-sa/3.0/

A proximity fuze is a fuze that detonates an explosive device automatically when the distance to the target becomes smaller than a predetermined value. Proximity fuzes are designed for targets such as planes, missiles, ships at sea, and ground forces. They provide a more sophisticated trigger mechanism than the common contact fuze or timed fuze. It is estimated that it increases the lethality by 5 to 10 times, compared to these other fuzes...

Background

Before the proximity fuze's invention, detonation was induced by direct contact, a timer set at launch, or an altimeter. All of these earlier methods have disadvantages. The probability of a direct hit on a small moving target is low; a shell that just misses the target will not explode. A time- or height-triggered fuze requires both a good prediction by the gunner and accurate timing by the fuze. If either is wrong, then even accurately aimed shells may explode harmlessly before reaching the target or after passing it. "In 1940 it was generally estimated that good antiaircraft brought down one plane for every 2500 rounds."[2] With a proximity fuze, the shell or missile need only pass close by the target at some time during its trajectory. The proximity fuze makes the problem simpler than the previous methods.

Proximity fuzes are also useful for producing air bursts against ground targets. A contact fuze would explode when it hit the ground; it would not be very effective at scattering shrapnel. A timer fuze can be set to explode a few meters above the ground, but the timing is critical and usually requires observers to provide information for adjusting the timing. Observers may not be practical in many situations, the ground may be uneven, and the practice is slow in any event. Proximity fuzes fitted to such weapons as artillery and mortar shells solve this problem by having a range of pre-set burst heights (e.g. 2, 4 or 10 metres, or about 7, 13, or 33 feet) above ground that are selected by gun crews prior to firing. The shell bursts at the appropriate height above ground.

World War II

British military researchers at the Telecommunications Research Establishment (TRE) Samuel C. Curran, William A. S. Butement, Edward S. Shire, and Amherst F. H. Thomson conceived of the idea of a proximity fuze in the early stages of World War II. In fact, the idea of a fuze was not new. Their system involved a small, short range, Doppler radar. British tests were then carried out with "unrotated projectiles," in this case rockets. However, British scientists were uncertain whether a fuze could be developed for anti-aircraft shells, which had to withstand much higher accelerations than rockets. The British shared a wide range of possible ideas for designing a fuze, including a photoelectric fuze and a radio fuze, with United States during the Tizard Mission in late 1940. To work in shells, a fuze needed to be miniaturized, survive the high acceleration of cannon launch, and be reliable.

The National Defense Research Committee assigned the task to the physicist Merle A. Tuve at the Department of Terrestrial Magnetism. Also eventually pulled in were researchers from the National Bureau of Standards (this research unit of NBS later became part of the Army Research Laboratory). Work was split in 1942, with Tuve's group working on proximity fuzes for shells, while the National Bureau of Standards researchers focused on the technically easier task of bombs and rockets. 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). Over 100 American companies were mobilized to build some 20 million shell fuzes.

The proximity fuze was one of the most important technological innovations of World War II. It was so important that it was a secret guarded to a similar level as the atom bomb project or D-Day invasion...