Measures for Progress: A History of the National Bureau of Standards

THE RADIO PROXIMITY FUZE 395
and other raiders of the German Fleet had either been sunk or immobilized—
but for air-to-air use against enemy bomber formations. Attack planes with
these proximity fuze bombs were to climb above enemy air armadas and
release their sticks over the formation.
Work on the bomb fuze was well under way before it was realized
that such targets had grown scarce, that the Allies, not the enemy, were
now sending out bombers in flood formations. The requirement was changed
to an air-to-ground bomb fuze, to effect airbursts over troops and other
targets of opportunity. When this fuze later arrived overseas it was also
fitted into fragmentation bombs. In napalm (gel gas) bombs, the fuze
eliminated ground penetration, to which the standard napalm bomb was
subject, doubling the area covered by the gel. In these various forms it was
used with deadly effect by the 12th Air Force in Italy against both troops
and materieL54
Since a bomb is not subject to setback at release, that is, the shock
of acceleration upon which the arming of the rocket fuze depends, a different
arming mechanism became necessary. The difference in fuze space in the
bomb also required some physical redesign. The greatest concern in the
bomb fuze, however, was with the dry battery used as a power source. As
had been learned with the rocket fuze, it deteriorated rapidly in storage,
lasting about a year ordinarily and not more than a month or 2 under tropical
conditions. At the subzero temperatures encountered in high-altitude runs,
the dry battery wouldn't work at all. Another means for powering the fuze
had to be found.55
The solution was found by eliminating the batteries and using the
arming system of the conventional bomb fuze. In that fuze a small wind-
driven vane spinning as the bomb falls actuates the arming mechanism only
after a certain number of turns of the vane. By attaching a miniature
generator to the vane, sufficient electric power could be obtained for the
proximity fuze. The generator assured almost indefinite storage life, per-
formed well over extreme temperature ranges, and increased the safety
factor since the fuze could in no way detonate the bomb unless the vane was
running at high speed.
The generator designed by Zenith Radio, measuring % by 2% inches
and built to run at 50,000 r.p.m., went into mass production. With it went
a rectifier assembly made by General Electric about half the size of a
cigarette, to convert the alternating voltage of the generator to direct current
for the fuze. Tests of the new bomb fuze began in May 1943, and by
British tests further disclosed that air-burst chemical bombs filled with a persistent agent
such as mustard gas contaminated seven times the area covered by a surface burst. Hin-
man, pp. 33—34; Baxter, p. 241.
Hinman, p. 18.