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

THE RADIO PROXIMITY FUZE 397
November specifications for quantity production were ready. Army Ord-
nance called for the fuze on all its bombs between the 100- and 4,000-pound
sizes. Approximately 1 million were made by Zenith, Emerson, Philco, and
other radio manufacturing companies.86
Subsequent modifications made in the bomb fuze included a device
designed at the Bureau by Jacob Rabinow to provide delay in arming and
permit the fuzed bombs to drop safely through deep formations of bombers,
and replacement of the vane mechanism with a miniature turbine, making
the whole rotating system in the fuze more compact. Design of special
components was initiated by Astin's group to insure optimum heights of
burst, and finally a new generator appeared, measuring a mere 11/8 by 13/s
inches,87
As the sophisticated generator-powered bomb fuze went into pro-
duction, the Navy through OSRD asked that it be adapted to their 5-inch
aircraft rocket. The major modification consisted in changing the arming
system from its vane gear back to the use of the acceleration provided by the
firing of the rocket. Production of both air.to.ground and air-to-air versions
began in December 1944, and both the Army and Navy used them in con-
siderable numbers in the last months of the war.88
A late adjunct to employment of the proximity fuze bomb was a
special bomb director mechanism, which together with toss bombing, in-
sured bringing the missile close enough to its target for maximum effect.
The toss-bombing principle and basic design of the mechanism, the acceler-
ation integrater bomb release, was first suggested by Col. Harold Morton
of Army Ordnance in January 1943 and developed under Alexander Ellett
at the Bureau.89
The object of toss bombing is to compensate for the gravity drop of
the missile in flight. Instead of depending on an educated guess about the
point of bomb release, as fighter pilots did in attacking bomber formations
or in dive bombing, the bomb director automatically computed the release
point as the pilot commenced pulling out of his dive. The resulting trajec-
tory of the bomb tossed it toward its target, allowing the pilot more time
to take evasive action against ground or ship fire.
Some 500 bomb director sets were produced for the Army and Navy
toward the end of the war, although only a few more than a hundred, fitted
Hinman, pp. 20, 31; Baxter, pp. 239,241.
87
Hinman, pp. 21—23; NBS War Research, p. 23.
88
Hinman, p. 24.
Letter, Acting Assistant Chief of Air Staff-4 to Col. H. S. Morton, Office of Chief of
Ordnance, Nov. 8, 1945, and attached correspondence (copy in NBS Historical File);
Rinehart MS, p. 158.