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

THE RADIO PROXIMiTY FUZE 389
ness of a round fitted with a contact or pre-set time fuze. In the case of very
large bombs whose damage is almost entirely due to blast and airburst a!-
most doubles the area of destruction created by bombs with conventional
fuzes.7°
Bombing runs and antiaircraft fire with ordinary fuzes rarely achieve
hits with more than 5 percent of the expenditure. Where foxholes or shallow
depressions in the ground offer good protection against anything but a
direct hit, even a deep foxhole gives scant protection against a projectile
exploding 20 or 30 feet overhead. To get that overhead-burst effect in
World War I, artillery counted on tree bursts or attempted to bounce shells
off rock walls or hillsides to reach troops below. The potential increase in
effectiveness and the estimate that manpower, supply, and other logistical
factors were enhanced by five through possession of a proximity fuze, thus
warranted almost any degree of expenditure and effort to perfect it.
The radio proximity fuze is essentially a tiny radio sending and receiv-
ing station about the size of a 100-watt light bulb. It operates by continuously
sending out radio waves. When the waves approach a sizable object—a
ship, plane, building or other structure, or open ground—they are reflected
back to the receiver in the fuze. As the waves reach a sufficient intensity
indicating their effective proximity, they operate an electronic switch that
detonates the fuze and the projectile.
The British began intensive efforts to perfect and produce their prox-
imity fuze in 1937. Remembering the zeppelin raids of the First War, they
intended to use the fuze primarily as a defense against enemy bombers. Their
work became known to scientists in this country in the spring of 1940, and
that June NDRC assigned research for a similar fuze to the Department of
Terrestrial Magnetism at the Carnegie Institution of Washington, where Dr.
Alexander Ellett of the University of Iowa was working on miscellaneous
ordnance components.7' Under a working arrangement with NDRC, Ellett
brought the problem to the. Bureau, where the team of Diamond, Hinman,
and Astin, which had constructed the radiosonde and radiotelemeter, was
most familiar with principles that might be adapted to the fuze.
By November 1940 NDRC had determined that two types of radio
proximity fuze were needed, one for rotating projectiles, sought by the Navy
u Statistical data based on Army and Air Force field tests with radio and conventional
fuzes, and agreeing with British findings, indicated these ranges of comparative effective-
ness. [Wilbur S. Hinman, Jr.) The Radio Proximity Fuzes for Bombs Rockets, and
Mortars (pamphlet of the Ordnance Development Division, NBS, 1945), pp. 5, 31—34
Hereafter cited as Hinman. See also Harry Diamond, "The radio proximity fuze,"
Nati. Radio News, 11, 16 (1945).
Liaison with the British fuze development groups began in August 1940 and continued
to the end of the war. See John S. Rinehart, MS, "Administrative history of Division 4,
NDRC" (November 1945), p. 224 (author's copy). Hereafter cited as Rinehart MS.