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

404 WORLD WAR II RESEARCH (1941-45)
Atlantic.105 The Huff-Duff investigation, however, was only a single aspect
of a much more extensive project at the Bureau involving the ionosphere
and its wide range of effects on radio communications of all kinds. Studies
of these effects, as manifestations of radio-weather, had already led to
techniques of predicting, with growing accuracy, their influence on
communications.
For good reason, then, a month after Pearl Harbor a Bureau letter
circular on radio-weather predictions was withdrawn from circulation and
all further open publication on the subject ceased. Its data on radio dis-
tance ranges had become military secrets and remained so throughout the
war.106
The influence of the ionized layers of the earth's upper atmosphere,
the ionosphere, on radio wave propagation had been recognized ever since
the independent experiments of Breit and Tuve and of Appleton in 1925
proved its existence.107 Through the next decade Norton, Kirby, Gilliland,
and Newbern Smith at the Bureau devised a number of techniques for ex-
tending the range of ionospheric measurements.lOS Because of the scarcity
of ionospheric data and because few realized its importance, use of such
data in radio communications before the war was relatively small. The
military value of precise knowledge of the usability of various radio frequen-
cies at specific times over specific transmission paths thus gave an enormous
impetus to the compilation of sky data during the war.
From the point of view of the services, the extreme crowding of the
radio-frequency spectrum made propagation data necessary for the best
selection and allocation of available frequencies. Security considerations
also dictated that the frequencies used be those least likely to be intercepted
by the enemy. Design of new equipment, especially antennas, depended upon
knowledge of radio propagation conditions. Finally, not only all radio aids
for air navigation over the North Atlantic, but radio direction finding, radio-
telephone, radar, telegraphy, and radioteletype required better knowledge of
propagation ranges, accuracy, and receivable intensities.
106
Baxter, pp. 38, 45; NBS War Research, pp. 43—44. The Mathematical Tables Project
of the Bureau, located in New York, did important work for the Navy on its Loran tables
and other computations. Interview, Dr. Franz L. Alt, June 30, 1964.
'o'
LC658 (1941). Excepted from classification were the standard frequencies and
other broadcasting services provided by the Bureau (see LC591, 1940).
For the work of Breit, Tuve, and Appleton, see RP632, "Studies of the ionosphere
and their application to radio transmission" (Kirby, Berkner, and Stuart, 1934) -
RP597, "A continuous recorder of radio field intensities" (Norton and Reymer,
1933); RP752, "An analysis of continuous records of field intensities * * *" (Nor-
* *
ton, Kirby, and Lester, 1934); RP1001, "Characteristics of the ionosphere
(Gilliland, Kirby, Smith, et al., 1937); RP1167, "Application of graphs of maximum
usable frequency * * 'p" (Smith, Kirby, and Gilliland, 1939).