Radio and Radar World War I & World War II
U.S. Army Signal Corps
This information originally appeared on the U.S. Army Signal Corps' historical website. The Corps has been charged
with managing the Army's communications systems since the Civil War, beginning with the "Wig
Wag," a method of waving a flag (or two) to indicate numbers and letters, similar to semaphore and other
Next to aviation, radio was considered to be the wonder of
the age during the early twentieth century. Initially known as wireless telegraphy, it freed long distance
communication from the constraints of wires. Wireless telegraphy meant exactly that Morse code transmitted by
electromagnetic waves instead of wires. The discharge of a spark across a gap caused by the pressing of a
telegraph key generated the electromagnetic waves that relayed the message. The years 1900 to 1915 constituted
"the golden age of the spark transmitter," with the names of Guglielmo Marconi, Reginald Fessenden, and Lee de
Forest the most prominent in the early development of radio.
Spark-gap technology possessed several important drawbacks. From a security standpoint, a spark transmission
could not be tuned; it covered a span of frequencies and could be intercepted by anyone with a receiver. Moreover,
the signals of all stations within range of each other caused mutual interference. Not only did the noisy spark
create a great deal of distortion, the consequent dissipation of energy over the broad band of frequencies
lessened the distance over which the signals could travel. Only with advances in continuous wave technology would
wireless telegraphy evolve into wireless telephony, or radio broadcasting.
The Signal Corps began
investigation into radio with its own electrical expert, 1Lt George O. Squire. He had received a Ph.D. from Johns
Hopkins in 1893, one of the first signal soldiers to get one of these advanced degrees. Squire developed a
wireless system that was first used in 1899, between Fire Island and the Fire Island Lightship at the north
approach to New York Harbor. This was the first wireless system ever placed in service in the Western Hemisphere.
1910 Major Squire demonstrated his multiplex telegraphy system. With this system many messages could be sent
simultaneously along the same wire. Voice signals could be sent by radio along telephone lines. Radio signals
could travel along the wires without interference with the regular telephone traffic. This "wired wireless"
provided greater secrecy than broad band and made more efficient use of existing wires.
Mainly through the
efforts of Squire and young engineers such as Edwin H. Armstrong, and through cooperation with American industry.
Armstrong had discovered the capabilities of Lee DeForest’s Audion and developed the super heterodyne radio
receiver which greatly amplified weak signals and enabled precise tuning. Other the important developments were
the perfection and mass production of the vacuum tube and, in cooperation with the Western Electric Company, of
the radio telephone, or voice radio, which went into production in 1918. But, it was too late to use in the war.
There was also some experimentation that looked toward radar.
Probably the most significant research between the wars pertained to radar, an
offshoot of radio. Radar is an acronym for radio detection and ranging and was not actually coined until 1940 by
the USN. The origin of Army radar research dated back to WWI when Major William R. Blair conducted experiments in
sound ranging for the purposes of locating approaching aircraft by the use of their engines. In the 1930s Blair
became director of the Signal Corps labs at Fort Monmouth and began investigating the pulse-echo method of
detection in the Signal Corps labs.
In December 1936, Signal Corps engineers conducted the first field
test of the radar equipment at the Newark, New Jersey, airport where it detected an airplane seven miles away.
May 1937, Signal Corps demonstrated its still crude radar, the SCR-268, a short-range radar set, for Secretary of
War Harry H. Woodring; BG Hap Arnold, Assistant Chief of the Army Air Corps; and others. The Secretary and BG
Arnold were impressed and the latter urged development of a long-range version for use as an early warning device.
With high-level support, the Signal Corps received money needed to continue its developmental program.
Signal Corps application of radar to coastal defense was an extension of its long-standing work in the development
of electrical systems for that purpose, which began in the 1890s. Because the National policy remained one of
isolationism, American military planners envisioned any future war as defensive. Hence the Signal Corps developed
the SCR-268, designed to control searchlights and anti-aircraft guns, and subsequently designed for the Air Corps
two sets for long-range aircraft detection: SCR-270, mobile set with a range of 120 miles, and the SCR-271, a
fixed-radar with similar capabilities.
early December 1941 the aircraft warning system on Oahu had not yet been fully operational. The Signal Corps had
provided SCR-270 and SCR-271 radar sets earlier in the year, but construction of fixed sites had been delayed and
radar protection was limited to six mobile stations operating on a part-time basis to test crews and equipment.
Find out more in "Getting the