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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 signaling flags.

Radio

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.

While performing searches for various engineering topics, it is often difficult to locate the desired material. That is because many documents are either buried deep within the results, or they are never indexed by the search engines in the first place. Government websites are good sources of information, but it typically takes doing multiple hit-and-miss searches within the website's database to find information. As time permits, I have been re-publishing documents that I find so that the search engines will index them.

Unless otherwise marked, U.S. government documents may be freely copied so long as the content is not altered from the original. Warning: Some of these documents have been processed with optical character recognition (OCR) software and might contain errors.

Building 821: Radar Test Building

Development of a Radar/SAR Assimilation System for
    Internal Wave Prediction
Early U.S. Navy Experimental Radars

Improved Doppler Radar/Satellite Data Assimilation

• Learning Morse Code Characters: A Replication of
   the Keller Method

Meteorological Studies with the Phased Array Weather
    Radar and Data Assimilation Using the Ensemble
    Kalman Filter

Pearl Harbor Revisited: U.S. Navy Communications
    Intelligence, 1924-1941

Radar Cross-Section Observations of the Echo I
    Communications Satellite

Radio and Radar World War I & World War II,
    U.S. Army Signal Corps

What Is Radar?

RF Cafe - U.S. Army Signal Corps' Radio & Radar History for WWI & WWII - equipment

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.

RF Cafe - U.S. Army Signal Corps' Radio & Radar History for WWI & WWII - recruiting posterIn 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.

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.

RF Cafe - U.S. Army Signal Corps' Radio & Radar History for WWI & WWII - SCR-268 RadarBy 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.

The 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.

RF Cafe - U.S. Army Signal Corps' Radio & Radar History for WWI & WWII - SCR-268 radar installation, 1944By 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.

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