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Article Excerpt
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Japan's stunning employment of air power on the first day of the Pacific War, in 1941, is readily acknowledged by most; but its corollary--the failure of U.S. air power in the Philippines and Hawaii is often overlooked. While this failure of American air power may be written off to the tactical--and operational--surprise achieved in Hawaii, this was hardly the case in the Philippines, where the U.S. Army Forces in the Far East (USAFFE) had many hours of warning. Both Hawaii and the Philippines had operational radar sets that tracked the incoming raids, yet Army Air Forces fighters failed to intercept the Japanese bombers. What went wrong? How did the technology that saved Britain in 1940 let America down?
Early U.S. Army Air Defense Concepts
The U.S. Army's involvement with the concept of area air defense can be traced to the late 1920s. In the era of small Air Corps exercises and slow First World War-era bombers, point defense of targets, such as airfields, was relatively easy. This changed in the 1930s. During exercises in Ohio in 1931, Air Corps fighter aircraft achieved little success against "enemy" bombers reported by a ground observer net. Later, Capt. Claire Chennault, an instructor at the Air Corps Tactical School, devised a warning system based on the British experience in World War I. This rudimentary air defense system, using ground observers coupled with filter centers, improved plotting techniques, and better command and control, achieved success in the Air Corps' May 1933, maneuvers. Additional exercises in the late 1930s, laid the foundation for the Army's air defense doctrine that was in place in 1941. (1) This system, though, was limited by its sensors--volunteer civilians spread across the countryside. America's primary air threat of the era was coming from offshore---where precious few observers lived and operated. Thankfully, technology was preparing to fill this gap with a new sensor--the radar set.
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The U.S. Army and Radar
The Army's relationship with radar technology dates back to the early 1930s, through development activities at the Signal Corps Laboratories, located at Fort Monmouth, N.J. Despite concurrent experimental activity in Europe, American radar research was independent of outside influences. Though hampered by a lack of funds and personnel, a practical demonstration was possible within a few years. On December 14-15, 1936, a successful test of the technology was conducted. This test led to the construction of a hand-built prototype, which was presented to the Chief of the Signal Corps on May 18-19, 1937, followed by a demonstration to the Secretary of War Harry Woodring a week later. (2) The technology was well received and gave birth to a development program that led to the creation of the SCR-268 searchlight controlling radar. (3) The Chief of the Air Corps Maj. Gen. Oscar Westover, who also attended the May demonstration and one on June 3, 1937, proposed an operational specification for a long-range early warning radar to meet Air Corps needs. (4) Emphasis on the Air Corps requirement sent Fort Monmouth's staff back to the drawing board. By early 1939, both a mobile (soon designated SCR-270) and fixed (SCR-271) version of an early warning radar had been developed. An engineering model of the SCR-270 was tested in June 1939, and a November demonstration to the Secretary of War--involving two radars located at Twin Lights, N.J. and Meriden, Ct. was deemed a success. (5) The Army established the 1st Aircraft Warning Company at Fort Monmouth on March 1, 1940, and soon thereafter took delivery of the initial production SCR-270A radar sets for operational testing. (6)
The SCR-270 Early Warning Radar
The Army adopted the SCR-270 in May 1940, and a contract for mass production was signed with Westinghouse in August. (7) The SCR-270 was a long-range search radar intended to provide early warning of an approaching air raid; the SCR-270 came in many variants. The first two systems delivered were SCR-270s, followed by five improved SCR-270As that incorporated minor changes to the antenna mount. The variant in production at the start of World War II was the SCR-270B, differing from its predecessor by having radar components moved from the antenna mount to the operations truck. (8) The SCR-270B was a mobile radar that required four trucks for transport; two vehicles were dedicated to moving the radar antenna, one truck to housing the generator and a fourth truck to house the transmitter, receiver, and operator position. (9) The SCR-270B had a nominal maximum range of 150 miles as marked on the oscilloscope display at the operator position, though the Army training manual for the system noted a maximum range against bombers at 10,000 feet as 80-120 miles and fighters as 50-75 miles. The radar operated within the Very High Frequency (VHF) band at 104-112 Megahertz, utilizing a 55- foot vertical broadside array antenna. (10) Though the antenna was placed on a tower and the transmitter and receiver were emplaced in a building, the SCR-271 was essentially the same as the SCR-270 in operation.
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The SCR-270B was operated by four persons. Two maintenance technicians supported the generators and electronics, while an operator worked the actual radar. The fourth man was a communication specialist who relayed targets tracked by the operator to a headquarters command post (called information centers in that era, filter centers in today's vernacular) via telephone or radio. The radar operator would manually rotate the antenna (via an antenna drive) across his assigned sector, a 360 degree scan taking about 90 seconds. Once the operator saw a return or "echo" on his five-inch "A" scope, he ceased his scan and rotated the antenna back and forth a few degrees until he determined the azimuth that gave the largest return. (11) The target azimuth was determined by reading three-inch high numbers painted on plates attached to the rotating antenna tower base. (12) Measurement of range was a little more complicated. Usually only 75 miles of the radar sweep was visible on the oscilloscope; a rotating knob allowed the oscilloscope to move back and forth across the entire 150-mile range of the radar. To get the range of a radar return, the operator would use a rotating knob to move the display until the echo was lined up under a vertical line etched in the center of the screen. A range associated with the position of the now-centered echo could then be read out in a small window associated with the rotating control knob. (13) The echo size grew with the number of aircraft, but it was not possible to identify the exact number of aircraft the radar was detecting. Finally, all radar returns were just that--raw energy reflected back from the skin of the target aircraft. The SCR-270 lacked an "identification friend or foe" or "IFF" transponder capability that enabled friendly aircraft to have a distinct response. While the Royal Air Force (RAF) had this function in their radars for the 1940 Battle of Britain, the Signal Corps was still developing an American IFF system in 1941.
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Another limitation with the SCR-270 was its inability to provide altitude data for targets that were being tracked. This liability was noted from the beginning by Air Corps commander Gen. Henry H. "Hap" Arnold, but there was little that could be done about it. Arnold unsuccessfully tried to acquire the SCR-268 to provide altitude capability to radar sites, but these radars were already behind in their delivery schedules due to the priority assigned to SCR-270 development. The Signal Corps attempted to provide an interim altitude capability with modifications to their existing radars. Engineers tried to increase the range of the SCR-268 to make it a stand-alone, three-dimensional radar capable of ground-controlled intercept; they also explored making a height finder attachment for the SCR-270. Unfortunately, both ideas were limited by the existing designs and the need to field a radar as soon as possible. (14) While the development of the Army's first radar set was not easy, it was only half the battle. The deployment of the SCR-270 was another challenge that needed to be overcome.
On March 10, 1939, the Chief Signal Officer was instructed to prepare a comprehensive plan for the organization and operation of an Air Warning Service for the continental United States and select overseas locations. The final study was completed in February 1940, and provided for twenty-three radar sites supporting nine information centers. (15) The first radar unit, the Signal Company, Air Warning, Panama, was formed in January 1940. In May 1940, it departed the U.S. and received two fixed-site SCR-271 radars in June. Located at Fort Sherman, Canal Zone, this building-mounted site became the first radar station in U.S. service. (16) Unfortunately for the U.S., world events limited the Army's methodical approach to fielding this new technology.
The German Blitzkrieg against Poland, in September 1939,...
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