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This is Volume One of The Army Air Forces in World War II, titled Plans and Early Operations, January 1939 to August 1942, edited by Wesley Frank Craven and James Lea Cate. The University of Chicago Press first published it in 1948, and the Office of Air Force History reprinted it in 1983. The front matter explains how the AAF historical program was set up during the war. The index covers Pacific, Atlantic and European operations, and nothing in the text concerns unidentified aerial phenomena.
“The Invaders”15 pages
T H E A R M Y A I R F O R C E S I N W O R L D W A R I 1 which could generate considerable power a t very short wave lengths. No one nation enjoyed a monopoly of these discoveries, but the most rapid progress in devising practical military applications was registered by the British. The basic problem of providing early warning to defending aircraft had been solved in Britain by 1939. A chain of radar stations along the coast provided reasonably effective information on planes approach- ing from the continent."' Thus, when the Germans began large-scale daylight raids against England in August 1940, the RAF was able to conserve its limited fighter strength by keeping the planes on the ground until an attack actually impended and thus to achieve a more efficient concentration of force.lo3 When the Germans switched to indiscriminate night attacks, British defenses for a time proved less effective,lo4 for advance warning of the enemy's approach did little good unless he could be found in the dark. Fortunately, the RAF, magnificently served by such advisers as Robert Watson-Watt, rapidly went beyond the original conception of radar as merely a device for early warning. Under the compulsion of war and the special lash of the night blitz, the British perfected and put into use a whole new series of electronic devices which guided every step in the proc- ess of intercepting enemy planes. T h e original radar equipment installed along the coasts of Britain had been well suited to handling daytime raids, for it had a long range- up to 2 0 0 miles. But these sets did not permit the fine discrimination between targets which was needed to guide night fighters to the immediate vicinity of enemy A new type of radar known as GCI (ground controlled interception) transformed the British sys- tem from one of crude warning into a machine for dependable control of interception. GCI equipment made it feasible to plot, virtually instantaneously, the positions of a large number of planes. Moreover, it displayed the information on an ingenious PPI (plan position indi- cator) scope, which was a cathode ray tube on the face of which a map of the region had been drawn. Aircraft within range of the GCI set were shown on the map as spots of light.lo6The British also developed equipment known as IFF (identification friend or foe) which indicated to a ground observer which of the targets in the PPI scope were friendly. The identification was accomplished by installing in friendly planes an electronic device-a simple short-wave radio transmitter- which sent coded signals when interrogated by a ground station.lo7 288
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