Page:A Concise History of the U.S. Air Force.djvu/60

 perform the same missions. The flights of the X-aircraft, however, provided critical knowledge for manned space travel and for the special materials used in a new generation of aircraft, starting with the SR-71 Blackbird reconnaissance aircraft. Strategic reconnaissance became the primary goal of space exploration. Fears of a surprise nuclear attack, based largely on the memory of Pearl Harbor, and the secrecy of events behind the Iron Curtain forced every administration after 1945 to seek information on the status and disposition of military forces inside the Soviet Union. Initially, U.S. Air Force and U.S. Navy aircraft were deployed along its vast periphery to take photographs and intercept radio and radar signals. In early 1956 the Air Force launched 448 unmanned camera-carrying balloons from western Europe propelled eastward by prevailing winds. Although inherently random in their coverage, 44 were recovered and provided tantalizing glimpses of some 10 percent of the Soviet Union's land area. At the direction of President Eisenhower, the Air Force, with the Central Intelligence Agency (CIA), and the Lockheed Aircraft Corporation developed the U-2, a single-engine glider aircraft capable of flying above 70,000 feet and beyond the range of Soviet air defenses. Eisenhower authorized U-2 overflights across the Soviet Union beginning on July 4, 1956, but, fearing that they might become a casus belli, he limited their number. Fewer than 25 missions occurred before a Soviet surface-to-air missile downed a U-2 flown by Francis Powers on May 1, 1960. The resulting diplomatic crisis ended aerial reconnaissance flights over the Soviet