missions, and because of the strong demand for more missile-site photographs, the U-2 was the major source of covert intelligence on the Soviet Union and had photographed about 15% of the country, producing almost 5,500 intelligence reports. The April flight was indeed tracked quickly, and Khrushchev said in his memoir that it should have been shot down by new SAMs, but the missile crews were slow to react. May 1960: U-2 shot down Eisenhower authorized one more overflight, which was to be made no later than 1 May because the important Paris Summit of the Big Four Conference would begin on 16 May. The CIA chose for the mission—the 24th deep-penetration Soviet overflight—Operation GRAND SLAM, an ambitious flight plan for the first crossing of the Soviet Union from Peshawar, Pakistan to Bodø, Norway; previous flights had always exited in the direction from which they had entered. The route would permit visits to Tyuratam, Sverdlovsk, Kirov, Kotlas, Severodvinsk, and Murmansk. It was expected, given good weather, to resolve missile, nuclear and nuclear submarine intelligence issues with one flight. Francis Gary Powers, the most experienced pilot with 27 missions, was chosen for the flight. After delays, the flight began on May Day, 1 May. This was a mistake because, as an important Soviet holiday, there was much less air traffic than usual. The Soviets began tracking the U-2 15 miles outside the border, and over Sverdlovsk, four and a half hours into the flight, one of three SA-2 missiles detonated behind the aircraft at 70,500 feet, near enough to cause it to crash; another hit a Soviet interceptor attempting to reach the American aircraft. Powers survived the near miss and was quickly captured; the crash did not destroy the U-2 and the Soviets were able to identify much of the equipment. Bissell and other project officials believed that surviving a U-2 accident from above 70,000 feet was impossible, so they used the pre-existing cover story. On 3 May, the National Aeronautics and Space Administration (NASA, the successor to NACA) announced that one of its aircraft, making a high-altitude research flight in Turkey, was missing; the government planned to say, if necessary, that the NASA aircraft had drifted with an incapacitated pilot across the Soviet border. By remaining silent, Khrushchev lured the Americans into reinforcing the cover story until he revealed on 7 May that Powers was alive and had confessed to spying