on the Soviet Union. Eisenhower turned down Dulles' offer to resign and publicly took full responsibility for the incident on 11 May; by then all overflights had been canceled. The Paris Summit collapsed after Khrushchev, as the first speaker, demanded an apology from the U.S., which Eisenhower refused. U-2 pilots were told, Knutson later said, if captured "to tell them everything that they knew", because they were told little about their missions other than targets on maps. Otherwise, Powers had little instruction on what to do during an interrogation. Although he had been told that he could reveal everything about the aircraft since the Soviets could learn what they wanted from it, Powers did his best to conceal classified information while appearing to cooperate. His trial began on 17 August 1960. Powers—who apologized on the advice of his Soviet defense counsel—was sentenced to three years in prison, but on 10 February 1962 the USSR exchanged him and American student Frederic Pryor for Rudolf Abel at Glienicke Bridge between West Berlin and Potsdam, Germany. Two CIA investigations found that Powers had done well during the interrogation and had "complied with his obligations as an American citizen during this period". Although the government was reluctant to reinstate him to the USAF because of its statements that the U-2 program was civilian, it had promised to do so after CIA employment ended; Powers resolved the dilemma by choosing to work for Lockheed as a U-2 pilot. The debris of Powers's aircraft was used to design a copy under the name Beriev S-13. That was then discarded in favor of the MiG-25R and reconnaissance satellites.Yefim Gordon: Soviet X-Planes. Midland Publishing, 2000, . The search for operational ballistic missile sites continued focusing on the Soviet railway system using Corona satellite images, with a resolution of twenty to thirty feet compared to two to three feet from U-2 cameras. Restructuring The U-2 shootdown in 1960 paralyzed the U.S. reconnaissance community and forced changes in policy, procedures, and security protocol. The United States also had to move swiftly to protect its allies: for example after the Soviets announced that Powers was alive, the CIA evacuated the British pilots from Detachment B as Turkey did not know of their presence in the country. The end of Soviet overflights meant that Detachment B itself soon left Turkey, and in July Detachment C left Japan following a Japanese governmental request.