Toward the end of Eisenhower's second term, Secretary of State John Foster Dulles commented that Soviet Premier Nikita Khrushchev and other senior Soviet officials had begun using the technologically advanced Tupolev Tu-114 aircraft for their travels, and it was no longer dignified for the president to fly in a propeller-driven aircraft. This paved the way for the Air Force's initial procurement of 3 Boeing 707-120 (VC-137A) jet aircraft, designated SAM (Special Air Missions) 970, 971 and 972.[21][22]