On Dec. 11, 1959, the U.S. and U.K. declared Thor Intermediate Range Ballistic Missiles operational. The Air Force initiated development of the Thor in 1954 as a tactical missile that could deliver a nuclear warhead up to 2,300 miles from a launch site in the U.K. On Dec. 27, 1955, Douglas Aircraft Corp. was awarded the prime contract for the airframe and integration of components. The first Thor flight was Jan. 25, 1957. Beginning in August 1958, 60 missiles deployed to U.K. to be operated by 20 RAF Bomber Command squadrons at Driffield, Hemswell, Feltwell and North Luffenham. Each base had five squadrons with three closely sited missiles, totaling 15 per base. RAF crews manned the missiles while U.S. personnel maintained the warheads. The first operational unit transferred to U.K. Bomber Command 77 squadron at RAF Feltwell in June 1959. All units were inactivated by September 1963.