 In 1959 Armstrong Siddeley and Bristol's engine division merged to become Bristol Siddeley, but were shortly purchased by Rolls-Royce in 1966, leaving RR as the only major British aircraft engine manufacturer.With the development of missiles, those roles that missiles could cover meant that certain aircraft in development could be cancelled.These included the next generation of supersonic interceptor for high flying bombers, the F.155 and the interim aircraft that would have covered it until introduction in 1963, namely the Saunders-Roe SR.53 and Saunders-Roe SR.177.