Originally conceived as a carrier-born maritime attack aircraft, the Blackburn design included many original features such as Boundary Layer Control, a system which blew hot air over the flying surfaces to increase lift when landing. The rotating bomb bay was also new and enabled easier maintenance, accessibility and reduced drag. The first model, the S Mk 1, entered operational service with the Fleet Air Arm in 1961. S Mk 2 became operational in 1964, powered by Rolls-Royce Spey engines that gave considerably more thrust.