THE Bristol Siddeley BS 605 retractable rocket boost unit has been developed primarily to provide additional thrust during take‐off for the Hawker Siddeley Buccaneer S.Mk.50 strike aircraft ordered by the South African Government. Unlike a number of other assisted take‐off rocket systems, the BS 605 system is designed to retract within the aircraft profile so that no drag penalty is incurred when the rocket boost is not in use. Although produced to meet the South African requirement for thrust boost on take‐off in the Buccaneer, the system could, with the necessary engineering modifications, be adapted to fit other aircraft.