First flight of the mixed-power plant SR.53 interceptor XD145 was made by S/L J.S. Booth from Boscombe Down on 16 May 1957. The SR.53 was powered by one de Havilland Spectre rocket motor and an Armstrong Siddeley Viper turbojet.
The Sanders-Roe SR.53 was an interceptor and used a rocket motor to climb to high altitudes. When it was at altitude it used a second Armstrong-Siddeley Viper jet engine, allowing it to remain at altitude. Only 2 were build.