Double Spectre rocket engine on a Blue Steel stand-off bomb, 1960.
© Science Museum / Science & Society Picture Library
The operational Blue Steel stand-off bomb carried Britain's nuclear deterrent between 1964 and 1975. Each was carried beneath a Vulcan or Victor aircraft and air-launched at altitude. Blue Steel used a Stentor rocket engine to accelerate to a maximum velocity of Mach 2. Stentor technology was subsequently used in the Gamma engines of the Black Knight ballistic test vehicle and Black Arrow satellite launcher. The Science Museum's Blue Steel is a test vehicle and is fitted with a Double Spectre rocket engine. Single Spectre engines were developed for the SR-53 interceptor aircraft.