Blue Envoy (a Rainbow Code name) was a British project to develop a ramjet-powered surface-to-air missile. It was tasked with countering supersonic bomber aircraft launching stand-off missiles, and thus had to have very long range and high-speed capabilities. The final design was expected to fly at Mach 3 (3,700 km/h; 2,300 mph) with a maximum range of over 200 miles (320 km).