The Bristol Thor was a 16" diameter ramjet engine developed by Bristol Aero Engines (later Bristol Siddeley Engines) for the Bloodhound anti-aircraft missile. The Bristol Aeroplane Company (formerly British and Colonial Aeroplane Company) began building primitive Bristol Boxkites in a former tram shed and became famous for the production of the war-time Blenheim and Beaufighter, the Brabazon airliner prototype, the Britannia and Freighter and the Belvedere and Sycamore helicopters. ...

Although Bristol Aero Engines acquired ramjet technology from the US company Marquardt, BAE put considerable effort into developing the Thor unit, including the construction of a high altitude test plant (HATP), with a supersonic test cell, at their Patchway site.

Maximum speed of Bloodhound Mk1 was Mach 2.2, but the much improved Mk 2 was capable of Mach 2.7.