The Bristol Thor was a 16" diameter ramjet engine developed by Bristol Aero Engines (later Bristol Siddeley Engines) for the Bristol Bloodhound anti-aircraft missile.

Although Bristol Aero Engines acquired ramjet

Ramjet

A ramjet, sometimes referred to as a stovepipe jet, or an athodyd, is a form of airbreathing jet engine using the engine's forward motion to compress incoming air, without a rotary compressor. Ramjets cannot produce thrust at zero airspeed and thus cannot move an aircraft from a standstill...

 technology from the US company Marquardt

Marquardt

Marquardt Corporation was one of the few aeronautical engineering firms that was dedicated almost solely to the development of the ramjet engine. Marquardt designs were developed through the 1940s into the 1960s, but the ramjet never became a major design and the company turned to other fields in...

, 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.

The Bloodhound Mk.1 could attain a speed of Mach 2.2

Mach number

Mach number is the speed of an object moving through air, or any other fluid substance, divided by the speed of sound as it is in that substance for its particular physical conditions, including those of temperature and pressure...

, while the Mk.2 was capable of just over Mach 2.7.