The phenomenol Bristol Type 188 was a research aircraft that flew in 1961 to test the effects of kinetic energy on a plane moving at Mach 2 at height. As such, it was made of stainless steel and was designed to break both Mach 2 and then 3. But technical problems soon developed that was no fault of the design- the promised Rolls-Royce Avon RA.24R engines were not delivered and so De Havilland Gyron DGJ.10s were substituted that guzzled fuel, which meant that the 188 never even reached Mach 2. It reached Mach 1.89, but still provided a wealth of information on the heat build-up on the aircraft. The aircraft also tested variable-geometry air intakes and exhaust, the data gained passed on to the Concorde program. At some angles the 188 looks like a British SR-71 type and could have reached Mach 3 with the RR engines and a few mods...

http://www.bredow-web.de/Museum_Cosford/Bristol_188_-_BAC_188/a_Bristol_188.jpg http://www.classicaircraft.co.uk/photos/photo082.jpg http://spacestation.carolan.info/Starship/Bristol188.jpg