The Bristol Engine Company was originally a separate entity, Cosmos Engineering, in turn formed from the pre-WW1 automobile company, Brazil-Straker. In 1917 Cosmos was asked to investigate air-cooled radial engines, producing the Mercury, a 14 cylinder two-row (helical) radial, which they launched in 1918. This engine saw little use, but a smaller and simpler 9 cylinder version known as the Jupiter was clearly a winning design. In the post-war rapid downsizing of military orders the company went bankrupt, and the Air Ministry let it be known that it would be a good idea if Bristol purchased them. The Jupiter competed with the Armstrong Siddeley Jaguar through the 1920s, but Bristol put more effort into their design, and by 1929, the Jupiter was clearly superior. In the 1930s they developed a new line of radials based on the sleeve valve principle, which would develop into some of the most powerful piston engines in the world, and could continue to be sold into the 1950s. In 1956 the division was renamed Bristol Aero Engines, and then merged with Armstrong Siddeley in 1958 to form Bristol Siddeley as a part of the airframe mergers that formed BAC. In 1966 Bristol Siddeley merged with Rolls-Royce, leaving only one major aero-engine company in England, Rolls-Royce.
In 1946, with the surplus capacity after WW2, the company started an offshoot, Bristol Cars, using pre-war BMW designs as the basis for a new car, the Bristol 400. The car company became independent in 1960, around the same time as the consolidation the British aircraft industry, but is still based at the Filton site.
Bristol Aeroplane designs include: