The Proteus was the Bristol Aeroplane Company's first successful gas-turbine engine design, a turboprop that delivered just over 4,000 hp (3,000 kW). The Proteus was a two spool, reverse flow gas turbine. Because the turbine stages of the inner spool drove no compressor stages, but only the propeller, this engine is sometimes classified as a free turbine. It was used mostly on the Bristol Britannia airliner, but saw some third party use as well.
The original Proteus Mk.600 delivered 3,780 hp (2,820 kW), and was going to be used on the early versions of the Britannia and the Saunders-Roe Princess flying-boat. The versions on the Princess were mounted in a large frame driving a single propeller through a gearbox, and were known as the Coupled Proteus. The Coupled Proteus was also intended to be used on the Mk.II versions of the Bristol Brabazon, but this project was cancelled. Only three Princess' were built, and only one of them flew, and by the time the Britannia was ready for testing they had decided to use the later Mk.700 engines instead.
At this point the Proteus proved to have troubling icing problems, causing the engine and aircraft projects to be delayed while solutions were found. The Mk.705 of 3,900 hp (2,900 kW) was the first version to see widespread production on the Bristol Britannia 100 and some 300 series. The Mk.755 of 4,120 hp (3,070 kW) was used on the 200 series (not built) and other 300's, and the Mk.765 of 4,445 hp (3,315 kW) was used on the RAF's Series 250 aircraft.
A unique variant of the engine was also used to power the four-wheel drive Bluebird-Proteus CN7, Donald Campbell's land speed record car. This had a drive shaft at each end of the engine, each to a separate axle.
Another use of the Proteus was for remote power generation in the South West of England in what were called "Pocket Power Stations". The regional electricity board installed several 2.7MW remote operated generation sets for peak load powered by the Proteus. Designed to run for ten years many were still in use forty years later.