The Bristol Proteus was the Bristol Engine Company's first mass-produced gas turbine engine design, a turboprop that delivered just over 4,000 hp (3,000 kW). The Proteus was a reverse-flow gas turbine. Because the second turbine drove no compressor stages, but only the propeller, this engine was classified as a free-turbine. It powered the Bristol Britannia airliner, small naval patrol craft, hovercraft and electrical generating sets. It was also used to power a land-speed record car, the Bluebird-Proteus CN7. After the merger of Bristol with Armstrong Siddeley the engine became the Bristol Siddeley Proteus, and later the Rolls-Royce Proteus. The Proteus was to have been superseded by the Bristol Orion which would have given a Britannia a 75% increase in power for cruising faster.

The Bristol Type 175 Britannia is a retired British medium-to-long-range airliner built by the Bristol Aeroplane Company in 1952 to meet British civilian aviation needs. During development two prototypes were lost and the turboprop engines proved susceptible to inlet icing, which delayed entry into service while solutions were sought.