The original Proteus Mk.600 delivered 3,780hp, 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 3,900hp was the first version to see widespread production on the Bristol Britannia 100 and some 300 series. The Mk.755 of 4,120hp was used on the 200 series (not built) and other 300's, and the Mk.765 of 4,445hp was used on the RAF's Series 250 aircraft.