In 1926 Bristol began studies to integrate the Burt-McCollum sleeve valve concept into selected new engine designs. The sleeve valve, which moved within the cylinders, functioned as both an intake and exhaust valve. Relative to an engine with conventional intake and exhaust valves, the advantages of the sleeve valve design included a lower parts count, operational smoothness, and improved fuel economy.

In March 1935, Roy Fedden and L.F.G. Butler began the design of the Bristol Hercules, the third Bristol engine model to incorporate sleeve valves. After overcoming difficult development problems, the Hercules was produced in larger quantity than any other Bristol engine. This engine, a Model VI, powered World War II aircraft such as the Short S.29 Stirling III, Avro 683 Lancaster II, Handley Page H.P.61 Halifax III, and Bristol 156 Beaufighter. After the war it powered such commercial aircraft as the Vickers 623 Viking IA, Short S.45 Solent 3, and Bristol 170 Freighter.