Rolls-Royce Limited increase its own production rates. By the late 1920s, aero engines made up most of Rolls-Royce's business. Henry Royce's last design was the Merlin aero engine, which was first flown in prototype form in 1935, although he had died in 1933. This was developed from the R engine, which had powered a record-breaking Supermarine S.6B seaplane to almost in the 1931 Schneider Trophy. The Merlin was a powerful supercharged V12 engine and was fitted into many World War II aircraft: the British Hawker Hurricane, Supermarine Spitfire, de Havilland Mosquito (twin-engine), Avro Lancaster (four-engine) (a development of the Avro Manchester with
Rolls-Royce RB211 turn Rolls-Royce from a significant player in the aero-engine industry into a global leader. Already in the early 1970s, the engine was reckoned by the company to be capable of at least 50 years of continuous development. The RB211 was officially superseded in the 1990s by the Rolls-Royce Trent family of engines, the conceptual offspring of the RB211. In 1966, American Airlines announced a requirement for a new short-medium range airliner with a focus on low-cost per-seat operations. While it was looking for a twin-engined plane, the aircraft manufacturers needed more than one customer to justify developing a new airliner.