Rolls-Royce Merlin exhaust flow and waste-gates, meant that this option was rejected in favour of the two-stage supercharger. Fitted with the two-stage two-speed supercharger, the Merlin 60 series gained 300 horsepower (224 kW) at over the Merlin 45 series, at which altitude a Spitfire IX was nearly faster than a Spitfire V. The two-stage Merlin family was extended in 1943 with the Merlin 66 which had its supercharger geared for increased power ratings at low altitudes, and the Merlin 70 series that were designed to deliver increased power at high altitudes. While the design of the two-stage supercharger forged ahead, Rolls-Royce also
Rolls-Royce Trent launched. When Boeing finally launched the 747-8 in 2005 it announced that the General Electric GEnx would be the only engine that would be available for the 747-8. On 6 April 2004 Boeing announced that it had selected two engine partners for its new 787, Rolls-Royce and General Electric. Initially, Boeing considered the idea of sole sourcing the powerplant for the 787, with GE being the most likely candidate. However, potential customers demanded choices and Boeing relented. Both engine types will have a standard interface with the aircraft, allowing any 787 to be fitted with either a GE or Rolls-Royce