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 Hawk of which 76 were built. Rolls-Royce Hawk The Rolls-Royce Hawk was a British aero engine designed by Rolls-Royce in 1915. Derived from one bank of six cylinders of the Rolls-Royce Eagle, it produced 75 horsepower at 1,370 rpm. Power was progressively increased to 91 hp by February 1916, and 105 hp by October 1918. After Rolls-Royce made the prototypes, the Hawk was manufactured under licence by Brazil Straker in Bristol between 1915 and 1918. During this period 204 engines were built, and the Hawk earned a reputation for high reliability. Many engines of this type were used to power the