Another solution to the high altitude performance problem was to fit the P-40 with a supercharged Rolls-Royce Merlin engine. This idea came from the British, as they noticed that their Allison powered Kittyhawks and Mustangs had poor performance at high altitudes, while their own Merlin powered Hurricanes and Spitfires did not have the same problems. Curtiss fitted the second P-40D with a 1,300 hp (969 kW) Merlin 28. Production aircraft had the American-made 1,390 hp (1,040 kW) Packard V-1650-1 Merlin. The resulting P-40F (Model 87B) was the first variant to carry the "Warhawk" name.