The F variant of the P-40 Warhawk was fitted with the US-made Rolls-Royce Merlin 28, but its altitude performance improved less than expected. It could barely compete with the German Bf-109 at a height below 15000 feet. However, it does feature excellent low altitude performance. It was tested in November 25, 1941 and about 1300 examples were produced in 1942. Their main service was in the French battlefield.