Close-up view of the Wright Whirlwind R-975 aircraft engine used in early Shermans. The tank version (made by Continental) has a large cooling fan at the front of the engine. The radial engine was apparently difficult to service and also available production was needed for trainer aircraft. The most successfull Sherman engine was the 400 HP Ford GAA V8. The Ford engine was originally intended as a 12 cylinder copy of the British Merlin for aircraft use, but was downsized for the M4 tank.