Pratt & Whitney R-985 The R-985 air-cooled engine was first used by the Army Air Corps in 1932. At that time, it was rated at 300 horsepower. Over the next ten years, further refinements were made, and during World War II some variants produced up to 450 horsepower. The R-985 powered thousands of military aircraft of various types in addition to being installed in numerous civilian types of aircraft. TECHNICAL NOTES: Type: 9-cylinder, air-cooled, supercharged radial Displacement: 985 cu.in. Maximum rpm: 2,300 Maximum hp: 450 Cost: $6,000 Click here to return to the World War II Gallery.