The Corsair was designed and principally operated as a carrier-based aircraft, and entered service in large numbers with the U.S. Navy and Marines in World War II. It quickly became one of the most capable carrier-based fighter-bombers of the war.[3] Some Japanese pilots regarded it as the most formidable American fighter and U.S. naval aviators achieved an 11:1 kill ratio. Early problems with carrier landings and logistics led to it being eclipsed as the dominant carrier-based fighter by the Grumman F6F Hellcat. Initially it was relegated to land duty with both the US Navy and Marines. Eventually the issues with difficulty in flying on and off carriers were remedied. It was powered by a 2000 HP Pratt and Whitney R-2800 Double Wasp engine turning a very large 13'4" constant speed propeller. In order to accommodate the very large propeller, the landing gear would have to be rather long, which would have been difficult to design to be strong enough to withstand hard landings aboard ship. The answer, instead was to add an inverted gull wing to provide the necessary clearance. The Corsair's initial prototype first flew in 1940.