The Corsair was designed as a carrier-based aircraft but its difficult carrier landing performance rendered it unsuitable for Navy use until the carrier landing issues were overcome by the Royal Navy Fleet Air Arm. The Corsair thus came to and retained prominence in its area of greatest deployment: land based use by the U.S. Marines.[6] The role of the dominant U.S. carrier based fighter in the second part of the war was thus filled by the Grumman F6F Hellcat, powered by the same Double Wasp engine first flown on the Corsair's first prototype in 1940.[7] The Corsair served to a lesser degree in the U.S. Navy. In addition to its use by the U.S. and British, the Corsair was also used by the Royal New Zealand Air Force, the French Naval Aviation and other, smaller, air forces until the 1960s. Some Japanese pilots regarded it as the most formidable American fighter of World War II,[8] and the U.S. Navy counted an 11:1 kill ratio with the F4U Corsair.[9