The Grumman F4F Wildcat is an American carrier-based fighter aircraft that entered service in 1940 with the United States Navy.The Grumman F6F Hellcat is an American carrier-based fighter aircraft of World War II. Designed to replace the earlier F4F Wildcat and to counter the Japanese Mitsubishi A6M Zero, it was the United States Navy's dominant fighter in the second half of the Pacific War.