However, the ineffective Pratt & Whitney powerplant nearly proved ruineous for the Grumman design. Thanks to the failure of this engine, the Navy went with the Buffalo for the time being. Grumman was no firm to give up lightly however. With a new P&W Twin Wasp engine, the new XF4F-3 totally outmatched the Buffalo in any department. It carried four 12.7mm machine-guns.  

    With these charateristics, and the war, the US Navy ordered 200 planes, of which the first F4F-3s were in service on the change of the years 1940/41.  Another 100 planes were produced for Great Britian, and the same country took over productions for Greece and France. F4F-3 saw combat in the early months of the war. 12 planes of the type operated off Wake for the Marine Corps, and sank a destroyer while shooting down several bombers. More battle was seen during the early carrier raids, the failed attack on Rabaul, and the Battle of the Coral Sea. By May 1942, however, the F4F-4 saw service, adding two more machine guns and foldable wings. While this resulted in a loss of performance, the added number of planes to be stored on a carrier was deemed to offset that handicap. F4F-4s were the planes that fought at Midway and Guadalcanal, winning the US many successes there. Finally, F4Fs were build at the Eastern Aircraft conglomerate, into August 1945. A thousand planes were flown in the Royal Navy. Most of the Wildcats build in late war were serving aboard Escort Carriers against submarines and in landing support. A special photo-reconnaisance version must be mentioned as well, the F4F-7. One exemplar was based on almost every carrier in 1942.  
The Wildcat was known as the Martlet in RN service until 1944.