The biggest change made to the F4F-4 was the installation of folding wings. The U.S. Navy requested this feature early in 1940. It took the Grumman company until April 1941 to fit hydraulically powered folding wings to the last F4F-3 produced, turning it into the XF4F-4 prototype.
The folding wing revolved through 90 degrees and then backwards, resting alongside the fuselage of the aircraft, somewhat resembling a roosting sea bird. The net effect was to result the width of the aircraft from 38 feet to 14 feet 4 inches, doubling the amount of Wildcats that would fit in any particular space. The original “sto-wing”, designed by Leroy Grumman, was hydraulically powered, and added too much weight to the aircraft (gross weight went up from 7,065 lbs for the F4F-3 to 7,750 lbs on the XF4F-4. Tests onboard the U.S.S. Yorktown in May 1941 revealed that the performance of the modified aircraft was too poor to be considered in combat. As a result, the production F4F-4 would feature manually folded wings. The same Pratt & Whitney R-1830-86 engine was used as in the F4F-3, so there was no increase in power to make up for the increase in weight.
The production F4F-4 was ordered in June 1941. The first aircraft were delivered at the end of 1941, just as American was forced into the war. The new machine featured manually folded wings, improved armour and had six .50 calibre machine guns (up from the four featured in the F4F-3). It was the F4F-4 version of the Wildcat that fought at Midway and on Guadalcanal. It was not entirely popular with experienced Wildcat pilots, used to the lighter, faster, more manoeuvrable F4F-3, but the increased number of fighters that could be carried on each carrier more than compensated for this. The F4F-4 had a maximum speed 23 miles per hour slower than the dash three, which it reached 2,500 lower. Its service ceiling was reduced from 37,000 feet to 33,700 feet.
Late production F4F-4s were equipped with wing brackets to allow the use of two fifty-eight gallon fuel tanks or two bombs. This attachment was standard on the FM-1 and FM-2 variants.
This designation was allocated to a proposed version of the Wildcat powered by a Pratt & Whitney R-1830-90 engine. An order was placed for this version, but cancelled before any were produced.
This was an American designation used for the Royal Navy’s Martlet IV