Grumman F4F Wildcat

At the end of May the modified XF4F-3 (G‑36) was flown at NAF Philadelphia, were it achieved speeds of 537 kph at an altitude of 6250 m. Its steering properties had greatly improved. Although the engine still had a tendency to overheat and the problems with directional stability were mostly unsolved, another three planes (now designated F4F-3) were ordered in August. After testing the XF4F-3 in NACA’s wind tunnel at Langley Field (Virginia) a dorsal fin extension was added in front of the tail fin and the tail plane’s span was increased. At the same time attempts were made to solve engine problems by increasing the airflow. In the end an intercooler and a pressurized fuel system were introduced which put an end to the malfunctions.

Series and Variants
The changes were made very quickly and mass production launched even before a contract had been signed with Bureau of Aeronautics, which proved to be an overly hasty move. When on 8 August 1939 the contract was finally signed for 54 Grumman F4F-3’s2  the Navy requested the removal of the 7,62 mm machine guns from the fuselage and wanted not one but two 0.50in caliber Colt-Browning M2 guns in each wing. The undercarriage was also to be reinforced and armor plating installed in the cockpit. The two lower windows were to be replaced with one. The changes in armament required reconstruction of the wings and moving the inflatable floats outwards. The construction of the first two planes was already too advanced to make these changes possible. They were both finished according to the original design giving the US Navy two fighters it had not ordered.

G-36A. Meanwhile a buyer was found for the still unfinished F4Fs in the form of a French purchasing committee, authorized to buy everything they could lay their hands on in the US. Unsurprisingly they were interested in a fighter plane with lots of development potential. All told, 81 planes were ordered, designated G-36A for the French.
The visitors from Paris didn’t want to take any risks with the engines, which still required some fine-tuning and requested Wright GR-1820-G205A Cyclones. This was a 9-cylinder radial engine with a single-stage, double-speed supercharger,
rated at 1200 hp. The propeller was a triple-blade Hamilton Standard. The armament would consist of six French 7,5 mm Darne machine guns, two over the engine and four in the wings; installed in France. The planes would also have French Radio-Industrie 537 radio stations and OPL 38 telescopic gun sights. The first G-36A flew on 11 May 1940 – the day after the German invasion of France. Only seven planes were built before France’s defeat. The French order was then taken over by the British, who needed planes to defend the Isles.

Starboard side with the prominent main undercarriage retraction crank visible in the center. The retraction took 28 turns.[Via Andre R. Zbiegniewski]

Representatives of the British Navy also noticed Grumman’s fighter very early in 1940 and ordered 100 machines, powered by Pratt&Whitney S3C4-G  engines (1200 hp) and Hamilton Standard propellers, now designated G-36B. Planes intended for the FAA – including the ex-French machines – were only supposed to have four half-inch guns mounted into the wings. The direction of throttle operation also had to be reversed from the French standard – to increase engine power the throttle was moved forward, while in French planes it was pulled back.
It might seem strange that the Americans were so keen to give away their latest fighter types to other countries. The reason for this was very simple. Representatives of the Bureau of Aeronautics counted on all the faults of the new design being eliminated at Grumman’s expense and thought that this attitude would force the constructor to make all the necessary improvements as soon as possible. Aircraft taken over from the French contract were named Grumman Martlet Mk.I and had serial numbers between AX824-829, AL236-262, BJ507-527 and BJ554-570. The first seven “French” machines were given numbers: AX 753, 754 and AL231-235. Nobody worried about such insignificant details as the American neutrality pact. The planes flew to Canada, where they were disassembled and shipped to Scottish Aviation workshops in Prestwick and Blackburn Aircraft Ltd workshops in Brough. They were then re-assembled, equipped with British radio sets, oxygen systems, telescopes, and batteries, and after test flights were delivered to combat units. The British received a total of 70 Martlet Mk.Is. Ten other planes (BT447-456) went to the bottom of the Atlantic along with the freighter SS “Ruperra”, sunk by U-46 on October 10th 1940, 500 miles to the north-west of Ireland.