Before the Fleet Air Arm took on charge the Martlet Mk Is, it had already ordered 100 G-36B fighters. The British chose the Pratt & Whitney R-1830-S3C4-G engine to power this aircraft; this too had a single-stage, two-speed supercharger. The FAA decided to accept a delay in delivery to get Martlets fitted out with the Grumman-designed and patented Sto-Wing folding wing system first fitted onto U.S. Navy F4F-4 Wildcats, which were vitally important if the Martlet was to be used from the first 3 Illustrious class carriers which had elevators that were too narrow to accommodate non-folding wing aircraft. Nevertheless, the first 10 received had fixed wings. The first Martlet with folding wings was not delivered until August 1941.
