Whi;st i cant put my fingers on my paper source material, I am fairly certain that it is true that the decisions to incorporate armour, self sealing tanks, and a six gun broadside were at the request of the british purchasing commission. these were known in the RN as martlet II, whilst they were concurrently developed as the F4f-4 for the USN. The decision to build to this standard was a british one, however.
The reason why most of the early deliveries were not to this standard, is because the majority of martlets received by the RN were foreign orders, principally french and greek orders diverted to to the RN. The first mkIIs were not delivered to the RN until December, after earlier deliveries of the F4f-4 to the USN had revealed serious problems in the fuel systems (i think, in any event the F4f-4s delivered to the USN in 1941 were not airworthy).
Later, the majority of f4fs were FM-2s, which were cut down versions adapted for use from escort carriers. these FM-2s retained the same level of protection afforded to the martlet IIs, but reduced armament. by the time of their introduction, the main fleet types for the Rn had progressed to the Hellcat and the corsair, but even so, by the time of the introduction of the FM-2, I think the inferiority of allied pilots was passing. no longer was acquiring an enemy target such a fleeting desperate affair. allied pilots were better, axis pilots were worse, and the FM-2 was really trhere for convoy protection (though it was often pressed into servicce for more frontline duties anyhow).
The FAA website gives this description about martlet usage:
Versions
Mk I British version of the F4F-3; Four 05in machine guns
Mk II British version of F4F-4 with folding wings, armour, self-sealing fuel tanks and six 0.5in machine
guns
Mk III
Mk IV
Mk V General Electric built FM-1 with R-1830-86 engine, four 0.5in machine guns with provision for
underwing stores or: FM-2 with 1,350hp Wright R-1820-56 Cyclone, with taller vertical tail
surfaces and on some aircraft provision for six 5-inch rockets under the wings
In total the Fleet Air Arm received 1172 Wildcat 1940-1945. The first Wildcat used by the Fleet Air Arm were 53 Grumman G-36a Martlet I, and 6 Grumman G-36a Martlet III diverted from a French order which had not been delivered before the Fall of France in 1940. The aircraft were all delivered to the British Purchasing Commission on 23 August 1940 and transferred to the first FAA unit 804 Hatston on 7 September 1940 (eg AX827), 778 squadron at Arbroath in September 1940 (eg AX826), 759 squadron at Yeovilton in October and November 1940 (eg BJ555) and 802 squadron at Donisbristle on 23 November 1940 (eg AL237).
Further aircraft in 1940 were lost when 20 Grumman G-36a Martlet I diverted from an undelivered French orders sank with SS Ruperra which was torpedoed 500 miles NW of Ireland on 19 October 1940.
The next Wildcat to be received by the Fleet Air Arm were in Spring of 1941, when 30 Grumman F4F-3a Martlet III ordered by Greek Purchasing Commission in August 1940 for shipment to Greece reached Port Suez in April 1941, then diverted to the Royal Navy under Lend-Lease transfer on 4 April 1941. These aircraft were subsequently involved in convoy patrols, one Martlet piloted by Sub Lt R Griffon shot down a S.79, forced two others to jettison bombs, then hit by return fire attacking a fourth, dived vertically into sea 50m N of Ras el Milh on 28 December 1941.
Martlet II started to be delivered in December 1941, when 54 were shipped from New York to Bombay arriving in March 1942 (AJ100), this was closely followed by further losses of 10 Martlet III in HMS Audacity on 21 December 1941.
With this situation, 16 Grumman F4F-3 [Martlet III equivalent] were loaned from the US Navy to 890 and 892 Squadrons during work up at Norfolk, Virginia, USA from 18 July 1942 until 12 September 1942 after which the aircraft were returned to the USN. All these aircraft were from the USN squadron VF-9, and carried 9F codes (they kept their US Nos: BuAer Nos 1858-3873).
By February 1942, the first major delivery of 220 Wildcat IV (ex Martlet IV until 1.1.44) was made. 806 squadron was equipped with Martlet II from July 1942 on HMS Indomitable, whilst most were shipped to the UK in September 1942 onwards, first reaching 896 squadron in November 1942, and 312 Grumman FM-1 Wildcat V delivered in June 1943 to 787 squadron and C Sqdn A&AEE in July 1943, and 1832 squadron from August 1943.
The Wildcat was one of the FAA's primary naval fighter up till the end of 1942. However, during 1943 Wildcat squadrons started to be re-equipped with either the larger Grumman F6F Hellcat or the Chance-Vought F4U Corsair.
However, orders continued and 288 Grumman FM-2 Wildcat VI were delivered in May 1944, firstly to AHU Stretton, and 881 squadron in July 1944. Many of these latter aircraft remained in service with the FAA until 1946. The final 82 Grumman FM-2 Wildcat VI were delivered in August 1945 up until November 1945, and mainly being sent out to the Far East and Australia