Definitely taken during the war, probably in September 1940 when the first were delivered from the USA. Note the tricolor rudder, a hat tip to the original French order for the aircraft, which was taken over by a hasty request from the Royal Navy while they were still on the production line.
It wasn't a request from the RN.
At 0330 on Monday, 17 June 1940, some five hours before the US Treasury froze all French assets in the USA, the head of the British Purchasing Commission, Arthur Purvis, signed a deal with French representatives, that assigned French interests in some 151 aircraft and engine contracts worth some $425m to Britain. Amongst those was the contract for 81 G-36A, Grumman's export designation for the F4F. These became known as Martlet I when they arrived in Britain in Sept 1940.
This decision was to
1. Obtain the aircraft
2. To convince the US public that Britain would fight on and
3. Because of what was seen as a "moral" responsibility since the two countries had worked closely together to procure aircraft in the US and it was seen, at least in part, as a joint commitment.
Arthur Purvis, who signed the document, said it was the hardest decision he ever made. He is said to have sat for half an hour, pen in hand, before appending his signature to the document.
$425 million in 1940 is about $8.5 billion in today's terms. All transferred with a single signature. No wonder he hesitated!
Article here about the Martlet /Wildcat in RN service.