Part of an AU I've been playing around with for ages and am nowhere near finished (doesn't help that the majority of the FD stuff for it was on a Flash drive I stood on a while back), but this is the latest idea to crawl out of my brain. The Fleet Air Arm Grumman Cougar F.1:
Back story's relatively simple. Action over Korea in the early 50s had demonstrated to British planners that their straight-winged fighters were at a massive disadvantage compared to the faster swept-wing MiG-15. Like the RAF taking delivery of a crap-load of Canadair Sabres to plug the gap between the Meteor and the Hunter, the Royal Navy ordered 100 F9F-6's from Grumman to bridge the gap between the Sea Hawk and the Scimitar. This annoyed Hawker no end, as when the order was placed in late 1951 they'd been flying swept-wing Sea Hawk variants for two years. Still, the order went through and the Cougar F.1 duly entered service with former Seafire squadrons from October 1953.
Unlike the Sabres of the RAF, the Navy's Cougars remained in service long enough to see service in the Suez Crisis. Flying top cover for Sea Hawk and Wyvern strike packages, two FAA Cougar pilots are credited with shooting down Egyptian fighters. The Cougar was phased out of front-line service by 1958, with reserve squadrons retaining them for another fifteen years.