Got distracted while supposedly doing proper work, so time for a burst of wartime What-If. Maybe it's just me, but I always thought that the Miles M.20 deserved a better chance than it actually got, so...
Miles Sea Merlin
After being developed as an emergency fighter in case of Spitfire and Hurricane production being disrupted, the Miles M.20 sat around doing nothing very much in the early part of 1941. When the FW-200 Condor began launching long-range attacks on merchant shipping out of the range of land-based fighters, the Royal Navy realised that it needed something that could intercept long-range aircraft and protect merchant shipping. Miles proposed using the M.20 as a disposable fighter in place of the Hurricane, since it was largely made of non-essential materials. The proposal was approved and rocket catapults were fitted to merchant ships...
...when someone at Miles decided to put floats on the plane so it could be winched back aboard. If the sea was calm enough for a landing, the plane could be reused; if not, then just ditch it as was the original plan. The lack of agility wasn't a problem as the fighter was never intended to go head to head with German fighters. And so, the Sea Merlin was born:
Basically just the standard M.20 prototype with a pair of modified Swordfish floats under the fuselage, the Sea Merlin was a useful stop-gap until MAC ships and escort carriers entered service. However, this being wartime the FAA was impressed enough with the aircraft's performance to order a dedicated carrierborne version, the Mark II:
The Mark II added an arrestor hook on the port side of the rear fuselage, some strengthening spars around this and a retractable main undercarriage. The Admiralty ordered it in preference to the Seafire, preferring the wider wheel track, longer range and better visibility for naval operations.
The Mark II was inevitably quickly superceded by the Mark III. This newer version of the Sea Merlin added a Rolls Royce Merlin 46 engine with an extra 300hp and replaced four of the .303 Browning guns with 20mm Hispano cannon:
The Mark III saw a significant performance improvement over the Mark II as its engine incorporated Bendix-Stromberg carburettors that allowed for negative-g to be pulled, in addition to the extra power and firepower.
The second generation quickly arrived in the shape of the Mark IV, which introduced the Griffon engine, a retractable tailwheel and other more minor improvements:
The Mark IV became the basis for the ultimate version of the Sea Merlin, the Mark V. All surviving Mark IV aircraft were brought up to the new standard by 1945:
The Mark V was armed with four 20mm cannon, equipped with a 1860hp Griffon VI engine and underwing hardpoints for 250lb of 500lb bombs. Although rather rapidly replaced in front-line units post-war by the Hawker Sea Fury and Supermarine Seafang, the Sea Merlin remained in service with the RNVR until the early 50s:
Sea Merlins saw action in all theatres of war that the Royal Navy fought in, going up against the best the Italian, German and Japanese forces could throw at it and proving especially deadly at low and medium altitudes. The last were replaced in service with Reserve squadrons by the Supermarine Attacker in 1952, not bad for a stop-gap fighter.