An idea i was playing with, inspired by reading various posts, about what could have gone not so well for the aforementioned air services either in choosing the designs used to equip them and /or tactics and doctrine, namely RAF, FAA, USAAF and USN/USMC.
Of course, i'd want this to be kept as plausible and reasonably possible, for instance for the USAAF i was thinking of the P-38 with 2 crew and rear turret (because almost everyone was designing the twin engine fighters with 2 or 3 crews and defensive armament in the day), focusing on the P-35/P-41/P-43/P-44 family because that is what they chose initially and was readily available, so delaying or even cancelling the P-47 altogether, no P-51 because it was initially designed for a foreign order anyway, instead having a Merlin P-60 later in the war etc. Can the B-29 be nerfed?
For the USN/USMC things like sticking with the F2A for longer because they chose it in the first place, thus delaying the F4F, building more TBDs delaying the TBF, F6F with R-2600 engine (say because the R-2800 was reserved for the F4U) etc. etc.
For the RAF, some were aghast at the idea that the RAF could have had more turreted and twin engine fighters (or rather "fighters", f.e. Blenheim was no fighter)) in Fighter Command in 1940 to the detriment of Hurricanes/Spitfires, so suppose this happens? Or maintaining priority for bombers for too long? Or a Mosquito with defensive guns? etc etc. I didn't really wanted UK invaded in 1940 because this "game" can't continue in Europe then, so suppose even if RAF fares much more badly in BoB, for some reason Hitler still doesn't invade.
So how can we realistically get say 1941 kill/loss ratios between the germans and allies, but as late as 1944/45? Similarily in Pacific, can we realistically get similar kill/loss ratios as in early 1942 between the japanese and allied air forces, but in 1944/45? Didn't really considered significant wanks for the japanese/germans to get to these ratio, but if necessary some relatively limited ones are OK.
Finally, for this WI didn't wanted to go into who wins the war in this scenario and all that, let's just run things to 1945 (can the US atomic program be realistically nerfed?) and leave that question for a different time and place for now.