Codebreaking, without a doubt- we got there eventually, imagine if we’d had the tech and the wherewithal to use it effectively from day one.
Ah but actually, that’d be a bit awkward,for the same reason as:
I imagine a Phalanx on US warships would have stopped a lot of kamikaze planes.
Need to figure out some other way to get them into the war I guess!
How about simulators? Training sims, tactical sims. Get everyone playing Civilization and Company of Heroes 😉
If it’s got to be a physical thing rather than an idea or practice, then how about high-level bombers. Very old tech now but being able to get above interception and air defence, and drop payloads anywhere would have totally changed the air war.
And it’s not such a gigantic tech leap either, the B52 came along in the 50s. Even if you have to drop iron bombs out of them, it’d be a terror weapon, a logistical win (since you don’t need to constantly replace your bombers and crews as they get shot down…). Not unlike the gotha raids in WW1, though more effective. Wonder if you could build 500 Bears instead of 7500 Lancasters?
It’s a pretty common trope, though. Anyone who likes the ideas in this thread could maybe check out Guns of the South.