The trouble with PTO TLs are, as said, it's already an Ameriwank, & it's damn hard to keep Japan from being stupid.
If Kimmel had sortied, you might end up with Nimitz forced to rely on his subs even more, which is (you guessed it
) worse for Japan.
It does likely mean the Bomb doesn't get dropped on Japan,
which might encourage somebody to drop it on Berlin or someplace when the Sovs get frisky in the '50s.
(They didn't have the Bomb phobia we do.)
So what about if Nimitz doesn't get the job? Or MacArthur says, "I'm staying."? Or MacArthur is killed by a sniper before he leaves the P.i.?
(Hint: any TL where MacArthur is killed by a stray asteroid or falling gargoyle is probably mine.
)
It's possible for Japan to make better calls at places, but they're few & far between, especially after the first 6mo. Not attacking Midway is one. Shutting the Panama Canal early is another. Mining the Golden Gate Strait & keeping it shut would be a good one, seeing how much the Sub Force relied on it. Mining & shutting Makalapa Channel at Pearl is a no-brainer IDK why IJN's subs never did.
A couple of less likely possibilities: Japan captures the intel outfit at Cast (Cavite, P.I., in the tunnels of Corregidor when they get there), or captures an intel officer who knows the IJN operational code (U.S. ID JN-25) has been broken (or maybe papers showing it).
Or just that the
maru code has been broken, which hinders USN subs while Hypo & OP-20G try to break it again. (Best if this is after about Sept '42.) Might help also if you can avoid Lockwood becoming COMSUBPAC; if that bastard Christie gets it, the Mark 6/Mark 14 problems might not get fixed before the war ends...
Keep in mind in a "shorter PacWar" TL. It means no Korean War, no ChiCom victory, & no Vietnam (or dramatically less chance). The first two, because the Sovs don't invade Manchuria or get awarded an occupation zone. Vietnam, there's at least a chance of FDR telling de Gaulle to get on his bike when he proposes keeping Vietnam postwar, or for Truman to be in the job long enough to recognize France needs the U.S. as much as the reverse, & put pressure on to decolonize. Might even offer the UK Commonwealth model, & make Vietnam & Algeria full partners. (This is my fave Francewank of the period.
) This does, of course, wipe out the career of Oliver Stone & turns "Forest Gump" into "Gomer Pyle, the Movie".