How about the IJN slipping into the Gulf of California and launching raids on the southern portion of the Southwest United States? I'm not sure if US relations with Mexico would allow them to slip in and out undiscovered or not, but I suspect money into the right hands (with or without Germany's assistance) would definitely assist that.
Why? That would serve absolutely no strategic or tactical purpose, and why would they
risk their carriers all the way over in the Eastern Pacific? Never mind that in 1939-40 there
wasn't a whole hell of a lot down there in the Southwest. Certainly nothing worth steaming
thousands of miles to attack. It would not serve the long range strategy of conquering China,
South East Asia and most of the Western Pacific. The attack on Pearl Harbor was a
tactical move in support of the Asia strategy, it was not an end in itself.
Japan would wait to move, just as they did in the RTL, and if the US had become involved
in a war with Germany, an Atlantic war with the USN being forced to send more ships out
of the Pacific reducing their ability to respond quickly, then it's entirely possible that Pearl
Harbor wouldn't happen. Japan would execute the plans of December 8, 1941 when they
moved against the colonial possessions of the weakened, war embroiled European powers,
and now the US, without the attack on Pearl being necessary, the Philippines would probably
have been hit even harder than in the RTL.
