So here’s the thing, if we’re playing hypotheticals. I’m assuming, and I think DrDeth is saying, that just about the only thing that changes on December 7th is that Pearl and the Philippines don’t get bombed, but that instead, the Japanese use their carriers somewhere in the DEI. Right?
The question what these carriers would have done cannot really be answered. I’m inclined to say that they would have been used tactically, because of the impossibility of a strategic deep strike–they would probably have been used to hit Singapore, the most obvious and most important target in the south-west Pacific. There’s very little else of worth around–certainly not Tarakan and Balikpapan, either of which the Japanese would need to take intact for their oil and refineries.
But the more interesting question I think is whether the U.S. would have sat idly by, and this question is a bit more complicated than I gave it credit. The U.S., the British, and the Dutch had been in discussions about their mutual defensive prospects. There had not been official word from Washington on whether the Asiatic Fleet would be permitted to cooperate directly with the others, but Admiral Hart (CinCAsiatic) decided on December 6th to do so–to make the destroyers at Balikpapan available to Admiral Philipps of the Royal Navy. That’s unusual, given that there was no official alliance or indeed war at the time.
However, Hart apparently was appraised by the USN representative at Singapore that Washington expected to be able to get a declaration of war out of Congress even if only the British and Dutch were attacked–or, at any rate, that the possibility had been implied that the US would support the British and Dutch. Furthermore, on Washington’s orders, the Asiatic Fleet had deployed three light vessels in the way of Japan’s southern invasion forces, perhaps (as Hart’s biographer speculates) to get another “incident” going. Roosevelt had not, of course, promised intervention–he could not, as he well knew–but had implied that the possibility existed and the Hart was to use his initiative to decide what to do. This brings a lot of pressure on him, but apparently (as noted above) he had decided to intervene. So what would he have done on December 7th, with Singapore in carrier-produced shambles and his ships not actually yet engaged? I’m inclined to think he would have tried to get into the scrape, and then the problem becomes, how does this change politics in the US: if Americans get killed because a subordinate commander decides to commit his forces without clear guidance from above, is this war? I don’t know. But I’m inclined to say that no hypothetical attack on the British and Dutch would have passed without the U.S. losing men and ships.
I’ll still say that the Japanese should have gone for even this unlikely event, tried hard to get the U.S. to stay out, and only accepted war with great hesitation, not sought it themselves.