I think you can make the argument that the US might have known Pearl Harbour could be a target, and would have been a good excuse to get involved in the war. But the attack itself, coupled with a general offensive across pretty much all of east asia, was not something anyone thought could be possible. Not at the level they did, anyway. The attack itself did very little actual long term damage (sorry to all the people who died) to the yanks fighting capabilities though.

I wonder how long it’ll take for them to gear up for it though. They must be really scraping the barrel now, and it’ll take years to bring up production. If that’s even possible in a Gig economy.