By the latter part of november, the japanese have etly amassed the most powerful aircraft carrier strike force in world history up until that time. Now you can't hide preparations for operations on that scale. And the british and th americans figure out that something bigis happening. They see troopships moving. They hear things in the codes that they've broken. It's a big thing, and it takes months and months, and they catch on to it. Ironically, though, it sort of attracts their attention in a way that diverts their attention from what's going on in the very northernmost islands of Japan.