I'm fledgling Pacific War historian (working on my MA) and I have met quite a few big names in the field. I have never come across a single historian that could consider something as insane as a Japanese invasion of the mainland United States. It was logistically impossible for the Japanese. Heck, I haven't met a Pacific War historian who seriously thinks that Japan could have successfully invaded Hawaii for the same reason. Japan's maritime transport capabilities were not even close to being up to the task. Not to mention the horrible mess that was Japanese inter-service rivalry which put any other nation to shame. The IJA would never, ever, ever, ever, ever, ever have gone with a plan that drained any more of their resources away from the Chinese theatre. One of the main reasons they agreed to the "Southern Advance" at all was because it was planned to be done "on the cheap" in terms of the number of IJA divisions that were required. The IJA shut down any talk of an invasion of Australia or landings around the Indian Ocean precisely because they were too difficult logistically and, more importantly, they proposed to drain off too many IJA divisions from China. If my memory serves, the proposed invasion of Australia would have involved five IJA divisions. Five. And the IJA shut it down because it was too much. Now imagine what a landing on the US mainland would have required in IJA divisions alone.
