I think that in WWII there was no chance that Japanese invasion on US mainland would have been successful. Admiral Yamamoto knew that on his famous quote:
Admiral Yamamoto was the former Japanese naval attache in Washington. Because of that he knew his US enemies well. He knew that they were wealthy and powerful. Because of that the only way for Japan to defeat US was to quickly de-moralize US military forces which would force them to negotiate peace with Japan.
Generally, if you expect tough fights and you need to launch an amphibious landing then you will need a supply base relatively close to the landing zones. You need to ship fresh troops and new supplies quickly. Where would be the Japanese forward supply base for the invasion on US mainland?
Should hostilities once break out between Japan and the United States, it is not enough that we take Guam and the Philippines, nor even Hawaii and San Francisco. To make victory certain, we would have to march into Washington and dictate the terms of peace in the White House. I wonder if our politicians, among whom armchair arguments about war are being glibly bandied about in the name of state politics, have confidence as to the final outcome and are prepared to make the necessary sacrifices.
Admiral Yamamoto was the former Japanese naval attache in Washington. Because of that he knew his US enemies well. He knew that they were wealthy and powerful. Because of that the only way for Japan to defeat US was to quickly de-moralize US military forces which would force them to negotiate peace with Japan.
Generally, if you expect tough fights and you need to launch an amphibious landing then you will need a supply base relatively close to the landing zones. You need to ship fresh troops and new supplies quickly. Where would be the Japanese forward supply base for the invasion on US mainland?