As I understand it the plan was to knock out all the US' aircraft carriers at Pearl Harbour so that they couldn't defend the Pacific. With freedom to cruise around the pacific Japan would be able to threaten the west coast with bombing raids rather than a land invasion and this should have been enough to make the US come to terms.
Yamamoto predicted that the Japanese could invade freely for a year and then would be in trouble and he was fully aware that Japan would lose once they failed to catch the aircraft carriers at Pearl Harbour. Also he was supposedly against declaring war on the US in the first place but was overulled.
Bookmarks