I’m sure there were plenty of invasion plans drawn up. None of that means any of them were necessary, or even practical. Doesn’t the Pentagon have scenarios in place for an invasion of Canada?
You ACTUALLY believe the invasion would not have taken place?
Operation Downfall which consisted of Operation(s) Olympic & Coronet was more then just a map exercise !
https://en.wikipedia.org/wiki/Operation_Downfall
These plans were presented to President Truman before he made the decision to use atomic bombs.
An alternative was to simply blockade Japan and starve them into submission.
Russia pledged to declare war on Japan at the Potsdam meeting. Their intentions were to occupy Japan as soon as possible. Given their behavior in Germany, Truman was wary of another East-West scenario. A starving Japan would provide a soft target for Stalin. President Truman wanted to end the war by unconditional surrender (per the Potsdam Declaration) as quickly as possible to prevent Russian occupation.
Read “Downfall, the End of the Imperial Japanese Empire” by Richard B. Frank. It provides minute details about the last few months of the war in Japan.
Please be aware that everything I’ve posted is based on my opinions based on facts known before 8/8/45. Key word: Opinion.