"I've also speculated that the U.S. had no intention of invading Japan anyway"
If that's true, my grandfather sure wasn't let in on the secret. He and the men he served with were prepared to invade Japan, but were certain they would never see their families again. They were steeled for battle, but terrified that they were facing the end.
'Til the day he died, he hated anything that had to do with Japan.
Right. And U.S. military personnel have spent 60+ years since the end of World War II preparing to fight any number of wars against any number of enemies. Some people were so focused on this that they probably retired from the military with almost a sense of disappointment that Soviet tanks never came rolling into western Europe.