General Discussion
In reply to the discussion: Hiroshima - quit lying to yourselves [View all]hunter
(38,311 posts)It was a huge operation and nobody was telling the people in charge, "Hey guys, don't worry about it, we have atomic weapons now."
The "massive troop movements" were a show of force, to both Japan and the Soviet Union. They were not there to invade Japan, even though that's what they all expected, that it would be the worst possible scenario.
The U.S. plan was to drop the two nuclear bombs, back off a bit, isolate Japanese forces and wait for a response. If Japan hadn't surrendered more bombs would have been dropped. If still they didn't surrender, only then would U.S. troops take the Japanese mainland, the way cleared by further atomic bombing.
The Manhattan Project was huge, built from the ground up to fight a full scale atomic war with the Nazis. It was also secret, fewer than 1% of workers knew what they were doing before the bomb was dropped on Hiroshima.