That's the story as I had understood it for a long time. However, it isn't true.
It turns out there was another one ready to drop on the 19th, two more in September, and probably three in October. They were expecting to crank one out about every ten days. It was felt that the initial shock and awe would either work or not work. And, in the event it didn't work, there was debate as to whether to drop the bombs as they were produced or to save them up for Operation Downfall, the planned invasion of the Japanese mainland. Of course, VJ Day came on the 15th, rendering the deliberations moot. Source.
“It turns out there was another one ready to drop on the 19th, two more in September, and probably three in October. They were expecting to crank one out about every ten days.”
Maybe we should have been gearing our European bombers up for trips to Mother Russia?
That aside - Think about what these scientists and engineers accomplished. To weaponize these devices and have both work perfectly using different technologies with only one prior tower test on one design. That was American can do at its finest. We can’t even rebuild a freaking skyscraper now (WTC site) or a Memorial (United 93) or a new refinery.
I am praying that our defense dollars are cooking up some special weapons for when we go to war with a major power like China or Russia. If not we are going to be filling lots of bodybags again.