Thanks Northern Yankee. Had the Bomb not made it in time, or just remained unused, the land invasion would have been hideously costly — but of course would have been preceded by conventional firebombing, which had nearly leveled almost four dozen Japanese cities and killed tens or hundreds of thousands. The island would have been cut off from needed supplies, starved out, deurbanized, disarmed (the hard way), and, okay, so now I’m starting to get the blue light going, I’d better stop... ;’)
My father flew B-29's out of Guam. A great story to read about the Japanese surrender and how it was almost thwarted is the book, The Last Mission, by James Smith. My father took part in that mission.
Lost an engine coming back from the bombing mission and had to land at Iwo. A tricky thing to do with those short runways.
Not only that, but most likely the Soviets would have gotten involved, and then you would have probably had a Japanese Civil War afterwards, ala Korea.