Honestly, I've put a lot of thought into this, and I think the answer is they did not put a lot of thought into it.

It's only afterwards that we realized the implications of the bomb. Sure some people involved in the project, for years, who were great and broad thinkers, distant from the day to day grind of the war, had some idea of what they were getting into.

But the A-Bomb was dropped because it was a bomb, and we were deploying every weapon we had at the Japanese at that point. For most involved, there was not a question of 'why' anymore than why we deployed the B-29, or napalm, or radar against the Japanese.

For the same reason we'd been using thousand bomber raids to do the same thing to every other city in Japan.

Plus, maybe to avoid an invasion.

The planned invasion of Kyushu also involved atomic bombs, but it made sense to use a couple as part of the strategic bombing campaign while you were mustering forces for the land invasion, on the off chance it got the high command to see sense.

Invasion. If it took months to dislodge a few thousand soldiers from a 5km island in the pacific, imagine fighting tens of thousands of them on their home turf and dealing with the millions of civilians becoming guirella fighters and suicide bombers. The easiest way was to use the brand new city annihilator to intimidate them into surrender.

>>1042706
Personally? A mixture of reasons.

The desire to prevent another Iwo Jima and the fact that the Soviets might have wanted to help in the invasion of Japan.

It wasn't a pretty decision to make. On one hand, you're literally using a new weapon whose effects are not completely known, on the other hand you want to not do any more invasions and seriously, fuck Stalin.

What would you do, as Truman?

>>1042706
It was a weapon that had been theorized and developed for nearly a decade, with little understanding of what exactly it did apart from make a huge explosion under the right circumstances.

Truman was no Roosevelt, he had no intention of working with Stalin on compromising with Japan like Roosevelt had done in Europe, he also had no qualms about using the bomb after hearing the disheartening casualty reports coming in after Iwo Jima. The public wanted to the war in Japan to be over like it was in Europe and was losing enthusiasm for the war effort, an invasion of Japan was calculated at more than 4 million casualties, aproxomitely 1 million of which would have been American troops.

It was a gamble that ultimately paid off and forced Hirohito to reign in his generals and personally concede defeat under threat of annihilation.

>>1042706
It almost certainly wasn't to keep the Russians out: the Soviet invasion plans started off by asking the Americans to give them more landing craft. Truman could have much more easily told the Soviets to build their own fucking boats.

>>1042774
14million* not 4, many of the casualties were expected from Japanese civilian conscripts which at the time, consisted of 40 million adult males.

Basically it would have been a slaughter akin to the Eastern Front, which would have devestated both Japan and the U.S. irreversibly.

The Soviets promised America that they would declare war on the Japanese at Yalta, and invaded Manchuria on the same day that Nagasaki was flattened. So no, the Americans did not nuke Japan to keep out the Soviets.

It was something monstrous but no matter how much I think of it I can't imagine a future without the bombs that is better, Japan would have lost a huge chunk of its population and probably end up divided like Korea.

I'm interested in this question as well

>>1042814
It was more of a weapon showcase to the Soviets. From what I understand, the Japanese feared the Soviets far more than the Americans. What difference does it make if one bomb destroys one city or if a thousand do? However, the Soviet's human wave tactics would certainly crush Japan.

The Soviets pushed the Japanese out of Manchuria with relative ease.