I have heard that the United States had secretly planned to drop the A-bombs on Hiroshima and Nagasaki in order to force Japan's surrender before the Russians could invade the Japanese mainland and control territory there. After VE day, the conferences at Yalta and Potsdam had resulted in the division of Germany between Western and Soviet control, and the writing was on the wall for the Cold War and Iron Curtain. The United States understood this, but still maintained their alliance with the Soviets on the Japanese front. The Soviets successfully invaded and liberated Manchuria and much of Korea (and subsequently held significant claims of influence there as they did in eastern Europe/Germany). It was clear that tensions were rising between Western and Communist forces in Europe, and the United States did not want to risk a divided Japan similar to what was happening in Germany, and needed to maintain a hold on the Pacific front against Communist expansion. Japan had incredible value in this sense, as it was still quite capable of being a regional power after the war. So, as a result, the United States dropped the bombs, effectively forcing Japanese surrender just weeks before a Soviet invasion of the mainland was to occur.
So my question is: is there any truth to this? And what sources can indicate this?
From the perspective of the US policy planners, the atomic bombs had a lot of positive things going for them. There is no real question about whether they would have dropped them one way or the other — they did a lot of "work," as historians might say. There wasn't just one reason, just as there wasn't just one person behind the decision-making processes that led to them being used. Some of the motivations of the various people involved included: wanting to end the war promptly to reduce further casualties; wanting to show that the investment in the atomic bomb project was justified; wanting to show the world the peril it was in if it did not support a strong United Nations and international control of atomic energy; wanting to give the US a strong position in the postwar.
Was maybe heading off the Soviets before they declared war one of the reasons? For some, it was a hope, to be sure. There is some evidence that this was a motivator for James Byrnes, for example, and a strong motivation for the timing of the bombs.
The US had desired Soviet assistance at Yalta but by Potsdam was realizing that once the Soviets get their hooks into a country they are hard to extract. The atomic bomb seemed like it might hold out the possibility of the war ending without a US invasion and without a Soviet invasion. If it did both, all the better.
The bombs were agreed to be dropped as soon as weather permitted once the Potsdam conference ended. (The first attack was planned for August 3rd but was delayed because of weather until August 6th.) The US did not have an exact date for the Soviet invasion but expected it in mid-August. So if the war would end before mid-August, the Soviets would get nothing of the territory promised them, and they would also not be in a position to put their hooks into China or Korea.
What actually happened, of course, was that the Soviets feared the same thing. After Hiroshima, when it was clear the Japanese would not immediately surrender, Stalin ordered his troops to accelerate the invasion schedule. They invaded at midnight (Transbaikal time) on August 8th/9th, just hours before the Nagasaki attack.
The US thought at the time, and it has been considered likely since then as well, that the Soviet invasion alone might cause the Japanese to surrender. Hence the importance of using the bomb as soon as possible.
But again, I would emphasize that this was one of the many motivations for the bombing. It was not the only one, and to see the dropping of the atomic bomb exclusively in terms of Cold War jockeying misses a lot. But so also does not including that in the analysis. To imagine the atomic bomb decisions (and I pluralize this because there was no single "decision" to use the bomb, but many "decisions" about how it would be used) as being monolithic or unified is also to make an error; there were a lot of different forces at work, with different motivations, but most in the US side of things saw the use of the atomic bombs as being in their interests.
For very close coverage of the various thinking going on between the US, the Soviets, and the Japanese at the end of the, Tsuyoshi Hasegawa's Racing the Enemy is very instructive, even if his ultimate conclusion (that the atomic bombs did not cause Japan to surrender and were not necessary) is controversial.
Going to page/u/restricteddata here as he is THE resident expert.
But on the topic of a possible USSR invasion of the Home Islands.
They did conduct landings of the Kuriles and in support of moving into South Sakhalin, but they were sloppy affairs. Against badly outnumbered garrison and still were bloodied and held up for a time before the surrender was announced.
Basically running old transport ships and destroyers ashore and hoping a port was captured before the men died was the extent of the plan. There were not sufficient numbers of landing craft of all sizes, heavy aircraft, and most of all escort ships to provide gun fire and ward off air attacks.
Any invasion of Hokkaido, which planning had begun, was going to require much more skill and resources in ships and heavy aircraft.
Basically it would have required going to the US Pacific Fleet for support and carrying of the troops to have a solid chance of success.
This however was a nonstarter as all amphibious resources were being marshalled for Downfall set to begin in only 2 months.