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When reading about Operation DownFall I noticed that if Japan had not surrendered following the nuclear bombs at Hiroshima and Nagasaki there could have been at least 7 more Nuclear Bombs ready for the invasion.

I am unable to find any information about the plans for these bombs or any plans regarding more bombs to be used before an invasion of Japan.

With Operation Downfall being developed it seemed that there was thought that a few nuclear attacks would not force Japan to surrender. I was wondering if there is any information about other nuclear bomb targets, before, during, and after an invasion of Japan?

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    Not really possible, we had only created 3 nuclear bombs at the time. 1 of them was used in the test, then 2 were dropped on Japan. Sure, we had the technological know-how to produce more, but it was going to take a considerable amount of time to do so. No one was actively planning more attacks.
    – Cody Gray
    Commented Feb 29, 2012 at 4:19
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    @CodyGray The document I linked to showed that we had another bomb ready to be shipped on August 19 and they were deciding whether to drop more if Japan didn't surrender.
    – Legion600
    Commented Feb 29, 2012 at 6:37
  • @CodyGray From what I understand the invasion of Japan was being planned for Nov 1, (3ish months after the bomb drops). Any idea how long it would take to create a bomb? Maybe the link has misleading info?
    – sealz
    Commented Feb 29, 2012 at 11:59
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    @CodyGray The US hadn't stopped producing nuclear bombs. On its last voyage, USS Indianapolis carried the outer part of another bomb (the plutonium core would be shipped by air). Truman decided to wait before dropping the third bomb.
    – David Thornley
    Commented Sep 27, 2018 at 20:52
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    There really wasn't any detailed planning based on the availability of nuclear weapons. The existence of A-bombs was a closely held secret, and the planners would not have been informed of them. Once they did become generally known, it was just a few days before the Japanese surrender, and then there was no need to plan an invasion. There's plenty to speculate about, and comments by people involved as to what they might have done, but there's not going to be anything solid.
    – David Thornley
    Commented Sep 27, 2018 at 20:54

3 Answers 3

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The book Manhattan, the Army and the atomic bomb has a chapter dedicated to the choice of bombing targets on pages 528 – 530. It makes clear that the original intention was to drop four bombs. Originally the targets selected were Kokura, Hiroshima, Niigata and Kyoto. Later it was decided to spare Kyoto for its historical relevance and bomb Nagasaki instead. Judging by this book, no additional bombings were planned. In particular, on page 541 it says:

[General Groves and General Marshall] agreed that, in view of Stimson's policy of using the bomb only to end the war, shipment of materials for a third bomb should be delayed until 13 August.

So there was no plan to use nuclear weapons in Operation Downfall. The atomic bombs were rather used to end the war before Operation Downfall becomes necessary. That matches what I know from other sources as well.

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    From my wiki link (nuclear weapons section) "Colonel Lyle E. Seeman reported that at least seven bombs would be available by X-Day, which could be dropped on defending forces." Depending on how you interpret that it seemed that they were planning on having bombs for the invasion but had not decided weather to use them or not.
    – sealz
    Commented Feb 29, 2012 at 11:54
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    @harper89: See answer by Legion600, he explains where this figure comes from. But the document he found also makes clear that these weren't real plans.
    – Wladimir Palant
    Commented Feb 29, 2012 at 11:58
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According to this document from the National Security Archive Electronic Briefing Book No. 162 at George Washington University they were planning on seven more bombs. As for targets however General John Hull states in the document (dated August 13 1945):

What General Marshall wants to know is the status of the development of these bombs now so we can best determine how to use them.

On finding that one bomb is ready to ship out Hull states:

...Two of them have had a tremendous affect on the Japanese as far as capitulation is concerned. the next one won't be effective in that respect. In other words, the Japs will or will not.

After further discussion of delivery expectations for other bombs and the use of them with American troops nearby, Hull concludes by saying he would like General Groves slant on how and when to use them. From this document it appears that while they were planning on building more bombs for use against Japan, they had not yet decided where to use them.

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  • Nice find! Just a note: General John E. Hull was involved in planning Operation Downfall, the document seems to refer to that. Still, the content and the date make it clear that there was no plan to support Operation Downfall with nuclear weapons - this is pure improvisation, not something that has been planned in a advance.
    – Wladimir Palant
    Commented Feb 29, 2012 at 6:19
  • en.wikipedia.org/wiki/… : Two more Fat Man assemblies were readied. The third core was scheduled to leave Kirtland Field for Tinian on 12 August,[131] and Tibbets was ordered by Major General Curtis LeMay to return to Utah to collect it.[132] Robert Bacher was packaging it in Los Alamos when he received word from Groves that the shipment was suspended.[133]
    – user2590
    Commented Jul 24, 2013 at 9:06
  • Thanks for the link to that PDF file Legion600 please could you add the citation for that document, or it's title?
    – user2357
    Commented Jul 23, 2014 at 1:34
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Professor Alex Wellerstein examined this question on "Restricted Data: The Nuclear Secrecy Blog" in a post titled "The Third Shot and Beyond" (April 25, 2012). He presented evidence that the U.S. military was contemplating (not necessarily planning) use of atomic bombs in the invasion of Japan. There were seven more bombs expected to be available by the end of October 1945, that is, in time for the scheduled November invasion. The United States at that time was able to produce up to three atomic bombs per month.

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