Say someone was sent back in time to roughly the time that they were considering using the nukes on Japan to end WW2. The time traveller wishes to minimize loss of life for both sides, but more so for the Allies; however, his biggest concern is avoiding the degree of cold war, mutual assured destruction, and threat of nuclear winter that occur later.

Assuming the Nukes will be used to end the war, what advice could be given to handle using of nukes, and later policies afterward, to avoid the resulting brinkmanship. He also wants to avoid actual loss of life due to use of nukes originally, or even limit the harm of radiation rendering areas uninhabitable, so long as the two nukes are sufficient to ensure the war ends, but the later cold war is the greater concern.

He is aware that Little Boy managed a more destructive blast radius due to it being set off in the atmosphere and can advise doing the same with Fat Man.

What strategy is most likely to work?

edit: to answer the questions I'm looking to avoid nuclear brinkmanship, not the entire cold war. The cold war is likely to happen, just minimize the odds that one will use the nuke (in this world changes have already happened to the timeline which means that this timeline is no longer assured to not use nukes as happened in ours).

I prioritize avoiding brinkmanship and/or use of nukes higher than the preservation of lives. However, if a solution also minimizes lives lost on either side without significantly increasing the risk of brinkmanship then the option which preserves lives would be preferred.

Also, remember we had exactly 2 nukes, with limited ability to produce more rapidly. Thus any solution should consider the fact that if the Japanese call the bluff after the second nuke there is no way to force them to surrender for some time.

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    $\begingroup$ What do you mean avoid the degree of cold war? What alternative are you looking for, a large conventional war, a weakened USSR dominated by the US, the other way around, the US and USSR in loving peace. Is the problem the thread of nuclear death that never came or the deaths in small conflicts? If he fears nuclear Armageddon why change anything we made it though without bombing each other why risk those close calls again by changing things? $\endgroup$ Dec 22, 2015 at 20:28
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    $\begingroup$ This question is also opinion based right now and might be closed. Which is more important saving lives during the initial two detonations in Japan or preventing cold war there needs to be a single criterion to objectively choose a right answer. $\endgroup$ Dec 22, 2015 at 20:32
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    $\begingroup$ The premise that we only had 2 nukes & limited production capacity is incorrect -- see my answer, and follow the link if you want more detail. $\endgroup$
    – Wingman4l7
    Dec 22, 2015 at 20:49
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    $\begingroup$ I'm no historian, but if you invited the Emperor to a demonstration of your new bomb, then dropped Fat Man on Moscow... you would incinerate two birds with one stone. $\endgroup$ Dec 22, 2015 at 21:16
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    $\begingroup$ Other world powers will eventually obtain this technology. At some point, even if it's not the end of WW2, that genie will come out of the bottle....it's a matter of who, where and when...and it could potentially be much, much more devastating. $\endgroup$
    – Tim
    Dec 23, 2015 at 2:42

15 Answers 15


The time you're describing represents a very tricky point in history. Here are some things you need to understand:


The War

The United States dominated the Japanese in aerial and naval combat. Shortly after Pearl Harbor pretty much every major Japanese ship was systematically hunted down and sunk. The US were taking losses clearing individual islands, but Japan no longer posed a serious threat to them.

Furthermore, the conflict in Europe was pretty much wrapped up, and this brought the issue of how to handle the Russians into the forefront. Stalin and the West were allies out of necessity, not because there was any love lost between them. Communism was seen to be akin to a dangerous and wildly contagious disease, and every country was jailing communists - even simply suspected ones - like there was no tomorrow. Russia was sponsoring communist movements all over the world (look at Germany pre-WW2, and their communist rebellions).

The US was very much aware that the next conflict may well be fought against their former allies, and very soon at that.

Desire To Use Nukes

So while a very complicated "victory" is being declared in Europe, the US is itching to test their brand new toys in a real-world situation. They could have ended the war any number of other ways - dropping nukes (especially 2 of them) was mainly due to their desire to send a message to the world (Russia in particular), and to see what would happen to the cities, and the surviving population. The Japanese were simply a convenient target, as the conflict in Europe had already wrapped up.

Japanese Political Situation

Even though the Emperor is the official leader of the country, the truth is that the political and military elite were the ones truly running the show. And those guys were not ready to surrender - they had too much to lose. You may be aware that knowing the Emperor was about to take the reins into his own hands and order the country to surrender they tried to storm his compound and kill/capture him. It didn't work out, but it was a close thing.

Your Arrival

So you see, there are quite a few reasons why the US wanted to make an example of the Japanese - and simply winning the war against them was not quite the main reason. Additionally, the Japanese public, military high command, and Emperor have to become convinced that fighting you is a losing proposition in order for a surrender to happen.

Your time traveler is going to have to be pretty persuasive to accomplish all that without knocking some heads together. Let's get down to business.

Shock & Awe

You need to make a terrifying example, such that the entire world will know how devastating the Atom Bomb is, not just some Japanese higher ups - that's why bombing a major city is such an attractive proposition. How do you achieve that effect while not killing hundreds of thousands of innocents?

I have two suggestions, which may both have to be implemented:

1. Nuke an island

Approach a heavily defended Japanese held island. You know that high ranking officers are commanding the troops. Some Japanese ships are somewhere off shore, waiting to engage American ships which they expect will soon deploy marines onto the beach. Now you set the stage for maximum effect.

Instead of assaulting their defenses, the US Navy stops quite far out (they're protected by their carrier squadrons and can engage at their leisure). A message is sent in the clear, and in most importantly, in Japanese:

Tomorrow, at 10:00 AM we will bomb this island with a terrifying weapon that you have never seen before. Everyone on the island will die. You have until then to surrender unconditionally, or we will destroy you.

Of course those officers scoff at you. The Americans must think were stupid! They even contact HQ to tell them about the funny Americans. Right.

Next morning - at 10:00 AM on the dot - a high-altitude bomber drops a nuclear bomb on said island. The surviving Japanese sailors - who will probably soon die of radiation poisoning - aren't laughing anymore.

The Japanese military high command are shocked beyond belief, and the Emperor definitely hears about this.

2. Something a little closer to home

Now the Japanese are apprehensive - the US just demonstrated overwhelming firepower, which can clearly be deployed from their carrier groups, and can wipe out an entire island, never mind a naval squadron, or a city.

The US demands that Japan surrenders, but let's say those old goats in power are not quite ready to do so. The Emperor is willing to talk things out of course, but the military high command is still pulling the strings, and they're obstinate bastards.

So now you have to up the stakes: US planes drop a nuke not on Hiroshima, or Nagasaki, but at sea, just a few miles off of the Japanese coast, and hopefully quite close to some major military installation / port.

The blast is enormous: the ocean boils, Japanese planes drop out of the sky like flies, ships roll over and are swallowed by the waves. Immediately afterward the Americans transmit a radio message in the clear:

"We drop the next one on your capital. There's no where you can hide. Surrender immediately."

Faced with such a disparity of power the Japanese will probably surrender, and furthermore, the US will have showcased their terrifying weapon to the world. The only ones not satisfied would be the "curious" few who wanted to see what killing a few hundred thousand civilians looks like.

Regarding Nuclear Brinkmanship

The nature of humanity is to be in conflict. The only reason we have stopped fighting among ourselves in the West is because it has become too unprofitable to do so. Up until the fall of the Soviet Union however, war among European powers was, to some, a certainty.

Every time a nation has invented a new weapon, strategy, or tactic, it's been held over everyone else's head, usually after first giving everyone involved a front row demonstration of their capabilities.

You can't stop the world from discovering nuclear fission. And once they do, you can't stop them weaponizing it because that's what we do. We exceed at killing one another.

Once a nation has nukes it will demonstrate it's awesome might to everyone else as a warning (see the US's behavior), and then once they do their opposition will sure as hell try to match them.

We are only lucky that the threat of mutually assured destruction actually kept the Soviet Union and the USA from turning this planet into a radioactive ash heap.

Again, there are two possibilities to preventing nuclear brinkmanship:

1. Saner mind prevail

You have a slim chance of using your knowledge from the future to explain to all parties involved just how deadly nukes are - what scientists decades later figured out about radiation poisoning, and the potential to literally end the world. Maybe by sitting them down and talking it out the world could come to some kind of agreement

2. Preemptive attack

You know how dangerous the Soviets became. You know the suffering they (and Stalin in particular) brought upon not only their own population, but on the Eastern block.

If you don't you should research the 60 or so million Russians that Stalin killed, the planned starvation in the Ukraine which killed another 20 - 30 million people, the pogroms in Moldova, and other atrocities many of which are still denied by the Russians.

Tell Roosevelt. Encourage him to drop a nuke on Moscow A.S.A.P. Don't let the Russians recover. Don't let them build up their strength. Simply kill that bastard and all the high ranking officials in one fell swoop. With the cancer cut out of the heart of the country the Russians may actually have a chance to build a sane country for themselves, and become valuable allies instead of incredibly dangerous enemies.

Note: this may seem counter intuitive, but I think you underestimate just how much the average Russian would have loved to see Stalin gone. Many people saw the invading German army as liberators. With some well planned propaganda most Russians would actually be quite grateful, even if it costs them Moscow. Not quite bloodless, but in my opinion this is the only way to stop the escalation of nuclear threats.

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    $\begingroup$ @corsiKlauseHoHoHo - His point is that the spread of soviet communism is directly responsible for the deaths of tens (if not hundreds) of millions of people, and stopping that by destroying Moscow would be worth the loss from a numbers perspective. I don't agree (because that was before most the people of Russia knew those leaders' true colors, and I think therefore it only would have incensed them and made an even MORE radical government in its place), but I do get what he's saying. If bombing Moscow did actually stop communism, it would have saved MANY times more than 4 million lives. $\endgroup$ Dec 23, 2015 at 21:02
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    $\begingroup$ Oh boy. " dropping nukes (especially 2 of them) was mainly due to their desire to send a message to the world " and the projected 250,000 American casualties resulting from a conventional invasion was - what? $\endgroup$ Dec 24, 2015 at 2:18
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    $\begingroup$ So much of "dangerouis evil Commies" and "bringing suffering" shit. Hello, do the STILL pour this kind of propaganda into your from the childhood? $\endgroup$ Dec 24, 2015 at 9:41
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    $\begingroup$ Wow, that was fast, how did you jump from Japan to anti-Russia propoganda? Bombing the leadership has definitely worked great for America so far hasn't it? Look what happened to Iraq and Afghanistan. $\endgroup$
    – simonzack
    Dec 25, 2015 at 4:52
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    $\begingroup$ @simonzack - everyone's a critic. Go write your own answer. $\endgroup$
    – AndreiROM
    Dec 25, 2015 at 7:13

I'd like to suggest a really strange answer to this question: the best thing a time traveler could do is keep their mouth shut.

Consider: what was the single most effective reason for Presidents to not launch weapons in the cold war? Everyone has seen what nuclear war is. Everyone knows what happened at Hiroshima. Everyone knows what happened at Nagasaki.

What better event to help drive the horror of nuclear war home than to have two cities bombed, with all the carnage associated with it. How many remember the result of the Trinity test? Can you remember why that test was important? (A hint for those who don't know the name: it was our first nuclear test, in New Mexico) Or perhaps do they know of the Bikini Atol, the site of the Baker tests of Fat Man grade weapons shortly after the war (23kT yields). Castle Bravo testing which came later at Bikini Atol saw the detonation of a 15,000kT thermonuclear bomb. What do we remember Bikini for? It's known because we irradiated an island and made it unlivable for the few native citizens there.

Now think about Hiroshima. Nagasaki. How much impact do those words have? Hiroshima saw about 15kT of nuclear explosion. Bikini Atol saw 42,200kT of nuclear explosions. How many associate bikinis with death and destruction rather than women trying to look sexy?

We remember Hiroshima. We remember Nagasaki. Why? Because they were not empty islands testing or demonstrating new toys of war. They were death. They were not blustering. They were not bluffing. They were a demonstration of just how far humanity will go in its quest for... well... whatever it's questing for.

The horror of nuclear warfare was not driven home by the shadows forever etched into the concrete. It was driven home by the horrors forever etched into our minds. This was not a toy. This was not something to bluster with. This was something real, some would say it was something evil, and no matter what, it was something we would have to deal with for the rest of humanity.

What better to ensure two nations do not play with their toys, for indeed they are not toys at all. Without it, surely we would find ways to downplay the risks of nuclear weapons and find ways to engage in even far more dangerous international games. We might have even fired a few salvos. Yes, salvos. Remember, while the Enola Gay dropped one small bomb at a time, we'd come a long way in tools to kill each other in the years that followed.

There is one case I'm aware of where nuclear testing brought the response you desire, and that was for one person, Dr. Julius Robert Oppenheimer. He witnessed the Trinity test. His understanding of the horror was complete without needing to see it used in combat. Shame he needed to be a top nuclear physicist and an eyewitness to get to that point:

We knew the world would not be the same. A few people laughed, a few people cried, most people were silent. I remembered the line from the Hindu scripture, the Bhagavad-Gita; Vishnu is trying to persuade the Prince that he should do his duty and, to impress him, takes on his multi-armed form and says, "Now I am become Death, the destroyer of worlds." I suppose we all thought that, one way or another.

  • $\begingroup$ The OP was asking how to achieve that shock and awe without the death of so many civilians, and I do think it's possible. Furthermore, you're not addressing the issue of a nuclear arms race after WW2 ends. While I understand what you mean about the psychological effects of Hiroshima and Nagasaki, I really do think that the same point (or a very similar one) could have been made without the bombing of civilian targets. $\endgroup$
    – AndreiROM
    Dec 23, 2015 at 14:17
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    $\begingroup$ @AndreiROM I think we just have different opinions about how the human mind handles scales, and how it remembers large events. $\endgroup$
    – Cort Ammon
    Dec 23, 2015 at 15:43
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    $\begingroup$ There was absolutely no need to nuke Nagasaki. The atomic bomb disrupted communication and it took quite a bit of time for Tokyo to learn the extent of the devastation. The Japanese High Command was meeting to decide what to do when we dropped the 2nd bomb on Nagasaki (and in an incredibly bad decision, the Americans moved the timing of this bomb up two days from the original timetable because of approaching bad weather). $\endgroup$
    – Peter Shor
    Dec 23, 2015 at 21:02
  • $\begingroup$ @petershor That quickly becomes a philosophical question about the word "need," though I don't disagree with you. The message is the same if you remove the three instances of "Nagasaki," which all simply echo Hiroshima $\endgroup$
    – Cort Ammon
    Dec 23, 2015 at 22:17
  • $\begingroup$ I guess we remember the Bikini Atoll mostly because of the (controversial, at the time) swimwear named for it. Which sort of supports your point. $\endgroup$
    – frIT
    Dec 26, 2015 at 9:23

Why do you need to use nukes to end the war? Just convince the US to accept the surrender terms that Japan was offering prior to dropping the bombs. Since the US accepted those terms after dropping the bombs, they were clearly acceptable.

While it is commonly thought in the US that the bombs changed Japan's stance, if you actually look at the terms offered before and after dropping the bombs, it was actually the US that changed its negotiating posture. Prior to that, they had insisted on an unconditional surrender, including the Emperor. Afterwards, the US accepted retention of the Emperor as part of the terms. After the Soviets entered the war, the US altered the surrender demands to allow the emperor to be retained.

Example source: http://www.globalresearch.ca/the-real-reason-america-used-nuclear-weapons-against-japan-it-was-not-to-end-the-war-or-save-lives/5308192

That cites General Douglas MacArthur as saying

The war might have ended weeks earlier, he said, if the United States had agreed, as it later did anyway, to the retention of the institution of the emperor.

Since the whole purpose of dropping the bombs was to avoid having to thank the Soviets for ending the war and to start the Cold War, there is no way to use the bombs without the nuclear brinkmanship. The nuclear brinkmanship wasn't an undesired side effect of dropping the bombs, it was the purpose. Or perhaps it would be better to say that it was the first move in the nuclear brinkmanship strategy.

Note that I'm not convinced that not dropping the bombs would have prevented nuclear brinkmanship. The USA and USSR were already positioning themselves for that. Even if the US had been less strident, there is no evidence that the Soviets would have been. But it's the most realistic way to get there.

There's even a credible argument that bombing Nagasaki and Hiroshima reduced the later nuclear brinkmanship. If your hypothetical time traveler reduced the effectiveness of the use of those bombs, they might well have been forced to use them in a later conflict where surrender wasn't imminent. As is, everyone was clear on their destructiveness. They had been field tested.

Everyone lived through the nuclear brinkmanship period without further use of nuclear bombs. Why change that? It seems far more likely that you'd disrupt that balance than improve it.

  • $\begingroup$ my fault for not clarifying the detail, but I'm assuming some other changes happened to the timeline, such that there is no longer a gaurentee that brinkmanship would not lead to use of the weapons. $\endgroup$
    – dsollen
    Dec 22, 2015 at 21:02
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    $\begingroup$ The idea that Japan was ready to surrender before the bombs is a minority opinion in a hotly debated historical topic; it is not an undisputed fact as presented here. $\endgroup$ Dec 23, 2015 at 0:06
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    $\begingroup$ Gobalresearch.ca is not a credible source. $\endgroup$ Dec 23, 2015 at 0:14
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    $\begingroup$ @LorenPechtel -- though I agree that Globalresearch.ca is not a credible source, documention is useful. Their store shows their bias, but a look at the article on RationalWiki is a more revealing analysis of their non-credible nature. $\endgroup$ Dec 23, 2015 at 1:26
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    $\begingroup$ The key to McArthur's quote is 'might.' Some Japanese were ready to surrender, others very much were not. If you look at the Battle of Okinawa, which ended just about 6 weeks before the nuclear bombings, it definitely did not indicate a country on the verge of surrender. As far as "running out of oil and steel just before the bombings," Japan had been running low on both since before the war even started. That's just outright false. They were in a much worse position by the end of the war, but largely due to American gains in the Pacific $\endgroup$
    – reirab
    Dec 23, 2015 at 6:06

The key issue in your question is nuclear brinkmanship in the post war world. The reality is that the Soviet Union had infiltrated many spies in the US and British nuclear programs, and I would not be surprised at all to find out that the Nazi nuclear program (as disorganized and chaotic as it was) was also infiltrated.

People were aware of the idea of nuclear energy in the 1930's, even if they were not entirely clear on how it could be harnessed (H.G.Wells wrote about an atomic bomb in "The shape of things to come", but described it more like we would think of a "dirty bomb"; continuing to "explode" for a prolonged period of time and leaving large areas uninhabitable). The idea of a nuclear weapon was "in the air", but perhaps fortunately the true difficulty in making a nuclear weapon is preparing the fissionable material, since with a sufficient quantity of U235 you can make what is essentially a low yield nuclear "pipe bomb". The Manhattan Project spent a billion 1940 dollars (over $15 billion in todays terms) to learn the methods of extracting fissile materials from uranium, and how to handle plutonium in its various forms.

So since people are aware of the possibilities of nuclear energy and have some idea as to how it works, there are two possible paths to take:

  1. Eliminate the Soviet spy program and stop the Russians from getting the bomb. Without the detailed information sent by the spy rings, the Soviet Union would have to carry out a Manhattan project of their own, which given the vastly smaller economy of the Soviet Union and the depleted industrial and scientific base in the immediate post war world, might prove to be virtually impossible.

  2. Test the bomb in secret, but hide the results from everyone. President Truman must then make the decision to launch Operation OLYMPIC and invade the Japanese home islands, inflicting over a million casualties on the fanatical last ditch defenders (and taking an estimated quarter million casualties on the allied side) to win the war in 1948. Since as far as anyone knows, the bomb does not work, there is less urgency in trying to duplicate nuclear weapons and the nuclear arms race does not go into high gear in 1949, when the USSR detonates its first atomic bomb.

Option two inflicts far more casualties (Japanese civilians were being drilled to attack allied troops with lances made from bamboo tipped with bayonets), but keeps the cold war much cooler, although without knowing the atomic bomb is a reality, the USSR might be tempted to "liberate" Western Europe in the post war period, unaware of the possibility of nuclear retribution.

Option one also squelches the cold war, since the USSR will have no effective counter, and indeed might be "convinced" to adhere to the Yalta accords and withdraw from Eastern Europe, but sets up a resentful and paranoid USSR which might indeed "eat grass" just to get the atomic bomb and have an equalizer to American power. (In a sense this is actually futile, America's true power is being a commercial empire and an oceanic power, capable of projecting trade and troops round the world, where continental powers like Germany and Russia are very disadvantaged in projection of trade and power by being surrounded by other rival land powers).

So your contrafactuals might lead to very unexpected results in the new timelines.

  • $\begingroup$ Agreed that "avoiding the degree of cold war, mutual assured destruction, and threat of nuclear winter that occur later" requires interfering with Soviet acquisition of the weapon, whether that means dealing with the spies, their scientists, or arranging for an accident during research so that they believe the weapon is too unstable to be an effective military option, I couldn't say. $\endgroup$
    – Ben Voigt
    Dec 22, 2015 at 22:47

Nuclear brinkmanship could not be avoided by modifying Allied strategy against Japan.

The world-threatening brinkmanship displayed during the Cold War resulted almost entirely from the mere existence of nuclear weapons. A ground war, or even an ICBM war, were unlikely to achieve either country’s goals given the much longer and more drawn out effort that would be required. Nuclear weapons are convenient because in theory, with enough of them, you could completely defeat you enemy in minutes.

The problem is, nuclear weapons were an inevitable result from WWII whether they were used or not. Nuclear physics had come into its own, and many nations were beginning to wrap their heads around the potential for a weapon. They would have been developed eventually.

A Cold War in a world with nuclear weapons is inevitably going to see their usage as an intercontinental threat. The resulting brinkmanship (though sometimes agitated by bad politics) will follow naturally.


I'm with Cort's answer on this one. Do nothing. Considering the circumstances the U.S. basically took action that resulted in the least loss of life possible.

At most, his advice could have been "slow down on the island hopping, no need for so many Marines to die...wait for the bomb program to be ready".

You have to consider the enemy we were facing. Acquiescing was not an option, they were a brutal and murderous entity bent on conquering and dominating us. We had to actually fight and win; it was not optional.

Now realize their death-before-dishonor culture (which they proved to be very real many times) and Operation Ketsugo already planned and ready to fight a mainland war of attrition with millions of soldiers and civilians projected as losses...we were very probably going to have to start killing dang near every man, woman, and child in Japan in order to end the war (they literally had 59 divisions of civilians planning to fight in it...for contrast the entire modern United States Marine Corps has 3 active duty divisions). That was not a tantalizing prospect to us, and we knew that.

Those bombs showed Japan that we could wipe them out, and have minimal losses to ourselves in the process. That meant that their planned war of attrition was absolutely pointless. That is the only reason they surrendered. And considering those bombings even had less loss of life than many traditional bombing campaigns had during WWII (drop incendiary bombs over and over on a city and the numbers will pile up) they, ironically, saved an enormous amount of lives on both sides.

As for the cold war...those political tensions had little to do with the bombs...those were simply the means by which the two sides made the threats over their political tensions. The soviets themselves killed many times their own citizens than the various wars over communism killed combined, and I see little way we could have stopped that without making WWIII.

  • $\begingroup$ Could you please cite your sources for "soviets themselves killed many times their own citizens than the various wars over communism killed combined"? You sound like broken Western propaganda record. Additionally, I highly doubt Japan was seriously thinking about "conquering and dominating" by the time bombs fell. $\endgroup$ Dec 24, 2015 at 14:09
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    $\begingroup$ @OlegV.Volkov 15 million is a reasonable estimate for the number of Soviet deaths caused by Stalin and his policies. If we don't count WWII as a "war over communism", which it really wasn't, then that is indeed many times more Soviet citizens than were killed in the Russian Revolution and WWI. $\endgroup$
    – Mike Scott
    Dec 24, 2015 at 15:33
  • $\begingroup$ @MikeScott, no, it is unreasonable and stinks of "dirty commies" propaganda. $\endgroup$ Dec 24, 2015 at 16:16
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    $\begingroup$ @OlegV.Volkov - I seriously thought things like Gulag camps were common knowledge, otherwise I would have cited. About 14 million in those camps alone over their existence (en.wikipedia.org/wiki/Gulag), the man made Holodomor (en.wikipedia.org/wiki/Holodomor) killing millions more, etc. etc. In total the estimates for communist civilian murders are estimated at a bit under 100 million (thecommentator.com/article/4230/so_how_many_did_communism_kill) It's impossible to know exactly for sure, and much of those numbers are likely missing. It could be much higher. $\endgroup$ Dec 25, 2015 at 23:24

While dropping the bombs was horrific - and in the end, unnecessary - I would be reluctant to try and change how things worked out in the end.

Destroying two cities made it obvious what would happen if an all-out nuclear war were to occur. So we ended up in a cold war where people were reluctant to use them.

Imagine though, in your changed scenario, that people aren't as afraid of nuclear weapons. In that case it seems possible that an actual nuclear war, with multiple sides using them, could occur later in the century. In the end that could lead to tens or hundreds of cities being destroyed.

So I would recommend not changing anything. I consider it a minor miracle that we've gotten this far without a nuclear war, and I just don't see the benefit being worth the risk.

The only possibility is that I would maybe stop after one bomb. That might be enough to show the might of the weapon and create the backlash against it, while still saving a city worth of people. Even still, that seems risky.

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    $\begingroup$ I like the caution. As callous as it may be to say, the loss of an additional ~300,000 people out of 60 million WWII casualties seems like a small price to pay for a guaranteed end to the war and a timeline that doesn’t (yet) involve nuclear apocalypse. $\endgroup$
    – Avernium
    Dec 22, 2015 at 21:28
  • $\begingroup$ @Avernium: Honestly I was reluctant to post this - the whole "greater good" thing is, IMO, a pretty dangerous philosophy. It's easy to end up on a pretty nasty slippery slope. But still... nuclear war. $\endgroup$ Dec 22, 2015 at 21:34
  • $\begingroup$ Dan, forgive me for not reading your answer before posting mine. I came to the same answer for the same reason. $\endgroup$
    – Cort Ammon
    Dec 22, 2015 at 22:46
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    $\begingroup$ Can you imagine the results if the first nuclear weapon to be used in war had been Shrimp instead of Little Boy? Remember that this was only about 8.5 years later. $\endgroup$
    – reirab
    Dec 23, 2015 at 6:11
  • $\begingroup$ Unnecessary? The Japanese literally had many times more civilians already on muster to start fighting than were killed in those two bombings. The traditional bombing of Tokyo killed more than EITHER nuclear bombing...yet it was ONLY the showing that we could destroy cities with impunity that made Japan's plans for an attrition style defense (that THEY planned on resulting in millions dead) patently pointless. Only then was surrender even an option for them. $\endgroup$ Dec 23, 2015 at 17:36

Detonate a nuke on a nearby uninhabited island as a demonstration & threat.

Added bonus if the island has a known amount of human infrastructure on it, the destruction of which can be examined later by the Japanese, as proof of the bomb's capabilities.

This course of action was actually debated at the time; dropping the bomb over a desert or a Japanese ocean port was also suggested. A written warning could have been disregarded as propaganda, but a detonation would have been impossible to ignore. The idea that a demonstration would deplete the limited stockpile of nuclear bombs was largely a myth; a third would have been available by late August, Little Boy's fuel could have been used to seed the construction of multiple "composite" bombs, and the invasion of Japan wasn't scheduled until November in any case.

That's the easy part. As for minimizing brinkmanship? I can't think of a particularly good solution for that. One off-the-wall possibility could be to widely disseminate plans for the construction of nuclear weapons. Then, the world's governments would be compelled to organize an independent inspection organization to control the, ahem, fallout -- and might be too busy to practice brinkmanship against each other.

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    $\begingroup$ Hiroshima, an actual city with lots of people, was bombed and there was hardly any reaction from the Japanese. So what effect would a "demonstration" on an uninhabited island have had? Zero. $\endgroup$
    – Mohair
    Dec 22, 2015 at 22:37
  • $\begingroup$ @Mohair: The gap between bombings was only three days; the Japanese spent at least one of them just figuring out what had happened. They then had to deal with the declaration of war by Russia only a couple days after that; "hardly any reaction" is an overstatement. $\endgroup$
    – Wingman4l7
    Dec 22, 2015 at 22:45
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    $\begingroup$ @Wingman417 That's ridiculous. They knew something really, really big had happened at Hiroshima within hours. Sixteen hours later, President Truman announced to the world what had happened, said there would be more, and called for the Japanese to surrender. Within 24 hours of the blast, Japanese scientists confirmed that it was an atomic bomb. The Japanese had all the facts, and they chose to do nothing. The Soviet Union declaring war was a triviality that played no part. $\endgroup$
    – Mohair
    Dec 22, 2015 at 23:05
  • $\begingroup$ @Mohair: Three days, when viewed from the perspective of a five-year war, is a very short period of time. I think historians disagree with you on the significance of the Soviet invasion threat and its role in the Japanese capitulation. Besides, the point is: what would a demonstration cost? I've already pointed out that the "we'll run out of nukes to use" argument was specious. $\endgroup$
    – Wingman4l7
    Dec 22, 2015 at 23:18
  • 3
    $\begingroup$ Even with losing 2 cities to nukes they still considered not surrendering. I have my doubts that a demonstration would have done anything other than make them think we didn't have the resolve to use them or use them widespread...which might have then required even more actual city bombings to overcome that implication and prove it false. $\endgroup$ Dec 23, 2015 at 17:31

(More a comment but it won't fit.)

1) Revisionists aside, it was a close thing whether the bombs were enough to cause a surrender. Thus all the demonstration answers don't work.

2) There was a very good reason against a demonstration--we knew there was a chance Little Boy would fizzle even if the mechanism worked perfectly. At the time we did not have the computing power to figure out the odds of this happening. (Now we do, it was a few percent.) If we announced it and then it didn't go boom we certainly would have failed.

3) Something to keep in mind: The bomb really was a great bluff. We didn't have a high enough production rate for them to be militarily important.

4) In the big picture I think nuking at least one city was a very good thing--it showed us the horrors in a limited scenario and thus kept later wars from going nuclear. Had we somehow avoided Hiroshima and Nagasaki the Korean war likely would have been nuclear and involved far more bombs.


The best suggestion I've heard, outside of not doing it: Don't admit that there was a single bomb or that it was nuclear. Tell a scientist that something is definitely possible and he's more than halfway to reproducing it. Simply keeping the existence of the technology classified might have slowed proliferation by up to a decade.

Nothing could have kept the cat in the bag forever, though.

  • $\begingroup$ Perhaps a piece of deliberate disinformation. Say we tell the world we found a cheap way to manufacture and contain antimatter (which was already known in theory). $\endgroup$
    – Joshua
    Mar 5, 2017 at 16:36

Send the time traveller back a little earlier, and have him suppress the MAUD report. Bury it in Lyman Briggs' office (as actually happened for almost a year) but cancel Marcus Oliphant's visit to the US in August 1941 - if necessary, bring his plane down mid-Atlantic.

Oliphant then met with the S-1 Uranium Committee. Samuel K. Allison was a new committee member, a talented experimentalist and a protégé of Arthur Compton at the University of Chicago. Oliphant "came to a meeting," Allison recalls, "and said 'bomb' in no uncertain terms. He told us we must concentrate every effort on the bomb and said we had no right to work on power plants or anything but the bomb. The bomb would cost 25 million dollars, he said, and Britain did not have the money or the manpower, so it was up to us." Allison was surprised that Briggs had kept the committee in the dark. (from the above Wiki article)

So Vannevar Bush never meets with the President in October 1941, nobody in America reads the Maud Report, the Manhattan Project in its actual form never even starts, and by mid-December, preliminary efforts on nuclear power plants have to be set aside as a long term pipe dream, to concentrate on the war effort, as America has a lot of catching up to do. (And the Soviet spies faithfully report the same long-term pipe dream to Moscow).

... and many of America's most brilliant minds and substantial capital are freed up to work on war-winning machinery, computers, code breaking machinery, guided missiles, jets, to bring the war to an end in 1944...

Once the war is over, there is no immediate need for offensive nuclear weaponry, and research on nuclear fission for power proceeds at peacetime rates, probably about as fast as 1950s today's research on fusion power technology. (And 1960s, 1970s, 1980s etc... up till today)


I've played around with the general plot of "time traveler goes back and changes some historic event" too - nice daydreaming activity. I've always come up on 2 problems that I feel may be significant plot holes if glossed over (and may make up their own main stories if addressed in depth):

  1. The problem of some random nobody turning up and wishing to influence policy at the highest level. Claiming to be from the future might often result in a lengthy diversion to some mental health (or criminal correctional) institution. One way to prove that one is from the future is prediction of events that are about to happen.

    I fear that our knowledge of the past may often be fragmentary and incomplete (for various reasons: loss of records/eye witnesses, necessity to "condense" history to only facts (subjectively) seen as relevant afterwards, the focus on "facts" and not including a focus on intangibles like leaders/population's attitudes and perceptions at the time, change in perception/recollection as time passes, tendency of victors to adapt history to suit their agenda, etc.) So the proof will not be forthcoming in all instances that may be required of the time traveler, thus casting doubt on his claims.

    (In Mark Twain's "A Connecticut Yankee in King Arthur's Court", the protagonist does not try to convince the others that he should be listened to as a wise and benevolent counsellor, he rather uses his knowledge of modern technology to gain power and thus control from inside the culture and its beliefs/norms, while keeping his origin secret. Now figure how your time traveler connives to become president/dictator of the US...)

  2. The Grandfather paradox: time traveler changes past in some critical way, altering the flow of history in a way that will remove the need (or even ability) for him to change history, thus reverting the flow of history to as it is ... ad nauseam.

I guess this may hint at why some other posters have suggested "let it be - say nothing". But one can always daydream of alternative timelines where the bombs were in fact not dropped, where Japan surrendered before the bombs, where Germany conquered the USA, etc. etc. etc. - our timeline being just one of many possibles, and not necessarily so remarkable as to need changing.


Invade with an army of time travelers from the future, and establish an apartheid regime via superior firepower and surveillance technologies across the world. Punish people not for the crimes they commit, but for the crimes you claim they would have committed had you not intervened. Blame the holocaust on political dissidents and Hitler's 'suicide' and Germany's defeat on your intervention. Use your access to the short-term future to conduct impossibly fast and thorough searches of all publicly accessible information networks to ensure that you effectively control all communication all the time. With the advent of perfect or psuedo-perfect human behavioral prediction machines, you can even avoid completely exterminating the intelligentsia (if you feel like not killing them) by ensuring that those smart people who will not be misbehaving are not killed. Manipulate the global environment as necessary to prevent revolution. By ensuring the obedience, isolation, and poverty of all 'primitive' humans, you can also ensure with complete confidence that they will not have access to nuclear weapons, nor the kinds of governmental representation that would be necessary to effect the sort of nuclear brinkmanship you are talking about.

We can take this further, and minimize the number of lives lost in the transition. To do so, we record, before our intertemporal invasion, the whereabouts, habits, etc. of the 'key players' in global affairs at the time, and note the sort of unexpected security breaches that inevitably frequently occur all the time. When we time travel, we assassinate each 'key player' and replace them with a loyal agent. Using our acquired political power, we replace everyone important with our army over the next few years. Japan surrenders to the US because we run the President and the Senate, and also the Emperor and his exceedingly well armed bodyguards. Once we effectively control everything, we can either end the charade and reveal ourselves, or just let people think they live in a discordant world while we in fact run everything from the shadows.

Suggested reference material:

I, Robot (the movie, not the book)
Metal Gear Solid: Sons of Liberty


Tell the scientists about nuclear fission, but also tell them it has been proved in your time that a fusion explosion would ignite the Earth's atmosphere, and so it was never done. There was in any case some concern about that possibility during the development of fusion weapons and before the first test, and hopefully your input would be enough to prevent fusion weapons from ever being developed and tested.


Cancel the Manhattan Project and label it an expensive, useless fiasco. Do what's necessary to erase contrarian evidence, up to and including murder.

If aplicable, say you're coming from a future where the US got so bogged down in this fiasco that it ended up losing the war against all probability.

Another possibility is to say you're coming from a future of actual nuclear apocalypse.

  • 3
    $\begingroup$ "Got so bogged down in the fiasco" is completely unbelievable, even to those working on it at the time. The Manhattan Project was expensive in absolute terms, yes, but in relative terms the total cost amounted to nine days of warfighting expenses. $\endgroup$
    – Mark
    Dec 23, 2015 at 19:44
  • 1
    $\begingroup$ The bombings of Hiroshima and Nagasaki each were not even the highest death toll bombings of WWII. Neither was even the highest death toll of a bombing on mainland Japan. Considering they ended the war before a projected invasion that likely would have killed millions...how is preventing them from happening supposed to minimize loss of life? $\endgroup$ Dec 23, 2015 at 20:52

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