43

It's August 6th, 1945. The first atomic bomb ever dropped hurtles to the ground. Its fuse fails and with a thunk it buries itself in the ground. The Enola Gay flies home, its crew worried they did something wrong.

Now the brass back in Washington have a problem; they just hand delivered an atomic bomb to their desperate enemies, and it might be easy to repair.

I couldn't find any contingencies about it, but I'm also not a professionally trained historian with access to primary sources. I did find plans, which were abandoned, for building a giant concrete containment vessel around the Trinity device in case that failed to completely detonate, so they could save the uranium.

My question is, what, if anything was their plan for this situation?

  • 20
    What questions do you have that are not answered here: en.wikipedia.org/wiki/Gun-type_fission_weapon "Even a "fizzle" would have completely disintegrated the device, while the multiple redundancies built into the "Little Boy" design meant there was negligible if any potential for the device to strike the ground without detonating at all." – AllInOne May 8 at 15:37
  • 45
    @AllInOne: Ryan is asking what, if any, contingency plan there was if the "negligible, if any" chance turned out to be non-zero after all. I think it is a fair question (albeit about a very unlikely event). – DevSolar May 8 at 15:39
  • 9
    What did your research reveal? (Please edit the answer into the question - questions should show evidence of prior research, and nobody should have to read comments to understand the question). – Mark C. Wallace May 8 at 15:44
  • 13
    Conjecture, the Fat Man would have been dropped on the same site as quickly as possible with an aim of destroying any remains before it could be moved and hidden. The "third bomb" was several weeks delayed link: warbirdforum.com/third.htm – Criggie May 8 at 23:31
  • 6
    Remember, Japan's surrender was already imminent at that time. – forest May 9 at 5:54
43

If the bomb failed to explode in any way (which was unlikely, see comments and Mark's answer), the USA still would not have to worry about it (too much).

They would win the war anyway within a few months, and pick up the wrecked bomb from wherever the Japanese had stored it.

Even if Japan could figure out what that bomb was supposed to be doing and repair it, they didn't have any delivery system that could reach mainland USA (with any degree of certainty).

More importantly, the USA knew Japan did not have the capacities to build a second bomb, so even the microscopic chance that Japan could deliver the salvaged bomb to some target would not have changed the outcome.

The USA had both the delivery system and the production capacity to build a second, third, fourth bomb (of the Fat Man design), quite aside from having the strategic upper hand so firmly that they did not actually need the A-bomb to win the war. Not even in the very, very unlikely scenario of a major city, Pearl Harbor, or any other single location taken out by the salvaged Little Boy.

  • 18
    Well, they didn't really have enough uranium to build a second, third, fourth Little Boy. – Vladimir F May 8 at 20:09
  • 24
    @Vladimir F: But the US certainly had the resources to build many atomic weapons within a few years. We know this because it did just that. – jamesqf May 9 at 4:25
  • 15
    Probably the most devastating thing the Japanese could have done with a captured bomb would be to send a submarine on a suicide mission to the Okinawa, to detonate it at the staging area for Operation Olympic. As the Crossroads Baker test showed, this would likely have contaminated the ships so severely that the invasion of the home islands would be put off for six months or more. Of course, this wasn't known until after the Crossroads Baker test... – Mark May 9 at 4:29
  • 8
    Perhaps, when the Japanese analyzed that bomb, to realize what it was and what little problem made it fail, in other words, the Americans have the bomb (and it was pure luck that it didn’t explode) and could easily come up with a next one that does work, they surrendered just as they did when experiencing the working bomb. After all, the message is almost the same. – Holger May 9 at 9:36
  • 3
    Plus - in the chaos of war why would the Japanese think that dud bomb was any different than any other dud bomb, many of which already littered their landscape? – mxyzplk May 10 at 22:10
41

The primary contingency plan was the design of the bomb itself. Little Boy was not a safe design: any number of unplanned events could cause a detonation. Foremost among these is impact: a 500 g impact, such as would happen after a 15,000-foot (4.5 km) fall, is sufficient to bring the bullet and target together, detonating the bomb. If the bomb hit water instead of land, the water would act as a neutron moderator, causing a criticality event and severe radioactive contamination. In the event of an airplane crash, any resulting fire will trigger the explosives, setting off the bomb.

In short, once the bomb is fully assembled, it's very hard to keep it from going off. In the event that the crew of Enola Gay had to abort their mission, they had no intention of trying to land with the bomb still aboard.

  • 11
    Michael MacAskill, the 500g impact would be the sudden stop upon hitting the ground. I have no idea what the actual acceleration would be, but that's what he's talking about. – Haakon Dahl May 9 at 4:29
  • 12
    @Michael MacAskill: (Sigh) It would have accelerated to terminal velocity as it fell. When it hit the ground, it would have decelerated rather quickly. Think bug on a windshield :-) – jamesqf May 9 at 4:32
  • 10
    @MichaelMacAskill just because the accelerations involved in a collision are very time-sensitive doesn't mean they aren't meaningful. If the detonation mechanism depends on a force between two internal components exceeding a certain magnitude then the local acceleration must pass the threshold to develop this force inertially. Accelerating at 90% of the rate for 10 times the duration would dissipate much more energy, but not in a way that would disturb the mechanism. – Will May 9 at 10:08
  • 5
    Don't count on the force of impact to trigger the bomb. Even a crude gun-type atomic bomb requires a carefully controlled explosion. Crashing against the ground would damage the bomb in ways that would prevent an explosion. Even a fizzle. – Rekesoft May 9 at 11:22
  • 9
    @MichaelMacAskill Discontinuities do not exist in nature except in very limited circumstances, and this isn't one of them. The acceleration spikes sharply upon impact, but that doesn't make it discontinuous or non-differentiable. – Nuclear Wang May 9 at 13:22
2

Adding to the above mentioned facts that the bomb would go off very easily and would be useless even after a fizzle, and that Japan was in no position to get a nuclear weapons programme off the ground, the U.S. didn't really need a contingency plan.

Japan had already started overtures for a general surrender before the bomb was dropped. The excuse the U.S. used for dropping the bomb was that they didn't like one of the conditions of the surrender, namely that the emperor would remain Japan's head of state. If the bomb hadn't gone off, the U.S. would have simply accepted Japan's surrender with the condition and leave the emperor on the throne, which the U.S. ended up doing anyway.

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.