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I understand that the U.S. has accidentally dropped bombs on ourselves many times without actually detonating the bombs. These accidents have caused craters, but no radiation (or in a couple cases, just a 'little radiation' that leaked into soil, etc). An easy google search will tell you more.

We've also accidentally transported armed nuclear warheads without realizing they were armed (see R. Maddow's book 'Drift')

But for my specific question... is it remotely possible that after a nuclear bomb has been dropped by accident, it could then detonate? That is, create a mushroom cloud?

If so, how? How would the failsafes fail?

WHY THIS IS WORLDBUILDING (because there have been complaints) I'm literally building a world in which such a thing could happen. I'm writing a novel where we have a different president, a slightly different governing system, and more or less the same military, but slightly more incompetent than it currently is. This world will reflect on our current world a good bit, but it differs a lot.

In the novel there is a nuclear detonation in the U.S. that is basically the U.S.'s own fault... want to figure out a way that it could believably happen)

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    $\begingroup$ This might be interesting for you, here is a list of military nuclear accidents that has happened so far. In particular, you should check out the Damascus Missile Silo explosion. This American Life did a great radio story on it that details the chain reaction of failure that lead up to such an incident, despite many redundant failsafes. $\endgroup$ – Hans Z Feb 13 '18 at 22:31
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    $\begingroup$ Actually armed active nuclear warheads rely on there not being enough fissile material in one place to achieve critical mass, while still keeping the cores close enough that they can be brought together quickly. These nuclear warheads were mostly made in the 70s, so as they get older and older, it's possible that the casings and shielding deteriorate with age, causing fissile material to gradually leak together until it reaches the flashpoint. $\endgroup$ – Hans Z Feb 13 '18 at 22:39
  • $\begingroup$ I recommend this excellent book: en.wikipedia.org/wiki/Command_and_Control_(book) $\endgroup$ – peufeu Feb 14 '18 at 14:49
  • $\begingroup$ Have you ever thought about how people in your novel will figure out what actually happened? $\endgroup$ – Noir Feb 14 '18 at 15:37
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    $\begingroup$ which kind of nuclear weapon, early gun-types nuclear weapons (see little boy) are fairly easy to set of accidentally, which is one reason we rarely build them anymore. $\endgroup$ – John Feb 14 '18 at 17:49

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Yes, it is theoretically possible. (nuclear) bombs do not look at flags or landmarks, they don't know if they are exploding in a friendly territory or not. They are just given some coordinates, their computer follows the trajectory from the launch point until the target point and then, KABOOOM, they explode.

If somebody, accidentally or willingly, would insert the coordinate of a friendly location and nobody should realize the error until the explosion, the blast would surely happen.

(the same can happen if instead of giving the coordinates to a computer, one gives the coordinates to a plane carrying the bomb)

That's why there are several redundant security layers in such systems, to reduce the chances of human failures.

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    $\begingroup$ In 1961 you guys got awfully close en.wikipedia.org/wiki/… $\endgroup$ – Borgh Feb 13 '18 at 10:33
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    $\begingroup$ @MMiller that should be a separate question, but the short answer is no. Nuclear bombs are designed specifically to never explode (weird as that sounds). $\endgroup$ – Erik Feb 13 '18 at 11:17
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    $\begingroup$ ...or rather, to not explode, until some very specific criteria are met. @Erik $\endgroup$ – nzaman Feb 13 '18 at 11:31
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    $\begingroup$ Mistakes like setting the launch codes to 00000000 ? $\endgroup$ – PlasmaHH Feb 13 '18 at 13:55
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    $\begingroup$ @MMiller There are a lot of failsafes, and the ones to prevent the bombs from detonating if they're damaged or involved in an explosion are robust and reliable, but it's the "security against humans" failsafes that are often bypassed. Things like setting the launchcodes to '00000000' because they couldn't figure out the software 40 years later, or propping open the secure blast-proof doors to the launch room with a monkey wrench or accidentally leaving a battery of nuclear tipped cruise missiles on the runway over a long weekend - all things that have happened and been reported in the US. $\endgroup$ – HopelessN00b Feb 13 '18 at 15:21
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Honestly, nuclear weapons (or American nuclear weapons, at least), have robust and effective safeguards to prevent a nuke from accidentally going off for technical reasons (like an electrical short in the triggering mechanism or being hit by gunfire or an explosion, or being set on fire, etc.), and are designed to be exceedingly hard to detonate anyway. The general design type in use is an implosion-type device that requires special, high performance trigger devices to initiate a spherical implosion that compresses the fissionable core to "critical mass" (density, really).

As a result, it's not really possible for an accident to detonate a nuclear weapon, from a technical standpoint. In fact, it's extremely difficult to deliberately detonate a nuke without all the required components and authorization codes, so the "terrorists steal a nuke and set it off" trope is pretty implausible, too.

Having said that, nuclear weapons are tools, which do what the human operating them tell them to do, not what the human operating them meant to tell them to do, which has resulted in dozens of "near misses" over the decades, and that's how you would plausibly detonate a nuke by accident - human error. While there are layers of safeguards in place there, they've been bypassed or failed frequently over the years, and many of those have made it into the press.

Nuclear launch codes set to 00000000 for 20 years.

Nuclear silo doors left open while the nuclear officer slept.

Six nuclear cruise missiles accidentally loaded onto a B-52 were missing for 36 hours.

...

And there are scores more, going back to the 50's, including a frightening list of instances where nuclear powers were close to deliberately launching nuclear weapons at each other under mistaken pretenses. It's not hard to imagine how coupling one of these incidents (or something similar) with a poorly timed drill or training exercise or weapons test could result in a live nuke being launched and detonated, and I think that's your most plausible approach here. Known, documented examples of human error with our nuclear weapons, coupled with some bad timing turns a training exercise into a nuclear detonation.

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    $\begingroup$ ...oh my god, the launch codes one actually happened. I thought PlasmaHH was joking when he posted that as a comment. That is legitimately horrifying. $\endgroup$ – F1Krazy Feb 13 '18 at 17:12
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    $\begingroup$ @F1Krazy It's actually even a fair bit worse than made it into that particular media blitz a few years back. Having identified the problem, they can't always correct it, because no one knows the 40+ year old computer platforms controlling these things, and there's no budget or motivation to replace it with something new. So the options (in some cases) are missiles that can't be reprogrammed ... leaving us with the choice of having nukes that can't be armed, or nukes that have to keep the default, all zeros launch codes. $\endgroup$ – HopelessN00b Feb 13 '18 at 17:17
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    $\begingroup$ It should also be pointed out that while modern nuclear warheads have fairly robust safeguards against accidental detonation, the earlier models did not. The Genie A2A rocket famously had issues where loose screws in the casing could cause the weapon to arm. $\endgroup$ – jdunlop Feb 13 '18 at 18:06
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There was an extremely close call in the 60s. the US Air Force came close to detonating a 4 megaton bomb over North Carolina. According to one engineer, "one simple, dynamo-technology, low voltage switch stood between the United States and a major catastrophe". More about that here

Human error is a major factor in all of the close calls we've had and therefore I feel it's perfectly reasonable for a nuclear accident to occur.

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  • $\begingroup$ I added this link as a comment (refresh issue I didn't see the answer when I posted the comment). I'll remove my comment and defer to this answer. $\endgroup$ – Twelfth Feb 13 '18 at 19:15
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    $\begingroup$ "of the four safety mechanisms in the Faro bomb, ... three failed to operate properly." And that's why there were four safety mechanisms. $\endgroup$ – RonJohn Feb 13 '18 at 21:33
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Not our bomb

Upset over Russian territorial grabs, Ukraine discloses that it still has nuclear weapons left over from Soviet days and is ready to use them. Frenzied diplomacy ensues, and ultimately the Ukranians agree to give up their nukes - but to the Americans. The US agrees to take them back for safe disposal.

These bombs are of ancient Soviet make, and the angry Russians refuse to provide information which might be of help dismantling them. Worse, in getting ready to use them the Ukranians have jerry-rigged these bombs to bypass the missing Soviet safety protocols.

On trying to disassemble and inactivate one, it is detonated.

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    $\begingroup$ Okay, I've read the back cover. I want the book! $\endgroup$ – psaxton Feb 14 '18 at 20:48
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    $\begingroup$ Nearly all the other answers are a subset of accidents have happened; failsafes have prevented accidents from becoming disasters; OMG if accidents can happen then the failsafes are bound to fail!!! This answer actually develops a novel concept and establishes a plausible scenario. $\endgroup$ – psaxton Feb 14 '18 at 20:55
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The "best" failure mode resulting in an accidental detonation would be if you dropped a semi-decommissioned first generation atom bomb, one with a "golden gun". In theory if a golden gun weapon hit the ground, very hard, at the wrong angle it could go off. That is it could if all the safeties had been pulled and the bomb casing had been removed so it hit the ground parallel to the axis of the firing mechanism. This is because golden gun bombs consisted, operationally, of a simple guide barrel and two subcritical lumps of fissile material that fit together when one of them is fired into the other. If the mechanical safeties had been pulled out the extremely rapid deceleration of hitting the ground could do the work normally reserved for the trigger charge. In actual bombs the golden gun was oriented perpendicular to the designed impact line so that accidental drops couldn't set them off even without the safety rods across the barrel. Modern bombs are a whole lot more complex and require a finely tuned detonation sequence to go nuclear so setting one off accidentally would be nearly impossible.

It should be impossible for a modern weapon to be detonated accidentally or through negligent handling but if a real bomb and a real arming code was slipped into a training exercise for nuclear deployment then you could get a deliberate mushroom cloud incident from a modern weapon.

FYI the highest nominal yield for a Gun-type Nuclear munition is for the W33 nuclear artillery warhead which was only retired in 1992 and had a tested nominal yield on 40kilotons.

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    $\begingroup$ Such an impact would cause a fizzle; quite possibly still a detonation, but 5% to 50% of the "intended" yield. Part of the point of the gun is to push them together fast, and terminal velocity isn't that fast. $\endgroup$ – Yakk Feb 13 '18 at 15:03
  • $\begingroup$ Does anyone in the world use weapons of that type? $\endgroup$ – Harper Feb 13 '18 at 15:37
  • $\begingroup$ What would a fizzle look like visually? Are we talking about a huge fire? $\endgroup$ – Muuski Feb 13 '18 at 15:37
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    $\begingroup$ @Muuski A fizzle is still a criticality event, still a nuclear chain reaction, it's just smaller than the nominal yield, at minimum something like Little Boy (which was a "gun" bomb) could theoretically fizzle at as little as 0.75kilotons or the equivalent of 750 tons of TNT which is still a huge blast but not enough to level a city by any means. The Wikipedia article on gun-type nukes is reasonably clear that an accidental release of such a weapon can cause full detonation. $\endgroup$ – Ash Feb 13 '18 at 16:39
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    $\begingroup$ This, I think is by far the most credible story line. 1960's gun-type bomb lying in a warehouse, gets picked up for transport to decommissioning by crews unfamiliar with these ancient things. When they turn a corner, it rolls out of the forklift/carrier/cradle/whatever, lands on its side and goes kaboom. Simple, and relies only on reasonable bad luck, and minor bureaucratic evasion/security about whether all of the old bombs had actually been decommissioned yet. $\endgroup$ – RBarryYoung Feb 13 '18 at 22:00
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Oh dear oh dear oh dear. Where do I start?

I highly recommend Command and Control by Eric Schlosser. It's an account of American nuclear safety and policy through the Cold War. It's an excellent, if somewhat alarming read.

There was a lot that could and nearly did cause a nuclear disaster, especially when they were being flown around by bombers, at least until saner, safety minded people finally prevailed and forced better safety standards.

What precisely could have gone wrong?

  • The X-Unit (a kind of power discharge device used to detonate the explosive 'lens' that set off the bomb) could accidentally be charged by a short circuit or old cabling. From there only a minor additional issue of any kind could have caused discharge and detonation.
  • An error in (manual!) assembly could have easily triggered the detonator in older nuclear weapons
  • Dummy 'training' nukes were stored right next to real nukes. Pre-assembled nukes of course had real atomic cores integrated into them.
  • Nuclear weapons were designed in such a way that a fire could cause safety features to be bypassed because of wires being close together.

Now it's our good fortune that this hasn't caused a nuclear accident to date but of the 32 broken arrow incidents to date any one of them could have ended in nuclear fire - many over US territory!

So yes, it's entirely realistic and it wouldn't be all too distant a world in which we look back and ask 'is there a world where we never had a nuclear accident'

Today's nuclear weapons are much safer by design, of course - a product of a great deal of hard work by many people - but it's not too hard to see how we could be back to that level of (hidden) risk.

In 2011, some technicians at the Los Alamos nuclear laboratory decided it would be neat to pose 8 plutonium rods for a photo op. They were close enough that reporters clustering around to take photos would have caused a criticality incident (from their bodies reflecting neutrons), killing everyone in the room. As it was it was realised and carefully defused in time. The safety team walked off the job in disgust afterwards, and to this day the lab still hasn't been able to satisfy safety checks and remains closed.

It's no effort at all to imagine a world not too far from now where growing political pressures and global instability have led to the development of new weapons. Where concerns about the ability to guarantee their detonation overrides concerns over how to prevent it. A new missile, built without the hard-won lessons of the nuclear age, 24/7 alertness drills, a miscommunication to an operator in Hawaii...

It would be all too easy.

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    $\begingroup$ Thank you, this is very helpful. More and more I'm realizing I need to read Command and Control! $\endgroup$ – Mike Miller Feb 14 '18 at 2:58
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    $\begingroup$ "As it was it was realised and carefully defused in time." As in pulling the rods apart by hand, which could also have caused a criticality event for the same reasons! $\endgroup$ – Eth Feb 14 '18 at 10:26
  • $\begingroup$ All in all it's a miracle nobody died that time $\endgroup$ – Pingcode Feb 14 '18 at 11:59
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My favorite story demonstrating that this is possible is the 1980 accident in Damascus, Arkansas. A maintenance accident led to the explosion of a Titan missile (it's fuel, not its warhead of course). The warhead itself was blown outside of the base's perimeter. If its safeties had failed, there'd be a big hole in Arkansas.

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    $\begingroup$ The problem with using that as an example of an accident that could happen is that it actually just goes to show how impossible it is for a technical accident to actually cause a modern nuclear weapon to go off. They're designed in the first place so that it can't happen (the fissile materials in the warhead are below critical mass), and then have multiple safties in place so that that the very precise triggering explosion needed to cause a nuclear detonation can't happen accidentally. The warhead was involved in an explosion that threw open a 740 ton blast door... and still didn't detonate. $\endgroup$ – HopelessN00b Feb 13 '18 at 23:03
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You mentioned that you've looked into previous broken arrow incidents; I'm curious, did you come across the B-52 crash in Goldsboro, NC (1961)? Long story short: the plane lost control, crew ejected, and the two Mark 39s -- 4 MT Hydrogen bombs -- it was carrying were somehow loosed during the descent. One hit nose first and buried itself 20'+ in a field. The other, known as the Faro bomb, opened its parachute and ran through all of its safety switches except the arm/safe switch physically controlled by the pilot.

Other terrible nuclear ideas we've had that may fit your plot line include the M-29 Davy Crockett Weapon System, because we needed a small portable nuke launcher that can be operated and carried by a three man team or mounted to a jeep. (up to two mile range and ~10-20 T yield)

GAR-11 Falcon Air-to-Air missiles, because dog fights are not interesting until you start throwing 250 T warheads at each other. 27 Oct 1962 they were deployed on F-102As to help Charles Maultsby's U-2 escape Soviet Air space and MiG interceptors; the pilots had individual control over the missiles.

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    $\begingroup$ While it is clear that you imply a "yes" answer. It would be better to say that explicitly and then give your examples. Doing that would turn this from "not quite an answer" to a very good answer. $\endgroup$ – ShadoCat Feb 14 '18 at 0:11
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During the cold war, this was actually a scenario which was not at all unlikely. Both the USSR and the United States were prepared to launch their arsenal as quickly as possible in case the other side showed any signs of aggression. Launching nukes quickly requires loose safeguards. Accidentally triggered world war III was a very common topic. Some cult movies from that era about that topic are War Games, Dr. Strangelove and various James Bond movies. But there are many more examples.

Common triggers are:

  • Miscommunication in the chain of command
  • Human error while handling the nuclear launch systems
  • Crazy supervillain tricking superpowers into nuking each other by staging a nuclear attack

However, if you want your story to take place after the Cold War, then all these scenarios will feel outdated and unlikely. The United States no longer face a threat of mutually assured nuclear destruction (no, North Korea is not a serious nuclear threat to the US mainland), so they no longer need a hair-trigger on their nuclear arsenal.

If you want to revive the cold war era fear of the world constantly being at the brink of nuclear annihilation, you might have to introduce a new nuclear arms race which would again warrant a way to quickly fire (and misfire) nuclear missiles.

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I'll quote an anecdote from the other side of the pond.

A Soviet ICBM firing drill does wrong in the 60s. Well, the ICBM is loaded with a mock-up of the bomb, but it does not land in the area anticipated. Meanwhile, in a town, like 9000 km from the designated goal area, a strange meteorite falls down and digs 3 meter down the street.

After an investigation, following turned out. The ICBM was set up by entring the fire distance and orienting the rocket to the correct azimuth of the destination. Some poor soul oriented the rocked correctly, but 180 degrees in reverse. The missile shooting and maintenance team got into deep trouble with military court.


What would you need:

  • The 60s technology. I bet that nowadays the coordinates of the destination are entered via a computer link. There would be failsafes to prevent typos, wouldn't they? Really? Really? So I'd speculate that one rather needs to choose "New York" or "Moscow" from the list than entering coordinates directly.
  • That was a bulk head. You'd need another mishap to mount the real warhead on the rocket. This makes it two very, very unpropable mishaps.
  • You might want to add an evil will of a second (or third) party to organise these mishaps.
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If you're willing to get into gray areas there are rumors that the US and Russia had 'backpack nukes' (or 'demolition nukes'). They were designed for two-man special ops teams who were dropped off some distance from the target and traveled overland to the target. Think of something that you would place at the base of a major bridge - a special ops team carrying conventional explosives couldn't take down the Golden Gate bridge but a team with a small nuke (Davy Crokett size) could.

Ditto a team that "accidently" drove a van off the bridge over a major dam. Conventional explosives won't do much but a small nuke, detonated under 1000 feet of water, should be able to screw up the internal gear (e.g., the power turbines) even if it doesn't punch a hole in the dam.

There are also theoretical 'briefcase bombs' that could be carried by an individual. I think that's less likely since you would either need so much shielding that it would be obvious (try looking casual as you carry around an 80 pound briefcase in one hand) or they would set off the radiation detectors that you don't realize are around. But that's pure conjecture on my part...

Anyway if you assume that the rumors were true then you can also assume that they're designed to be easily set off by special ops teams - there may not be the usual safeguards. Given what we know happened with real weapons it's not hard to imagine something similar with one of these rumored nukes.

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Other contributors have noted several indirect safegoards (physical keys, electronic keypads). However there are other safeguards in the detonation sequence itself. A carefully choreographed set of events must take place in some designs. For instance, the crush bombs achieve critical mass by taking a hollow uranium soccerball and detonating explosives on each panel. The safeguard in this case is that the triggering explosives must detonate at nearly the same time to cause a nuclear explosion.

The implication is that whatever set of mistakes / actions that lead to a nuclear detonation would have to avoid interfering with these carefully choreographed events. From my example: If the wires to the explosives on the soccer ball were cut, you couldn't just sodder them back together. Changing their length or their conductance "may" be enough to keep the explosives from detonating at just the right time (resulting in a bunch of broken uranium plates or the fizzle described above).

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Yes.

Can you accidentally shoot yourself in the foot with a pistol? There isn't really a difference except for scale.

You are already accepting a guidance/engine failure as a real world scenario, you are only needing the arming sequence also fail simultaneously. It is a system, systems fail. It may be extremely unlikely that all the moving parts fail simultaneously, but the "is it possible" question is most assuredly yes.

The "how" is as easy to find as opening a browser and searching for weird stories about how things break...

  • Targetting GPS failure: the system thinks it is in the right place, so it arms.
  • Structural Failure: The physical impact of the failing rocket.
  • Government Contractors: The failsafes never worked, but no one ever noticed.
  • Human Error: Like the Russian rocket from years back... someone installed the failsafe hardware upside down, and by some ridiculous but real-world miracle of ineptitude, it worked inversely.
  • Act of God: Lightning strikes as the misfiring missile is about to crash otherwise harmlessly, and triggers the reaction.
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  • $\begingroup$ Random downvoter has a critique? $\endgroup$ – OhkaBaka Feb 13 '18 at 22:39
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    $\begingroup$ This does not touch "how" or "failsafes" even remotely. It is your opinion not backed by any facts, any data. $\endgroup$ – Mołot Feb 13 '18 at 22:43
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    $\begingroup$ @Mołot, I agree. It would have been better if it was in the form of: yes but this is what would have to go wrong simultaneously for that to happen. $\endgroup$ – ShadoCat Feb 14 '18 at 0:17

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