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A Simple scenario; you have a guy with a gun (a very big and loud gun), and a ticking nuke with seconds left. All the controls, buttons, and wiring on the thing are in a different language, and he’s just as likely to push the “explode now” button as the “stop explode” button. So he decides to shoot the thing in an attempt to disarm it.

  • The bomb itself is sitting in the open, not armored, moving, or hidden.
  • The bomb is based on real world or near-near future technology.
  • The guy is armed with an anti-material rifle and a handful of rounds for it.
  • Assume very high penetration ability of the munitions, but not magical ability.
  • The guy has no real knowledge of the specifics of how this bomb works besides “the dangerous part is probably in the middle.”

The main question; is it feasible (/likely) that shooting a nuclear bomb with a high powered man portable rifle actually disarms the thing? (would this be taught as a last chance desperation maneuver, or taught as a never-ever-do-regardless of it going off anyways thing.)

Secondarily would this just be a partial disarm, resulting in a smaller boom? Or would something like just a detonator going off and spreading radioactive material everywhere out the new ventilation holes?

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    $\begingroup$ I'm pretty sure that smashing the thing with a sledgehammer would be enough to stop it going off. Nuclear weapons are pretty complicated beasts to set off and destroying most of the components would/should stop the detonation. I'm not supplying this as an answer as I only think this is the case (no time to go look it up and supply proofs). $\endgroup$ – Snow Dec 15 '16 at 15:53
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    $\begingroup$ Hmm. Nukes are built to withstand tremendous forces. They're also incredibly stable unless actually triggered in the correct sequence. He might succeed in setting off the explosives in the warhead without actually triggering a chain reaction. Or he might be able to damage the trigger mechanism to the point where nothing happens at all. Difficult to say. $\endgroup$ – AndreiROM Dec 15 '16 at 15:53
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    $\begingroup$ I am Groot. I am Groot? I am Groot! $\endgroup$ – Cort Ammon Dec 15 '16 at 19:37
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    $\begingroup$ You'll be looking for this scene: youtube.com/watch?v=7CkTYPnJS0E $\endgroup$ – Separatrix Dec 15 '16 at 19:39
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    $\begingroup$ Now I really want to see the specs for a nuclear weapon with a "stop explode" button... $\endgroup$ – Ghotir Dec 15 '16 at 21:05

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It depends. Are we talking about a bomb built by a foreign state, or a bomb built by futuristic terrorists in a basement?

If it's the terrorists, anything is possible, because lord knows how they built it. In that case it's probably a dirty bomb, and anything you do to it will turn it into a dirty bomb, so the best you'll accomplish with your stunt is doing the job for them

If it's a large nation-state built bomb, however, shooting the bomb will, at worst, do nothing and maybe leak a little radiation, and at best, disable the bomb. I'll let you decide what exactly happens in this case.

I know you said that the markings on the bomb are in another language, but I'm going to assume they stole the designs from the USA, or at least have followed a development progress similar to the USA, in order to give you references on where we stand now with our nuclear arsenal.

We no longer use touchy explosives. The explosives used in modern nuclear weapons are some of the most stable explosives which can still be considered explosive, due to the 1968 Thule Air Base B-52 Crash. In that crash, one of the nuclear bombs being carried had a partial detonation, due to a fire destroying the controls and activating the explosive during an airplane crash. It became a dirty bomb, spitting crap all over the place. Cleanup was somewhat successful, but the biggest thing we got out of it was less sensitive explosives and fire-proof electronics boxes.

We no longer use touchy control electronics. “Until my death I will never forget hearing my sergeant say, 'Lieutenant, we found the arm/safe switch.' And I said, 'Great.' He said, 'Not great. It’s on arm.'” (1961 Goldsboro B-52 Crash). Two nuclear weapons on this plane crash nearly blew up. The first bomb completed it's arming sequence, but failed to explode because a single safety switch was switched off. The second nuclear weapon carried in this plane had also partially armed... but this one's switch was ON! The only reason it didn't go boom was because it hit the ground so hard it disintegrated before it could completely arm itself.

Our nuclear weapons are specifically designed to not work at all. "Bypassing a PAL should be, as one weapons designer graphically put it, about as complex as performing a tonsillectomy while entering the patient from the wrong end." Permissive Action Links. After all the close calls and near misses, President Kennedy put the kibosh on the slapdash weapons we had lying around. PAL refers to the arming and triggering systems used in a modern nuclear warhead; it requires encrypted arming codes, has intentional "weak links" in the system designed to fail safe in anything but an intentional detonation... it's designed to fail except when a very specific sequence of actions are intentionally taken.

Note that that complexity is involved in making it EXPLODE. It's very easy to make it not work with a PAL.

I doubt shooting the bomb is considered an intentional activity.

Ensuring that nukes don't accidentally explode was so important that the USA gave the tech to the Soviet Union. They developed their own system, but used the American system as a template. Ironically, the Nuclear Nonproliferation Treaty made it illegal for the USA to provide any guidance on how to safe weapons, an therefore they had to use a dodge to help France build their own PALs. China asked for data on PALs, but President Clinton said no, both for legal and security reasons (but I'm sure the security reasons could have been dodged). Pakistan refused to use USA PALs that were offered, because they fear a Kill Switch, but the NNT means we can't help them build a system they trust.

In the case of China, though, I'd expect even more paranoid bombs to ensure that only a central command order could launch and explode them; Pakistani bombs are likely proofed similarly to the USA, except without the full PAL style system.

In short, as another answer said, nuclear bombs are built to fail except in very specific circumstances. A bomb labelled in a foreign language would likely be the same, and if I was holding a rifle next to a bomb about to go off, and the only choices were to wait and explode or shoot and maybe explode, I'd take the chance.

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    $\begingroup$ So in summary, the default mode of operation for a Nuclear Bomb is to fail. For it to explode is an exception. $\endgroup$ – Nelson Dec 16 '16 at 4:20
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    $\begingroup$ @Nelson Exactly. $\endgroup$ – Zoey Boles Dec 16 '16 at 5:00
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    $\begingroup$ Er, you guys might want to read Schlosser's Command and Control (amazon.com/dp/0143125788) before you come to the comforting but not necessarily true conclusion that nukes are designed to fail. To the extent that it is true, it's not because of design but because initiating a nuclear explosion is not an easy thing to do (so shooting and damaging the bomb would actually work). But weapons design, in general, is about making things go Boom! even in the hands of morons, not making them fail by default. Also, other nations may have even less safe designs than those employed by the US. $\endgroup$ – Viktor Toth Dec 16 '16 at 13:26
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    $\begingroup$ @MukulKumar Preventing a critical mass of fissile material from blowing up is much, much harder than designing a mechanism intended to assemble two non-critical masses into one critical mass. (Oversimplification of course) $\endgroup$ – T. Verron Dec 16 '16 at 16:28
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    $\begingroup$ Most if not all extant nuclear warheads are implosion devices that require precisely timed detonation of precisely aligned explosive "lenses" .It's probable that one bullet would damage it enough to reduce its yield, maybe enough to prevent any nuclear criticality. Break the timing electronics and failure is certain. If the bomb does not detect an assault and detonate itself, a man with a sledgehammer (or a fully loaded assault rifle) can almost certainly render it inoperable. $\endgroup$ – nigel222 Dec 16 '16 at 18:24
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Generally speaking, punching a hole in the side of a nuke is pretty much guaranteed to stop it functioning as a nuke. Anything which upsets the symmetry of the explosive detonation will cause a "weak spot" which will allow the developing explosion to squirt out and squib the blast.

Of course, this is what is referred to as a "dirty bomb" when talking about terrorists these days. All conventional explosives can be assumed to detonate, and the resulting blast will distribute radioactive material around the area. If you're really unlucky, a gun-type uranium bomb might still function at a much lower yield, but this is still better than letting the damned thing go off at full power.

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    $\begingroup$ It won't be all that dirty--it's plutonium in there, not nuclear waste. $\endgroup$ – Loren Pechtel Dec 15 '16 at 23:03
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    $\begingroup$ @LorenPechtel -- a mess of Pu getting scattered about is quite messy indeed, though $\endgroup$ – Shalvenay Dec 16 '16 at 0:34
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    $\begingroup$ It's still better to shoot and risk only contaminate a limited area compared to the larger radius of a full blast. $\endgroup$ – SRM Dec 16 '16 at 3:39
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    $\begingroup$ @Shalvenay The threat is way overrated. Get a grain of plutonium in your lungs and you'll eventually die of it but it's a heavy metal, it doesn't make very good dust. If you don't inhale it the threat is basically zero. $\endgroup$ – Loren Pechtel Dec 16 '16 at 5:54
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    $\begingroup$ It's the reaction and byproduct that's super radioactive. A nuclear bomb going off in the atmosphere is a billion times worse than a bunch of weapons grade plutonium grounded up and spread all over the place. $\endgroup$ – Nelson Dec 16 '16 at 8:28
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Unlike your average TV bomb, nuclear weapons in general are very carefully designed not to explode.

They are very unlikely to have an explode now button, and much more likely to feature a very large well labeled (possibly in several languages) stop button, something like your standard big red stop button on most industrial machinery. Arming and detonating them tends to be a very complicated process involving multiple keys, codes or other complex arming mechanisms, not likely to be accidently done.

If however you found some cobbled together poorly labeled DIY nuclear explosive a few shots from a gun could possibly disable it or more likely misalign things sufficient to keep it from causing a full nuclear explosion. It would still be quite likely to explode from all the conventional explosive contained in the device which are used to smash the fissile materials together. I'm not an expert on conventional explosive devices but I would generally advise against shooting them.

So your hero might save the city from nuclear destruction, but he is likely do die from the conventional explosion and the general area will probably be a government cleanup site from all the spread of the nuclear material.

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    $\begingroup$ I'm pretty sure that nuclear weapons in fact have neither an explode-now button nor a do-not-explode-now button. I can't think of a single scenario in which an explode-now button would be useful; a do-not-explode-now button would seem likely to disable the bomb when it landed, turning it into a gigantic dud. Any nuclear bomb needs to be inside a very strong enclosure, since they require extremely high pressures to begin the explosion. Shooting such a thing would make little difference. $\endgroup$ – David Richerby Dec 15 '16 at 20:26
  • $\begingroup$ @DavidRicherby I think you need to make the distinction between a bomb: stationary with accessible buttons and a visible timer as listed in the question; and a warhead which is a delivery vehicle for the bomb from either a plane or a missile which is likely to have a durable housing and no visible exterior indicators or controls. $\endgroup$ – Josh King Dec 15 '16 at 20:47
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    $\begingroup$ Here's a picture of a nuclear bomb. Where are the buttons of which you speak? $\endgroup$ – David Richerby Dec 15 '16 at 20:57
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    $\begingroup$ @DavidRicherby That's clearly the design where you slap it hard on the side, next to the text DO NOT CHOCK, like you did with old TV sets. $\endgroup$ – a CVn Dec 15 '16 at 21:17
  • $\begingroup$ @David Richerby that's a missile. They aren't just sitting around "about to go off." It doesn't fit the question. A bomb as described in the question is some sort of suitcase nuke -- think tactical nuke, not strategic nuke. $\endgroup$ – SRM Dec 16 '16 at 3:37
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So nukes are pretty complicated, and kind of depend on things happening exactly right.

Implosion nukes (most modern nukes) have a pit of material surrounded by shaped charges. These charges are positioned so that they push a majority of the force inward toward the pit, and so compress it down to critical mass. In order to get all the charges to go off at EXACTLY the same time, they will do things like make sure that all the wires hooking up the charges are the same length, so that the speed of light isn't a factor. If the near side of the charge goes off a millisecond before the far side because the electrons had a shorter path, you could get a fizzle instead of a boom.

So if you shoot the nuke, it is likely that you'll disrupt the blast pattern, and could cause the explosion to be off center. This would keep it from going supercritical, but there is a chance for nuclear material to be spread out as a kind of dirty bomb. Also it's still several pounds of explosives, so anyone standing close is going to be in danger.

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  • $\begingroup$ Precisely because nuclear weapons by using a large conventional explosion to compress the nuclear material and initiate fission, and then containing that fission explosion to compress the fusible material enough to initiate fusion, they're enclosed in extremely strong cases. Shooting at such a case is unlikely to make much difference. $\endgroup$ – David Richerby Dec 15 '16 at 20:27
  • $\begingroup$ A nuclear weapon going BOOM would not be critical, it would be supercritical or possibly prompt critical. The "pure" critical state is where the nuclear reaction is in a steady-state, neither increasing nor decreasing, such as for example in your run-of-the-mill nuclear power plant during everyday operation. See en.wikipedia.org/wiki/Critical_mass#Explanation_of_criticality. $\endgroup$ – a CVn Dec 15 '16 at 21:20
  • $\begingroup$ @DavidRicherby It is an anti-material rifle, which is designed with armor piercing in mind. It might not be useful against a tank with multiple layers of armor, but it can pierce things with lighter armor. $\endgroup$ – AndyD273 Dec 16 '16 at 15:07
  • $\begingroup$ @MichaelKjörling You are right, super critical is the the correct phrase. $\endgroup$ – AndyD273 Dec 16 '16 at 15:08
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Shoot the control box

Nukes are touchy things that have to be very carefully timed and manufactured to go off properly. Destroying the control box removes all the timing gear that will make the bomb go off.

Fat Man style bomb

A look at the Fat Man bomb shows that shooting the main part of the bomb won't do much to stop bomb from exploding. I don't know what the tolerances are for distorted/misplaced explosives but this guy won't save himself by shooting the explody parts.

Little Boy style bomb

Since the Little Boy bomb relied on shooting a projectile down the center of the bomb into a uranium target, disrupting the firing tube may prevent the bomb from going off.

Always aim for the control box

The best way to stop a nuke from going off is to make sure it never gets the signal to detonate in the first place. Shoot the control box.

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  • $\begingroup$ Unless there is some failsafe that is triggered if the control box fails. This kind of circuit would be pretty simple to do. $\endgroup$ – AndyD273 Dec 15 '16 at 19:12
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    $\begingroup$ @AndyD273 That failsafe would be "don't explode if the control box fails" as explained in the other answers. $\endgroup$ – Nobody Dec 15 '16 at 19:41
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    $\begingroup$ @AndyD273 What Nobody said. What you describe would be not a fail-safe, but a fail-deadly. Remember, fail-safe doesn't mean a device is safe from failure (cannot fail), but rather that it is safe in case of failure (fails to a safe state). Another example of a fail-safe is automatic brakes on trains, where for example a lever or pedal must continually be held in a neutral position by the driver; if the driver fails to do so, then the train "fails" to a safe state by engaging the brakes, thus stopping. $\endgroup$ – a CVn Dec 15 '16 at 21:30
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    $\begingroup$ @MichaelKjörling I guess it depends on your point of view. If the purpose of a train is to transport people safely, then the fail safe is automatic brakes to make sure that it does that. If the purpose is to explode and kill a lot of people, and that is what it is designed to do, then a fail safe could be to make sure that it does that. Booby trap might have been a better word choice though. $\endgroup$ – AndyD273 Dec 16 '16 at 15:02
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You can also look at it in a different way. Nuclear bombs are designed to be as powerfull as possible. Shooting it will make it either less powerful, or will change nothing at all. You won't make it worse by shooting at it.

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While the other answers are correct that anything which disrupts the symmetry of the initiating explosion might be sufficient to cause a fizzle or engage one of the multitude of safety devices which prevents nuclear weapons from detonating during transit or in flight, this might need to be caveated somewhat.

Thermonuclear weapons (H-Bombs) have a fission device which is the first stage to irradiate and initiate the fusion fuel for the much more powerful second stage. In order to contain the vast energy output of the trigger for the critical microseconds, a "tamper" made of depleted uranium is often used as the casing of the weapon. Since Uranium is quite dense, it is also used as armour for main battle tanks (such as the M1 Abrams).

For you, this means your anti material rifle will need to be one of the larger ones available (using a .50 BMG round is probably the minimum), and you will have to ensure you use AP ammunition to penetrate the casing and cause damage within. You will also need some detailed knowledge of the layout of the device, so your round penetrates the casing and hits the fission trigger, otherwise you plow a hole though the Lithium deuteride fusion fuel.

enter image description here

A 25mm Barrett XM-109 should do the trick

Of course, you could simplify matters by simply hammering the thing with an actual .50 HMG, and put enough holes in it that statistically you will damage some critical component, but that is hardly elegant.

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  • $\begingroup$ That is correct, although with H-bombs being larger, rarer and strategic (ie less likely to be forward-deployed or dispersed) the chances of coming across one in the given scenario is much less likely than an A-bomb. $\endgroup$ – Matt Bowyer Dec 16 '16 at 11:28
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Probably worth considering that nuclear bombs are (often) designed to hang off the outside of a high-speed jet aircraft, fall several thousand metres and either smash into the ground or through the surface of the water before exploding.

If you do smash the inside of a modern weapon then one of more of the fail-safes will almost certainly prevent its detonation. If it's an older weapon then you might succeed in only damaging the precise implosion device, turning it into a dirty bomb instead of a full-on nuclear weapon - probably still bad news for your protagonist and everyone nearby, but much less bad than a full nuclear detonation. The chance of actually setting it off with a rifle shot is basically zero - high explosives are very insensitive (due to the conditions described above) and the impact of a shot would do nothing. You can even set them on fire without a bang - US soldiers in Vietnam would sometimes use HE as a cooking fuel.

But there is a chance that even with a high-powered rifle that all of that might not work if it's still in the casing, and the richochet could well kill or seriously injure your hero. Probably better to unbolt the thing and then start pulling bits off or cutting wires inside.

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  • $\begingroup$ "nuclear bombs are (often) designed to ... either smash into the ground or through the surface of the water before exploding" Citation needed, as either of those scenarios appears likely to turn the weapon into a "dirty bomb" instead of a (relatively) clean nuclear weapon. $\endgroup$ – a CVn Dec 15 '16 at 21:26
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    $\begingroup$ @MichaelKjörling Nuclear bunker buster for weapons designed to penetrate the ground before exploding; nuclear depth charge for air-dropped anti-submarine weapons designed to explode underwater. $\endgroup$ – David Richerby Dec 15 '16 at 21:48
  • $\begingroup$ @DavidRicherby Very true, but do those really count as "often"? And isn't it primarily the delivery vehicle that is designed to penetrate the ground or surface of the water, rather than the nuclear weapon itself? $\endgroup$ – a CVn Dec 16 '16 at 8:20
  • $\begingroup$ @MichaelKjörling I'm not sure what the proportions of the various types of weapon were in different countries' arsenals, so I don't know if it's "often" or not. As for weapon vs delivery vehicle, I think you're trying to make a distinction that doesn't exist, perhaps confusing the terms "weapon" and "warhead". A weapon is a warhead in a delivery vehicle; sure, it's the casing that penetrates but that's a part of the weapon. $\endgroup$ – David Richerby Dec 16 '16 at 8:52
  • $\begingroup$ To be fair, the core may well be removed from the weapon/delivery vehicle - whether to save weight or to help with disguise, although that may well increase its detectability by radiation monitoring, $\endgroup$ – Matt Bowyer Dec 16 '16 at 11:23
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It comes down to where he shoots and how the weapon is designed.

If he can see the explosive core and shoots it it is no longer a nuclear bomb. It's hard to imagine a core that can still function correctly after taking a bullet. The whole point of all the complex engineering of the bomb is to perfectly symmetrically crush the core. What do you think will happen if you fire bullets into any reasonably soft piece of precision engineering??

If the bullet hits a detonator the result very well might set off the detonator and the shooter dies (but he dies anyway when the timer runs down) but again it's not a nuclear bomb.

Now, if his target choice is bad we have some different options

If the bullet tears through the electronics he may block the detonation signal, he may block the timer, he may block the proper distribution of the detonation signal (resulting in merely a conventional explosion) or he may set it off (full nuclear yield.)

Finally, if he shoots it's power source it depends on how it's built and how much residual power might exist in capacitors. If the weapon was designed to salvage fuse it goes off (full yield), otherwise it depends on whether the capacitors still have enough charge when the timer runs to zero.

Note that in all cases "conventional explosion" means the plutonium core is scattered about to some degree. I would not want to enter the area for a while without breathing gear or a very good dust mask but it's nowhere near as nasty as a dirty bomb. If the emergency crews know it's a failed nuke there should be no radiation casualties.

My personal choice would be to put my first round into the core, upon seeing that it was torn up I would then aim for power sources--a single large capacitor if I saw one (my understanding of modern military weapons is that they are set off by dumping a very high current through a wire, this is more complex than a traditional blasting cap but basically immune to being set off by shock. Kill the capacitor and it's not going off), otherwise batteries.

While you only specified one type of weapon the same basic reasoning applies to most any weapon the police or military might carry. Things with enough boom would no doubt cause a conventional detonation. The only things that wouldn't be of use are the subdual weapons police carry (taser, mace etc.) Hollywood almost always gets this very wrong, the only way the bad guys can ensure the bomb can't be defused by smashing it is by denying access to the bomb with something that will set it off very quickly if breached. This will make for a pretty big package as you have to set it off before the jet of a large shaped charge can destroy the core--and said jet is moving at NASA-type velocity.

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Shooting at a nuclear weapon with a gun is unlikely to achieve anything much.

A fission bomb works by using conventional explosives to compress the fissile material enough to allow the chain reaction to start. A fusion bomb works by using a fission bomb to compress the fusion core enough to allow its chain reaction to start. The first of these things requires a case strong enough to contain the conventional explosion so that the effect is to compress the fission core, rather than just blow the weapon apart. The second of them requires a case strong enough to contain the fission explosion for long enough to get the fusion reaction going, rather than just blowing the weapon apart. Both of these things require a case that's strong enough that it shouldn't care much about being shot at.

Also, why would there be an "explode now" button or a "don't explode now" button? It's hard to imagine why the first one would ever be used, and the second one sounds like a great way to have your bomb fail to detonate if it happens to hit the ground the wrong way.

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It could work. It could go off. It could make no difference. Since we don't really know the specifications of the bomb, it's not possible to say with any authority.
Personally, I'd say press a button at random; far better odds if this is all the information you have. Unless of course, this bomb's in Hollywood--then run around like a headless chicken till the timer says less than 10 seconds left. Then shoot.

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    $\begingroup$ Press a button? What button? Why would a weapon have an "Actually, please don't explode" button? $\endgroup$ – David Richerby Dec 15 '16 at 20:29
  • $\begingroup$ @DavidRicherby: Well, perhaps you think your bomb is very well hidden but your friend does not arrive with the get-away car. Now you really, really wish your bomb had a "please don't explode" button. $\endgroup$ – Zan Lynx Dec 16 '16 at 3:19
  • $\begingroup$ Evil Overlord says, "My bombs always have a Don't Explode button. That way, when it gets pressed, I know the hero is definitely in range and I can explode without missing." ;-) $\endgroup$ – SRM Dec 16 '16 at 3:41
  • $\begingroup$ @DavidRicherby: The OP indicates that the bomb has buttons, one of which may or may not stop it. I would expect a self respecting bomb maker to at least test his trigger mechanism before mounting it on a bomb, which implies start, stop and reset buttons at the minimum. If the bomb has a timer, I would also expect a set time button and buttons for increasing or decreasing the default set time. It's only professional--if you want repeat customers, that is. Even a suicide bomber's bosses wouldn't want the bomb going off before they've finished giving them their orders, especially if face to face. $\endgroup$ – nzaman Dec 16 '16 at 6:03
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    $\begingroup$ An actual bomb most likely has some sort of data port leading to the detonator mechanism, and the parameters of the detonation i.e. time delay, altitude of detonation, yield if the box is "adjustable" would all be entered from the computer in the cockpit or command centre of the missile silo or submarine. There would be no switches on the actual bomb itself. $\endgroup$ – Thucydides Dec 17 '16 at 3:39

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