Imagine Comrade Kim has a fit of insanity and launches a nuke. Either at the US fleet or at a US military base. Unbeknown to anyone, a technician secretly disables the device before launch so it doesn’t go off. The warhead splashes down in shallow waters where it is retrieved by a nearby Western ship - not necessarily US.
What happens next?
Fix the technician’s work and politely send it back ?
We’d know as soon as, or very shortly after, the missile was in the air. Some military response would come within minutes after this is confirmed and after we’ve spoken to Russia and China and our allies to inform them. Whether it would be conventional or nuclear in nature, I don’t know.
A conventional response would probably be a very heavy cruise missile and air strike with the goal of destroying any further launch capability of NK, along with their artillery pointed at Seoul. It would probably lead to war. A nuclear response might obliterate Pyongyang and most NK forces within several miles of the DMZ, if not more.
If the missile failed within minutes, before we can confirm it’s on the way to us or our allies, then we’d probably treat it as any of the other failed missile launches.
“Some crazy person aims a gun at you and fires - but misses. You’re heavily armed - what is your response?”
That’s basically what we’re talking about here. Puting a nuke on a missile and firing it is a declaration of nuclear war, whatever the outcome.
Prediction: DPRK bases and infrastructure (such as they are) will become a memory - conventional munitions, most likely. ROK takes some initial damage, then returns that damage in spades, and grabs off a hunk of DPRK territory. China invades DPRK to 'stabilize the situation." Putin plays about the periphery. Lengthy diplomatic exchanges - very nearly as angry as nuclear wepons themselves - lasting decades. DPRK (or what’s left of it) becomes essentially a puppet state of China.
I have a feeling, or a hope, that the Chinese have finally had enough of this blustering from NK and is going to, or probably already has, cut NK off from anymore resupply of weapons, parts and munitions.
I do not know which parts are made in NK and which are imported but all of these failed missle launches must be consuming some vital parts. The Chinese policy of restraint is now one of watching NK consume things they will no longer supply, starving then out and letting them deplete stocks in the futile show of force.
And the Chinese are well aware that should NK actually launch and detonate a nuke that the US will be required to respond. And I don’t think our required response will be to nuke a bunch or NK civilians. A lot of fairly pin point strikes can be made by the US without serious conflict with China, probably with there tacit OK.
It’s really not, though. A single person who misfires can maybe reasonably be taken out without much collateral damage.
Even if NK is dumb/crazy enough to launch a nuke, attacking back has 0 chance of eliminating the threat without massive damage to probably both North and South Korea (and the potential for a much bigger conflict, given the hand at the helm of state).
I’m not saying that we shouldn’t respond, but it’s not as simple as that analogy.
I believe that Fearless Leader or Beloved Leader or Bad Hair Leader, whoever, would have a predator drone accident.
In theory, the military response ought to be the same as if the nuke went off as designed.
In practice, I don’t think the media or public would have much stomach for a war, just like how people who are convicted of attempted murder don’t suffer the same as people convicted of “successful” murder. Without several thousand or millions of people dead, it’s hard to rile up the public.
Imagine if Bush had launched a big war in Afghanistan after the 9/11 hijackers were all thwarted (as opposed to them successfully executing 9/11.) The American public would think, “What a needless warmonger Bush!” People don’t get upset over something that didn’t happen.
Who can authorize the strike on Trump? Oooh, you meant Lil Kim.
If you point a gun at a whole SWAT team, and pull the trigger, and it doesn’t go off (and you don’t have any more bullets but they aren’t sure of that), well, there’s no taking it back. They would basically fire 300+ rounds into your body. I would assume the USA would order an ICBM launch - probably from a land base, since the submarine launched nukes have more strategic value - of a few dozen missiles onto North Korea. What’s left would be a fallout strewn wasteland populated by starving survivors.
Essentially the reason Clinton didn’t kill Osama bin Laden with a cruise missile.
Sadly, the response to a failed nuclear attack by NK would be to show them how it’s really done.
I like the part in the OP where it has to be somehow fucked with to prevent it from going off! 
I believe you’re being deliberately obtuse - it’s pretty clear that my meaning came through.
Only true if SWAT already had their guns pointed at you - at which point their volley would be a semi-reflexive response to an imminent threat to their lives. Imagine instead that you aimed/fired at the SWAT truck as it was just pulling up to your crime scene, and then you had a change of heart, so you threw down your weapon and put your hands up before they even got their weapons drawn. They would not fire on you. SWAT and other officers neutralize deadly threats if the must, otherwise they simply take perps into custody; they aren’t (supposed to be) about punishment or retaliation.
International diplomacy (to include war), OTOH, does sometimes include elements of retaliation or punishment/consequences that are applied well after the immediate threat to life and limb has ended, the most recent being the US cruise missile attack on the Syrian air base. If NK did deploy a dud nuke at US forces, I don’t doubt there would be a military response, probably one that takes down the NK government.
I think it is unlikely that Dear Leader would just launch a nuke. As mentioned, this is the Korean version of suicide by cop, so he would probably launch an all-out attack on Seoul and only threaten to fire missiles if the US didn’t stay out, which they wouldn’t.
Ultimately it doesn’t make any difference - a single missile strike, even an unsuccessful one, artillery strikes on Seoul, invasions of SK - all the functional equivalent of a gilt-edged note to the US and SK saying “please blow me into bloody kimchee along with a few hundred thousand of my bestest friends”. Possibly not with nukes, but that also makes little difference - we didn’t use nukes in the first Gulf War and we had to back off from shooting people in the Highway of Deathbecause it was so easy it made the world sick.
An attack like that isn’t going to turn out well for anyone, least of all Kim.
Regards,
Shodan
**Bolding **mine.
This is not clear from the scenario presented - The only thing we would know, initially, is ‘shot fired’ - with no knowledge of whether or not there were additional rounds. And since IRBMs aren’t something we’d be able to count easily until readied, we’d have no idea if there was a second shot waiting to be fired.
He might think that the US would not have the will to respond. After all, Jeremy Corbyn has said that he wouldn’t use nukes, and, well, just how strong is the opposition to nuclear weapons in the US? I know CND used to have a big voice.
That was my thought, too, but the OP had a technician disabling it.
Sorry, I guess that is the same thing. I prefer to thing that the NKs can’t make one that works.