[mikeash]

I'm skeptical that the PALs are as easy to bypass as this article says. It's possible that the arming code includes critical information necessary to properly detonate the bomb, such as timing info for firing the various detonators. Even if it doesn't, the critical PAL hardware is deep inside the bomb, requiring the bomb to be disassembled to get to it, then reassembled afterwards, and that's not quite as easy as swapping out your car's spark plugs.

[sargun]

So, the PALs can be completely disabled at the pull of a plunger. This plunger takes <1s to pull and I'm sure that 1 of those soldiers on base could pull it. Once this happens, the bomb is no longer immediately valuable as it has to be remanufactured.

There is also a tamper-resistant membrane that prevents individuals from getting to the fissile material, and nuclear payload. This could render the bombs likely free of design information. In fact, it turns out these bombs have a ton of conventional explosives inside of them as well and adjusting the timing could make harvesting the fissile material a pain in the ass.

Design: http://i.imgur.com/tv7JVXC.png

Source: http://web.stanford.edu/class/ee380/Abstracts/060315-slides-...

[jacquesm]

Interesting reading. Thank you for posting that.

[Nokinside]

B61 bombs have command disable mechanism. It can be rendered permanently unusable just by entering 3-digit code and pulling a handle.

It's also possible to encode the required code physically into the explosives by mixing high and slow explosives randomly in each bomb. PAL code is then needed to adjust the timing of the detonators so that detonation front is symmetrical. Even if you bypass all the electronics, it's impossible to guess the timing without the code.

[lighttower]

You can still extract the warhead for use in a dirty bomb

[sdenton4]

Command and Control lays out the internal fight over Pals; the military wanted easy access and reliable bombs, and the Pals added complexity, reduce ease of access in an emergency, and so on. So the parts of the military less concerned with safety were arguing for more promising designs. I believe the early Pals could be over ridden with a screwdriver. But yeah, I don't know about these particular ones.

[mikeash]

Yes, I've read that book (highly recommended, by the way, for anyone else reading this who's interested in the history of nuclear weapon control and accidents), and if these were the older PALs I wouldn't have any problem with that statement. But "control" seems to have won that fight eventually (for the most part... Navy nukes still don't have PALs) and I'd imagine that modern PALs are far more robust than those early ones.

[red_admiral]

Are those the same PALs that were (allegedly) set to 00000000 for most of the Cold War?

[mikeash]

Sort of. Those were on Minuteman missiles, and that was put to a stop long ago. The PALs in the B-61 these days should be much more sophisticated and much less useless.

As I said in my other reply, I'd totally believe it if this was happening in past decades, but it seems much less likely now.

[teh_klev]

But the problem isn't nuclear detonation, it's about using the weapons as a dirty bomb:

With a few hours and the right tools and training, you could open one of nato’s nuclear-weapons storage vaults, remove a weapon, and bypass the pal inside it. Within seconds, you could place an explosive device on top of a storage vault, destroy the weapon, and release a lethal radioactive cloud.

[mikeash]

Those are two separate ideas. You don't need to bypass the PAL if you just want to blow it up conventionally to spread radioactive material around.