"Launching" a nuclear weapon is not the only option. They can also be transported over land or water via train or boat. Many are small enough to fit into a van, and some kiloton sized weapons can be carried by a person in a large backpack. It would be difficult to track a weapon detonated in this fashion and it may not be a nation that is directly involved -- but stateless individuals. Who do you retaliate against then?
On delivery, you're of course completely correct. A ship container based weapon would be nearly impossible to track. Even if you used X-ray scanning on every container, it wouldn't likely find a weapon stashed in a container of machinery parts.
But you still need to get the weapon. Move it to a ship container. Get that container onto the boat in a non-suspicious manner. And then you have to have set it to be remotely detonated. Possible? Totally. But the organizational skills that would be required for those kinds of logistics aren't in ready supply.
And yes, if a terrorist organization pulled all of that off, we'd retaliate against the wrong country again most likely. People would want an immediate response. The investigation could take ages.
There are divisions of the CIA and other organizations whose only job is to try to buy weapons of all kinds. That way they can identify who is selling, what's possible, and track down the supply lines.
In December, an aircraft carrying 35 tons of weapons from North Korea to Iran was seized. It had piles of shoulder fired missile weapons. The interesting part is this: Let's say they were model A. Iran already makes model C. Why would Iran buy model A's? To resell them and create plausible denial. "How could we have been involved in that attack. We make model C..." So there is definitely a lot of misdirection going on.
But with nuclear weapons, the community is very tight. The requirements are extraordinary. I think that the threat is so big, that the USA, the Russians and other key players are all cooperating to make sure nuclear materials and weapons are better tracked, accounted for, and are more difficult to detonate without the proper equipment. So even if somebody lifted a weapon off of a B-52, the worst we'd get is a somewhat dirty high explosive explosion. But no nuclear yield.
And to mstrze, a lot of people believe the USA will do it is that we've done it before. We've shown that like all other countries, we're willing to lash out at somebody even if it's not the right one.
We're using unmanned drones to kill people from a distance. They're controlled by some 24 year old in Nevada as an example. Has this airman positively identified somebody? Or did he kill the guy with a beard that is 6'2" tall? How much of a reach is it for us to say that we've found a facility building chemical weapons and that we want it permanently incinerated? A conventional weapon might not burn up the contents. A nuclear one most certainly would.
Since we are perceived to have no respect for getting the right guy, a lot of people are concerned that we would indeed unleash a nuclear weapon if we felt justified. I don't think we would. I know people in that industry, and I know how seriously it's all taken. But it's still a concern for a lot of people.
