Rev_Blair Rev_Blair:
It doesn't have to be a tiny nuclear device though Rosco. It can be individual components for a larger, simpler device. It can be parts of a dirty bomb. You can float one in on a tanker and destroy New York from the harbour. Those are all, according to the world's intelligence agencies, far more likely scenarios then an open and easily traceable attack. The concept of MAD still works.
That's the thing, ships are now scanned before they enter a major harbor, especially New York Harbor I would imagine. A ship comiing in with a bomb on board would very likely be sunk or boarded quite quickly.
Like I said I would be more worried about someone launching a cruise missle from hundreds of miles away from the sea or from the land in a neighbouring country, cruise missles are hard to defend against and the technology is now widely enough available that all but the most backward states could manage to build one.
What's more is that unlike ballistic missles, cruise missles can be derived from readily available weapons that don't raise much suspiscion, for example the Israelis slightly modified a common antiship missle {one that's available to the likes of Iran, among others} and turned it into a nuclear cruise missle.