HalcyonDaze
Contributor
The Koreans would have to find a super silent sub that we could not detect, let alone find a sub with a range that could get close to our coasts. As said above, the MK IV would be heavily damaged by corrosion beyond any use to them. Secondly the point is moot because I'm sure there is now monitoring on the suspected site so that nobody runs off with it.
There's also the issue that a Mark 4 bomb weighed about 10,000 pounds - a little difficult to fit on a "small" submarine. Given that it was essentially a mass-production version of the WWII Mark 3, which was an air-droppable version of the original Trinity bomb set off in New Mexico, I also think the NKs probably have an equivalent device of their own without rummaging around in Canadian waters. I doubt it's anything but a historical curiosity today; when I was stating it could have been an issue would have been circa 1950 when it was a new design. The only valuable component of an old bomb would be the actual fissile material, and in this case it's not present.
There were a few instances of parties trying to grab nukes or nuclear weapon delivery systems for intelligence purposes during the Cold War; the idea was to figure out what the other guy had and what it could do. The most famous (or infamous) was the US attempt to salvage a Soviet missile sub in the Pacific in 1974. Depending on which version of the story you get, they may or may not have recovered nuclear torpedoes or missiles. I suspect the whole story on that one will be classified for quite a while longer.