Shows you're thinking, sorta.
So... Pumpkinhead Kim has a nuke cargo ship milling aimlessly about the Pacific, waiting for a daily call on the satellite phone. It doesn't come through, they toodle over to Frisco and go boom.
Two problems. First, how do they even get past the Coast Guard? That's gonna be one suspicious looking ship. Voyage not filed with the harbormaster. Ship's registration can't be reliably confirmed. Refusing to be boarded. US inspectors? We ain't got no inspectors. We don't need no inspectors! We ain't got to show you no stinking inspectors!
A smaller craft might improve their chances of slipping by, though it's a stretch. It'll certainly improve their chances of sinking in a storm while in transit. They need an oceangoing vessel here. A canoe won't do. Plus, too much hardship and the crew may die before the call comes. As the Chinese mine employee said: "SUPPLIES!!!"
Second problem: the longer they go in circles in the middle of the ocean, waiting for the call, the greater their chances of being detected by satellite recon and other means. Speed is an important component of stealth. And this just isn't speedy.
A submarine? Very difficult to track, but we have an advantage there. We have the technology and infrastructure to track subs, and they haven't the means to track ours. We can seize their harbors by surprise, but they won't be able to sneak up on ours.
Best they can hope for is to hit some remote piece of coastline far from the patrols. Kill a few humans and a lot of seagulls. Acceptable? What are the alternatives?
Maybe that's why Kim is going to all that trouble to have ICBMs. Could be he knows something you don't.