Once spent some time talking to a guy who maintained nukes . . . he didn't get into too much detail, but it seems that nukes need periodic skilled maintenance in order to remain viable. (I think he said something about spalling off the surface of the pit?) Something that's been sitting unattended for 5 decades might not even fizzle . . . especially if it's been under salt water all this time.
And if it was an H-bomb . . . don't they use tritium? With a half life of just over 12 years, by now it would be down to ~1/16 or less of the tritium it started out with.
The "tick ... tick .... tick" implying that the bomb might some day blow up was a joke.
Many years ago, I believe it was in the 1980s I read a book that I then loaned to my father. IIRC it was by Clive Cussler, and the basic theme was that there had been, secretly, a third attempted nuclear strike on Japan to end WW2 but the B-29 that had carried the bomb had crashed at sea. Decades later (contemporary to the publication of the book or maybe a few years ahead...) some Japanese evil tycoon type discovers this and locates the crashed B-29 and recovers the weapon. It was a pretty cleverly written book and involved the protagonist in a Byzantine plot that really kept one's interest piqued.
After reading it my father (who was an engineer and actually
did know something about nuclear weapons) suggested a problem with the storyline. I guessed that after half a century immersed under the ocean, plus what must have been a fairly violent crash, the chances of a nuke being in working order were slim to ziltch. Yea ... that was pretty much what my father was thinking.
But, hey, just for the fun of it; "tick .... tick .... tick ..... "