There is still a missing H-Bomb somewhere near Tybee island near Savannah Georgia. That was in 1958.
Yes. "Best" case now is it is an A-Bomb, as the tritium needed to make it an H-Bomb has long since decayed.
After soaking in seawater, sand and silt all these years it's unlikely that the electronic are in any shape to set off the conventional charges needed to compress the pit and initiate a nuclear reaction.
For that matter, the explosives themselves are probably degraded beyond the BOOM stage and might only *pop*.
Still, having a big enough lump of fissile material out there somewhere is worrisome all by itself...