Yeah? What harm is that going to be? A bit of environmental contamination on the sea floor? That's harm, sure, but it's pretty tame as such things go. A full-scale nuclear explosion? Not actually on the table. Terrorists with submersibles and scuba gear bringing it up and disassembling the inoperative rusting hulk in some far-fetched attempt to reconstruct a nuclear bomb? That's not "harm", that's a Tom Clancy novel, and it's a dud because they shot their nuclear engineer before he warned them that their tritium needed to be purified from helium-3 so most of us are safe unless the President gets into a standoff with the Soviets and starts World War III.