It would likely be a lot more useful to have a robotic, very deep water, research and “ecological repair” submarine.
The latter purpose is to “tidy up” some extremely toxic mostly radioactive dumping grounds, by covering them many yards deep in underwater concrete, pumped down from the surface.
We can, for example, thank the Soviet Union for dumping expended nuclear reactors and many curies of high grade nuclear waste into the Arctic Ocean, where it is a continuing risk to northern Europe and North America.
Likewise, a lot of chemical weapons, especially blister agents, were dumped at sea and present long term hazards to their regions.
And the submarine, designed for research instead of war, does not have to be quiet and can carry research equipment instead of weaponry.
Good idea.
sidebar, the Soviets also destroyed the Aral Sea basin.