Turtle (also called American Turtle) was the world’s first submersible vessel with a documented record of use in combat. It was built in 1775 by American David Bushnell as a means of attaching explosive charges to ships in a harbor, for use against the Royal Navy during the American Revolutionary War.
Not safe though. No flared end.
Yes, we’ll call it “the submersible”. I should have gone into marketing.
Edit: or maybe “the depth charge”.