David Bushnell, who designed the submersible while he was completing his studies at Yale, called it a “Turtle,” but in sketches it looked more like an egg: an oval shape, made from two adjoining half-shells joined together with tar and steel bands. Overall, it was just large enough for a grown person to sit in, which that was all Bushnell needed — stealth and an element of surprise to attach timed underwater mines to the hulls of British ships during the Revolutionary War.

On this day, September 7, in 1776, the Turtle became the first underwater attack ship. Patriot Ezra Lee piloted the Turtle into New York Harbor and moved below the surface up to the 64-gun sloop HMS Eagle.  The plan was to drilling into the ship hull to attach explosive, but Lee ran into a metal layer that he couldn’t penetrate and left the bomb to float free. Neither the Eagle nor the Turtle were damaged in the explosion.

Several more attack attempts would be made with the Turtle but all similarly failing due to operator lack of skill. Only Bushnell had the skill to operate it, but he was too physically weak to try. Still, Bushnell’s designs were not a total loss: the underwater explosives he developed, even when left free floating, succeed in sinking a number of British ships.