David Bushnell (1754–1824), of Westbrook, Connecticut, was an American inventor and a veteran of the Revolutionary War. He is credited with creating the first submarine ever used in combat. He called it the Turtle because of its look in the water. His idea of using water as ballast for submerging and raising his submarine is still in use, as is the screw propeller, which was used in the Turtle.

Bushnell proved that gunpowder could be exploded under water. He also made the first time bomb. He combined these ideas to attack ships by attaching a time bomb to their hulls, while using a hand powered drill and ship auger bit to penetrate the hulls. He used the Turtle in attempts to attack British ships which were blockading New York Harbor in the summer of 1776. His efforts failed because the boring device was unable to penetrate the copper sheeting lining in the ships' hulls which was designed to protect against parasites in their previous destination, the Caribbean.

More Info: en.wikipedia.org