Submersible 'Turtle', 1776.
© Science Museum / Science & Society Picture Library
Model, showing interior. The 'Turtle' submersible was designed by David Bushnell and Phineas Pratt, who intended to use it to attack the British fleet in New York harbour during the American War of Independence. The one man vesel contained lead ballast to keep it upright, and was powered by two hand-operated propellers, one for moving the submersible up and down, the other for left and right. Depth was controlled by two foot pumps which let in or expelled water. The intention was to dive beneath the hull of the ship to be attacked, bore a hole in its hull, and place a 150 lb explosive charge and clockwork timer. The 'Turtle' made three attempts to attack British ships, notably HMS 'Eagle', flagship of Admiral Howe, but none were succesful.