6. Turtle
The ‘Turtle’ is best remembered as the first submarine ever used in combat. It was invented by a graduate of Yale called David Bushnell during the American Revolution. This was a one-man human-powered wooden craft that relied on foot treadle and hand crank for its propulsion and could submerge and resurface as guided by its pedal-operated water tank. It also had a lead ballast to keep it vertical inside water.
The sub could be used to approach a rival ship undetected and plant a mine of 150 pounds of gunpowder using a screw. The first person to use the Turtle in a military operation was Continental Army private Ezra Lee on September 7, 1776, against the British warship HMS Eagle in New York Harbor. With only some minimal training, Lee tried to attach a time bomb to the hull of the ship but had to abort the mission when he was unsuccessful. Bushnell quit the submarine project after failed attempts to use the sub to sink enemy ships. The invention, however, went down in history as a brilliant effort.