Turtle (also called American Turtle) was the world's first submarine, or by modern standards a submersible, 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. Connecticut Governor Jonathan Trumbull recommended the invention to George Washington, who provided funds and support for the development and testing of the machine.

Several attempts were made using Turtle to affix explosives to the undersides of British warships in New York Harbor in 1776. All failed, and her transport ship was sunk later that year by the British with the submarine aboard. Bushnell claimed eventually to have recovered the machine, but its final fate is unknown. Modern replicas of Turtle have been constructed and are on display in the Connecticut River Museum, the U.S. Navy's Submarine Force Library and Museum, the Royal Navy Submarine Museum, the International Spy Museum, and the Oceanographic Museum (Monaco).

American inventor David Bushnell had the idea of a submersible vessel for use in lifting the British naval blockade during the American War of Independence. Bushnell may have begun studying underwater explosions while at Yale College. By early 1775, he had created a reliable method for detonating underwater explosives, a clockwork connected to a musket firing mechanism, probably a flintlock adapted for the purpose.

After the Battles of Lexington and Concord in April 1775, Bushnell began work near Old Saybrook on a small, individually manned submarine designed to attach an explosive charge to the hull of an enemy ship. He wrote to Benjamin Franklin that it would be "Constructed with Great Simplicity and upon Principles of Natural Philosophy."

Little is known about the origin, inspiration, and influences for Bushnell's invention. It seems clear that Bushnell knew of the work of Dutch inventor Cornelis Drebbel. According to Dr. Benjamin Gale, the many brass and mechanical parts of the submarine were built by New Haven inventor Isaac Doolittle, whose shop was just half a block from Yale.

Bushnell is given the overall design credit for the Turtle by Gale and others, but Doolittle was well known as an "ingenious mechanic", engraver, and metalworker. He had designed and manufactured complicated brass-wheel hall-clocks, a mahogany printing-press, brass compasses, and surveying instruments. He also owned a brass foundry where he cast bells. At the start of the American Revolution, Doolittle built a gunpowder mill with two partners in New Haven to support the war, and the Connecticut government sent him to prospect for lead.

The design of the Turtle was necessarily shrouded in secrecy, but Doolittle probably designed and crafted the brass and moving parts of the Turtle, including the propulsion system, the navigation instruments, the brass foot-operated water-ballast and forcing pumps, the depth gauge and compass, the brass crown hatch, the clockwork detonator for the mine, and the hand-operated propeller crank and foot-driven treadle with flywheel.

According to a letter from Dr. Benjamin Gale to Benjamin Franklin, Doolittle also designed the mine attachment mechanism, "those Parts which Conveys the Powder, and secures the same to the Bottom of the Ship".