To Defeat the Royal Navy During the American Revolution, a Rebel Inventor Designed a Secret Weapon: a Bomb-Carrying Submarine

During the American Revolution, the Turtle made history as the world’s first combat-ready submarine. If all went according to plan, the driver of the acorn-shaped submersible—constructed out of oak and iron hoops—would descend, draw close enough to a warship to attach a bomb to its hull and then make their escape by ascending to the surface. Connecticut inventor David Bushnell designed the Turtle as a secret weapon for the patriots to wield against the British.

Nearly 250 years ago, on the night of September 6-7, 1776, the vessel targeted the Royal Navy’s flagship, the HMS Eagle—and failed. In the centuries since, however, the story of the souped-up submersible that went up against the greatest navy in the world has served as a testament to the revolutionary spirit. Bushnell started experimenting with gunpowder while enrolled at Yale University in New Haven, Connecticut.

He knew that a bomb affixed to a ship’s hull would inflict more damage than one placed on its deck. First, he had to figure out how to get explosives to work underwater. Then he would turn to the question of how to transport the device.

As early as 1771, students at Yale had gathered at a local pub to debate how to defeat the Royal Navy in “the inevitable war with Britain,” says Mark Jacobson, a historian at the International Spy Museum in Washington, D.C. To bring his vision to life, the inventor worked with his brother Ezra Bushnell, as well as his teachers, mentors and colleagues at Yale. Frese write in Turtle: David Bushnell’s Revolutionary Vessel.

Milestones in submarine history By the time the Revolution began in the spring of 1775, Bushnell had nearly finished the hull of his invention. Regarding the submersible’s name, the inventor later told Thomas Jefferson that “the external shape of the submarine vessel bore some resemblance to two upper tortoise shells of equal size, joined together, the place of entrance into the vessel being represented by the opening made by the swell of the shells, at the head of the animal.” The Turtle could hold just one person at a time. After climbing into the vessel, the pilot would use a pedal-operated front propeller and a hand crank to move, submerging only upon nearing the enemy ship.

To descend, they would fill the central chamber with water by opening a valve, leaving just enough room to breathe at the top. Small windows let in light, and the bent snorkel shape of the air vents prevented water from seeping in while the Turtle was submerged. Inside, the barometer and compass were coated with a bioluminescent fungus called foxfire so the pilot could make them out in the dark. (Unfortunately, this fungus only produced light above a certain temperature, making it impossible for the patriots to use the Turtle in the winter.) A “large powder magazine” designed to be screwed onto an enemy ship’s hull rested above the submarine’s rudder, equipped with a timer that would allow the pilot to set off the bomb at “any proposed length of time under 12 hours,” as Bushnell later told Jefferson.