By Eliza McGraw
History Correspondent

In the early morning hours of September 7, 1776, the dark, choppy waters of New York Harbor concealed a secret that would eventually change the course of naval history. Beneath the waves, encased in a cramped, acorn-shaped vessel of oak and iron, a lone Continental Army sergeant named Ezra Lee was attempting the impossible. His target was the HMS Eagle, the 64-gun flagship of the British Royal Navy, then the most formidable maritime force on Earth.

Though the mission ended in a frustrating mechanical failure, the vessel—David Bushnell’s Turtle—marked a turning point in military engineering. As the world’s first combat-ready submarine, the Turtle represented the birth of asymmetric warfare and the first time humanity attempted to weaponize the "undersea domain." Today, 250 years later, the legacy of this "effort of genius" endures as the direct ancestor of modern naval technology and special operations.

I. Main Facts: The Anatomy of a Revolutionary Invention

The Turtle was not merely a boat that could sink; it was a sophisticated piece of 18th-century engineering designed to solve a specific tactical problem: how to destroy a superior navy without a fleet of one’s own.

Design and Construction

Constructed primarily of reinforced oak planks and bound by heavy iron hoops, the Turtle earned its name from its unique silhouette. David Bushnell, the inventor, later described it to Thomas Jefferson as resembling "two upper tortoise shells of equal size, joined together." The vessel stood roughly seven feet tall and was designed to be operated by a single person.

The submarine featured several groundbreaking innovations:

• Propulsion: It utilized two hand-cranked propellers—one for horizontal movement and one for vertical ascent and descent. This was the first recorded use of a screw-style propeller for maritime propulsion.
• Ballast System: To submerge, the pilot would use a foot-operated valve to flood a central chamber with water. To rise, the pilot had to manually operate two bilge pumps to expel the water.
• Life Support: The air inside the cabin was sufficient for only about 30 minutes of submerged activity. Two snorkel-like tubes provided fresh air when the vessel was near the surface.
• Internal Lighting: Because candles would consume the pilot’s precious oxygen, Bushnell used foxfire—a bioluminescent fungus—to coat the dials of the barometer and compass, allowing the pilot to navigate in total darkness.

The Weapon System

The Turtle’s "sting" was a detachable powder magazine containing 150 pounds of gunpowder. This "torpedo" (as the term would later be applied) was to be screwed into the wooden hull of an enemy ship using a hand-operated auger. Once attached, a clockwork timing mechanism—engineered by New Haven clockmaker Isaac Doolittle—would trigger the explosion after the Turtle had paddled to a safe distance.

II. Chronology: From Yale University to New York Harbor

The development of the Turtle was a multi-year saga of intellectual curiosity meeting wartime desperation.

1771–1774: The Intellectual Incubator

The story begins at Yale University in New Haven, Connecticut. As early as 1771, Bushnell and his fellow students gathered at local taverns to debate the inevitable conflict with Great Britain. They recognized that the American colonies could never hope to match the Royal Navy ship-for-ship. Bushnell began experimenting with underwater explosions, proving that gunpowder could be detonated beneath the surface—a feat many scientists of the era thought impossible.

1775: Building the Prototype

When the Revolutionary War broke out in April 1775, Bushnell accelerated his work. Working with his brother Ezra and a network of Yale mentors, he spent four years refining the hull and the internal systems. By the time the British began their siege of Boston, the Turtle was nearly ready.

Summer 1776: The Shift to New York

The British eventually evacuated Boston and moved their fleet to New York City. The Turtle followed, transported secretly via a small sloop. Tragedy nearly struck when the primary pilot, Ezra Bushnell, fell dangerously ill. With the mission at risk, Sergeant Ezra Lee was recruited and underwent intensive training in the Connecticut River to master the submarine’s complex controls.

September 6–7, 1776: The Attack on the HMS Eagle

Around midnight, Lee was towed into the harbor by whaleboats before submerging to approach the Eagle. He managed to maneuver beneath the flagship, but his attempt to drill into the hull failed. Historians believe he struck an iron strap or a copper-sheathed section of the ship. Exhausted and running out of air, Lee was forced to retreat as dawn broke. To distract pursuing British guards, he released the powder magazine, which exploded harmlessly in the harbor, sending a massive geyser of water into the air and terrifying the British sailors.

October 1776: The End of the Turtle

Following two more unsuccessful attempts in the weeks that followed, the Turtle was lost. The British sank the sloop carrying the submersible during a skirmish in October 1776. While Bushnell later claimed he salvaged the vessel, its final resting place remains one of the great mysteries of the American Revolution.

III. Supporting Data: The Physics of Failure and Success

While the Turtle did not sink a ship, its technical data provided a roadmap for future generations.

The Limits of Human Power

Modern reconstructions of the Turtle have revealed the immense physical toll the mission took on Ezra Lee. To reach the Eagle, Lee had to pedal and crank against a strong outgoing tide in the Hudson River. Calculations suggest that a single human operator could generate only a fraction of the horsepower needed to combat significant currents, explaining why Lee was "exhausted" by the time he reached his target.

The Foxfire Variable

One of the most fascinating technical failures involved the foxfire lighting. During the winter months, Bushnell discovered that the bioluminescent fungus lost its glow in cold temperatures. This environmental constraint effectively grounded the Turtle during the colder months of the war, highlighting the extreme sensitivity of early "high-tech" weaponry.

The Cost-Benefit Ratio

From a strategic standpoint, the Turtle was an incredibly efficient investment.

• The British Flagship: Cost tens of thousands of pounds and carried over 500 men.
• The Turtle: Cost a mere fraction of a standard sloop and required only one operator.
  Even in failure, the Turtle forced the British to move their fleet further out into the harbor, complicating their logistics and proving that "asymmetric" threats could disrupt superior forces.

IV. Official Responses: Genius Recognized

Despite the mission’s failure, the leaders of the American Revolution recognized the brilliance of Bushnell’s invention.

George Washington’s Assessment

General George Washington, who personally funded part of the project, remained a staunch supporter of Bushnell. In a 1785 letter to Thomas Jefferson, Washington wrote:

"I then thought, and still think, that it was an effort of genius… It was an ingenious combination of powers, for which the inventor deserves great credit."

Washington’s endorsement was significant; it signaled that the American military was willing to embrace radical, unproven technology to overcome the odds.

Thomas Jefferson’s Curiosity

Thomas Jefferson, ever the scientist, maintained a correspondence with Bushnell for years. He was fascinated by the mechanical details of the submersible, particularly the timing mechanisms and the method of underwater propulsion. Jefferson saw the Turtle not just as a weapon, but as a scientific breakthrough in fluid dynamics and pressure.

The British Reaction

The British, for their part, were initially baffled. While they didn’t immediately recognize the Turtle as a submarine, the explosion in the harbor caused a "great alarm." Later British naval reports acknowledged the threat of "infernal machines," leading to increased vigilance and a permanent shift in how the Royal Navy protected its ships at anchor.

V. Implications: The Legacy of the "Tortoise"

The Turtle was the "ancestor" of several modern military and civilian technologies.

1. The Age of the Submarine

While it took another century for metallurgical and engine technologies to catch up—leading to the internal combustion and electric motors of the late 19th century—the Turtle proved that underwater navigation was possible. It paved the way for Robert Fulton’s Nautilus (1800) and eventually the Confederate H.L. Hunley, the first submarine to actually sink an enemy ship in 1864.

2. The Screw Propeller

Perhaps the Turtle’s most lasting mechanical contribution was the screw propeller. At a time when ships were moved by sails or oars, Bushnell’s use of a rotating screw to move through the water was revolutionary. This concept would become the standard for almost all maritime vessels by the mid-1800s.

3. Special Operations and the Navy SEALs

Historians at the International Spy Museum and the Naval War College draw a direct line from Ezra Lee to the modern Navy SEALs. The Turtle was the first attempt at a "stealth" maritime insertion. The concept of a lone operator or a small team using technology to strike a high-value target from beneath the waves is the foundational doctrine of modern special forces and "frogmen."

4. Asymmetric Warfare

In the 21st century, the Turtle is studied as the first modern example of asymmetric warfare. It demonstrated how a technologically inferior insurgency could use "disruptive innovation" to challenge a global superpower. Today’s use of underwater drones and unmanned submersibles is the logical conclusion of the path David Bushnell started at Yale 250 years ago.

As America approaches its 250th anniversary, the story of the Turtle serves as a reminder that the Revolutionary War was won not just with muskets and bayonets, but with the "effort of genius" that dared to look beneath the surface of the water for a way to secure liberty.