in the wee hours of the morning in New York Harbor, an explosion tore through the hull of the HMS Eagle, Admiral Richard Howe's flagship. Though carpenters and crew rushed to save the vessel, it sank, carrying twenty-five men with it while the rest fled to shore and nearby ships.

The British suspected an accident with the stored gunpowder, but two more explosions sank ships the next night. Eventually word came from old notes provided by a Loyalist spy that the Americans had a sort of "sub-marine" attack ship.

The Turtle (pictured) had been invented by the young Yale student David Bushnell. While a freshman, he had begun experiments with underwater explosives, proving that gunpowder exploded underwater. He sought help from Isaac Doolittle, a New Haven clockmaker, and created the first time bomb. To implement the explosive on the hulls of ships, Bushnell designed a boat that could dive under the water. Something like an upturned clam, the one-man boat was made of two steel-reinforced wooden shells covered in tar. A hand pump and bilge tank allowed the intake and expulsion of water, thus increasing or decreasing the density of the craft and allowing it to sink. Six small windows allowed for bearings along with a compass lit by the bioluminescence of foxfire from fungus on cork.

"Good illustration of divergence.One success can lead to a trend." - reader's commentCalled the Turtle, the boat was manned by Sergeant Ezra Lee, who would later become part of Washington's secret service. Dodging the iron plate at the Eagle's rudder, Lee was able to secure the bomb and sneak away before spotted by soldiers. As the watch increased around the panicked British fleet, the Turtle was too easily discovered, so Washington set Bushnell on the task of improvements. The general referred to the craft as "an effort of genius" that had much promise for the future.

While improving the Turtle, copies of which had success in New York, Boston, and Baltimore through the course of the war, Bushnell was also made Captain in the Corps of Sappers and Miners. Explosives he devised helped push the British to surrender during the Siege of Yorktown. After the war, Bushnell traveled to France where he met with inventors Benjamin Franklin and Thomas Jefferson with his letter of introduction from Washington. While Franklin was more enthused with the Parisian balloon launches, Jefferson became captivated by Bushnell's ideas. Bushnell returned to America and took up teaching until 1800, when he was called up by Jefferson to build up America's naval forces. A fleet of short-range submarines launched from important ports seemed perfect to the defense-minded president.

"Yeah, it could have happened...one spectacular success leading to imitators. All the Turtle really needed was a little more luck." - reader's commentBushnell was made a Captain of the Navy and began implementing Jefferson's defense plan. His submarines, now in a steel shell with improved diving, longer range and higher speed, as well as a "periscope" invented by Jefferson himself, populated the key harbors of America. While the Marines would show the naval prowess of America during the destruction of the Barbary pirates in Jefferson's term, Bushnell's Turtles would be pivotal defense in the War of 1812, keeping much of Britain's navy at sea and minimizing coastal raiding.

Bushnell died in 1824, and his Turtle designs were scarcely updated until the Civil War when ironclad ships began to dominate naval battles. With improved torpedoes, new Turtles were able to dive under ironclads and attack their weaker bellies. The South made effective use of Turtles combating the North's blockade, prompting the US to develop anti-Turtle detection techniques, some precursors to sonar. Shipborne Turtles would also play major roles in the naval battles of the Spanish-American War.

Upon the entry of the United States into World War I, US submarines carried out hunting of the German U-boats that had plagued Allied shipping. Sonar was more fully developed and shared among Allies, causing a push for defensive science to improve subs' ability to hide. By World War II, submarine warfare was doing for undersea combat what aircraft carriers did for above the waves. German u-boat-mounted V-2 rockets, for example, were used for several hit-and-run attacks against the Eastern Seaboard.

Since the Cold War, submarine technology has continued to improve to the point boats can stay underwater for as long as crew morale can endure hibernation techniques while automation and water-class Predator drones patrol the seas.