<P> After the Battles of Lexington and Concord in April 1775, Bushnell began work near Old Saybrook on a small, individually - manned submersible designed to attach an explosive charge to the hull of an enemy ship, which, he wrote Benjamin Franklin, would be, "Constructed with Great Simplicity and upon Principles of Natural Philosophy ." </P> <P> Little is known about the origin, inspiration, and influences for Bushnell's invention . It seems clear Bushnell knew of the work of the Dutch inventor Cornelius Drebbel . </P> <P> According to Dr. Benjamin Gale, a doctor who taught at Yale, the many brass and mechanical (moving) parts of the submarine were built by the New Haven clock - maker, engraver, silversmith, brass manufacturer and inventor Isaac Doolittle, whose shop was just a half block from Yale . Though Bushnell is given the overall design credit for the Turtle by Gale and others, Doolittle was well known as an "ingenious mechanic" (i.e. an engineer), engraver, and metalworker . He had both designed and manufactured complicated brass - wheel hall - clocks, a mahogany printing - press in 1769 (the first made in America, after Doolittle successfully duplicated the iron screw), brass compasses, and surveying instruments . He also founded and owned a brass foundry where he cast bells . At the start of the American Revolution, the wealthy and patriotic Doolittle built a gunpowder mill with two partners in New Haven to support the war, and was sent by the Connecticut government to prospect for lead . </P> <P> Though the design of the Turtle was necessarily shrouded in secrecy, based on his mechanical engineering expertise and previous experience in design and manufacturing, it seems Doolittle designed and crafted (and probably funded) the brass and the 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". The most historically important innovation in the Turtle was the propeller, as it was the first known use of one in a watercraft: it was described as an "oar for rowing forward or backward", with "no precedent" design and in a letter by Dr. Benjamin Gale to Silas Dean as "a pair of oars fixed like the two opposite arms of a windmill" and as "two oars or paddles" that were "like the arms of a windmill...twelve inched long, and about four wide ." As it was probably brass, it was thus likely designed and forged by Doolittle . Doolittle also likely provided the scarce commodities of gunpowder and lead ballast as well . The wealthy Doolittle, nearly 20 years older than the Yale student Bushnell, was a founder and long time Warden of Trinity Episcopal Church on the Green, and was in charge of New Haven's port inspection and beacon - alarm systems--suggesting that Doolittle provided much of the political and financial leadership in building the Turtle as well as its brass and moving parts . </P>

Who designed the turtle america’s first submarine
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