In the past I have written about various surprising technologies that were developed and sometimes employed as early as the War of 1812, which was otherwise a conflict that revolved around weapons such as cannon and flintlock muskets that had been in use and relatively unchanged since the era of Marlborough at the beginning of the 18th Century.
One of my major dislikes is Steampunk and its adherents, because in trying to combine make-believe clockwork technology in Victorian era fashion they ignore the truly amazing accomplishments and inventions that were actually in existence, not only during the Age of Steam but during the Georgian period! The submarine is one of these inventions. The famous American Turtle is usually ascribed to a Revolutionary War exploit, but a copy was made in 1813 and actually made an attempt against a British 74-gun warship. Robert Fulton himself devised a strange craft he called the Mute because it had a "silent" drive system, but very little information can be found on it. Presumably it was broken up when he died in 1814 but maybe it lies in the mud off the old Brooklyn Navy Yard or the Brown Brothers shipyard, waiting to be uncovered. Submarine warfare would wait another century and the development of diesel electric propulsion, not to mention screw propellers, to truly come into its own.
This excerpt from Submarine Warfare, Past and Present (published in 1907!) by Herbert C. Fyfe contains about as good a description of the submarines of 1812 as I've found: