Maybe someone left the porthole open?
One of the earliest submarine designs was, believe it or not, partially sail-powered. Designed by American inventor Robert Fulton in the late 1790's and called the Nautilus, the craft could submerge up to 25 feet, and was designed to drag boxes of explosives alongside enemy ships in order to sink them.
Fulton tried to interest Napoleon and other French revolutionary leaders in the design, but his proposals were rejected. Fulton soon moved back to America to found the first passenger steamship line on the Hudson River.