Submarines changed naval warfare, increasing the risk of maritime travel from hostile countries.
Underwater ships have existed in various forms for ages. There was a semi-underwater boat built for Tsar Peter the Great in 1720, and also one allegedly built during the US revolution in 1776.
Steamboat baron Robert Fulton built one for the French in 1800 and another for the British in 1804. However, neither country commissioned a ship.
During the US Civil War, a Confederate (Southern) submarine, Hunley, sunk a ship. During testing, the Hunley killed two of her test crews. But, on Feb. 17, 1864, she sank killing her third crew.
The first submarine that seemed to consistently work was built in 1878 by George Garrett and John Holland, financed by Thorsten Nordenfelt. By 1885 they had refined their design into a fully functional submarine, the Nordenfelt I.