Designs for underwater boats or submarines date back to the 1500s and ideas for underwater travel date back even further. However it was not until the 19th century that the first useful submarines began to appear.
During the Civil War, the Confederates built the H.L. Hunley,the submarine that sank a Union ship. The U.S.S. Housatonic was built in 1864. But it wasn't until after World War I began that the first truly practical and modern submarines were invented.