After Ross Winan’s 1858 Cigar Ship, the idea of cigar-shaped vessels of war was widely circulated – coverage of his invention in Scientific American helped sparked the development of the David Boats, and perhaps F.D. Lee’s Torpedo Ram – which never got its iron shield, but was of similar shape and size. While Winan’s sons tried to interest the U.S. and Russian Government in cigar-shaped gunboats, the Confederacy took a more direct approach with the C.S.S. Manassas.
This link has several great renderings of the Manassas well as several period engravings. http://www.cityofart.net/bship/manassas.html