Anti Invasion Floating Mortar

Also known as Naysmyth's Submarine Mortar and the Steam Ram, the Anti-Invasion Floating Hammer was a semi-submerged naval ship design conceived and published by inventor James Nasmyth in 1853. The mortar had a length of 80 feet (24 m) and a beam of 30 feet (9.1 m) and was equipped with a small steam engine that drove a single propeller. The walls of the mortar were 10 feet (3.0 m) thick, protecting it against potential enemy gunfire of that period. At the front of the boat was a hollow brass cap shaped like a ram that was 9 feet thick. Inside the ram was a case filled with a heavy charge of explosive powder. With only the funnel and a domed structure covering the pilot being visible above water, the mortar sought to attack enemy ships by ramming the hull with the explosive-filled ram at speeds of over 10 knots (19 km/h; 12 mph). Because of potential dangers associated with its means of attack, the Anti-Invasion Floating Mortar was never built.