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.

About
The mortar had a length of 80 ft and a beam of 30 ft and was equipped with a small steam engine that drove a single propeller. The walls of the mortar were 10 ft 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 kn. Because of potential dangers associated with its means of attack, the Anti-Invasion Floating Mortar was never built.