In 1813 steamboat engineer and businessman Robert Fulton wrote a series of letters to retired President Thomas Jefferson regarding his proposals for a new kind of naval weapon. He had discovered that cannon could be shot underwater, with devastating effect at close range on a target vessels hull. This was accomplished by loading a cannon, with enough wadding to keep the powder dry and a tin or brass tube enclosing the priming quill. I believe a lit portfire was dropped from the surface of the water down to the quill to set off the cannon. He also mentions his design for the steam battery Demologos, which would have a unique catamaran design to enclose its vulnerable paddle wheel. When finished in 1815 it could make 2 knots, and while not intended as a seagoing warship, the idea of a travelling, invincible floating fortified coastal battery terrified the Royal Navy.
New York July 8th 1813
Thomas Jefferson Esqr.
Sir on the fourth inst, I sent you a letter containing drawings, details and observations on my experiments on firing cannon under water, and the consequences of such a mode of conducting maritime war on the preceding pages is an exact copy of Commodore Decatur's opinion in favor of this discovery, which from so experienced an officer must have weight with those who are not familiar with nautical affairs. The object now is to give a fair experiment to this discovery by building a vessel and fitting her in the best manner to secure (illegible) and for which Congress should appropriate 100,000 dollars. In which good work I hope for the friendly aid of your influence on your friends in both houses. Since my last letter to you I have composed the steam engine to work in the ship in such manner that it is within the wooden walls principally below the waterline and out of danger of shot from the enemy. I have this day sent a copy of the commodores opinion to Mr Madison you will have the goodness to send the letter to him, with such opinion of the plan as you think it merits.I am respectfully your most obedient Robt Fulton