Hi Francis, apparently there were at least 20 submarines of one sort or another operating in the ACW. Some more successful than others.
The Union used them mainly for mine and harbour clearance, the Confederacy for destroying blockading ships.
There were also torpedo boats, that appear to be almost submerged.
Torpedoes were of the spar variety, an explosive charge at the end of a pole rammed into or attached to a ship and exploded.
The next stage will be to scratch build a divers.
Something like the picture I hope!