The ship consisted of a heavy, round iron turret? on the deck, which housed two large cannon. The armored deck was barely above the water line. Aside from a smoke stack and a few fittings, the bulk of the ship was below the water line, to prevent damage from cannon fire (torpedos? were not a worry for another 50 years).
It was lost at sea during a heavy storm, swamped by high waves.
Not to be confused with a [computer monitor]?.