Cutaway diagram of the USS Monitor. USS Monitor was innovative in several respects, including the first 360-degree rotating armored gun turret on an operational warship. All but 18 in of the hull was completely underwater and was protected by an armored "belt". Her keel was laid on 25 October 1861, and she was launched 118 days later.
A fine view of the sheer scale and complexity of the big gun turret for a Battleship. In this case, this appears to be a British 15" gun mounting, of the type mounted on R class batlleships, "Queen Elizabeth" class and Renown and Repulse.