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.
USS Monitor was the first ironclad warship commissioned by the United States Navy during the American Civil War. She is most famous for her participation in the Battle of Hampton Roads on March 9, 1862, the first-ever battle fought between two ironclads. The Monitor fought the ironclad CSS Virginia (the former frigate USS Merrimack) of the Confederate States Navy.