Inboard plans of the ironclad warship USS Monitor. USS Monitor was the first ironclad warship built by the United States Navy during the American Civil War. Designed by John Ericsson in 1861 and assembled in 101 days, this revolutionary vessel was powered by steam and had a revolving gun turret. She engaged with the Confederate ironclad vessel CSS Virginia at the Battle of Hampton Roads, Virginia, 9th March 1862. This episode was the first meeting in combat of ironclad warships and signalled the end of the era of wooden ships. Although the confrontation was inconclusive, with neither ship able to sink the other after three hours of exchanging fire, the Monitor prevented the Virginia from gaining control of Hampton Roads and thus preserved the Union's