USS Monitor was one of the Navy's first ships protected by plates of iron armor.
Monitor was designed to fight in shallow coastal waters and in rivers, so she sat low in the water and needed no sails. The ship was powered by a steam engine.
To fight the enemy, Monitor had an iron turret containing two heavy guns that turned in any direction. This eliminated the need for separate rows of guns on the decks of frigates and sidewheelers. While ironclads proved to be good warships, sailors found them hot, stuffy, and uncomfortable to live in. "Monitor" now refers to any ironclad ship.