One of the most famous Union ironclad ships was the USS Monitor, which was the first ironclad built by the U.S. Navy. Other Union ironclads included the USS Cairo, the USS New Ironsides and the USS Galena.
Ironclads were designed to protect vulnerable wooden ships from fire and other damage. They typically consisted of a wooden frame plated with iron. Many of them were older ships to which builders simply added iron plates, although the Monitor class ships were specifically designed to be ironclads. The U.S. Navy did not have any ironclads at the beginning of the Civil War. The Confederacy began building them immediately because they did not have many ships at all. Its first ironclad was a captured Union ship that had been known as the USS Merrimac. The Confederates repaired it and installed iron plating, rechristening it the CSS Virginia.
Although ironclad ships may have existed as early as the 16th century, they were generally slow and impractical. The Civil War, the first war to use ironclads in battle against each other, proved that these ships were more effective than traditional wooden ships. The USS Monitor was particularly successful because of many design innovations that made it fast and maneuverable. Other innovations included rotating gun turrets to allow the ship to attack regardless of its position, which was much more efficient than older designs that required the ship to change direction to fire.