What was the iron-clads ships names?

USS Monitor and CSS Virginia (formerly USS Merrimac). They fought on the second day of the Battle of Hampton Roads in 1862, but their inconclusive duel is more commonly known today as the battle between the Monitor and the Merrimac, or the battle of the ironclads.

Not only was this the first time two ironclads fought in the US Civil War, it was the first time in war history that two ironclads fought each other.