An Ironclad is the name given to the first armor plated fighting ships. The introduction of the ironclads would soon make earlier wooden fighting vessels obsolete.
At the Battle of Sinope in 1853 a squadron of Turkish frigates was completely destroyed by Russian shellfire which - apart from being one of the immediate causes of the Crimean War - had every major navy in the world scurrying to build armor-plated ships, or cover their wooden-hulled vessels with iron. The first true ironclad was the French "La Gloire" in 1859. The British followed the next year with the first all-iron warship, HMS "Warrior". "Ironclad" became the generic description for such vessels until "Dreadnought" replaced it in 1906.
The first engagement (really a duel) between ironclad ships during the Battle of Hampton Roads which took place in 1862 during the American Civil War between CSS Virginia (previously USS Merrimack) and USS Monitor. Neither ship was able to seriously damage the other, although both clearly outclassed wooden fighting ships. The first major battle in which ironclad ships took part was the Battle of Lissa between Austria and Italy on 20th July, 1866.
Encyclopedia of Military History, Dupuy & Dupuy, 1979