What was the name of the first seagoing ironclad warship?

The first seagoing ironclad warship was La Gloire, usually written simply as Gloire.

Designed by French naval architect Henri Dupuy de Lôme, Gloire was launched in 1859 and entered service in 1860. She combined steam propulsion and sailing rigging with 120-millimetre wrought-iron armor, creating a warship capable of operating on the open sea while resisting contemporary explosive shells.

Gloire had a wooden hull beneath its armor, so “ironclad” did not necessarily mean that the entire ship was made of iron. Its design emerged from lessons of the Crimean War, especially the vulnerability of wooden warships to new naval guns and armored floating batteries.

The CSS Virginia and USS Monitor were later American Civil War ironclads, not the first seagoing example. HMS Warrior followed Gloire in Britain’s response to the new technology and was notable for having an iron hull. Gloire’s appearance accelerated an international naval race to build armored steam warships.