the world's first steel warship -- the French 'Redoutable' (1876)

Redoutable was a central battery and barbette ship of the French Navy. She was the first warship in the world to use steel as the principal building material. She was preceded by the Colbert-class ironclads and was succeeded by Dévastation-class.

Compared to iron, steel allowed for greater structural strength for a lower weight. France was the first country to manufacture steel in large quantities using the Siemens process. At that time, steel plates still had some defects, and the outer bottom plating of the ship was made of wrought iron.

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