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. 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. All-steel warships were later built by the Royal Navy, with the dispatch vessels Iris and Mercury, laid down in 1875-1876.