Early experiments showed that wrought iron was superior to cast iron, and wrought iron was subsequently adopted for naval use. Early European iron armour consisted of 4 to five inches (roughly 10 to 13 cm) of wrought iron backed by up to 36 inches (roughly one meter) of solid wood. Experiments were also carried out with laminated armour, but these did not lead to any improvements and single plates was preferred. Many ships made during the US Civil War used laminated armour but this was necessitated by lack of facilities for manufacturing single plates of proper thickness.
While armoured ships may been built as early as 1203 in the far east, in the Western world they first become common when France launched the first ocean-going ironclad La Gloire in 1859. The British Navy responded with HMS Warrior in 1860, triggering a naval arms race with bigger, more heavily armed and armoured ironclads.
Due to the ever increasing thickness of the armour, and the associated weight, proposals was made from an early date to faceharden the iron or weld steel plates to the front face of iron armour. Efforts to carry out these proposals failed for many reasons, primarily because the metallurgy at the time was not up to the task.
By the mid to late 1870s iron armour started to give way to steel armour, which promised to reduce the thickness, and therefore the weight, of the armour.
While cast iron has never been used for naval armour, cast iron was used for land fortifications, presumable due to the lower cost of the material. One well known example of cast iron armour for land use is the Gruson turret, first tested by the Prussian government in 1868.