Iron armour

While cast iron has never been used for naval armour, it did find a use in land fortifications, presumable due to the lower cost of the material.

Among its members was Sir William Fairbairn, a noted civil and structural engineer who had also built over 80 iron vessels before retiring from shipbuilding.

This committee worked four years, between 1861 and 1865, during which time it formulated the best performing armor with the metallurgy as then known, suggested ways for improving its production and quality and helped develop more effective shot against ironclad vessels.

However, when the Special Committee tested both types of plate in 1863, it found that rolled iron was superior to hammered due to greater uniformity in quality.

The committee and iron manufacturers worked together on how to more easily produce rolled plate, which became standard use in warships beginning in 1865.

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.