 From 1859, armour was added to ships based on existing frigate and ship of the line designs.The additional weight of the armour on these first ironclad warships meant that they could have only one gun deck, and they were technically frigates, even though they were more powerful than existing ships-of-the-line and occupied the same strategic role.The phrase "armoured frigate" remained in use for some time to denote a sail-equipped, broadside-firing type of ironclad.