 Iron @-@ built ships used wood as part of their protection scheme . HMS Warrior was protected by 4 @.@ 5 in ( 114 mm ) of wrought iron backed by 15 in ( 381 mm ) of <unk> , the strongest shipbuilding wood . The wood played two roles , preventing <unk> and also preventing the shock of a hit damaging the structure of the ship . Later , wood and iron were combined in ' sandwich ' armor , for instance in HMS <unk> . 
