 The use of iron instead of wood as the primary material of ships ' hulls began in the 1830s ; the first " warship " with an iron hull was the gunboat <unk> , built by Laird for the East India Company in 1839 . There followed , also from Laird , the first full @-@ blown warships with metal hulls , the 1842 steam frigates <unk> and <unk> for the Mexican navy . But a thin iron skin , while not being susceptible to fire or lethal <unk> like wood , was not the same thing as providing iron armor calculated to stop enemy gunfire . 
