The unsuitability of unarmored iron for warship hulls meant that iron was only adopted as a building material for battleships when protected by armor . However , iron gave the naval architect many advantages . Iron allowed larger ships and more flexible design , for instance the use of watertight bulkheads on the lower decks . Warrior , built of iron , was longer and faster than the wooden @-@ hulled Gloire . Iron could be produced to order and used immediately , in contrast to the need to give wood a long period of seasoning . And , given the large quantities of wood required to build a steam warship and the falling cost of iron , iron hulls were increasingly cost @-@ effective . The main reason for the French use of wooden hulls for the ironclad fleet built in the 1860s was that the French iron industry could not supply enough , and the main reason why Britain built its handful of wooden @-@ hulled ironclads was to make best use of hulls already started and wood already bought .