 The question of whether the new ships should be powered entirely by oil @-@ fired boilers was less controversial . The design staff was generally in agreement with the standard practice of using coal @-@ fired boilers for two @-@ thirds of the power plant , with the remainder being oil @-@ fired boilers . Coal @-@ fired boilers were preferred because the coal , stored in the sides of the ship , provided additional protection , particularly for the battlecruisers , which carried less armor than their battleship counterparts . The finalized design was approved on 23 May 1914 . 
