Following the demonstration of the power of explosive shells against wooden ships at the Battle of Sinop , and fearing that his own ships would be vulnerable to the Paixhans guns of Russian fortifications in the Crimean War , Emperor Napoleon III ordered the development of light @-@ draft floating batteries , equipped with heavy guns and protected by heavy armor . Experiments made during the first half of 1854 proved highly satisfactory , and on 17 July 1854 , the French communicated to the British Government that a solution had been found to make gun @-@ proof vessels and that plans would be communicated . After tests in September 1854 , the British Admiralty agreed to build five armoured floating batteries on the French plans , establishing the important Thames and Millwall Iron Works within the docks .