The United Kingdom possessed the largest navy in the world for the whole of the ironclad period . The Royal Navy was the second to adopt ironclad warships , and it applied them worldwide in their whole range of roles . In the age of sail , the British strategy for war depended on the Royal Navy mounting a blockade of the ports of the enemy . Because of the limited endurance of steamships , this was no longer possible , so the British at times considered the risk @-@ laden plan of engaging an enemy fleet in harbor as soon as war broke out . To this end , the Royal Navy developed a series of ' coast @-@ defence battleships ' , starting with the Devastation class . These ' breastwork monitors ' were markedly different from the other high @-@ seas ironclads of the period and were an important precursor of the modern battleship . As long @-@ range monitors they could reach Bermuda unescorted , for example . However , they were still armed with only four heavy guns and were as vulnerable to mines and obstructions ( and enemy monitors ) as the original monitors of the Union Navy proved to be during the Civil War . The British prepared for an overwhelming mortar bombardment of Kronstadt by the close of the Crimean War , but never considered running the smoke @-@ ridden , shallow @-@ water gauntlet straight to St. Petersburg with ironclads . Likewise , monitors proved acutely unable to ' overwhelm ' enemy fortifications single @-@ handed during the American conflict , though their low @-@ profile and heavy armour protection made them ideal for running gauntlets . Mines and obstructions , however , negated these advantages — a problem the British Admiralty frequently acknowledged but never countered throughout the period . The British never laid down enough Devastation @-@ class ' battleships ' to instantly overwhelm Cherbourg , Kronstadt or even New York City with gunfire . Although throughout the 1860s and 1870s the Royal Navy was still in many respects superior to its potential rivals , by the early 1880s widespread concern about the threat from France and Germany culminated in the Naval Defence Act , which promulgated the idea of a ' two @-@ power standard ' , that Britain should possess as many ships as the next two navies combined . This standard provoked aggressive shipbuilding in the 1880s and 1890s .