Castles of Steel: Britain, Germany, and the Winning of the Great War at Sea is a work of non-fiction by Pulitzer Prize-winner Robert K. Massie. It narrates the major naval actions of the First World War with an emphasis on those of the United Kingdom and Imperial Germany. The term "castles of steel" was coined by the British First Lord of the Admiralty Winston Churchill in reference to the large number of the Royal Navy's battleships he saw at Spithead in 1914.