The EOC 10 inch 40 caliber guns were a family of related guns designed by the Elswick Ordnance Company and produced by Armstrong Whitworth in the 1890s for export customers. EOC 10 inch 40 caliber guns were the primary armament of armored cruisers, ironclads and pre-dreadnought battleships built or refit during the 1890s. These guns and their licensed derivatives armed ships of the Argentine Navy, Imperial Japanese Navy, Regia Marina and Spanish Navy. They served in the Russo-Japanese War, Italo-Turkish War and World War I.