The four ships were the most advanced battleships in the Royal Navy at the outbreak of the First World War, though they were soon surpassed by the five ships of the . They all saw extensive service during the war with the Grand Fleet, where "Iron Duke" acted as the flagship for the fleet commander, Admiral John Jellicoe. Three of the ships, "Iron Duke", "Benbow", and "Marlborough", were present at the Battle of Jutland; "Emperor of India" missed the battle by being in dock for periodic refit. The four "Iron Duke"-class battleships saw limited active duty following the end of the war; they were all demilitarised under the terms of the London Naval Treaty signed in 1930. "Iron Duke" was reduced to a training and depot ship and lasted in that role until 1946 when she was scrapped. "Benbow" was scrapped in 1931 and "Marlborough" followed in 1932. "Emperor of India" was sunk as a gunnery target in 1931 though was later re-floated to be scrapped in 1932.