The three armoured decks ranged in thickness from with the greater thicknesses outside the central armoured citadel. The front and sides of the conning tower were protected by 11-inch plates, although the roof was 3 inches thick. The spotting tower behind and above the conning tower had sides and the torpedo-control tower aft had 3-inch sides and a 2-inch roof. In the interests of saving weight, the "Colossus"-class ships eliminated the anti-torpedo bulkheads that protected the engine and boiler rooms, reverting to the scheme in the older dreadnoughts that placed them only outboard of the magazines with the same thickness from . They did retain the 1-inch armour plates protecting the boiler uptakes.