The main armament of the "Illustrious" class consisted of sixteen quick-firing (QF) QF 4.5-inch Mk I – V naval gun dual-purpose guns in eight twin-gun turrets, four in sponsons on each side of the hull. The roofs of the gun turrets protruded above the level of the flight deck to allow them to fire across the deck at high elevations. Her light antiaircraft defences included six octuple mounts for QF 2-pounder ("pom-pom") antiaircraft guns, two each fore and aft of her island, and two in sponsons on the port side of the hull.