In the "Illustrious" class, armour was carried at the flight deck level—which became the strength deck—and formed an armoured box-like hangar that was an integral part of the ship's structure. However, to make this possible without increasing the displacement it was necessary to reduce the overhead height of the hangars to 16 ft (4.88 m) in the "Illustrious" class hangars and 14 ft (4.27 m) in the upper hangar of the "Indomitable" and 16 ft (4.88 m) in her lower hangar; these compared unfavourably to the 17 feet 3 inches (5.3 m) of the "Essex" class, 17 ft 6 inches (5.38 m) in "Enterprise" and 20 ft (6.10 m) in "Saratoga". This restricted operations with larger aircraft designs, particularly post-war.