Illustrious displaced about 1,400 tons more than Ark Royal while carrying roughly half as many aircraft, a clear measure of the armored hangar's cost. That exchange bought a four-and-a-half-inch belt and hangar sides plus a three-inch flight deck, creating a genuinely protected aviation box. The sharper criticism is that later members inherited hangar heights of about 4.3 to 4.9 meters, limiting the aircraft they could operate. Constructors and the Third Sea Lord recognized the compromise and repeatedly sought another thousand tons, but policy kept the design close to 23,000 tons. A 24,000- or 25,000-ton ship with roughly six-meter hangars could have preserved armor while gaining far more aircraft flexibility. The class remained a good carrier within its imposed constraints, though its restricted growth margin limited future adaptability.
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Illustrious traded aircraft flexibility for armored protection
The Illustrious class gained a heavily armored hangar but carried fewer aircraft and inherited restrictive hangar heights from a design held close to 23,000 tons.