Armouring a carrier for its likely threat

How should carrier armour differ from that of a battlecruiser or battleship?

A carrier needs protection against air attack and internal blast spread more than a very heavy battleship-style belt.

The answer starts from the carrier’s likely opponent: aircraft rather than another capital ship’s main guns. That shifts protection away from an exceptionally heavy side belt and toward deck armour able to resist bombs. Torpedo defence remains important because underwater damage can immobilise the flight deck even when the aviation spaces survive. More internal armoured bulkheads can also prevent an explosion from propagating through the hangar and machinery spaces, producing a protection scheme tailored to preserving aviation function.