Armoured flight decks strengthened the whole carrier

The flight deck was not simply a plate placed above the hangar; thicker decks and structural continuity helped the hull spread loads and survive damage. Additional steel between the hangar and lower ship made several levels contribute to hull rigidity rather than relying on a single armour plate. Incoming weapons that penetrated the top layer would also lose energy before reaching the decks below. That strength made the ships more expensive and slower to construct, illustrating why survivability could not be added without consequences elsewhere in the design.