War plans against Japan drive carrier survivability

The Royal Navy's late-1920s and 1930s planning treated war with Japan as a realistic possibility rather than an abstract exercise. Confrontations in January 1939 and the Asama Maru incident of January 1940 show British and Japanese forces facing one another in peacetime. A blockade of Japan would place carriers far from Britain's main industrial base and within reach of land-based aircraft. In that setting, a somewhat smaller air group could be preferable if armor, subdivision, and structural strength kept the ship repairable in forward facilities. That choice also required a forward aviation support ship to provide aircraft engineering facilities that would ideally be carried aboard the carrier itself. The Illustrious compromise therefore joined strategy, geography, logistics, and damage control rather than expressing a simple preference for armor over aircraft.