Aircraft carriers emerge as capital ships around 1930

When did the Royal Navy begin treating aircraft carriers as capital ships?

Around 1930, broadly in step with other navies, as carriers became principal instruments of fleet and national power.

The shift came at roughly 1930, broadly alongside similar changes in other navies. Capital ship is a strategic category rather than a single hull type. A navy's capital ships are its principal means of expressing national power. In a major fleet that category can include carriers, battleships, and battlecruisers, while a smaller navy may rely on cruisers for the same function. Carriers gained the status through growing strategic importance rather than a simple change of official terminology.