Why aircraft carriers were not unproven before the Second World War

Were aircraft carriers still largely unproven before the Second World War?

No. Major navies had tested them extensively in exercises and operations and had already developed ideas for carrier strikes on fleets in harbour.

Britain, the United States, and Japan had experimented with carriers in exercises and operations before 1939, while France also had Béarn available for carrier work. Their navies were already testing how aircraft could support fleets rather than treating the carrier as an unexplored novelty. British planning for strikes on enemy ships in harbour grew from concepts already developing at the end of the First World War. The technology and doctrine were still maturing, but the basic military value of carrier aviation had been demonstrated well before the Second World War.