Why cruiser gun caliber follows naval doctrine

What role would new British heavy cruisers have filled, and why did the Royal Navy favor 6-inch ships?

The Royal Navy's operational analysis valued 6-inch volume of fire, while the US preference shifted toward that same solution as carrier escort became more important.

The Royal Navy judged the extra punch of an 8-inch gun insufficient to offset the volume of fire delivered by 6-inch cruisers. That calculation matched British operational expectations, while early-war US doctrine made heavier cruisers more attractive. As the US Navy became increasingly carrier-centered, its preferred cruiser role shifted toward the rapid-fire 6-inch battery and the air-defense screen it supported.