British and American navies needed different cruisers

Why did the Royal Navy and US Navy prefer different kinds of treaty cruiser?

Britain needed numerous light cruisers for worldwide trade protection and blockade, while the United States prioritized heavy cruisers for a decisive Pacific fleet battle before turning to blockade.

The right cruiser depended on the strategic task assigned to it. The Royal Navy expected a long war of trade protection and blockade across a global network, making numbers and reach especially important. The US Navy focused first on fighting through the Pacific and defeating Japan's main fleet, a problem better suited to the heavy cruiser. American planners could address blockade after that battle, potentially using armed merchant cruisers once the major enemy force had been removed. Two capable navies could therefore make different choices within the same treaty system.