Which 1929 navy offers the most freedom to redesign?

Which navy could be transformed most dramatically in the ten years before the Second World War?

The Royal Navy is the choice here because its existing infrastructure permits immediate changes, while American expansion would first require industrial investment and continuing congressional support.

In this hypothetical appointment, control of a navy comes with a reasonable budget and reliable supplies. The preferred choice is the Royal Navy because it already has the infrastructure needed to redirect construction. The United States has enormous potential, but expanding its yards and retaining congressional support would consume part of the available decade. Existing British facilities would allow work to begin sooner.