Unlimited Ark Royals free British yards for the rest of the fleet

If Britain in 1939 had a dry dock that could endlessly copy one ship class, which class should it choose?

Ark Royal, because cloning a modern carrier removes the hardest aviation shortage and frees conventional yards to build the rest of the fleet.

Escorts are a poor copying choice because ordinary yards can already build them in numbers. Older capital ships are unattractive because cloning an unmodernized design creates a second modernization burden. The serious candidates become a Town-class cruiser or Ark Royal, with the carrier favored because Britain lacks enough flight decks at the start of the war. Choosing a modern, scarce, and complex ship makes better use of the fictional copying ability than duplicating a type the existing industrial base can already mass-produce.