Radical Admiral-class redesigns would cost nearly a new ship

Which alternate main-armament layout would justify redesigning an Admiral-class sister?

A twelve-gun 15-inch layout offered the strongest gain, but the required reconstruction would be so costly that a new ship was preferable.

Changing an Admiral-class sister to a markedly different main armament would require much more than substituting turrets. Magazine geometry, barbettes, structural support, ammunition handling, stability, and fire control would all have to be reconsidered. A twelve-gun 15-inch layout offered the clearest capability increase among the proposed variants. Even that improvement would be so expensive that building a new ship would often be the better use of the same resources.