Twenty dual-purpose six-inch guns demand beam and deck space

How large would a battleship need to be to carry twenty autoloading dual-purpose six-inch guns?

A beamy capital ship could carry ten twin turrets, perhaps on a Queen Elizabeth- or King George V-sized basis, depending on superstructure and firing-arc choices.

Ten twin turrets offer an alternative to a four-gun mounting. Four pairs could sit along the sides, with additional mounts forward and aft, creating strong broadside and end-on fire. The arrangement needs considerable beam and careful superstructure design, but it does not automatically require an unprecedented hull. A rough size comparison ranges from Queen Elizabeth and King George V dimensions to a larger G3-sized battlecruiser depending on the rest of the design.