High-tensile steel, aluminium fittings, and triple turrets all reduced weight. The source paper put the saving at about 1,800 tons for three triple turrets, compared with 1,500 tons for four twin turrets. The decisive arrangement grouped the main battery forward around a shortened protected volume. This kept magazines central and permitted heavier armor over vital spaces. The resulting citadel concept went beyond ordinary all-or-nothing armor by concentrating the weapons and internal layout as well as the protection around them.
Chapter · 49:45-55:18
Citadel layout concentrated guns, magazines, and armor
The Nelson design demonstrates how triple turrets and a short armored citadel traded firing arcs for thicker protection.