What gun calibre suits a modern capital ship?

What gun calibre would suit the proposed resilient, multi-domain capital ship?

Roughly six inches is the preferred balance for most of the ships discussed. The original comment's units are unclear, and a larger calibre still has to justify its weight and loading demands.

The proposed capital ship prioritises area control, physical resilience, command and control, and support for operations ashore. The comment mixes inch symbols and centimetres, leaving its intended gun size unclear. Roughly six inches, or 152-155 mm, is the preferred calibre for most of the modern ships considered here, with 9.2 inches as the next useful balance of shell effect and rate of fire. In the interwar comparison, rapid-firing six-inch guns could deliver more explosive over time than eight-inch guns, especially against targets with limited treaty-era protection. A 9.2-inch gun is credited with enough additional shell effect to change that balance again. Automatic six-inch guns already existed after World War II, and modern machinery is expected to make their firing rate close to that of five-inch mounts. The larger gun still requires more weight, space, and ammunition storage, but an illustrative extra thirty tons is judged manageable on a ship of 10,000 tons or more if allowed for from the beginning. Smaller ships of a few thousand tons face a different proportionate burden. The Falklands War and other conflicts support retaining guns for air defence, general-purpose fire, and operations ashore alongside missiles.