Choosing a battlecruiser's gun caliber

Should a battlecruiser carry 16-inch or 18-inch guns?

Use the capital-ship caliber of the period as the starting point, then account for infrastructure and treaty constraints.

The main-gun caliber of contemporary capital ships provides the reference point for a British battlecruiser. German choices are contrasted with that practice because supporting infrastructure could favor a smaller weapon. G3's 16-inch guns are connected to worldwide support arrangements and expectations about treaty limits. Larger calibers were considered or desired, but the infrastructure for sustaining them globally constrained the choice. An era and a supporting naval system are therefore needed before a preference for 16-inch or 18-inch guns can be meaningful.