Where battleship gun caliber reaches diminishing returns

With 1945 technology, where do the tradeoffs of larger battleship guns become unacceptable?

About 18 inches is one practical limit, while Fleet of Oceans considers 20-inch guns viable with accepted tradeoffs; 16 to 16.5 inches is preferred for value.

Even with the best radar fire control available in 1945, a battleship still needs enough shells in a salvo to guide corrections. An 18-inch practical limit meets Fleet of Oceans' counterargument that 20-inch guns can remain viable if a navy accepts the tradeoffs. Both positions allow that 16- to 18-inch weapons would dominate ordinary fleet construction, with only a few 20-inch status ships. A 16.5-inch gun is preferred for value, although an established 16-inch navy would gain too little to justify changing its existing caliber. The extra half-inch makes more sense when moving up from 14- or 15-inch guns.