Why favour a 16.5-inch battleship gun?

What is the best calibre for a battleship gun?

The preference offered is 16.5 inches, combining heavy penetration with a useful rate of fire before larger weapons impose a substantial loading penalty.

The preference for 16.5-inch guns rests on keeping a high rate of fire at a large calibre. Beyond that size, the loading cycle is expected to reduce the frequency of salvos sharply. With visual fire control, each salvo helps establish the opponent's position and correct the range, so slower firing also delays adjustment. A super-heavy 16.5-inch shell is suggested as a way to increase hitting power without moving to a larger gun. Armour capable of resisting such a shell is judged to demand an exceptionally heavily protected ship.