Visual ranging places the target within an estimated distance band, so the ship must fire and observe shell splashes before correcting onto it. Radar supplies a much more precise range and bearing for the fire-control solution. That difference matters greatly for six slow-firing 20-inch guns because every ranging salvo consumes time and a large share of the available battery. Sensors can therefore compensate for a weapon's poor salvo volume.
Notable Point · 39:10-40:00
Why radar ranging changes the gunnery problem
Optical rangefinders provide a band that spotting salvos must refine, while radar supplies the range and bearing data needed to train the guns directly.