Different systems perform different jobs, and their combined capabilities make the ship useful; ships then reinforce one another as a formation. Against a fast missile, fighters and area-defense weapons should engage first, point-defense missiles follow, and close-in guns remain the final layer. A 20 mm gun may lack the energy needed against some modern missiles, but that limitation does not invalidate the layered concept.
Notable Point · 1:20:46-1:23:01
Layered defense instead of one perfect weapon
A warship's defense comes from complementary sensors and weapons across several ranges, not from demanding that one gun defeat every threat.