Why missile size determines useful modern armor

Should a modern battleship rely on layered defenses backed by enough armor to stop ordinary naval gunfire?

Possibly against Harpoon-sized threats, but very large anti-ship missiles create a different protection problem that modest armor cannot solve alone.

No armor scheme makes sense until the attacking missile is defined. A ship facing Harpoon-sized weapons might combine extensive soft-kill and hard-kill defenses with enough structure and armor to contain lighter damage. A weapon in the Soviet P-700 Shipwreck class brings far greater mass and energy, changing what passive protection can plausibly achieve. Modern survivability must answer a range of threats through active defense, redundancy, and armor rather than treating armor as a universal solution.