How modern warships use passive protection

What passive protection remains useful in modern naval warfare?

Subdivision and local splinter protection keep blast and fragments away from vital spaces, but modern heavyweight torpedoes remain extraordinarily difficult to survive.

Modern passive protection uses subdivision to confine damage and prevent a blast from spreading through several compartments. Local protection, including materials described as variations on Kevlar, protects machinery spaces and the combat information centre. A missile hit can disable a ship's fighting capability while leaving it afloat and able to return for repair, although the outcome depends on the missile and where it strikes. A modern heavyweight torpedo presents a harder problem because an under-keel explosion removes supporting water and subjects the hull to its own unsupported weight. Strengthening the keel enough to resist that effect carries a substantial weight cost. A larger explosive charge can then attack a wider area, while the added structure itself increases the weight the hull must support.