Protecting a ship from an under-keel torpedo

Can a ship be protected against a torpedo exploding beneath the keel?

Yes, but it needs a false keel or comparable structure below the main keel with enough protection depth to absorb the blast.

An under-keel detonation attacks a different part of the ship from a conventional side hit. Protection begins with a false keel or sacrificial structure below the main keel. That added depth must contain an underwater-protection system able to absorb the explosion before it breaks the primary hull girder. Protection has to be placed where the weapon delivers its energy.