During the Iran/Iraq War of the 1980’s, huge oil tankers sustained hits from cruise missiles and continued sailing. When the cruiser USS Princeton was nearly sunk in a mine field, she managed to limp away, sheltered in the wake of one of these supertankers. The secret is being heavily compartmentalized, and filled with liquid, thus are virtually unsinkable. A system of “water protection’ for warships was first used in Royal Navy monitors during the 1st World War. Later, the battleships Nelson and Rodney shipped 2000 tons of sea water in its hull to boost its 14 inch armor belt. Some designs of the Arsenal Ship of the 1990’s included flooding the hull to give it a lower profile, but could have also helped defend it from mines and torpedoes.
Such a warship would be vast in size like the tanker, and perform various missions: a cruise missile carrier, carry V/STOL aircraft or unmanned planes, while performing sealift and amphibious missions. In place of crude oil, seawater would be loaded for buoyancy and added protection.