A lot of what keeps MRAP occupants alive after hitting a mine is the V-shaped bottom that deflects energy and blast away from the vehicle. The composite armor is mostly to protect against thermal effects and plasma jets.
As little as 3-6 inches of water, depending on depth, is enough to render the plasma jet unable to penetrate less than 1” of Krupp steel armor. The modern solution to spaced armor countermeasures against shaped charge warheads is the duplex or tandem warhead and that would work here as well, but those don’t appear in a reliable form until the 1980s and they don’t become common on the battlefield until the 2000s - not developed at any time that battleships were common front line combatants.
Put it to you this way - a torpedo with a standard single shaped charge warhead would be unable to do much of anything to old USS Texas there other than poke holes in her antitorpedo blisters. You would have to hit her somewhere where the blisters aren’t and those are mostly bilges.
Good point. The ceramic core has a structural function in a conventional HE blast as well as disrupting the shaped charge jet.
I have to say my limited knoweldge of composites is foam or honeycomb core which is much ligher than the skin, but with very little modulus, or yield strength.
In this case the core is as dense or more dense than the composite skin.
These glass or ceramic core armour can have very high yield strength and hardness, but they have poor fracture toughness.
“Water tank” armor would only work against shaped charge.