Originally posted by pyro-manic
Janos: Modern warships have practically no armour. They rely on active defence (i.e. shoot down/dodge the missiles before they hit) and advanced damage control. A modern warship would have a very hard time against anything built before 1950 in a head-to-head fight. An Exocet wouldn't even slow a battleship down. Modern warships are designed to fight modern battles, ie against other high-tech weapons and aircraft, rather than against brute force. They will be designed to counter guided missiles rather than shell fire, so they will have lots of point-defence turrets (Phalanx guns and the like), lots of ECM equipment, and will not have any armour plate, as a missile doesn't deliver anywhere near the energy of a 15-inch shell. Rather they'll have a few layers of "skin, to stop the missile penetrating right into the ship and gutting it, and will rely on agility to avoid taking a hit. Most modern warships will be destroyed (or at least critically damaged) if they take more than one or two direct hits - see the Sheffield and Antelope in the Falklands War - whereas an old-style warship could take a dreadful beating before sinking.
A carrier, for example, is insanely durable. It can take direct hits and shrug them off - well, of course there's structural damage, but sinking a carrier is not an easy task, even if we assume you get a direct line of fire and all that jazz. Some navy geeks who go ape**** every time we're talking about sinking US carriers tell that carriers could propably survive a near-vicinity hit of tactical nuke without sinking, but they wouldn't be battle capable after that, nor would the crew be very fine.

A modern missile packs a HUGE punch, and can engage targets well beyond the ranges of conventional cannons - the artillery is pretty much dead in present navies, except for CIWS and so on.
A current naval asset is not easy to sink, because they do have steel armour, but they're pretty easy to damage if you play your cards right. It's just not feasible to armour the entire top structure of a ship - radars, antennae, bridges, weaponry - because it could hamper their abilities and add weight. A ship can survive a missile hit or maybe not, but usually missile hits don't outright sink the ships. A torpedo hit (I know there's at least a plan, if not implementation, of CIWS system being able to shoot at underwater targets!), on the other hand, can and will.