(Hi! I’m Alex from Cirsova! I’m very excited to be one of the new writers here at Dice Monkey and would like to thank Mark for giving me this awesome opportunity!)
“Why does armor make you harder to hit?” is a frequent question and complaint I’ve heard about the mechanics of Armor and its effect on combat in Dungeons & Dragons. “Shouldn’t it reduce or block damage?” It’s ironic that people involved in such an imaginative hobby lack the imagination and logic that explains this phenomenon.
Attack roll below that which hits Base (unarmored) AC +/- Dex – Miss.
Attack roll that would hit the base AC +/- Dex, but is below that which hits a magically augmented base AC – The attack is seemingly turned aside by an unseen force, missing.
Attack roll that would hit base (unarmored) AC +/- Dex & +/- Magical modifiers, but below that which hits the armored value – A glancing blow deflected by the armor without causing wound. If the character has a shield, more likely this attack is blocked by a shield, unless the monster’s attack roll is sufficiently high that it would have hit the character had he or she not been equipped with a shield.
An example of narrative AC theory at work:
A monsterling has a thac0 of 19. He gets a 16 on his attack roll, hitting AC 3.
If the monsterling were fighting someone wearing leather armor (AC 7), he’s managed to either find a weak spot or simply stab his way through the armor.
Now, take that same roll, meaning the monsterling is attacking with the same strength and ferocity; this time he is fighting someone with plate mail (AC 2). His attack still hits, because he rolled high enough to hit a base AC +/- Dex mods (which we can assume is the difficulty to hit a standard sized opponent who has taken a fighting stance). However, since his opponent was wearing plate mail, the armor deflects the blow, preventing any damage.
Why to-hit uses strength and not dexterity:
At first, it did not make sense to me either that a Strength bonus would make you less likely to ‘miss’. If all combat results are defined as “hit” or “miss”, then of course a Dexterity bonus would make more sense. But if we use the above narrative combat interpretation, we see that armor doesn’t make you harder to hit, but harder to hurt. Strength bonus helps determines how much of the armor you were able to slash or bash through. If you get a chance, see if you can find one of those History Channel videos where someone tries to actually push a sword through a breast-plate. Notice how much shoulder they have to put into it to get a sword tip through a metal plate?
Any time an attack roll hits an opponent’s Armor Class, assume that the attack both connected and landed with enough force to do bodily harm.
A suggestion for blunt weapons:
One of the advantages of blunt weapons was they transferred the kinetic shock through the armor of the opponent to his body. Even if it didn’t draw blood or pierce armor (though spiked hammers were really good at this; they were pretty much medieval can-openers), they’d knock an opponent flat, leaving them prone. Consider with blunt weapons that an attack that would hit a base unarmored AC +/- Dex mods +/- any magical modifiers has caught the opponent, broken through any ‘magic aura’ of a whatever of Protection + whatever, and connected with shield or armor. The blow has not pierced the armor, doing HP damage, but the kinetic force of the blow connecting has a chance to stun the victim (Save vs. Paralysis), knocking them down.