An obvious refinement in handling armor in RPGs is making armor reduce damage instead of the original D&D reducing the chance of taking damage. Intuitively that’s what armor does, right? It doesn’t make you better at dodging, it just reduces how much you get hurt when you get smacked. A lot of pretty good games over the years have taken that tack, including one of my favorite combat systems, the microgame Melee that formed the basis of The Fantasy Trip and later on GURPS.
The thing is, the phrase “roll to hit” is a misnomer. It’s really roll to hurt. We don’t, except in some special circumstances, really care if the blow missed completely or hit the armor and bounced off. What we want to know is if the blow actually hurt enough to bring the foe closer to defeat. From there it’s easy to see that the “space” of possible results from an attack are basically the same whether you treat armor as reducing the chance of rolling for damage or reducing the damage once rolled: the target isn’t hit at all, the target would have been hurt but for armor, and the target is hurt. Editions of D&D with rules for “touch attacks” only needing to beat the AC of an unarmored man make this explicit… really any attack that would have hit an unarmored man but didn’t beat the AC of the target can be presumed to have hit but failed to penetrate the armor1.
In fact, the only real difference between the two approaches is that armor as damage reduction introduces an extra oddity that usually needs to be addressed. In the standard D&D AC system armor can make it unlikely that a blow scores a wound, but a blow that finds a chink in the armor can be just as deadly to an armored man as an unarmored man: an arrow to the eye slit2 will kill a knight just as dead as a peasant. In contrast, in systems that use armor as DR it’s often the case that once you have a reasonable amount of armor, it becomes literally impossible for a single blow to kill an average man. If an arrow does 1d6 and chain armor stops, say, 4 points, then a first-level fighter with at least 3 HP can’t ever be killed with a single arrow.
To compensate for this, DR systems almost always add further complication. Typically they include “critical hits” that introduce the possibility that if you roll well the damage is then multiplied by some factor large enough for weapons to once again pose a deadly danger to the average man. Others will introduce things like differentiation between weapons that can pierce through the armor and weapons that will bounce off, so an arrow or warhammer might be more dangerous to a heavily armored fighter than a club or saber, or add “called shots” so that if you want to actually hurt a knight in plate armor with your arrow you have to take a penalty to the roll representing aiming for the eye slit. Which is all well and good, but wouldn’t actually be necessary if you hadn’t introduced the complication of damage reduction in the first place. It’s several extra steps to get back to “against heavy armor you need to get extra lucky or good if you want to do significant damage.”
When I was younger I used to heavily favor such complications; it’s only comparatively recently that I’ve come around to preferring the simpler “chance to hurt” abstraction. I still enjoy me a good critical hit, but I like ’em like Dungeon Crawl Classics or Arduin, where they are used to add a big dollop of flavor with results that are more specific and usually much grittier than a straight double hit point damage. In a system where damage is usually abstract: 3 points, 4 points, 8 points, it’s nice to have the occasional “your ear is torn off” or “your forearm is shattered” as long as it doesn’t become something you have to calculate every blow.
- and when it comes to simulation, that’s probably a more accurate representation anyway. Most of the time if you’re hit while wearing armor you won’t take the same wound that an unarmored person would take, except shallower. If it didn’t find a weak point in your armor chances are you won’t take any damage at all, what damage you do take will often be in the form of a bruise or broken rib instead of a gash or hole in your flesh. The only game I can think of off-hand that did that level of simulation was CORPS, which took the physics-based intuition even farther and made armor reduce some damage, and then convert some of the remaining damage into less lethal concussion damage. Of course, at the level of abstraction Hit Points represent you could/should simply interpret differing amounts of damage as representing different levels of wound anyway, but if you’re doing that there’s even less reason to care whether “no damage” is a 13 on the to-hit roll vs AC 14 or a 10 on the to-hit roll vs AC 10 but a 3 on the damage die against 4 points of DR. ↩
- a reasonable interpretation of rolling high damage against an armored knight, even if there’s nothing explicit in the mechanics dictating that’s where it hit. ↩