Monday, April 3, 2023

Armor as Damage Reduction

One of the first blogposts of the OSR that I remember being widely celebrated and discussed was "Shields Shall Be Splintered!" by Trollsmyth. If you've somehow never read it before, take a moment to follow the link and do so. The post isn't long and the idea behind it is a simple but clever one. 

I found myself thinking about Trollsmyth's post again recently, as I was re-reading a section of Unearthed Arcana that I rarely see discussed. In the Dungeon Masters' Section of the book, you'll find descriptions of new armor types. Among these are field plate armor and full plate armor, which, in addition to filling out the AD&D armor class table all the way to AC 0, introduce two new mechanics into the game that, so far as I recall, doesn't exist anywhere else: armor as damage reduction and damage to armor. 

Here's how those mechanics are described in the description of field plate:

For every die of damage that would be inflicted upon the wearer from any attack, physical or magical, the armor will absorb 1 point of the damage. (On a damage roll of 1, the wearer would take no damage.) For example, the armor will absorb 1 point of damage from the strike of a long sword, and the damage from an ice storm (3–30, or 3d10) would be reduced by 3 points, and the damage from the breath weapon of a 9 HD dragon is reduced by 9 points. However, after the armor absorbs 12 points of damage in this fashion, it is damaged and must be repaired. Until repairs are made, it cannot absorb further damage and is considered one armor class worse in protective power. Damaged field plate may be repaired by a trainer armor [sic] at a rate of 100 gp per point of absorbing power restored, and one day of time per point restored.

Full plate armor functions more or less identically, though its absorption is 2 points per die of damage and it has a total absorption capacity of 26 points before it needs repair. 

A couple of thoughts occurred to me as I re-read this section. Firstly, I had apparently forgotten the rules associated with these new armor types. I suspect that's because, like so many things that later appeared in Unearthed Arcana, I remember more strongly the original appearance of field and full plate in Gygax's "From the Sorcerer's Scroll" column in issue #72 of Dragon. Unless my recollection is gravely in error, those new types of armor did not provide any reduction to the damage inflicted on their wearers. Instead, they were simply better types of plate with accordingly better AC ratings. Damage reduction/absorption is thus something new to UA (though, as always, I am happy to be corrected on this point).

Secondly, I had long understood the rating of a type of armor in AD&D (and D&D, for that matter) to represent how difficult it was to damage its wearer. Characters with lower AC ratings were not "harder to hit," but harder to damage. I know that D&D often speaks of a "to hit" roll, but I take that to be shorthand for "to hit in a way that results in damage." If so, does an additional layer of damage absorption make any sense? Does this addition to the way hits and damage work in AD&D do violence to the combat rules or only to my peculiar interpretation of what hit and damage rolls represent in AD&D?

Armor as damage reduction isn't a new idea. Many RPGs that followed in D&D's wake – RuneQuest being one of the best examples – view armor in this fashion. However, those games broadly divorce the difficulty of striking an opponent in combat from the armor that they wear. D&D has always been a bit more vague on this subject, partly in the interests of efficiency. Whatever else you might say about D&D combat, it's fast. D&D has always sacrificed "realism" for speed of play, which I think is the right call in most cases. That's why I find the damage absorption rules for field and full plate rather odd. To my mind, they don't fit with the overall philosophy of D&D combat.

Of course, re-reading this section of Unearthed Arcana also made me wonder if Gygax's thinking had changed on the matter of armor and/or combat. If so, what might we have seen in his version of Second Edition? Might we have seen a broader implementation of damage reduction in the game? It's a question with no definitive answer, but it's fun to ponder nonetheless.


  1. I've always viewed D&D take on armor as damage reduction via reducing hits that actually cause damage. In other words some blows that are near misses are actually hits that the armor turned aside or a shield absorbed.

    The gamey part is that the armor does not degrade at all even under many blows. There are many takes that do account for this...Hackmaster is always my first thought since armor almost becomes a necessary liability.

  2. D&D combat was fast, then you had hit point inflation, iterative attacks, and endless debating on effects.

  3. Given that hit points represent only combat endurance i.e. how long can this character continue fighting? My view that armor class is a simple rating that states "If you are wearing armor it will take more successful attacks before you are incapacitated and unable to fight." The better the armor the more attacks it will take.

    However saying that doesn't help with narrating the result of an attack or figuring out the nuances when the object of an object isn't just about reducing a character combat endurance. For example an attack that takes effect with a touch.

    What I find helps is remember that for system that have armor as damage reduction the end result is basically the same. Either the attack succeed and damage is inflict or it doesn't. The advantage of armor as damage reduction is that it is clear you get the inbetween result of the target is struck but the damage was too low thus the target doesn't suffer damage.

    The implication of this that in any system with armor as damage reduction you can calculate the odds of an attack causing damage. Then come up with another procedure (mechanics) that will produce the same set of odds via another procedure.

    One of the reason I picked OD&D as the foundation for my Majestic Fantasy rules because after I played it RAW I found out of all the editions of classic D&D the odds it produced came the closest to how things turned out in GURPS.

    Then I tweaked things further so I could rule on stuff like hitting a chalice out of a lich's hand. Or figuring out when an attack resulted in a successful touch. The result is what you saw when you reviewed the Basic rules of Majestic Fantasy RPG.

    So basically I now find the debate between AC and Armor as Damage Reduction a non-issue. If one is doing a clean sheet RPG do what make senses. But either way can be made to work and work well. And both approaches have their pros and cons.

  4. I always thought the Unearthed Arcana rule added unnecessary complexity and forgot what the to-hit roll actually represented.

    ie: the chance to do a hit that penetrates the armour and does damage.

  5. GURPS used to have a "Passive Defense" component to its armor descriptions, which was a number that would add to your defense roll, like parry or dodge. Even in situations when you couldn't make an active defense roll (because you did an all-out attack, for instance), you could roll against the Passive Defense number alone to see if any hit got through at all. As I recall, the harder and smoother the armor, the higher the Passive Defense number. I think there was an upper limit, but I don't recall it. If your opponent landed a hit despite any active defense roll or any Passive Defense, your armor then reduced damage by a different number the usual way. Thus, GURPS had a system in which armor made a character harder to hit AND absorbed damage.

    I assume they took it out of 4th edition because it was too fiddly? I never thought it was, though; in practice it just acted as a modifier to your defense roll just like any other modifier, such as higher ground, or small size, or whatever. Maybe it was deemed too much in light of 4th edition's higher level of "crunch" generally compared even to earlier versions of GURPS, but I don't know, as I never wound up actually playing 4th edition.

    1. There's an official answer to this on the FAQ ( Basically, it was removed because it led to results that stopped making sense if you looked at them too hard. A character with Dodge 6 (Basic Speed 6, or Basic Speed 5 w/ Combat Reflexes—both above-average!) was over 5 times as likely to Dodge successfully while wearing PD 4 plate armor than while wearing PD 0 clothing, suggesting that more than 4 out of 5 "successful" Dodges by such a character were actually glancing hits.

      The full rule-change is this:
      - Armor PD is removed.
      - Shield PD remains, but is renamed to "Defense Bonus" (DB). It applies to all active defenses, but does nothing unless you have an active defense to begin with, or if the attack is coming from behind or from the flank opposite to your shield hand.
      - Active defenses get a universal +3, regardless of your equipment! This makes encounters where you have to defend yourself unarmored much more survivable.

      For that last reason alone, I think removing PD was a good choice. You shouldn't need armor to reliably duck a punch.

  6. Worth noting that any amount of per-die damage reduction at all has fairly major effects on how the most common damage-causing spells will work. Magic missile only rolls a d4, and most of the go-to spells like scorching ray, fireball and lightning bolt are multiple d6 pools. Knock a point or two off all of those smaller dice and you're mitigating a lot of damage - at least until your armor fails, which will happen quickly. Weapon damage tends to be one or two dice (plus static mods) for the most part, so there's less mitigation per attack and the dice involved are often larger sizes, letting them push more of their damage through as well. There are exceptions - 2d4 damage weapons are sad compared to d8 ones - but mostly weapon-users aren't as impacted by UA damage reduction. Monster attacks are all over the place, but single, double or triple die rolls are more common than the big small-die pools of many offensive spells.

    The Mending spell has changed a lot over the years, but becomes more important with those UA armor rules regardless of design intent - I've never seen a GM that used field/full plate that didn't allow magical repairs. The rules also provide a strong mechanical push toward proficiency or skill systems so characters can make their own repairs.