Tuesday, September 22, 2020

AD&D Rules: Weapon & Armor Class Adjustment

Another post about AD&D - which I mean as 1st edition AD&D, as I never played and won't be running 2nd edition.

Today: Armor Class Adjustment, aka Weapon vs. Armor Type.

This is one of the rules I wanted to try, but never really played with. I'd bust it out when I was trying to run combats just like the one in the AD&D DMG (p. 71), and the adjustments were written on the AD&D record sheets, but it didn't really see any play. That's despite some bits that would have make a munchkin smile - more on that, below.

Weapons getting a bonus or penalty versus a specific armor type is one "those rules" in AD&D. You know the ones - fiddly, very specific, based on some odd assumptions, and provide a lot of complexity for a relatively limited gain. And it's spread across two books, as usual - the adjustments are in the PLAYERS HANDBOOK, and how to apply them appears in the DUNGEONMASTERS GUIDE.


If you allow weapon type adjustments in your campaign please be certain to remember that these adjustments are for weapons versus specific types of armor, not necessarily against actual armor class. In most cases, monsters not wearing armor will not have any weapon type adjustment allowed, as monster armor class in such cases pertains to the size, shape, agility, speed, and/or magical nature of the creature. Not excluded from this, for example, would be an iron golem. However, monsters with horny or bony armor might be classed as plate mail if you so decide, but do so on a case-by-case basis. Naturally, monsters wearing armor will be subject to weapon type "to hit" adjustment.

It applies to armor, using weapons, and not against monsters unless you choose to use it. And it's explicitly optional, which is not always the case for AD&D rules. I think the best explanation of its use in play isn't in any of the books, it's in Dragon Magazine #74, in an article explaining how to use the Combat Calculator.*

Regardless of the actual armor class a piece of equipment provides its wearer, the apparent AC of that armor is the same as for all armor of that type. The armor class adjustments given in the Players Handbook, and reproduced on the Combat Computer, only apply to apparent armor classes ? those between 2 and 10 inclusive. For example, a man in +3 chain mail has an armor class of 2, for combat purposes. But the apparent AC of his armor is 5, just as for all types of chain mail. The armor class adjustments for weapons apply to all objects of a certain armor type, magical or not.
Laura and Tracy Hickman**, Dragon #74, p. 41 (June 1983)

This rule is easily misunderstood, too. It's weapon vs. Armor Type, not versus Armor Class. It's an easy mistake to make - such as here.

The problem of monsters, and armor type for unarmored monsters, is an issue. Most people deal with it by ignoring this whole rule. A gamer named Rob Paige mailed Dragon Magazine to find out, and received this answer:

Armor class dilemma

In regard to the Combat Computer in issue #74: I have found it a great help in running my campaign, and I think you did a great job in explaining how to use it. However, I have a problem with apparent and enhanced armor class.
Obviously, not all creatures wear armor with set AC values, but instead they depend on their natural armor and/or dexterity. The article states, "regardless of the actual AC a piece of equipment provides its wearer, the apparent AC of that armor is the same for all armor of that type." This presents problems.

Suppose I wish to handle melee between a group of adventurers and a xorn. The xorn wears no armor, is not too quick on its feet, and (to the best of my knowledge) doesn't improve its AC value through any magical means. Thus its AC value of -2 must be enhanced by its natural stone-like shell. What is the apparent AC of stone-mail?

The same goes for the apparent AC of, say, Asmodeus. To the best of my knowledge he does not wear any armor. Since his AC of -7 is obviously enhanced by some means, what would his apparent AC be - 10? That can't be right.
This is mostly a minor complaint (since I'm sure there are many DMs out there who disregard AC adjustments altogether) but if there is any reasonable answer to this dilemma, I would be happy to hear it.

Rob Paige
Cheney, Wash.

We checked out this question with Tracy Hickman, who is on the TSR design staff was the creator of the Combat Computer. He told us what we expected to hear - namely, that no provision exists in the AD&D(tm) rules for taking AC adjustments in to consideration in cases like the ones Rob describes, which is why the Combat Computer didn't address the question.

The problem can't really be solved (short of an official addition to the rules), but it can be handled in one of two ways:
(a) Don't use any armor class adjustment for weapon type against creatures with an AC of better than 2, when that armor class can't be equated to an "apparent" AC, or (b) Treat any "problem" AC as if the creature in question had an actual armor class of 2, which is as low as the armor class adjustment table in the Players Handbook goes. - KM

Dragon #82, p. 4 (February 1984)

"KM" is Kim Mohan, editor of Dragon Magazine at this time.

The logic in the answer makes sense - either use it where it applies, or apply the bottom modifier to everything below. With Unearthed Arcana, the existance of Field Plate (AC 2, 1 with shield) (which is also in the DMG, p. 27) and Full Plate (AC 1, 0 with shield) extends these rules to AC 0. In case B you could treat everything below AC 0 as AC 0.

Neither is really satisfying, though, is it? The first is more so, to me, but it's not that great. Once you're chucking the rule sometimes, why are you not chucking the rule the whole time and just making your life easier? It's really not as easy, as, say, armor divisors in GURPS that only work against worn DR - differentiating worn DR from natural DR is easy enough as it's defined seperately in the ruleset from the get-go. In D&D, what makes your AC your AC is really only clear for PCs and NPCs, and can be guessed to a degree with humanoid foes.

The second means that against anything with AC 2 (or AC 0) or better, certain weapons are just totally hosed . . . and others are great. Two-handed swords get a +2 to hit against everything in the game. Monks have enough trouble with open hand, but now they'll be at -7 to hit anything with negative AC (-9 if using UA and AC 0, and even worse with a bo or jo.) Geez, thanks. The only saving grace on that is that -7 is so damn much it just sets all below-zero ACs to -8 to -10***, which at a sufficiently high level a monk can hit with a 17-20. The 17th level Grandmaster of Flowers hits AC -10 on a 20. Meanwhile Joe Schmoe level 1 fighter with a two-handed sword (+2 vs. AC 0, or AC 2) hits AC -7 with a 22 (a natural 20, +2, if using the rules under Progression on the Combat Tables, DMG p. 82).

Like I said, unsatisfying. This starts with a good, basic idea - some weapons penetrate armor well, some are designed to fight less-armored folks and do better against them - ye old longsword vs. rapier comparison (one's for dealing with armored foes, by armored foes, and the other for killing other people in town). Then it turns it into a quick shopping trip for the best weapon vs. AC 2 (or AC 0) and just using those, and hosing people who chose poorly. I also makes for nonsense like ghosts (AC 0) and brownies (AC 3) being best dealt with by using armor-piercing weaponry, just like red dragons (AC -1) and bullete (AC -2 in spots) or umber hulks (AC 2).

There are some aspects to the rule, though, that make it attractive to bonus-hunting players:
- one magic item, the Staff of Striking, is always the best possible weapon versus an AC type. That's a +2 to +4 to hit every type of armor.
- two-handed swords are amazing. Weapon Speed 10 sucks if you're using those rules, they need a lot of room - 6' - but get a +1 to +3 against every armor type except AC 10. +2 or +3 against most armor types is huge - it takes 18/00 ST to get a +3 to hit, and this would stack.
- the footman's flail is an excellent one-handed weapon, especially if you use ruling b) from Kim Mohan's answer. Amusingly, it's -1 vs. AC 10 and +1 vs. AC 9, so picking up a shield gives you +1 to your AC and the flail comes and negates it.
- A morning star is a good second, although it doesn't get that sweet plus against everything that answer b) give the footman's flail.
- daggers and shortswords make great backstabbing weapons against magic-users, who are usually going to be AC 10 armor type, getting +3 and +2 to hit, respectively.
- long bows are amongst the best anti-armor ranged weapons. Not composite ones, though, just traditional ones. This is the "Crecy and Agincourt were won by bows shooting through plate" line of thought, which I think more modern history has discarded.

Some of those make the rule attractive to use - you get some real choice in weapons, and trading off a shield and a faster and lighter sword for a zweihander suddenly seems an awesome choice, and not just for 1d10/3d6 damage. I'd expect to see a lot of guys who take two-handed sword, footman's flail, and dagger for melee and a longbow for their missile weapon.

Of course, this requires: - another number to look up; - another number to apply to AC prior to a table lookup; - accepting the fishy numbers (and weirdness were armor type changes if you have a shield, and mysteriously matches the next better armor without a shield) - deciding how to deal with monsters, both for and against.
I've mentioned Anthony over at The Blue Bard a few times in this series. He uses these rules . . . but applies it to Armor Class, not Armor Type. He also only applies it for weapons, for PCs, so monsters don't use these rules. Like I said before, I'm not sure I could live with that.

This falls under one of those rules I'd like to try, just to see how they affect play - especially in scenarios where the PCs face a variety of armor types with a variety of weapons. But they're really a set of rules that don't completely cover the game system in front of you. The gaping hole of how to handle monsters and monster attacks - either ignore them or apply a patch - doesn't really add a lot of attraction to using it. But I might try, just to get the actual play experience of them. You really need to see a rule in actual play to see how it really plays . . . but you don't need to see how a rule will play to know if you're interested in trying it out or not. So we'll see.

* I had one of these, assembled and working . . . and I sold it years ago when I was clearing out old stuff, along with a bunch of character record sheets for AD&D. I kind-of regret selling the record sheets, but honestly I didn't need them and don't need them. I really regret selling the combat calculator, especially right now. I may need to make one using this post.

** The Dragonlance Hickmans, yes.

*** Really, really important rule in AD&D - Important Note Regarding "To Hit" Adjustments, DMG, p. 70. Modifiers that lower your "to hit" instead improve the AC of the target, so you're not making it impossible to roll a 20 and hit some of the ACs where only a 20 can hit (see Progression on the Combat Tables, DMG p. 82) if you're using that optional rule. Not that the example combat uses them this way, but it's worthy of its own post.


  1. I’m pretty sure this rule was meant to mimic something in Chainmail. The rule debuted in Greyhawk alongside weapons having different damage dice, and the two are meant to be used together. Unlike weapon speed factor and weapon length, I think Gygax actually used these.

    1. Yeah, it's in Greyhawk, p. 11-12, and it says they're from Chainmail:

      "For those who wish to include weapon types in the determination of hit probabilities the following matrix drawn from the 'Hand-to-Hand Combat' section of CHAINMAIL is offered."

      It doesn't offer any rules either for using them for, or against, monsters. I'm not sure if he used them, or not - I wonder if he ever said? For all that it's in Greyhawk, it's listed as an optional rule and it's still rather incomplete for a system where fighting monsters is such a big deal. Oh well.

      Space needed for weapons is there, too, something we did use occasionally when people fought in cramped places.

    2. I was mostly talking about weapon length in initiative. As I understand it, weapon length mattered in the first round (when everyone is closing with each other), weapon speed thereafter.

    3. As far as I can tell, weapon length only matters if one side is charging (under Melee At End of Charge), or other "precipitously moving into melee" (under Strike Blows), both on DMG, p. 66. Otherwise, like you said, that's about it.

  2. I knew some players - at Oxford University, in the early 1980s - who did actually use this rule in play. They ended up with large tables on their character sheets with their actual THAC0s for armour class against armour type. The one I still know happily abandoned this when he joined groups who didn't trouble themselves with the rule.

    I /think/ there was an explanation in a Dragon magazine Sage Advice column about how to set armour types for monsters, but since it was during the period when they refused to acknowledge the existence of any errors at all in the AD&D rules, I wasn't taking much notice, and don't remember the rule.

    1. I'll keep an eye out for that Sage Advice. Hopefully it's different than the one I quoted above. I have the Dragon Archive, but the software that made the whole whack searchable is incredibly outdated by this point, so I long since just copied the PDFs off the CDs. I'll have to look into how to search a lot of PDFs all at once . . . and somehow find "weapon vs. armor type" when the words used - weapon, armor, AC - probably show up 20-30+ times per issue . . .

    2. Agent Ransack is a good tool for massed PDF searches on Windows. It costs money, but not very much. It is fast and can use regular expressions. I can search the GURPS 4e corpus with it in about a minute.

    3. I've downloaded it and I'll check it out. Thank you!

  3. One thing that really bugged me about this table is the treatment of shields. If the numbers are calculated for an armor *type*, why should the adjustment change if you have a shield? If the adjustments are based on the way the weapon interacts with the construction of the armor, which I believe is the justification, it cannot be universally true that a given armor type always presents the same adjustment to difficulty as the next best armor type (of a different construction) plus a shield.

    It would work better if you didn't have the AC 2 column (in the PHB) or the AC 0 column (post UA) and made it clear that AC 9 was the only one where a shield applied.

    1. I agree that's an additional oddity. Weapons that work especially well against shields (say, flails, presumably) or poorly (maybe bows?) should get just a flat modifier based on the shield. So many things to fix, here, though.

  4. Yeah, this is one of those rules in AD&D and supplement D&D that I really like in principle, but find difficult in practice. We do still use it, when we remember to, in our AD&D game, but it's the one that requires more rulings than most others. I'm also not entirely on board with some of the specific numbers chosen. It did let me, when I statted up firearms for AD&D, have the muskets basically ignore armor while also reducing the inherent accuracy of the weapons. Now, I'd probably adjust those numbers so that armor had some effect, but I did love that the rule let me do that.

    As I'm sure you know, the problem with "armor + shield" crossing over with "other armor" wasn't so much of a problem in earlier D&D, since ACs were more linear. The introduction of new armor types and the introduction of an additional armor class so that they went to 10 instead of 9 in AD&D kind of screwed the whole thing up. In D&D, of course, no armor was 9, light armor was 7, medium armor 5, and heavy armor 3. Adding a shield bumped those by one point. No crossovers: odd numbers have no shield, even numbers do. (As an aside, it's been speculated—I forget by whom—that the normal AC range, from 2 to 9, was intended at some point to be connected to a 2d6 roll, but the evidence for that seems scant.) AD&D added a new AC6 and bumped the lower ACs a point in order to make way for armor that was stronger than leather but not so good as chain.

    1. Like I said, I like the concept of the rule - not all weapons interact the same way with armor (or different armor types.) The execution seems so incomplete. And it's clearly carried over from earlier rulesets without fully adapting it to the next one - the Greyhawk one doesn't deal with monsters in the Greyhawk supplement well (contrast that with how it handles differentiating weapon damage by type and monster damage), and the AD&D one just imports and expands without addressing the whole issue of armor types + shields when it expands those types. It's maddening.

      Making it easier to model firearms is good, but I suppose you could just reduce armor class where it matters - ignores worn armor, say, or reduces the base AC of anything with armors (A, B, C) to AC 8 or something like that.

      Not that plate wasn't designed with firearms in mind, of course. It's only in modern historically inaccurate hindsight that we see firearms as suddenly coming along and making armor obsolete and blowing holes in it like it was made of rice paper.

    2. Completely agreed. It's also interesting how modern experimental hoplology—notably from Tod's Workshop lately, but also others—has been changing the way a lot of us think about these things.


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