Friday, March 30, 2012

Armor Class Numbers?

Because you died when you were hit in Chainmail, we were using damage dice, hit dice and armor classes within about a month of our starting to play Blackmoor (winter of 1970-71). Dave Arneson told me he based the armor class system on an American Civil War Ironclad game, although I can not tell you what game it was at this point, though.” Original Blackmoor  Player Greg Svenson.

(As it happens, the Ironclads game was never published, but the rules were related to the Napoleonic game Don’t Give up the Ship)

It’s the special nature of Ironclad ships that requires different wargame rules.  The point of Ironclads weren,'t just that they were low to the water and hard to hit, it was also that the armor plating was famously hard to penetrate.  Arnesons' Civil War Ironclads game may have had ships with hit points ranging from 1-100, and a combat table or some mechanic indicating the chance to penetrate armor class by weapon type (6pdrs, 12pdrs, musket etc.), resulting in variable damage by weapon.   This is entirely consistent for both a ACW Ironclads game, and for Blackmoor.  In such a game, the hit points for a given type of ship/individual are fixed, but stronger attacks have a more damaging effect against weaker armors and vice versa, once a hit is successfull.   This would require two steps (presumably two tables) a chance to hit/penetrate step and a damage step - as with D&D.  Arneson might easily have translated Weapon type vs Armor Classs into attacker level vs Armor Class.  So as the character/monster levels up and becomes a stronger weapon on the table, they gain more attack/damage dice. 

It has been suggested (and repeated on Arnesons own website) that Armor Classes in original D&D reflect ship classes, i.e. 1st class ship of the line, 2nd class ship and so on..)

I’ve never seen a statement directly from Arneson confirming that "descending" AC numbers were his idea, but, on the other hand, there have been a couple from Mr. Gygax.  On the Troll Lords (C&C) forum Gary Gygax wrote:

“I rather stepped in it when I reversed the AC system in the Chainmail man-to-man rules for the OD&D game. Had I not, then better armor classes would have simply progresses in higher numbers.”  Sun Sep 23, 2007 4:47 pm

What Gygax points to is that the Armor Classes in D&D are identical to the categories for armor in the Man to Man section of CHAINMAIL, except, in CM the first category is Unarmored and the last (for people) is plate and shield.  So if one were to simply assign numbers or “classes” to those categories, Unarmored would be AC 1 and plate and shield would be AC8.

It’s not known if Arneson used the CM categories, (or, perhaps more likely the 8 categories of armor found in Domesday Book #7 that became the basis of those in CM), for AC from the start, or if he simply adapted them at some point, but it does look like he did originally equate unarmored with AC 1 and so on.  Consider this quote from the FFC:

"To figure out when you got to a higher level, you took the creature's Hit Dice (whatever it was on that level) and AC and multiplied by 1000 for the points needed to progress to 2nd level. After 2nd level, the creature would simply need 50% more points for each subsequent level: 2000, 3.000, 4500, 6,750, etc."

So a character with 1HD and an Armor Class of 9 (Unarmored) would need a whopping 10,000 points to get to second level!?  Likewise a 2 HD creature would need 11,000 points (2+9 * 1000).  It makes sense, however with an ascending, worst to best system.  If AC1 is the normal AC for an unarmored human and they start off with 1HD, then by Arnesons system (1+1*1000) they need 2000 XP to advance to second level.  This is exactly the XP a fighting man needs in OD&D for 2nd level and it is also the exact figure Arneson gives in his example of how the system works.  Indeed, the example he gives (“2000, 3.000, 4500, 6,750, etc.") would be a very unlikely scenario unless AC1 was typical for HD1 creatures.

That’s circumstantial, to be sure but that’s not the only reference in the FFC;

"Robots: I roll one 6-sided dice for Armor Class, and another dice for the number of Hit Dice."  Of course, this gives robots a AC range of 1-6.   Why not 1d8? Possibly this is a very old note of his, predating the use of polehedral dice.  Arneson doesn’t indicate anything to suggest anything other than AC1 through AC6 is meant.  AC1 doesn’t exist in D&D.

And yet:

In the FFC we are told that the first six levels of Blackmoor dungeon were re-keyed for the 1976 Gen Con tournament using the standard Original Collectors Edition print of OD&D.  Most of the monsters do indeed match exactly those found in Monsters and Treasures, but there are a few critters that aren’t from the M&T lists.  Of those, seven are given an Armor class of 1:

Giant Scorpions
Evil Priests
Giant Beetles

To me, it looks very much like AC for non-standard “monsters” was determined randomly exactly as Arneson advocated for Robots, which sometimes results in AC1.  Since AC1 makes no sense in OD&D, it might be that Arneson was simply comfortable switching between ascending and descending systems in his own head.  In any case it strains credulity that unarmored magic users and presumably lightly armored priests would have an Armor Class rating better than that of a Dragon or a paladin in full plate and shows again how much Arneson loved random elements in his games.

And lastly there’s this memory from original blackmoor player John Snider:

 “Armor .. I thought it was 1-8, my Boozero character started at 1 if I remember correctly” (personal correspondence)

Who can say for sure?; but it does look like the first AC system was ascending. unarmored at AC1 to plate and shield at AC8.  As far as I know, there are only two games that incorporate an AC system that is identical with what seems to be Arneson’s original: Spellcraft and Swordplay and my own Dragons at Dawn. 

Basic Fantasy, it should be mentioned, is almost identical, except it adds 10, so that, instead of AC8, in BF it’s AC 18.

ACKS, unfortunately, really missed an opportunity here for a nice symmetrical homage to both Arneson and to CHAINMAIL.  ACKS also has an ascending AC system like Arnesons, but instead of starting with AC1 as unarmed, they went to AC 0.  So ACKS is “wrong” by one point, which is not hard to add, of course.  Shame that the designers let that one slip by.  (I brought it up during development, but as often happens, I feel like a voice howling in the wilderness).


  1. Sorry to be commenting on this old post, but I've been researching Chainmail and it's use exclusively with OD&D for all combat resolutions. This all started recently as a query on ODD74 forum found here:
    Eventually, I found my way to your blog. Anyway, I thought you might find it interesting that the 3rd ed. of Chainmail does indeed use ascending AC. You can find it present in the "Individual Fires with Missiles" table where it is an ascending rating from 1 to 8 that corresponds to the "Man-to-Man Melee Table" on the same page. So, it seems Gygax did use AAC prior to OD&D being published. Why he changed it is another question all together.

    Hope you see this comment and thanks for your research into these subjects. I've found them insightful.

  2. This comment has been removed by a blog administrator.

  3. We've all heard the "ascending AC makes more sense" story so many times. The truth is that it doesn't really matter how AC is defined if all we care about is a way to differentiate weaker from stronger armor. We could use "armor type L, C, P, L+S, C+S, P+S" or whatnot, as long as there was a table somewhere that somebody designed to express the basic "to hit" mechanic in those terms.

    Now obviously it's nicer to have a more abstract mechanic, one that applies, for example, to monsters that don't actually wear armor as well. Hence numbers instead of weird letters. The tables as well as the monster stat blocks become simpler: It doesn't matter whether something has AC 4 because it's wearing "chain and shield" or because it's "smallish and quickish" as it were, in the end both are equally hard to hit (within the limited confines of the game anyway).

    If you're with me so far, see if you can't go the last step. What we're really after is a simpler, faster way of doing things. And the question becomes "well, given the confines of the other pieces of D&D, what's the fastest/easiest/most convenient way to decide between a hit or a miss" and nothing else. And it turns out that descending AC actually provides that way: d20 + level + AC + mods ≥ 20 That's Delta's Target 20 mechanic, and it works so well precisely because it's using descending AC. You can find out more about it here: As far as I am concerned, this mechanic is totally worth the "price" of having descending AC in the game.

  4. I think the civil war ironclads game was called, "Don't Give Up the Ship."