Armor Class in Chainmail

The man-to-man combat system of Chainmail contains a number of elements that anticipate but differ from  Dungeons & Dragons. As originally specified in the first edition of Chainmail, the chance to hit in combat depended upon both the sort of weapon used by the attacker and the type of armor worn by the defender. This led to an accuracy system that may seem counterintuitive in hindsight - a halberd, for example, is less effective against a target in no armor than it is against one attired in chainmail, presumably because the unencumbered defender can dodge more easily. When Gygax added a table for bowshot in the August 1971 issue of the International Wargamer (about four months after first edition Chainmail), he provided a more recognizable precursor to the Dungeons & Dragons concept of armor class. This same table would eventually turn up in the second and subsequent editions of Chainmail.

We must first of all note that the "Individual Fires with Missiles" table uses the construction "class of armor worn by the defender," a first version of the term "armor class." Earlier, first edition Chainmail called this quality the "defender's armor protection type," a slightly more cumbersome construction. The actual term "armor class" first appeared in the January 1972 International Wargamer in a later set of Chainmail revisions, which noted that "attacks from the rear and right flank negate the shield, if any, for armor class."

The second thing we note from the table is the quantification of armor class into numbers that range from 1 to 8, with 1 being the least armored and 8 being the most. This of course inverts the eventual OD&D system, in which 9 is the least armored and 2 is the most, but each increment represents the same eight states of armor, ranging from unarmored through leather, chain and plate, with or without a shield (though the ordering is slightly different). While in the melee tables of Chainmail, it is sometimes easier to hit a more armored target with a weapon, as with the halberd described above, the "Individual Fires with Missiles" table works differently: it is always harder to hit more armored targets with bowshot, regardless of the type of weapon.

More obscure even than these early references to armor class in Chainmail is the concept of "weapon class." We see this referenced throughout the man-to-man rules from first edition Chainmail (table shown above) forward, as a way of explaining the relative speed of different weapons. The first blow in melee is struck by the attacker unless the defender "has a weapon which is two classes higher," for example. This quality was quantified from the start: "each weapon listed has a number designating its class." The lightest weapon, the dagger, has a weapon class of 1, while the heaviest, the pike, ranks as a 12. A standard sword is a 4, a two handed-sword a 10. These weapon class factored not only into the initiative determination, that is of who hits first, but also into how many blows are struct. When facing off against an opponent whose weapon is four classes higher than your own, you get two attacks "during every melee round." If the opponent's weapon is eight classes higher than yours, you may take three attacks.

The second edition of Chainmail introduces parry rules that also favor lower weapon classes. By the time OD&D came around, however, the idea of weapon classification would be discarded, while armor class would assume a prominent role. The quantification of armor class remains incomplete in OD&D, however: if you look at the text for magic armor or Rings of Protection, for example, the effects of these items reduce the to-hit roll of an attacker rather than reducing the armor class of the defender. The notion that effects would add or subtract from armor class is a later invention: although armor class is quantified in OD&D, it isn't the fluid quantity that AD&D players would expect. In this respect, the armor class of OD&D does not stray far from the precedent of Chainmail.