Combat Across Chainmail, OD&D, and Greyhawk

OD&D's "alternate" combat system was derived from Chainmail and became the basis for the standard D&D combat system as developed since Greyhawk, but it has certain quirks which distinguish it from its predecessor and its many successors. I'd like to offer an alternate development of the "alternate" combat system from Greyhawk, with a view to doubling down on its innovations rather than reconciling it with what came before or after. First, though, I'd like to summarize the development of combat systems from Chainmail to OD&D to Greyhawk.

Abbreviations for citations, most of which I'm taking from the annotated Delving Deeper Book I: Heroes & Magic, a retroclone of the original Dungeons & Dragons:

  • CM3: The third edition of Chainmail, 1975. The first edition was published in 1971.
  • M&M: The first volume of the original Dungeons & Dragons, Men & Magic, 1974.
  • M&T: The second volume of the original Dungeons & Dragons, Monsters & Treasure, 1974.
  • U&WA: The third volume of the original Dungeons & Dragons, Underworld & Wilderness Adventures, 1974.
  • GH: The first supplement for the original Dungeons & Dragons, Greyhawk, 1975.
  • PHB: The second volume of Advanced Dungeons & Dragons, the Player's Handbook, 1978.
  • MB: The second edition of Dungeons & Dragons Basic by Moldvay, 1981. Published alongside Cook's Dungeons & Dragons Expert, thus they are known together as BX.

Throughout this post, I include B&W screenshots from my forthcoming OD&D retroclone called Fantastic Medieval Campaigns. The Greyhawk screenshots, however, are original. You can open the full-size image to better read the text.

Chainmail: Medieval Miniatures

  • Units: 1 figure represents 20 persons.
  • Time: 1 round represents 1 minute.
  • Distance: 1 inch represents 10 yards.

Chainmail was primarily a manual for mass-scale war gaming, where each figure on the board represents 20 people (CM3, p. 8). There are two procedures you can use: turn-based or simultaneous (CM3, p. 9). For the turn-based procedure, both sides roll a die and whoever rolls the highest can decide whether to move first or last. For simultaneous procedure, orders are written on paper and they are just resolved simultaneously (likely being interpreted by a referee). The nitty gritty of turn procedure either way is as follows:

  1. Move: Again, this part is handled either by turn-based initiative or by simultaneous resolution. Some units are able to "split-move", which means they can move for part of their rate, shoot missiles, and then move for the rest of their rate.
  2. Artillery: Heavy ranged weapons like catapults and cannons are fired.
  3. Missiles: Archers and crossbow users shoot their shots. This is different from "split-move".
  4. Melees: Melee units that are in proximity to each other fight.

Catapults fire their projectiles at an arc so that they land in a specific place within a maximum range (CM3, pp. 12-3); there is an optional rule to randomly adjust the distance of the shot by d6-d6 inches (positive means overshooting, negative means undershooting). Cannons shoot in a straight line and bounce across the battlefield, and it hits whichever figure it lands on each time until it stops bouncing (CM3, pp. 13-4). Bombard guns can be treated as catapults or cannons; however, if you shoot them at an arc, they don't bounce.

Crossbow users and archers may fire every turn (CM3, pp. 11-2). Archers may fire twice if they do not move and are not attacked that turn. Ranged units may fire once if they move up to one-half of their normal movement; otherwise they may fire once only if they beat their opponent’s die roll. Heavy crossbow users cannot reload their weapon if moved over one-half of their movement. Missile units are most effective in large numbers, since the x-in-6 chance of defeating another unit depends on how many attackers are shooting at them. Firearm users are exempt from this, however; they only need to roll for accuracy based on distance (CM3, p. 13).

Melee resolution depends on the unit-types of the attacker and defender (CM3, p. 40). There are three kinds of foot units (light foot, heavy foot, armored foot) and three kinds of cavalry units (light horse, medium horse, and heavy horse). The likelihood that one unit will defeat another is expressed in how many dice the attacker rolls, and what score must be met on at least one die. For example, a light foot against a light foot must roll 1 die and try to get a score of 6. Sometimes, there must be multiple of an attacking unit in order to roll against one stronger defending unit; for example, there must be at least 4 light foot units attacking a heavy horse unit in order for 1 die to be rolled to attack. Meanwhile, a heavy horse unit can roll 4 dice to attack a light foot unit, and they succeed on one roll of 5+.

One-on-One Scale 

  • Units: 1 figure represents 1 person.
  • Time: 1 round represents 1 minute.
  • Distance: 1 inch represents 10 yards.

Chainmail also includes rules for a 1:1 unit scale, for up-close fights and skirmishes rather than big battles (CM3, p. 25). Rather than unit type, this ruleset is concerned with weapons and armor.

The missile firing matrix is a function of weapon type (short bow, crossbow, composite bow, etc.) versus armor type (leather, chainmail, plate, with or without shield) (CM3, p. 41). Also considered is the distance between attacker and target, which is given in three ranges (short, medium, long). The attacker rolls two dice, and tries to attain a score equal to or greater than the value on the matrix. For example, a short bow wielder firing at a target wearing chainmail 5" (representing 50 yards) away must roll 8+.

Likewise, the melee table indexes weapon versus armor, and describes what two-dice score must be attained in order to land a hit (CM3, p. 41). For example, a sword-wielder attacking someone wearing plate mail must roll 10+. The "weapon class" of the attacker and defender determines whether the defender is able to parry and/or counterattack during the exchange. For example, a dagger-wielder can choose whether they subtract 2 from someone attacking them with a sword, or to counterattack them instead; on the other hand, they can totally outmaneuver a polearm-wielder, allowing them to deal the first blow and subtract 1 from their attacker's blow.

Fantasy Supplement

  • Units: It's complicated.
  • Time: 1 round represents 1 minute.
  • Distance: 1 inch represents 10 yards.

The fantasy supplement of Chainmail seems to interface with both the 20:1 and 1:1 scales. Armies of elves and orcs and dwarves and goblins are described in terms of the mass combat unit types. For example, a goblin unit attacks as 1 heavy foot unit, but defends as 1 light foot unit (CM3, p. 43). However, the significant 'fantasy' figures have 20:1 ratings alongside a special matrix for 'fantasy combat' which pits dragons against wizards or ogres against treants (CM3, p. 44). For example, a dragon fights as 4 heavy horse units but cannot be attacked by mass units; at the same time, a dragon can also defeat a werewolf on a two-dice score of 4+.

This all is complicated by a Q&A exchange on ENWorld between user RFisher and Gary Gygax, where Gygax claims that the fantasy figures were only ever used in 1:1 combat and that the two scales were not ever mixed in play [1]. This seems to contradict the usage of mass melee types on the table, and also OD&D itself which says: "Battles involving large numbers of figures can be fought at a 20:1 ratio, with single fantastic types fighting separately at 1:1 or otherwise against but a single 20:1 figure" (U&WA, p. 25).

Possible interpretations of the fantasy Chainmail supplement against the 'word of God' include that fantasy units exclusively fought each other and that heroes gave bonuses to their unit rather than serving as a separate unit in mass combat [2]. At the same time, this does not explain why fantasy units have ratings for mass combat attack, and why Gygax's own adaptation of The Hobbit as a Chainmail scenario uses mass combat alongside hero units representing Thorin and his entourage. I think it's more likely that no one cared, but a more formalized system would be nice.

Dungeons & Dragons: Fantastic Medieval Wargames

  • Units: 20:1 or 1:1.
  • Time: "There are ten rounds of combat per turn" (U&WA, p. 8). Presumably per exploration turn, i.e. one combat round is 1 minute, but there has been some discussion about whether each round is one tenth of a Chainmail turn [3]. I agree with the more usual reading.
  • Distance: 1 inch represents 10 yards.

OD&D assumes by default that the Chainmail rules are used for combat on individual and mass scales. The then-latest edition of Chainmail is listed as recommended equipment (M&M, p. 5). Moreover:

  • "Dedicated to all the fantasy wargamers who have enthusiastically played and expanded upon the CHAINMAIL Fantasy Rules, with thanks and gratitude. Here is something better!" (M&M, p. 1).
  • "[Elves] also gain the advantages noted in the CHAINMAIL rules when fighting certain fantastic creatures" (M&M, p. 8).
  • "[Halflings] will have deadly accuracy with missiles as detailed in CHAINMAIL" (M&M, p. 8) [4].
  • "Non-player characters and men-at-arms will have to make morale checks (using the above reaction table or 'Chainmail') whenever a highly dangerous or un-nerving situation arises" (M&M, p. 13).
  • "Fighting Capability: This is a key to use in conjunction with the CHAINMAIL fantasy rule, as modified in various places herein. An alternative system will be given later for those who prefer a different method" (M&M, p. 18).
  • "Invisibility: A spell which lists until it is broken by the user or by some outside force (remember that as in CHAINMAIL, a character cannot remain invisible and attack)" (M&M, p. 24). 
  • "[Fire ball] explides with a burst radius of 2" (slightly larger than specified in CHAINMAIL)" (p. 25).
  • "[Lightning bolt] is otherwise similar to a Fire Ball, but as stated in CHAINMAIL the head of the missile may never extend beyond the 24" range" (M&M, p. 25).
  • "The Elemental will remain until dispelled, but the Magic-User must concentrate on control or the elemental will turn upon its conjurer and attack him (see CHAINMAIL)" (M&M, p. 28).
  • "Special Ability functions are generally as indicated in CHAINMAIL where not contradictory to the information stated hereinafter" (M&T, p. 5).
  • "GOBLINS: These small monsters are as described in CHAINMAIL" (M&T, p. 7).
  • "GIANTS: As stated in CHAINMAIL, Giants act as mobile light catapults with a 20' range" (M&T, p. 8).
  • "GHOULS: As stated in CHAINMAIL for Wights, Ghouls paralyze any normal figure they touch, excluding Elves. They otherwise melee in the regular fashion and are subject to missile fire" (M&T, p. 9).
  • "PIXIES: Air sprites as described in CHAINMAIL, Pixies can be made visible, or make themselves visible, but they are naturally invisible to human eyes" (M&T, p. 16).
  • "[Dwarves] are otherwise as outlined in CHAINMAIL" (M&T, p. 16).
  • "Elves on foot may split-move and fire. Mounted Elves may not split-move and fire, for they are not naturally adapted to horseback" (M&T, p. 16) [5].
  • "HORSES: As explained in CHAINMAIL, war horses melee" (M&T, p. 20) [6].
  • "Horn of Blasting: A horn whose sounding has the effect of a double bombard (see Vol. III and CHIANMAIL) on non-living materials such as walls, gates, etc." (M&T, 38) [7].
  • "If a joust takes place (use rules from CHAINMAIL) the occupant of the castle will take the loser's armor if he wins, but if the character wins the castle owner will host all in the party for up to one month, supply them with two weeks of rations, and provide warhorses (Heavy) if the party so requires" (U&WA, p. 15) [8].
  • "The basic [land combat] system is that from CHAINMAIL, with one figure representing one man or creature. Melee can be conducted with the combat table given in Volume I or by the CHAINMAIL system, with scores equalling a drive back or a kill equal only to a hit. Battles involving large numbers of figures can be fought at a 20:1 ratio, with single fantastic types fighting separately at 1:1 or otherwise against but a single 20:1 figure" (U&WA, p. 25).
  • "Most firing and melee [in aerial combat] is based on CHAINMAIL" (U&WA, p. 25).
  • "Bombing: If necessary this form of attack can be allowed, with the largest flying creature being able to carry a bomb load equal to the missile from a large catapult" (U&WA, p. 28).
  • "All missile fire, including the various forms of catapult fire, are as in CHAINMAIL. Catapult hits will do points of damage to the ships, and when sufficient points have been scored the ship sinks. Large shapes have from 18-24 points of possible damage before singing, small ships have from 9-15, and a boat but 3 points" (U&WA, p. 30).
  • "Once boarders are on the enemy ship combat takes place on a man-to-man basis (CHAINMAIL)" (U&WA, p. 31).

You get the point.

However, Men & Magic (D&D Vol. I) offered an "alternate" combat system in case the reader would prefer it over Chainmail—having a similar chassis, especially with respect to armor class (it seems that Arneson or Gygax took 2d6 scores, inverted them, and turned them into the armor class range of OD&D), but using the newfangled twenty-sided die. It resembles much more closely the combat system that would be typical of Dungeons & Dragons but, like I had mentioned prior, without much of the baggage developed since.

Player characters have a number of hit dice which determines how many points of damage they can sustain before getting killed (M&M, p. 6). A number of six-sided dice equal to the character's hit dice value are rolled, and that is how many 'hit points' that character has; sometimes characters are given a flat bonus to their total hit points, such as +1 or +2 (M&M, p. 18).

A character's likelihood of hitting an opponent is a function of their character-type level and their target's armor class; the player then rolls a twenty-sided die to attain a score equal to or greater than the score listed in order to land a hit (M&M, p. 19). For example, a fourth-level fighter must roll 14+ when attacking an opponent with an armor class of 2 (representing plate mail or equivalent). Upon being hit, the target takes 1-6 points of damage unless otherwise noted. Monsters have a similar attack matrix, but it is based on their hit dice value rather than their character-type and level since monsters don't have those (M&M, p. 20).

Even more interesting is what Monsters & Treasure (D&D Vol. II) says about monsters' hit dice value: "Attack/Defense capabilities versus normal men are simply a matter of allowing one roll as a man-type for every hit die, with any bonuses being given to only one of the attacks" (M&T, p. 5). For example, since a troll as "6 + 3" hit dice (6 dice plus 3 pips bonus), the troll attacks six times and can make one of those attack rolls with a +3 bonus. Some monsters also have special damage rates, such as the frost giant which rolls 2 dice plus 1 pip for damage for a range of 3-13 hit points (M&T, p. 8). With it being able to attack 10 times per turn and once with a +1 bonus, since it has "10 + 1" hit dice, that makes the frost giant especially scary as an opponent.

The text opens up certain ambiguities, in my view. For example, if more hit dice means more attacks for monsters, does the same hold true for human characters? Or is this a difference between hit dice representing physical strength versus hit dice representing skill, fortune, or other non-physical factors? As per Gygax in Advanced Dungeons & Dragons:

Each character has a varying number of hit points, just as monsters do. These hit points represent how much damage (actual or potential) the character can withstand before being killed. A certain amount of these hit points represent the actual physical punishment which can be sustained. The remainder, a significant portion of hit points at higher levsiels, stands for skill, luck, and/or magical factors. A typical man-at-arms can take about 5 hit points of damage before being killed. Let us suppose that a 10th level fighter has 55 hit points, plus a bonus of 30 hit points for his constitution, for a total of 85 hit points. This is the equivalent of about 18 hit dice for creatures, about what it would take to kill four huge warhorses. It is ridiculous to assume that even a fantastic fighter can take that much punishment. The some holds true to a lesser extent for clerics, thieves, and the other classes. Thus, the majority of hit paints are symbolic of combat skill, luck (bestowed by supernatural powers), and magical forces.

PHB, p. 34.

Yet one reason why fighters, and even mages and clerics, might have additional attacks is because they are mapped to the fantastic unit scale in Chainmail where heroes and wizards have the capabilities of four or two units respectively. At the same time, this reopens the discussion about whether such units participate in mass combat because heroes and wizards are defined with respect to mass combat capabilities; for example, a wizard has the capability of two armored foot units or else two medium horse units if mounted (Chainmail, p. 30).

What we should glean from this is that the "alternate" combat system in OD&D is not consistent or complete. Looking in the context of what OD&D tries to accomplish overall, we can think of it as guidelines for a fantastic medieval campaign which primarily is built on Chainmail with respect to combat, but can also be fitted into other systems such as the "alternate" one in Men & Magic. This was a time before grand all-encompassing systems and, more importantly, a time before D&D as a cultural phenomenon with its own expectations and associations.

Supplement 1: Greyhawk

The Greyhawk supplement for OD&D introduces many new factors for the "alternate" combat system, signaling a shift altogether from Chainmail. Now ability scores inform a character's proficiency in combat, with strength modifying attack and damage rolls in melee [9]; interestingly, the language implies that only fighters receive the benefits of a high strength score in this respect (GH, p. 7). Hit dice for characters also changes; rather than being in terms of six-sided dice plus bonus pips, each class is now assigned a different die size to determine hit points (GH, p. 10); for example, fighters use eight-sided dice, clerics use six-sided dice, and both mages and thieves use four-sided dice [10]. Monsters' hit points are also now determined using eight-sided dice instead of six-sided ones, making them more resilient than most characters except for fighters.

Greyhawk also expands upon the original attack matrices in Men & Magic, in an attempt to port the Chainmail one-on-one melee matrix where different weapons are more effective against different kinds of armor (GH, pp. 13-4). As pointed out on Delta's D&D Hotspot, Gygax made a grave error in his calculations because instead of modifying die scores per armor class (e.g. for a first-level fighter, no-armor needs a score of 10 and plate mail needs a score of 16; M&M, p. 19) he only modified with respect to no-armor [11]. This means that a weapon like a mace, which ignores almost all armor in Chainmail, is treated as if it doesn't affect armor at all. Likewise, weapons against which armor was effective in Chainmail end up ignoring armor in Greyhawk. I have created correct tables, if you are interested [12].

Finally, Greyhawk adds variable weapon damage not only by type of weapon but also depending on whether the opponent is 'man-sized' or 'larger' (GH, p. 15). For example, a dagger deals 1-4 damage against a man-sized enemy and 1-3 damage against a large enemy, whereas a sword deals 1-8 damage against a man-sized enemy and 1-12 damage against a large enemy. Monsters also now have not only variable damage but also variable numbers of attacks. Instead of being determined by their hit dice value, they are based entirely on the monster designer's discretion. A troll, which before could attack six times per round, now has three attacks: two claw attacks (for 1-4 damage) and one bite attack (for 1-8 damage) (M&T, p. 5; GH, p. 16).

These changes diminish the scale of the "alternate" combat system and makes it, perhaps, less "fast and furious" than when it was originally designed (U&WA, p. 8). Although the intent was in part to bring back some of the mechanical granularity from Chainmail, it does not succeed at this and it also introduces more complexity and specific detail which slows down the game. The system would yet become standard for Dungeons & Dragons, being replicated in Advanced Dungeons & Dragons, and with variable weapon damage being presented as an optional rule in 1981's D&D Basic (PHB, pp. 37-8; MB, p. 27).

An Alternate Route

Greyhawk represents just one path D&D could have developed. Of course, it was the path taken by history, but that does not mean it was necessarily the only way that the system presented in OD&D could have developed. Specifically, Greyhawk increases variability between character abilities, complicates the 'processing' of the game with formal attack-types and dice sizes, and reduces the scope of what can occur in a single round of combat, ultimately contributing to a more complex and slower game with less of the abstractions afforded by OD&D. What would D&D have looked like if the designers seized upon different aspects of the "alternate" combat system, with a different set of goals?

Let's take for our basis that 1 hit die represents not just the capability to take damage, but the capability to deal it. In OD&D, this manifests as 1 attack per 1 hit die, with a bonus being added to any one attack if indicated (remember, "6 + 3" hit dice means up to six attacks with one getting +3 to hit). Assuming that this applies to player-characters just as well as it does to monsters, which seems to be the case, the effect is that an attacker has the potential to one-shot-kill any opponent of equal hit dice in one round, so long as the attacker is able to succeed at all the attack rolls. User waysoftheearth on the odd74 forum did the math, and it results in much quicker encounters [13]:

We see immediately that all equivalent challenges will take an average of 3 to 5 rounds to resolve, with the least HD contests being resolved only somewhat quicker that the most HD contests. A fight between 1 HD protagonists (including 1st level fighters) will take, on average, 3 rounds to resolve. A fighter between 9 HD protagonists (including 9th level fighters) will take, on average, 5 rounds to resolve.

The issue with this, and maybe this is something Greyhawk tried to fix, is that there are two rolls for each attack. Our troll would have to roll to hit, then roll for damage, then roll to hit, then roll for damage, then roll to hit, then roll for damage, then roll to hit, then roll for damage, then roll to hit, then roll for damage, then roll to hit, then roll for damage. Compare this to Greyhawk where a troll has three attacks, and they are specific and named. The user above notes that this is no different than having to roll for many attacks from multiple opponents, but I think keeping units and their actions as discrete as possible is more desirable; also, having to roll to hit for each damage roll increases, however slightly, the duration of an encounter since there is a good chance that each attack could fail by itself.

I would change this to having there be just one attack roll, or else being able to freely distribute hit dice among attack rolls against different targets. One benefit is that we are not numbering attacks with hit dice, but hit dice are always keyed to six-sided dice specifically. You can hold onto however many six-sided dice your character has, knowing that when you land an attack they'll be what you roll. Another benefit is that it bypasses the often-imposed distinction between "normal" or "man-sized" characters versus "fantastic" or "large" characters, since all differences in capability or resilience are encoded in hit dice as a measure of physique or fortune; compare this to OD&D as written, where monsters only deal such extra attacks against "man-sized" opponents. Finally, there is a particularly interesting edge case for weak minion monsters like skeletons or goblins: having 1/2 (one-half) hit die, they deal only 1-3 damage on a hit rather than 1-6. This makes it much easier to pit player-characters against them.

That being said, there is also a mental load in having to roll so many dice anyway, and also having to justify whether they are distributed between one or many opponents. At the same time--and this is an issue raised in the same thread--making only one attack means you are betting all or nothing on the one attack, whereas an attack roll for each damage die is more likely to have at least some damage dealt. Part of me wonders if a segmented round system, like the one in Advanced Dungeons & Dragons, could reconcile the two methods: perhaps 1 attack with 4 hit dice takes 1 segment of time, meaning you can try to hit for all that damage immediately, but you have a chance of losing it all; whereas 4 attacks with 1 hit dice takes 4 segments of time, so you're more likely to land a hit but you're wasting time while e.g. someone else is hitting you. That adds much more complexity, though.

Still, I hope it's interesting that there are other ways in which OD&D could have been further developed besides the route Gygax et al. actually took. Thinking about the pros and cons of each system, and why they changed what they did, is helpful to understand your own preferences for what you want out of a D&D.





[4] C.f. "[Halflings] can fire a stone as far as an archer shoots, and because of their well known accuracy, for every two Halflings firing count three on the Missile Fire table" (CM3, p. 29). This must only be a reference to the 20:1 missile fire table, since the 1:1 table does not depend on how many units are firing. What’s the truth, Gary?

[5] C.f. "[Elves] can perform split-move and fire, even though they are footmen" (CM3, p. 29).

[6] The categories of horses from Chainmail are listed: light horse, medium horse, heavy horse. Also listed are draft horses and mules.

[7] A section of the 1:1 rules describes rules for structures and siege weapons.

[8] Another reference to heavy horse units in Chainmail.


[10] The thief class was originally introduced in Greyhawk (p. 4). See my post about how this impacted D&D beyond pure mechanics:





  1. This was an interesting read as always. Would you mind adding a link to annotation 13 for that specific thread? I would be curious to read through it myself.

    1. This comment has been removed by the author.

    2. oh yes, thank you for catching that! the link has been added now :)

    3. Thank you! Although now that I actually click on it it tells me I am not allowed to view the thread, presumably because I'm not registered on the forum. Oh well.

    4. if you're interested, it's totally worth registering! lots of good conversations on there going back to the 2000s :)

    5. I was intrigued enough that I looked into it. Apparently I already do have an account for whatever forum software they're using, but having to write up a fucking membership acceptance request just to lurk on a forum? Yeah that's just silly.


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