The Tangled Origins of D&D’s Armor Class, Hit Points, and Twenty-Sided Die Rolls To-Hit

In 1977, when I first read the Dungeon & Dragons basic rules, the way armor class improved as it shrunk from 9 to 2 puzzled me. Shouldn’t higher numbers be better? Players just used AC to find a row on a table, so rising ACs would have worked as well. Magic armor introduced negative ACs, making the descending numbers even more awkward. Also, many of the demons described in 1976 in the Eldrich Wizardry supplement sported negative armor class.

D&D’s designers seemed to think rising armor classes made more sense. The game rules stemmed from co-creator Gary Gygax’s Chainmail rules for miniature-figure battles. Chainmail rated armor from 1 to 8, with better armor gaining higher values. Co-creator Dave Arneson based his Blackmoor fantasy campaign on Chainmail. His campaign developed into D&D. In Blackmoor, higher armor classes represented better armor.

So how did the first D&D rules set the puzzling convention of descending armor class?

The answer lies toward the end of the genesis of D&D’s combat system.

In the original D&D rule books, the combat system that everyone used appears as the Alternative Combat System. “Alternative” because players could just use the combat system from Chainmail instead. When Dave launched Blackmoor, he tried the Chainmail system. But it focused on battles between armies sprinkled with legendary heroes and monsters. For ongoing adventures in the dungeon under Castle Blackmoor, the rules needed changes. Original Blackmoor player Greg Svenson recalls that within about a month of play, the campaign created new rules for damage rolls and hit points. (More recently, Steve Winter, a D&D designer since 1st edition, tells of playing the original game with the Chainmail combat rules.)

Much of what we know about how Dave adapted the rules for his Blackmoor campaign comes from two sources: a 2004 interview and The First Fantasy Campaign, a raw publication of notes for his game. Most quotes in this post come from those sources.

Chainmail’s melee combat matrix

To resolve melee combat, Chainmail used a combat matrix. Players matched the attacking weapon or creature against the defender, rolled a pair of 6-sided dice, and consulted the table for an outcome. “That was okay for a few different kinds of units, but by the second weekend we already had 20 or 30 different monsters, and the matrix was starting to fill up the loft.”

Dave abandoned the matrix and extended Chainmail’s rules for missile attacks to melee combat. In Chainmail, ranged attackers rolled 2d6, and tried to roll higher than a target number based on increasing armor classes. Blackmoor gained melee to-hit rolls.

Chainmail’s man-to-man combat and ranged combat tables

In Chainmail, creatures lacked hit points, so a single hit killed. But with extraordinary individuals like heroes, wizards, and dragons, a saving throw allowed a last chance to survive. For example, the rules say, “Dragon fire will kill any opponent it touches, except another Dragon, Super Hero, or a Wizard, who is saved on a two dice roll of 7 or better.”

Under rules where one hit destroyed a character, Dave tried to spare player characters by granting saving throws against any hit. “Thus, although [a character] might be ‘Hit’ several times during a melee round, in actuality, he might not take any damage at all.”

But the system of saving throws still made characters too fragile to suit players. “It didn’t take too long for players to get attached to their characters, and they wanted something detailed which Chainmail didn’t have,” Dave explains.

Chainmail battle on a sand table

“I adopted the rules I’d done earlier for a Civil War game called Ironclads that had hit points and armor class. It meant that players had a chance to live longer.” In a Chainmail battle that featured armies spanning a sand table, hit points would have overwhelmed players with bookkeeping. But the Blackmoor players liked the rule. “They didn’t care that they had hit points to keep track of because they were just keeping track of little detailed records for their character and not trying to do it for an entire army. They didn’t care if they could kill a monster in one blow, but they didn’t want the monster to kill them in one blow.”

When players rolled characters, they determined hit points. For monsters, hit points were set based “on the size of the creature physically and, again, on some regard for its mythical properties.” Dave liked to vary hit points among individual monsters. To set the strength of a type of monster while rolling for an individual’s hit points, he probably invented hit dice.

Dave said he took the armor class from Ironclads, but the concept came from Chainmail and the term came from its 1972 revisions. I suspect Dave meant that he pulled the notion of hit points and damage from a naval game that featured both armor ratings and damage points. Game historian Jon Peterson explains, “The concepts of armor thickness and withstanding points of damage existed in several naval wargames prior to Chainmail.” Still, nobody has found the precise naval rules that inspired Dave. Even his handwritten rules for ironclad battles lack properties resembling armor class. Perhaps he just considered using the concept in a naval game before bringing the notion to D&D.

In Blackmoor, Dave sometimes used hit locations. Perhaps naval combat inspired that rule. When ships battle, shells that penetrate to a boiler or powder keg disable more than a cannonball through the galley. Likewise, in man-to-man combat, a blow to the head probably kills.

Dave’s rules for hit locations only reached D&D in the Blackmoor supplement, which came a year after the game’s release. But hit locations made combat more complicated and dangerous. Realistic combat proved too deadly for the dungeon raids in D&D. So D&D players never embraced hit locations. Even Dave seemed to save the rule for special occasions. “Hit Location was generally used only for the bigger critters, and only on a man-to-man level were all the options thrown in. This allowed play to progress quickly even if the poor monsters suffered more from it.” Dave ran a fluid game, adapting the rules to suit the situation.

By the time Dave’s fantasy game established hit points, 2d6 to-hit rolls, and damage rolls, he showed the game to Gary Gygax.

Next: Gary Gygax improves hit points by making them more unrealistic, and then adds funny dice

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