In 1972, Dungeons & Dragons co-creator Dave Arneson introduced his Blackmoor campaign to co-creator Gary Gygax. The campaign stemmed from Gary’s Chainmail rules, but Dave’s game transformed the rules for miniature-figure battles into something new and irresistible—something that broadly resembled D&D.

My last post explained how Dave shaped a combat system that featured hit points, 2d6 to-hit rolls, damage rolls, and armor classes where higher numbers represented better protection.

Based on Dave’s demonstration, feedback, and notes, Gary added his own contributions to make the D&D game that reached print. In Pegasus issue 1, Dave recalled that Gary and his Lake Geneva group “had a lot more spare time than I did and they had a lot of ideas, so they came up with their own version of the rules.”

Gary changed Dave’s combat rules in 3 key ways:

• Hit points became less realistic and more fun.
• To-hit rolls switched to a twenty-sided dice, creating a new market for funny dice.
• AC ratings flipped to make lower values better, forcing awkward, negative ACs on players.

Unrealistic hit points

Gary’s changes let characters gain hit points as they leveled. In Blackmoor, Dave wrote, “As the player progressed, he did not receive additional hit points, but rather he became harder to hit.” Dave based armor class on armor, but fighters gained better saving throws. By the Blackmoor rules, saves applied to weapon attacks, so fighters could avoid damaging blows. “Only Fighters gained advantages in these melee saving throws. Clerics and magicians progressed in their own areas, which might or might not modify their saving throws.”

In Chainmail, a hero fought as 4 ordinary soldiers and a superhero as 8. D&D translated this scheme by making heroes 4th-level fighting men and superheroes 8th level. When Gary reconciled Dave’s rules for hit dice with the notion of heroes that fought as several men, he probably decided to give characters more hit dice as they leveled. The mechanic seemed unrealistic. After all, nobody gets 10 or more times more durable through experience. But rising hit points helped power the game’s success. They boosted the positive reinforcement of leveling. Plus, heroes capable of unrealistically surviving many blows supported D&D’s combat-intensive, dungeon-bashing style. These advantages helped make the game so appealing.

Every “realistic” system to follow D&D echoed Dave Arneson’s original method of using hit points to measure a character’s body’s physical capacity to survive injury. In D&D, hit points rise as characters advance, and that turns hit points into an elegant damage-reduction mechanic. As characters level, they essentially reduce the damage they take from blows.

Using hit points for damage reduction boasts a number of virtues:

• Combat plays fast because players do not have to calculate reduced damage for every single hit.
• Although damage is effectively reduced, the reduction never makes a combatant impervious to damage.
• Once characters gain enough points to survive a few blows, hit points provide a predictable way to see the course of battle. If a fight begins to go badly, the players can see their peril and bring more resources like spells and potions to the fight, or they can run. In a realistic fight, things can go bad in an instant, with a single misstep resulting in death.
• Most attacks can hit and inflict damage, providing constant, positive feedback to players while everyone contributes to the fight. Realistic combatants do not wear down from dozens of damaging blows; instead each hit is likely to kill or maim. In more realistic systems like Runequest and GURPS, when two very skilled combatants face off, they block or dodge virtually all attacks. The duels turn static until someone muffs a defense roll and lets a killing blow slip through. This model may be realistic—it reminds me of those Olympic competitions where years of training turn on a single, split-second misstep—but the realistic model lacks fun. No popular sports begin as sudden-death competitions where the first to score wins.
• Battles can gain a dramatic arc. Fights climax with bloodied and battle-worn combatants striving to put their remaining strength into a killing blow. No one likes to see the climactic battle fizzle with a handful of bad rolls, especially at their character’s expense.

Bottom line: Using hit points for damage reduction enables a combat system where you can hit a lot, and hitting is fun.

Funny dice

When Dave adapted the Chainmail rules for his Blackmoor campaign, he kept using ordinary 6-sided dice. He later explained, we had “no funny dice back then.”

The twenty-sided die may not have reached Dave’s corner of gaming yet, but Gary had funny dice and they enchanted him. At first, polyhedral dice only came from vendors in Japan and the United Kingdom, so getting a set required significant time and money. But by 1972, polyhedral dice started arriving from domestic sources. Gary recalled buying his first set from a teacher-supply catalog. In 1972, Creative Publications of California started selling 20-sided dice in a set of polyhedrals, and word spread among gamers. By 1973, Gary wrote an article touting funny dice. “The most useful are the 20-sided dice,” he explained. The original d20s came numbered from 0 to 9 twice, so most gamers rolled twice to generate a percentage from 1-100. Gary noted that gamers could do more. “Color in one set of numbers on the die, and you can throw for 5%—perfect for rules which call for random numbers from 1-20.” As an example, he mentions being “busy working up chance tables for a fantasy campaign game.” Gary found his new d20 so irresistible that he changed Dave’s 2d6 to-hit tables into D&D’s d20-based system.

Descending Armor Classes

As Gary reworked his attack table, he discovered that switching to descending AC numbers created a mathematical elegance. Game historian Jon Peterson describes how this system appears in a draft of the D&D rules. “If you were a first-level fighter rolling to hit, the number you needed was equivalent to 20 minus the armor class of your target. To hit AC 2, you needed an 18, to hit AC 3, a 17, and so on. Armor class descended to make it easy enough to calculate your needed roll that you wouldn’t even have to consult a table.”

If D&D had settled on this system, we might now be rolling a d20 to hit, adding the foe’s AC, and trying to reach a target number based on our character.

D&D reached players with a muddled system that kept descending armor classes, but hid any reason for the scheme. So players wondered why lower armor class represented better protection. Usually, bigger is better.

What happened?

When Gary expanded D&D to account for a greater range of levels than 9, he lost the mathematical simplicity. While the draft rules just present to-hit numbers for fighters up to level 9, the published D&D rules extend the table up to level 16 and beyond. To keep a steady advancement over a greater range of levels, Gary reworked the table and broke an elegant design. This left a system where players just used armor class to reference a row in a table and where intuitive, rising numbers could have worked just as well.