





One flips through gaming books and sees all of these numbers and hears complex terms like COMBAT MATRIX, descending armor class, combat modifiers. The deal is that it is harder to talk about math than it is to just solve the problem. None of the math problems that we’ll have to solve during play will involve any tool more advanced than a basic calculator, and everybody can use a calculator! Once you get going with the system it forms an algorithm and players can quickly do the math in their head, as it isn’t anything that you don’t do every day anyway.





THAC0 simple means, “To Hit Armor Class 0” When the second edition included this as core, it revolutionized the game, sort of. It was always kind of there, but what it allowed was for us to write down just one number on our character sheets and this would help us figure out what we needed to roll to hit a target regardless of how challenging the target was to hit.





Inventing a system this easy to use took a lot of testing and tinkering, prior to Dungeons and Dragons, the game’s inventers played wargames, and one always had to come up with a system which randomized if a hit was successful or not in a fast and concise manner. Dice proved a great universal method. Once we figure out a system, then we have to figure out how to describe the system so that others can use it as well, which since math is never changing, math is the best way to figure all of this stuff out.





Prior to the THAC0 system, the game designers created Combat Matrixes, tables that when rolled against, told you if you hit or not, some of these were more complex than others, but they all strove to achieve the same goal, the more universal the better.





We get the term Armor Class from Wargames as well, specifically Naval Combat where different ships had different amounts of armor to protect them, players found that a descending armor class was more functional in the game than ascending Armor Class systems, but in Naval Combat, the ships AC never changed, the same goes for all mass combat systems, so when Gygax wrote the Chainmail Rules, he used a universal Armor Class system shared by all of the troops in a battalion.





When it came to D&D, the terminology was kept, and we have the AC system, but instead of a fixed number, the number for an individual target isn’t constant. A ships ability to hit another ship always stayed the same, but with individuals we wanted to simulate improvement, this required some additional thinking, and more complex combat matrixes.





In the first edition of AD&D, players wanted lots of ways to fight and modify things to make an opponent either easier or harder to hit depending upon choices that each player made. The AD&D system kept this matrix hidden from player view by putting it in the DMG, you rolled the dice and the DM told you if you hit or not. This provided a mystery because you didn’t know how the DM achieved this target number, as the DM wanted to keep all of the stats secret. It didn’t work, players caught on to the formula, either from sneaking a peek at the DMG or just playing enough to realize the DM’s system. This also required even more work on the DMs part, and users were coming up with their own methods of changing it up to make it easier for them to come up with a universal system that could still be modified quickly.









Detractors instantly rejected this method, saying that it dumbed down the game, and others claiming that it made combat too difficult to figure out. 2e was still learned, not by yourself and on your own, but by playing the game with others who had been taught by somebody else who already knew how to play the game. If one looks at the THAC0 system by itself, it can be confusing, but all it takes is the player sitting next to you to help you figure out if you hit or not for a couple of sessions before it is permanently implanted in your brain in a way that will never go away . . . ever.





In third edition, they changed descending AC to ascending AC which really threw 2ers for a loop. You play with this system enough it becomes ingrained in you and even something as simple as making AC 1 as bad is enough to throw you off, so I know that going back to a descending AC is the same way for others, just know that us holdouts didn’t refuse to move on to 3e because of ascending AC, when it comes down to it, 3e is too ridged of a system when you get used to the freedom that earlier editions allow.





So what is the formula? Well, it is easy. Look at the THAC0 grid, and find the number you need for your level. This number never changes, it doesn’t float around, and it is always the same. When you have a modifier you don’t apply it to your THAC0, you apply it to your opponents Armor Class. Thus, a sword+3 doesn’t change your THAC0, it changes your opponent’s AC from 4 to 7. Penalties also change your opponents AC, if you have a -2 to your roll, you take it from his AC, which turns an AC of 4 to an AC of 2.

Simple yet elegant, isn’t it! Suddenly all of the complaints that it requires to much math are dismissed. The problem wasn’t the system; the problem was that people kept trying to modify their THAC0 numbers.





Once you get it figured out, and can start playing with more advanced rules, the THAC0 system still functions. Now you can have missile combat and melee combat taking place in a forest at the same time using the same ruleset without having to change anything. The floating AC rule allows combat to flow smoothly and naturally so that both sides can focus on play without having to get all technical.





IS THE THAC0 SYSTEM BROKEN?





Broken, no; subjective, very. If you up and decide to use a different method of deciding how combat is resolved, then you aren’t playing AD&D. Taking it out makes all of the other rules in the AD&D system not work anymore, period. The game encourages you to tinker with the AC system, applying modifiers as you see fit to factor in advantages and disadvantages depending on where exactly each battle is taking place. Can you get carried away with modifiers? You bet! And the AD&D system will let you do this, but the DM can always decide exactly how many or how few of the optional rules and modifiers work best for their particular game.





We had to go here, I hope that I was able to clear up some confusion about how the THAC0 system is supposed to work, because it isn’t this mechanic that weakens the game, but what LOTS of people do with it that does, which we can now explore.

It was a bunch of computer scientists at UCLA who were playing the game regularly that figured out that you didn’t need the entire combat matrix for the game to function, that if you just told them how to hit AC 0, and add all of the modifiers separately, you just needed to know one single number. Gone were the pages and pages of overly complex combat matrixes. For whatever reason, Gygax didn’t like it, it is briefly mentioned in the DMG, but dismissed as too simple. Dave Cook however saw it as the ever elusive universal system so it was officially added to the 2e mechanics, and it made play a lot faster.