Let’s take a look at The Combat Matrix & THAC0 in AD&D, and find out why it is the best version of Dungeons & Dragons in this How to Play Advanced Dungeons & Dragons series. Buy the AD&D Dungeon Masters Guide Handbook: https://www.drivethrurpg.com/en/product/17004/dungeon-master-s-guide-1e?src=hottest_filtered&affiliate_id=50797
AD&D Combat Computer: https://dlsaga.com/the-dragon-magazine-combat-calculator/
Transcript
Cold Open
In modern D&D, Armor Class is just a number you have to beat. But in 1st Edition, Armor Class is a material. It represents the difference between hide, chain, and plate—and your choice of weapon is the key that unlocks those defenses.
Intro
Welcome to another DragonLance Saga episode. My name is Adam and today I am going to talk about the Combat Matrix and THAC0 in Advanced Dungeons & Dragons. I’d like to take a moment and thank the DLSaga members and Patreon patrons, and invite you to consider becoming a member or patron — you can even pick up AD&D and Dragonlance media or get $10 by signing up to StartPlaying.Games using my affiliate links. I’m referencing the Players Handbook, Dungeon Masters Guide and Dragon Magazine #74 for this information. If I leave anything out or misspeak, please leave a comment below.
Discussion
Preface: Abstract vs. Simulation
The biggest difference between AD&D and modern D&D (like 5th Edition) is the philosophy of combat. The mechanic of rolling a d20, adding or subtracting modifiers, and rolling over a target number is the exact same. The difference is that modern D&D is abstract. AC 18 is just a difficulty class; it doesn’t matter if that 18 comes from Plate Mail or a very high Dexterity. You just roll a d20 and add a flat bonus.
AD&D 1st Edition is a simulation. Here, Armor Class is inherently tied to a specific armor type. AC 3 is Plate Mail. AC 5 is Chain Mail. Because the game identifies what you are wearing, it allows for a layer of strategy that modern games have lost.
Weapon Effectiveness vs. Armor Types
In 1e, weapons are naturally more effective against certain types of armor. Think about the physics: a Longsword is a versatile blade, but it struggles to find a gap in Plate Mail. A Mace, however, doesn’t need a gap—it just needs to crush.
The “Weapon Type vs. Armor Class” table (found in the PHB) gives you specific bonuses or penalties based on your target’s armor. A Long Sword might get a +1 to hit someone using a shield (AC 9), but a penalty against someone in Plate Mail (AC 3). This makes perfect sense! Just as you would choose a silver weapon for a Lycanthrope or a blunt weapon for a Skeleton, a smart 1e player chooses their weapon based on the armor the enemy is wearing. It rewards tactical preparation over just having the “highest damage die.”
The Attack Matrix & The “20 Block”
To manage this, we use the Attack Matrix. If you open your Dungeon Masters Guide, you’ll find the “Attack Matrix” tables. There is one for Fighters, one for Clerics, one for Thieves, and one for Magic-Users. To use it, you find your level on the top and look down to the defender’s Armor Class on the left. The number where they meet is what you need to roll on a d20.
You’ll also notice the “repeating 20s.” For a low-level Cleric, hitting AC 0 requires a 20. But hitting AC -1 through -5 also requires a 20.
This is the “20 Block.” It represents the limit of human skill vs. superior protection. It ensures that no matter how good the armor is, there is always a “puncher’s chance” to land a hit, while preventing high-level characters from becoming mathematically untouchable.
Demystifying THAC0
Now, we can’t talk about the Matrix without mentioning THAC0—which stands for “To Hit Armor Class 0.” While this term didn’t become a household name until the end of 1st Edition and the start of 2nd, the math is right there in the 1e tables.
THAC0 is simply the number a character needs to hit an enemy with an AC of 0.
If you know your THAC0, you don’t always need the table. The formula is: THAC0 minus Target AC equals the number you need to roll. Example: If your Fighter has a THAC0 of 18, and you’re swinging at an Orc with AC 6, you subtract 6 from 18. You need a 12 to hit. It’s a quick mental shortcut that speeds up combat significantly.
Tools of the Trade
I know what you’re thinking: “Adam, that’s a lot of tables to look at during a game!” But you don’t have to do the math yourself. Back in the day, Laura and Tracy Hickman designed the AD&D Combat Computer—a physical dial (published in Dragon Magazine) that allows you to simply turn the wheel to your level and find your target number instantly. You can find a link to print it in the description!
Additionally, if you play online, modern custom character sheets for 1e can automate these calculations, applying your Strength and magical bonuses to the Matrix for you.
Afterword
The Combat Matrix isn’t “clunky”—it’s deep. It turns every combat encounter into a puzzle where your gear choices matter. When you finally land that hit against a knight in full plate because you swapped your sword for a flail, it feels earned in a way that modern “math-stacking” just can’t replicate.
Outro
But that is all the time I have to talk about the Combat Matrix and THAC0 in AD&D. Do you think the Weapon vs. AC modifiers add too much complexity, or do you miss that level of realism in newer editions? Have you ever used the Hickman Combat Computer? Leave a comment below.
I would like to take a moment and remind you to subscribe to this YouTube channel, ring the bell to get notified about upcoming videos and click the like button. This all goes to help other Dragonlance fans learn about this channel and its content. Thank you for watching, this has been Adam with DragonLance Saga and until next time, remember:
The essence of a role-playing game is that it is a group, cooperative experience.
