Armor: Passive Defense vs. Damage Reduction

This week we’re talking about the two most common ways of handling armor in table-top role-playing games and the one I’m going to use in Crowfield.

This post has given me a lot of problems. I know what I want to say, but figuring out how to start it has eluded me. Also, I started out with my preferred position and calculated the numbers to support my case. Looking at those numbers made me realize that I was wrong and that the “inferior” system might actually be superior!

The Terms

I’m stealing two terms from GURPS here:

Passive Defense (or PD) is a way of handling armor that makes the wearer harder to hit. This is the method used in Dungeons & Dragons where wearing armor adjusts your armor class in such a way that your opponent has to roll a higher number in order to score a “hit.”

Example: Swinfar the Barbarian is fighting a goblin. Without armor, Swinfar would have an armor class of 10, meaning the goblin has to roll a 10 or better to hit him. But Swinfar is wearing leather armor, making his armor class 12. The goblin rolls to hit and gets an 11. He misses; he would have hit Swinfar if it wasn’t for that armor!

Damage Reduction (or DR) is a way of handling armor that doesn’t affect the opponent’s chance of scoring a hit, but it reduces (or eliminates!) the damage taken from that hit. This is the method used in Tunnels & Trolls and the fourth edition of GURPS (previous editions used both PD and DR).

Example: Swinfar the Barbarian is fighting a goblin. Swinfar is wearing leather armor, which has a DR of 1. Because armor doesn’t affect the goblin’s chances of hitting, the goblin hits on a 10 or higher. The goblin rolls to hit and gets an 11: a hit! He rolls for damage and gets a 3. Swinfar’s armor soaks up a point of that damage, meaning that Swinfar only takes 2 points.

My Druthers

Does it really make sense that wearing armor makes you harder to hit?

If anything, might it not slow you down just a little bit and make you ever so easier to hit?

Once you’re hit, doesn’t it make sense that the armor would reduce or eliminate the damage you would otherwise take?

These were all my thoughts back in 1985 when Ernie first introduced me to Man to Man, the game that would eventually become GURPS. These were also my thoughts when I sat down to start writing this post.

Thoughts & Numbers

So, if I want to add damage reduction to Crowfield, the rule changes would be pretty simple:

• AC is now equal to 10 + DEX bonus + Shield bonus. Armor doesn’t make you harder to hit. Shields are used to block blows, so I still count them as AC adjustment.
• Armor provides the following DR:
  • Leather: DR1
  • Chain: DR2
  • Plate: DR3
• Magic armor adds the bonus to the DR. Seeing that all weapons do 1d6 damage, a DR of 6 or more would make the character invulnerable in melee except to magic weapons; so DR should never exceed 5

Let’s consider Swinfar and the Goblin again. The goblin does 1d6 of damage, and doesn’t get any bonuses to hit Swinfar.

Case 1, Swinfar is unarmored: The goblin hits 55% of the time. When he hits, he does an average of 3.5 hit points. That means that the goblin inflicts, on average, 1.925 hit points of damage per round.

Case 2, Swinfar is wearing plate (DR3): The goblin still hits 55% of the time. But now when he hits, he does 1d6 - 3 for Swinfar’s armor. Because the roll can’t be negative, the average roll for 1d6 - 3 is 1. In this scenario, the goblin inflicts on average, 0.55 hit points of damage per round.

Excellent! The system is working. By wearing armor, Swinfar is taking significantly less damage from the goblin.

But wait! How does that compare to the original rules? Let’s look:

Case 3, Swinfar is wearing plate (AC16): Because armor makes Swinfar harder to hit, the goblin now hits only 25% of the time. But when he hits, he does the full 1d6 for damage. In this scenario, the goblin inflicts on average, 0.88 hit points of damage per round.

This was my eye opener. Even in the original rules, the armor is effectively soaking damage. And it does it without causing us to have to do subtraction every time the goblin scores a hit.

Conclusion

Back in the 1970’s, when I first started playing D&D, I didn’t fully grok how the combat system was abstracting things. I thought a “to hit” roll was to see if you really hit. I thought hit points measured a character’s health. I covered most of these things in a previous post.

The point is that my dissatisfaction wasn’t caused by the rules themselves, but by my (mis)understanding of them. I won’t take all the blame, because my understanding was based on the way everyone around me understood and played the game as well. I won’t blame them, either, because (as I’ve mentioned before) the original rules are so poorly written the no one can understand them.

Once you get it out of your head that the “to hit” roll is not a single “chop” of the sword against a single opponent the rest of the system starts to make more sense. The abstraction covers the character’s or monster’s performance over the entire round of combat against one or more opponents. The “to hit” roll that indicates a “miss” doesn’t mean that the player didn’t make contact with his weapon, just that any contact he did make was ineffective. Likewise a “hit” that causes “damage” doesn’t even necessarily mean that the opponent was wounded; it just means that the opponent is that much more likely to be defeated.

Additionally, the existing rules are more streamlined.  In the fight above, using the DR system, about half the time the goblin "scores a hit, but it bounces harmlessly off of your armor." So you have to roll to hit, then roll damage only to find out it wasn't good enough to defeat the armor. The single "to hit" roll speeds up play.

I will be leaving the system as is, and not switching to DR.