Armor as Dice: Keeping the Mystery

Armor as dice is a good way of simplifying and speeding some aspects of GURPS combat. It makes it pretty easy to determine if an attack penetrates armor – do the damage dice exceed the armor dice? If yes, injury occurs. If not, it doesn’t.

Simple and binary. Maybe too much so. In my Alien Menace game, when +Peter V. Dell’Orto or +Jake Bernstein got tagged by a blaster for 3d(5) against 10d armor there was no doubt as to the outcome – you were going to take 1d injury per shot. Period.

In that case, the chance of injury was 100%, and the average injury was caused by 3.5 points of penetration, maximum 6 points.

In rules-as-written GURPS you’d roll the 3d damage against 1/5 of DR 35 or DR 7. That’s about a 12% chance of no injury at all, average damage was 3.68, with a maximum of 11 points. You get an injury more than the maximum 6 points using armor as dice about 20% of the time.

If I increase the overmatch by as little as 1d (3d penetration vs 1d effective armor, or getting hit with 3d(10) instead of 3d(5), normality reverts itself, with 1% chance of getting by unscathed, and a tiny fraction of the time getting higher than the max Armor as Dice value of 12. 

So this is really an extension of the edge case of when penetration is more than armor, but by less than about 1d.

I think the solution to the problem, such as it is, is that if penetration less armor is lower than or equal to 1d+1, add 1d-4 to the penetration and roll it. Sometimes it’ll come out as a non-penetration, sometimes you’ll get in a few extra HP . . . but mostly it’ll keep the right flavor. You either totally overmatch the armor and always cause injury, or the blow pings off and is no real threat.

But as it happens, the deliberate challenge I posed to my players – weapons that just barely overmatched their torso armor – fell right smack into an edge case.

Who’d a thunk it?

Parting Shot

This post started as me wondering how to keep the mystery for the players. They know their damage rolls (usually but not always 6d for the rifles), but by only rolling injury, they know exactly how strong their foes’ armor is. That means I have to roll all damages (which is less fun for them) if I don’t want to give key bits of tactical data away, such as how strong the armor is. 

That’s a real downside to Armor as Dice, since if you roll at all, you are either in the middle of the edge case or blasting through.  Maybe that’s OK, but I like the feeling as a player of rolling my hit and damage rolls, then seeing the effect. In a +RPTools world, or +Roll20, this is often done as a macro: Bob rolls 10 against a skill of 14, succeeding by 4. He hits twice, and rolls 6d6 and 6d6 for 16 and 29 points of damage if his foe fails to defend. Very common MapTool and Roll20 macros there. When playing on a VTT, that sort of automation does speed the game.

For Alien Menace, I’m not too worried about metagame knowledge from my players – they’re long-time gamers, authors, and all-around good guys. But as a general case, while I like armor as dice for many reasons, this isn’t one of them.

A solution by +Luke Campbell offered by Varyon


Over on the GURPS Forums, Varyon comments that one thing that would fix this quite a bit is to change “roll injury as Nd” where N is the penetration dice less the armor dice to “roll injury as 1d x N, where N is still the same.

So the players, on any injury, are rolling 1d. No information need be given out other than the fact that armor was penetrated. Bonus, from my perspective, is it increases the variability of injuries. If you like grazes and hitting the vitals with a 1d roll . . . I wonder if it can be the same roll. If you slam down a 1, you check to see if it was a graze or not (with N being max damage), and if you roll a 6, you have hit something important, and can increase the damage as a result.

Bah. That’s another post. For this one, I think treating Nd+M as 1dxN+M is the answer I was looking for.

10 thoughts on “Armor as Dice: Keeping the Mystery

  1. Why not add 1d-4 to *all* damage rolls? Or even 2d-7? It is easier to remember and won't matter much on the bigger dice pools anyway.

    As for PC knowledge, I could see going in two different ways:

    A. Not only allow the players to know the explicit number of dice when they hit, but when they are damaged have them roll their armor dice vs a target number. Players get to roll more, which tends to make them happy. (So when they're hit, instead of rolling 1d (or 2d-4 or whatever) for the enemy, have them roll 2d vs. 10 and the shortfall is the damage they take. This isn't symmetrical, but it is elegant and fun.)
    B. Require damage dice to have at least N odd colored dice. (That is, N dice that are easily distinguishable from the others). Then it is easier for the GM to subtract off some dice. (And it doesn't have to be the complete armor either. If the enemy is obviously armored (GM knows it is 3d), tell the players to roll two fewer dice and subtract off the yellow one yourself.)

    1. "Why not add 1d-4 to *all* damage rolls? Or even 2d-7?"

      Could; but it only matters if the damage is 1d+1 or less larger than the armor. Mostly because it's another math step, and it complicates automatic character sheets like GCA.

      Point A: I'm not sure I follow what you're trying to do here, so I can't comment.

      Point B: I play exclusively on a VTT, so requiring colored dice doesn't work for me.

    2. A: If a player has N dice of armor vs a X dice attack, instead of having the NPC attacker roll (X-N) dice, have the players roll (X*3.5 – Nd6) yes, the players know the enemy damage, but they get to roll dice to see how well they do. This makes many players happy for obscure reasons.

      B: Can you make your VTT display a list? Nd6, d6, d6, d6 would work equivalently.

    3. That just inverts the usual players roll damage, subtract DR as constant. It's legit as a method, esp with a way to limit variability of protection but it's not something that will appeal to me or my players I think.

  2. I'd second Martin's idea: make Nd+M damage into (2d-4)xN+M damage. It gives damage a slight curve, so you don't just have 6 linear positions, and gives you a 1 in 36 of doing more than "maximum" damage. Treat rolls of 4 or less as 1/2, rounded up.

    So if Pete's character gets his by a heavy plasma doing 6d(5) damage with his DR 10d armor, he'd take 4d damage, rolled as (2d-4)x4. Possible damages:

    Roll Dmg
    2,3,4 2
    5 4
    6 8
    7 12
    8 16
    9 20
    10 24
    11 28
    12 32

    Damage is swingy, but not as swingy as 1dx4 (equal chances of 4, 8, 12, 16, 20, or 24). Average damage is a little lower (12.8 versus 14) as is the minimum damage, but maximum damage is a little higher.

    It also has the advantage that players can't tell if their weapons are almost penetrating armor: they always roll 2d-4, and on very weak hits you just subtract another 3 instead of mulitplying.

  3. The 1d x multipliers is a good way to do gun damage. I've had that on my "for my next post-apoc game" list for a while. A 3d pistol doesn't roll 3d6, but rather 3 x 1d6, and does 3, 6, 9, 12, 15, or 18 damage. That fixes the "assault rifles always do average damage" issue, too.

    For the other problem, you can always implement the "graze" approach – hit by 0 or defense roll missed by 1 means reduced damage. So 10d vs. 8d armor might do 5d instead, and not penetrate. Criticals will either use the table, or, if they do max damage like in Basic Combat, just compare the max as dice. 6d6 = 36 = about 10d, and it penetrates based on that, and would get 2d past that 8d armor I mentioned.

    Just throwing those out there so I don't have to add 1d-4 or 2d-7 to my die rolls when I fire 12 times a second.

    1. My suggestion would be that you just roll 2d for all gun damage, and then the GM subtracts 4 (for solid hits) or 7 (for grazes) and multiplies it by the hidden adjusted multiplier from your gun damage and the armor value.

      So if you hit a mutonoid with 4 shots from your 10d SAW, and 2 shots hit his torso (armor value 10d) and 2 hit his face (armor value 7d), with damage rolls of 5, 12, 4, and 8, then the mutonoid takes 0 and 5 injury to the torso and 2 and 12 injury to the face. No extra hassle for you, and the GM doesn't provide you any information about how good the armor is.

  4. Since you are using a VTT, you could write a damage rolling script that outputs sequential damage amounts based on the number of dice. For example for a 6d6 weapon with the die roles (5, 3, 1, 6, 2, 4):

    1d6: 5
    2d6: 8
    3d6: 9
    4d6: 15
    5d6: 17
    6d6: 21

    This would allow the players to roll damage, but only you would know how many of the dice got used to calculate the damage.

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