Conditional Everything
I’m a fan of Douglas Cole’s Conditional Injury article. In short, it replaces ablative HP with wound levels, which may accumulate. Where in default GURPS, a 100 HP longship can be carved apart by a hundred knife slashes, you need to inflict at least 10 HP injury to start making a dent.
Conditional Injury has received some attention in blog posts:
- ChaoticGM has two posts on tweaks, and an extra one on rapid fire.
- Mailanka has a deep dive with far more details than I give here, and has used them for space combat.
- GreysonWHY has two posts on combining KYOS and conditional injury.
- Doug himself also posted a small play feedback post on his blog.
- Grayscale a post on how to make it more like GURPS by using individual wounding thresholds. The included table is great, by the way.
Now, this post goes into another direction: What if we rework most of the GURPS damage mechanism to use the same scale as CI?
By default, playing with CI works like this:
- Your target has a Robustness Threshold, that you have pre-computed. For an average human, that’s RT 4.
- After a hit, you roll damage as usual. For a 9mm auto pistol from Action II, that’s 2d+2 pi, so let’s say we rolled 9 damage. As usual, you subtract armour. For a leather coat, that’s 1 DR. 8 penetrating damage make this (table lookup!) Wound Potential 3.
- Then, you get a modifier based on damage type and hit location; pi is -2.
- You then compute basic severity, which is just Wound Potential - Robustness + Severity Modifiers; in this case, it’s -3, which is a Minor Wound.
This jumps between different scales: You have damage in dice until it has penetrated, then it’s in severity. DR is always measured in points, robustness always in severity.
But, instead, we can pull everything together into a single scale.
Conditional Everything
The main observation is that detailed and exact numbers don’t matter. Every step on the severity scale is +50% more injury. We don’t care about small differences in numbers.
Conditional Damage
Every weapon gets its own Wound Potential. That’s just the average damage rolled. As examples, here’s a few weapons from Action II:
| Name | Damage | Wound Potential |
|---|---|---|
| Pistol, 9mm | 2d+2 | 4 |
| Assault Carbine | 4d+2 | 5 |
| Battle Rifle | 7d | 7 |
| Anti-Materiel Rifle | 6dx2 | 8 |
That’s very straightforward to convert. It’s also fundamentally easy to compare. How much is 2d+3 vs 3d-1? Is a weapon doing 3d+2 damage worth upgrading to when your current one does 2d+5? How much do they penetrate?
Conditional Armour
This is more difficult: While we can use directly convert armour values to Armour Potential (an Assault Vest with Plate’s 35 DR become AP 7), we can’t directly subtract AP from the Wound Potential. Otherwise, we’d suggest a 12-pounder cannon (6dx5 damage, i.e. WP10) fired at someone with the aforementioned vest (AP 7) is effectively a penetrating wound of 3, for less injury than a pistol shot at an unarmoured human. That’s, clearly, not right.
Indeed, looking at the RAW GURPS numbers, we get an average of 105 damage for the 12-pounder, of which 35 DR is subtracted. That makes it 80 penetrating damage, for a WP of 9. Clearly, just linearly subtracting doesn’t work.
Instead, let’s look at the extreme first: An Armour Potential that’s the same as the Wound Potential means there’s not going to be any damage: Damage and DR are matched for no penetration. For other values, let’s say that we have a weapon attack of 100 damage (RT 10), and see how much damage gets through for different armour levels (this is without loss of generality, since the scaling stays the same any damage value):
| Armour Potential | Penetrating Damage | Wound Potential |
|---|---|---|
| 10 (DR 100) | 0 | None |
| 9 (DR 70) | 30 | 7 |
| 8 (DR 50) | 50 | 8 |
| 7 (DR 30) | 70 | 9 |
| 6 (DR 20) | 80 | 9 |
| 5 (DR 15) | 85 | 10 |
Looking at these numbers, it’s clear that armour that’s more than 4 levels worse than the weapon just doesn’t protect. I’m not quite happy with “reduce WP by 1” happening at both Armour Potential that’s 3 less and 4 less; this seems to create more cognitive work to remember. I’ll therefore drop the 4 less down to no reduction. That’s an inaccurate representation. In the Action II values above, it makes a difference when shooting an Anti-Materiel Rifle at a non-plate armoured vest: In the simplified case, it’ll not reduce wounding; in the non-simplified case, it’ll reduce wounding to 7 (which then promptly is a Mortal Wound rather than instantly fatal, so, uh, it doesn’t matter much.)
So, the new table is
| Armour is… | Wound Potential… |
|---|---|
| the same as WP | is None. |
| 1 less than WP | is reduced by 3. |
| 2 less than WP | is reduced by 2. |
| 3 less than WP | is reduced by 1. |
| 4 less than WP | is not affected. |
For the armours in Action II, you get the following values:
| Name | DR | Armour Potential | Proof Against… |
|---|---|---|---|
| Ballistic Sleeves | 8 | 3 | |
| Ballistic Leggings | 12 | 4 | 9mm pistol |
| Vest | 12 | 4 | 9mm pistol |
| … with plates | 35 | 7 | Battle Rifle |
Conditional Armour Piercing
Adding armour-piercing options is fairly easy: You lookup the armour divisor on the same SSR table. Then, you modify the Armour Potential above based on this. Common modifiers are:
| Armour Divisor | Change Armour Potential by… |
|---|---|
| (0.5) | +2 |
| (2) | -2 |
| (3) | -3 |
| (5) | -4 |
| (10) | -6 |
This means the “common” AP ammo, used on a pi gun, essentially reduces armour potential by 2, then reduces your own wounding potential post-penetration by 1.
Blunt Trauma
Blunt trauma is very easy to handle—if you’re wearing flexible armour and are attacked by a crushing attack that doesn’t penetrate, you still take Wound Potential -4 injury (no type modifier). For non-crushing, it’s -6.
Variable Injury and Damage Roll
The above results in a deterministic damage procedure—you attack an enemy with a weapon, and they’ll always be injured with exactly the same severity. GURPS does have a damage roll for a reason, though. How can we also get one?
It turns out to be very simple: Assume a weapon with 3d damage. That weapon’s damage roll is the same as a normal GURPS skill roll. When do we “move” between severity levels? When we roll a 3, 4, or 5, we drop severity by 4, 3, and 2 respectively. Roll a 7, and you drop it by 1. On the other extreme, a 15 will be a new severity level.
Simplifying this somewhat (and inverting it, for the “lower is better” skill rolls work at), do the following: Roll 3d. If you roll a 7 or less, you cause one more severity level. 14 or more, and you reduce it by one severity level. A crit fail/success doubles these.
Summary
In total, our new rules look like this:
- Every weapon has a Wound Potential rather than a damage value.
- Every character has a Robustness value rather than HP.
- Every piece of armour has an Armour Potential rather than DR.
- On an attack, you take the Wound Potential of the weapon, and do a damage roll. 7 or less and you increase WP by one; 14 or more and you reduce it by one. Critical failure/success double this.
- If your armour potential is the same as the WP, you take no damage. If it’s 1/2/3 less, wound potential is reduced by 3/2/1. Otherwise, it’s not affected at all. Use the remaining Wound Potential (modified by damage type and hit location as in the original article) to compute final severity.
I quite like these rules: It’s fairly easy to see how armour protects, it avoids the calculations necessary with Conditional Injury, and it still keeps the accumulation features intact.