Calculate the DPS (Damage Per Salvo) averages of a weapon to a given defense profile in the grimdark table top war game Warhammer 40,000 by Games Workshop.

Data won’t be provided here. Maybe at some point we can import data from the same source that BattleScribe uses. For now, you have to do your own data entry using data sources you legally purchased.

I haven’t connected all of the functions up yet. I had it working deep in my notes file, but I wanted to both document and open source this work. I should have it fully functional soon.

Clone this repository. It’s not published yet :(

Emacs, org-babel, your favorite codex, and the codex of your nemesis.

You need a table with an attack profile and a separate table with a defense profile.

The attack profile table is a table with the following fields:

name

The name of the profile. Could be the weapon name, but might also include the yielder. This is for human identification and is arbitrary. A name could be “Shuriken Pistol” but it could also be “Farseer Shuriken Pistol”, because Farseers use a different ballistic skill. You will need this name to select the row for computation.

bs

The ballistic skill of the attacker.

a

The number of attacks (for fights) or shots (for shooting) this attack profile has.

s

The strength of the attack. Must be a number. Cannot be “2x” like it is seen in some printed profiles. You must resolve the final strength.

ap

The armor (armour) penetration value of the attack.

dmg

The damage of the attack. You can use dice notation here. So it can be 2, d6, d3, d3+3, etc. Does not yet support 2d6.

special

Not yet used. This is reserved for special behaviors of weapons, such as shuriken weapons that switch to AP -3 on a wound roll of 6, or one of the 2d6 damage but only take the highest result. Ideally this will be terse yet readable labels.

The attack table itself needs a name which you can use to pick it for computation.

The order of the columns isn’t important, though examples will follow a consistent format that loosely follows the order of calculations and/or the profiles listed in the codeces.

Example:

Hey look I made Craftworld Eldar weaponry useful!

#+name: aeldari-fixed-weapon-profiles
,| name              | bs | a | s | ap | dmg | special |
,|-------------------+----+---+---+----+-----+---------|
,| Shuriken catapult |  3 | 4 | 4 |  0 |   1 |         |

The defense profile is a table using the following columns:

name

Name of the defender. It could represent a specific model or even a specific model under specific circumstances. It could be something like “Plagueburst Crawler” but might also be “Axe Wraithblades with Fortune”. Use an identifier that is helpful to you.

hit

This is any to-hit modifiers imposed by the defender. This might be due to cover or some other indicator that would reduce the roll value to hit. This is not a ballistic skill modifier, which would normally be indicated on the attacker profile. Most entries will have this at 0.

t

The toughness of the defender.

v

The normal armor save of the defender. Use 7 if there is no armor save.

i

The invulnerable save of the defender. Use 7 if there is no invulnerable save.

res

The damage resistance. Not given a name under normal circumstances: The damage resistance is typically stated like “reduce the damage by one to a minimum of one”.

fnp

“Feel No Pain”. Not a formal rule in 9th edition - it comes up frequently enough though and is more or less exactly the rule as it was in prior editions. This is the ability to shrug off damage (after it is unsaved and the damage value is computed). Use 7 for no Feel No Pain.

special

Reserved for special defender properties. Not supported yet. This will be a terse but human friendly set of names. An example of a special rule that could be supported is the Eldritch Wraith Construct rule, which reduces AP -1 values to AP 0.

pts

Points value. Not used yet.

army

The army this belongs to. One example is “Death Guard”. This is a human friendly display name. The defense table could include hypothetically every defense profile and so there is utility on filtering or sorting by army.

You might notice there is no wounds value anywhere. This is because it is not yet relevant for computation.

The defense table itself needs a name which you can use to pick it for computation.

,Nobody kills a Deathshroud Terminator. Nobody.
#+name: dream-deathshroud-terminiator-defense-profiles
,| name                   | hit | t | v | i | res | fnp | special | pts | army        |
,|------------------------+-----+---+---+---+-----+-----+---------+-----+-------------|
,| Deathshroud Terminator |   0 | 6 | 2 | 4 |   1 |   5 |         |     | Death Guard |
,| Deathshroud Champion   |   0 | 8 | 2 | 3 |   1 |   5 |         |     | Death Guard |

Here’s an example using some Craftworld Aeldari weaponry against some Deathguard units. Data tables are not included.

(require "40k-dps")
(append
  (wh40k/damage-probability-all-weapons-to-defender
                           "aeldari-weapon-profiles"
                           "defense-profiles"
                           "Pox walker")
  (wh40k/damage-probability-all-weapons-to-defender
                           "aeldari-weapon-profiles"
                           "defense-profiles"
                           "Deathshroud Terminator")
  (wh40k/damage-probability-all-weapons-to-defender
                           "aeldari-weapon-profiles"
                           "defense-profiles"
                           "Plagueburst Crawler")
  )

Taking the results above:

This means firing an AML starshot missile at a Pox Walker will shave off more than than half a wound. In the game all damage is done in whole numbers, so this more-than-half wound is meaningless by itself. It’s important to understand that this is an average, and averages only see consistency in high sample sizes. Or at least the probability of the average reflecting the reality approaches 1 (100%) as the sample size (number of attempts) approaches infinity.

We aren’t doing infinite rolls, but we are usually firing more than one thing, possibly more than one time. The number starts to get more useful when outcomes are considered. In other words, instead of expecting a single missile to remove half a wound from a pox walker, consider that a unit of 20 pox walkers could be killed by about 24 missile shots (20 / 0.83). Even fewer if you use the new blast rules! With a group of 20, we get a full 6 shots, so that’s 20 / 1.667 = 12 (even) salvos needed.

That number could vary quite a bit, but it should give you an idea of the action investment you want to make. In a 5 turn game, dedicating a single missile launcher to them wouldn’t achieve the result of blasting them off an objective, let alone doing so in a timely manner. However a full War Walker squadron (three units) that packs two AMLs each means you could have them dead or close to dead in two rounds, and almost certainly all of them in 3. Even in that case, they are still scoring for at least two turns. By the Emperor, Deathguard are tough!

Scatter Lasers are interestingly a close second. Shuriken Catapults are about a third of the effectiveness, but might be easier to shore up in numbers. It takes ~12 AML shots to bring them down (6 War Walkers), or 36 Guardian Defenders. The Defenders are roughly 2x cheaper in points, but the 12” vs 48” range difference might make it worth the points investment.

Remember all of this is an approximation. In our Pox Walker blast example, the blast rule would have diminishing returns as the number of models went down. The current system does not account for this, and is an exercise left to the consumer.

The program does also not handle clever wound allocation. For example, a Deathshroud Terminator has three wounds. If a unit of 3 is attacked and the attacker produces 1, 2, and 3 damage, the defender could allocate 2 and then 3 on the first model, and 1 on the next model. So one model is lost, even though enough damage was generated to destroy two models (six total damage). At the moment, 40k-dps doesn’t even know about the Wounds characteristic, so it can’t handle this yet. However it would be great to get to one day.

Make something up, like Squats against… other Squats?