Quickie Mass Combat Rules

I came up with some streamlined mass combat rules to handle a battle in my Reavers campaign with 30+ participants on each side.  It worked pretty well, so I thought I’d share it.  I didn’t want a huge system, but I wanted something that would work smoothly, that would incorporate the PCs organically without turning into some weird “minigame” or requiring them to be commanders.

Quick Mass Combat Rules

Army Builder ™

Break each side up into units of n creatures, where n=5, 10, or whatever makes sense for the scale of the conflict.  Units should be mostly homogeneous.

Unit Initiative = Median initiative of the creatures in the unit.

Unit HD = Total HD of the creatures in the unit.

Unit hp = Total hp of the creatures – break them up into n boxes of equal hp, one box per creature.

Unit AC = AC of each creature.

Unit Move = Slowest move of the individual creatures.  Loosely track units on the battlefield so it’s clear who they’re in contact with.

Unit Attack = Normal attack bonus of the creatures + ½ times the number of creatures in the unit.  (10 creatures = +5 attack bonus.)

Unit Damage= normal damage + the number of creatures in the unit.  (10 creatures = +10 damage.)

Saves = save of each creature.

Targeted spells can only take out the appropriate number of individuals.

Area effect spells, apply as unit damage.  Might not be “fair” to the fireballers, but whatever.

Named NPCs and PCs can engage specific targets in the unit, and get engaged by them separately from the unit attacks.


Units roll once to attack other units using their unit attack versus the other unit’s AC.  If they hit, they roll damage, duh.  As a unit takes damage, you cross off boxes for each creature-sized increment of damage they take.  You can “half cross” off a box for leftover damage that’s about half a creature’s  hit points.  As armies take damage and boxes get crossed off, their attack and damage bonuses based on the number of creatures in the unit go down commensurately.

After that, it’s rulings not rules baby!

Playtest Example

A pirate attack on a Chelish manor house!  There are 30 attacking pirates, and they have a wagon-mounted swivel gun.  Each pirate is a War2 with Toughness – they have 20 hp each, but only attack at +3, do 1d6+1 damage each and have an AC of 13.  The PCs are their “men on the inside”.

The keep is defended by 30 human guards (War1) with only 5 hp, but AC 17 and damage of 1d8+1 (longsword +3).  It is also defended by 10 orc soldiers (was 15 before the PCs got their hands on them) that are War1s but have an effective hp of 22 because of their orcish ferocity, AC 15, and attack with a greatsword at +5 for 2d6+4 points of damage.

I split them up into units of 10.  I slap this up on the whiteboard.

Pirate Unit 1 – AC 13, Atk +8, 1d6+11, 20 hp each

o o o o o o o o o o

Pirate Unit 2- AC 13, Atk +8, 1d6+11, 20 hp each

o o o o o o o o o o

Pirate Unit 3- AC 13, Atk +8, 1d6+11, 20 hp each

o o o o o o o o o o

Manor Guard Unit 1- AC 17, Atk +8, 1d8+11, 5 hp each

o o o o o o o o o o

Manor Guard Unit 2- AC 17, Atk +8, 1d8+11, 5 hp each

o o o o o o o o o o

Manor Guard Unit 3- AC 17, Atk +8, 1d8+11, 5 hp each

o o o o o o o o o o

Orc Soldier Unit 1- AC 15, Atk +10, 2d6+14 melee; Atk +5, 1d8+10 missile, 22 hp each

o o o o o o o o o o

The local evil priest was going to summon some units worth of devils to participate on the manor’s side, but the PCs had to rain on that parade by murdering him.

The pirates approach the gate.  It will take them five rounds to batter the gate down, I estimate, during which the orcs (who are manning the parapets) will get largely free missile attacks on them.  The party caster cleverly pops a fog cloud on the parapet, however, interfering with that plan.  Five of the orcs are manning the gate and five are up in the parapet; the guards are running around getting formed into units.

The PCs break their cover and charge the orcs at the gate and kill most of them.  The other five orcs (giving up on missile fire) have just come down from the parapet and the first unit of guards is approaching as they raise the bar and pirates pour in!

One unit of pirates can enter a round.  The first unit of pirates (reflected on my battle mat by a random big handful of pirate paper minis) moves in and is caught between the remaining unit of 5 orcs and the first unit of guards.  Since the orcs are already down 5 men, their stats are now

Orc Soldier Unit 1- AC 15, Atk +7, 2d6+9 melee; Atk +2, 1d8+5 missile

x x x x x o o o o o

The soldiers hit easily and roll 20 points of damage, killing one of the pirates.

Pirate Unit 1 – AC 13, Atk +7, 1d6+10

x o o o o o o o o o

The guards hit easily too, but roll minimum and only do 12 points of damage, so I only half-cross off one of the pirates.

Pirate Unit 1 – AC 13, Atk +7, 1d6+10

x \ o o o o o o o o

The pirates attack the orcs, hit, and do 15 points of damage.  I arbitrarily round down, because I’m the DM.

Orc Soldier Unit 1- AC 15, Atk +7, 2d6+9 melee; Atk +2, 1d8+5 missile

x x x x x / o o o o

The PCs swing into action and attack the orcs.   This is handled via normal one-on-one combat rules; one doles out enough damage to wipe one out and the other finishes off the wounded orc (he only does 6 points of damage, but as it’s still fresh in my mind that that guy took 15 before, I am generous and x him…).

Orc Soldier Unit 1- AC 15, Atk +6, 2d6+7 melee; Atk +1, 1d8+3 missile

x x x x x x x o o o

The second pirate unit comes in through the gate the next round.  Guard Unit 2 is lining up behind Guard Unit 1 but can’t attack the pirates and Guard Unit 3 is being held in reserve.  One pirate unit attacks the guards and one attacks the orc soldiers; the PCs focus on the orcs.

One attack from Pirate Unit 2 hits and does 15 points of damage, enough to kill three of the guards in one swoop.  Pirate Unit 1 and the PCs manage to mostly kill the orcs that round.  Three pirates are down in Pirate Unit 1 by the time they finish mopping up the orcs.  The PC cleric channels energy to heal the three fallen pirates.  Are they dead or bleeding, I wonder?  I just have him make a Heal check – he rolls very high, so all three are savable with his healing burst.

After this round the battle is clearly turning into a slaughter; the pirates are easily killing multiple guards a round while the guards can only do in about half a pirate a round – logical, given 5 hp level 1 guys against 20 hp level 2 guys.  Guard Unit 3 withdraws and closes the inner courtyard door; sadly for them the PCs have the keys to another smaller door and lead some of the pirates (Diplomacy check to get some to follow them; I figure DC 10 and each 2 additional levels of success gets an additional pirate – they roll high and 5 pirates peel off from wiping out Guard Units 1 and 2 to go with them) on a sally through the barbican and fall upon the hapless Guard Unit 3.  The manor’s commander gets killed at range by one of the PCs.  Then it’s all over except for the plunder.


This system worked great for this size of combat and level of combatants.  It would have more problems for higher level creatures or creatures with all kinds of weird powers.

The players liked it because it was concrete – it didn’t turn into some weird separate minigame, their characters were still on the battlemat fighting as they normally do.

I liked it because it fits on a quarter page.  My tolerance for huge bolt-on rulesets is diminishing sharply with age.

One weakness was that low damage units were very useless…  Next time I will experiment with allowing an additional damage roll per 5 points the attack roll beats the AC by, so that orcs rolling 18 to hit AC 13 pirates get 2 damage rolls.    I tried to do some Excel simulation of that but quickly got bored.

Similarly high AC units might not be as cool as they should be – though I think it comes out OK on average.  There were a couple misses from the pirates against the guards, meaning zero damage for a whole round.

Suggestions are welcome!

P.S.  Yes, I declare these rules Open Game Content, use them, steal them adapt them, mutilate them.

5 responses to “Quickie Mass Combat Rules

  1. rorschachhamster

    I like that a lot and will use it. Thanx for sharing.

  2. I see another LPJ Design release in your future…

  3. Heh, cool. I do want to brush up its handling of magic a little bit; I had to do the healing burst thing on the fly. The playtest combat was light on casters (and monsters) so it could use a little extra development there.

    You’ll be happy to know I’m also working on ship combat rules for next session…

  4. I use a REAL simple rule, the rule of averages (modified by a d20). It involves learning no new rulesets and no new minigames.


    • That does seem like a good simple system. I don’t quite understand the damage part though.

      To use the pirates on guards analogy, you’d say that on average, melee +3 vs. AC 17 is 7 hits out of 20… So for 10 person units, that’s 3 or 4 hits of… Average damage? Or just “two strikes and you’re out?” That part seems not really described.

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