20:1 mass combat in practice

Here is one huge simplification of old school D&D combat. I’ve written about this before, and I’m sorry if I end up repeating myself.

[Also, I got a bit carried away in this post, so it might sound rambly... you've been warned! ;) ]

Assuming most creatures have 1 HD, deal 1d6 damage, and hit AC 0 only on a 20, each 20 creatures deal 1d6 damage per round against AC 0 on average. So, we could say that unit damage is 1d6 for a unit of 20 creatures.

[In a game like B/X, where you hit AC 0 on a 19–20, the average damage is 2d6 instead of 1d6.]

However, for each point of the target’s AC, 1d6 is added to damage. So, a unit of 20 archers deals 1d6 damage to a unit of 20 bandits, plus 5d6 if the bandits’ AC is 5, or 7d6 if it is 7, etc. Likewise, if your damage is 1d8, then you start with 1d8 and add 1d8 for each point of AC (you can use 1d6+1 if you don’t have many d8s). 

All very intuitive.

You don’t have to roll to hit—just roll damage. Each roll of 4 or more removes one creature from the opposing unit. Rolls of 1–3 can be added together to remove more creatures.

The “remnants” of each wounded unit are immediately added together into new units if they succeed at whatever morale check you deem necessary. This is an abstraction.

So you can easily run, say, a clan of 60 dwarves attacking a lair with 100 bandits with just a few rolls. Shall we try?

Let’s say the bandits have the initiative. The dwarves have AC 4; so each 20 bandits deal 1d6 plus 4d6 damage, a total of 25d6 for 100 bandits. We roll 25d6* and get:

6, 6, 6, 6, 6, 6, 5, 5, 5, 5, 5, 4, 4, 4, 4, 4, 3, 3, 2, 2, 2, 2, 2, 1, 1

[Notice that we could roll each unit separately for more detail; for example, maybe one unit breaks and the other does not, etc.].

16 dwarves are killed immediately from the 6s, 5s and 4s, plus four deaths by adding the rest (3+1, 3+1, 2+2, 2+2; the last 2 is discarded].

20 deaths is very convenient, otherwise we'd have to discuss what to do with units of 17 etc.

But for now, 40 dwarves remain. They pass their morale check and attack. Their damage is 1d8 according to B/X, and the bandits AC is 6. This means 1d8+6d8 for each 20 dwarves, for a total of 14d8:

8, 7, 7, 7, 7, 7, 6, 3, 3, 2, 2, 2, 1, 1

Only 10 kills! 90 bandits remain. By this time, it is obvious that the dwarves, having smaller numbers and having lost initiative, are nearly doomed.

If we attack with only 80 bandits next, we'd roll 20d6:

6, 6, 6, 6, 6, 5, 5, 5, 5, 4, 4, 4, 3, 3, 3, 2, 2, 2, 1, 1

Another 16 dwarves are dead. Now we have 24 dwarves against 90 bandits. Let's "put aside" 4 dwarves and 10 bandits and continue with 80x20. Twenty desperate dwarves attack (7d8):

8, 7, 6, 5, 4, 3, 2

Six bandits killed. 84 left, 80 will attack again:

6, 6, 6, 6, 5, 5, 5, 5, 4, 4, 4, 4, 3, 3, 3, 2, 2, 2, 1, 1

16 dwarves killed, only 8 remain.

By this point, you can decide the dwarves are defeated, captured, or routed. You can easy estimate the losses on the bandit's side (about 20%). 

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And this was not much slower than an usual D&D combat of say, 4 PCs against a dozen goblins. 

This is exactly the goal: you can insert your PCs in this battle, and they could even turn of the tide of the battle.

Assuming the PCs are fighting against bandits, a cleric could cast bless and add 1d8 damage to an unit of 20 dwarves. A mage could fireball 20 bandits in the first turn.

A fighter could kill multiple bandits, although we probably need special rules for that: like in OD&D, maybe give him one attack per level, so a strong level 6 fighter can kill maybe 2-4 bandits per round.

Is this enough to change the tide of battle? Let's try adding a party of three level 6 PCs.

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The bandits attack first, reducing the dwarves from 60 to 40. A fireball reduces the bandits from 100 to 80, and the fighter reduces them to 77. The 40 dwarves, 20 being blessed, roll 15d8 to attack:

8, 6, 6, 6, 5, 5, 4, 3, 2, 2, 2, 2, 2, 1, 1

68 bandits remain. Since we get 5d6 for each 20 bandits, lets roll 17d6 for the 68. Here the GM is averaging and abstracting a bit.

6, 6, 5, 5, 4, 4, 4, 4, 4, 4, 3, 3, 3, 3, 2, 2, 2

About 27 dwarves are left. Let's roll 10d8, assuming a few of them are still blessed. Again, the DM is averaging and trying to get to the right ballpark:

8, 8, 7, 7, 6, 5, 4, 3, 2, 1

Bandits are reduced to 61. Fighter kills 3, MU kills other 2 with magic missiles, cleric blesses again. Now there are 56 bandits, but let's add a twist: 20 bandits attack the fighter. The fighter's AC is 2, so he takes 3d6 damage. 36 attack the dwarves: let's roll 8d6.

6, 6, 5, 4, 4, 3, 2, 1

21 dwarves are left. Roll 8d8 since most are blessed:

8, 8, 7, 6, 5, 4, 3, 2.

49 bandits left, soon reduced to 42 by the PCs. Roll 10d6 against dwarves:

6, 6, 5, 5, 4, 4, 3, 2, 1, 1

14 dwarves left. Roll 5d8:

8, 7, 6, 4, 2

38 bandits left. 20 bandits attack dwarves (5d6) and 18 attack the AC 2 fighter (3d6 or, let's say, 3d6-1). And AD&D fighter is likely to be severely wounded at this point but alive:

6, 5, 4, 2, 1

Only 11 dwarves left, the fighter is severely wounded and the MU out of good spells (of course, if I gave him TWO fireballs they might have won). 

The battle is nearly lost but I want to see it to the bitter end. Let's go!

Dwarves (8, 7, 5, 3) kill 3 bandits. Fighter and mage kill 4 more. Cleric heals fighter. 

31 bandits are left, but now 20 of them decide to attack the cleric. With AC 3, the cleric takes 4d6 damage. Ouch! 11 bandits (6, 4, 2) kill 2 dwarves.

9 dwarves (8, 6, 5, 2) kill 3 bandits. 28 left, reduced to 24 by the desperate PCs. They attack the remaining dwarves, rolling 6d6 (6, 6, 5, 3, 2, 1). 

Only 5 dwarves left, they attack (7, 3) and kill one bandit. the PCs also attack; 19 bandits are left, and they'll finish the dwarves (6, 5, 4, 3, 2). A single dwarf is left.

Now there are 3 PCs and one dwarf against 19 bandits. They manage to reduce them to 15. The fighter, slightly healed by the Cleric, takes 2d6 damage and barely survives. The GM decides the last dwarf falls killing one bandit, and the PCs also attack to reduce the bandits to 10.

The cleric takes 2d6 damage. Bandits are reduced to 7. Fighter takes 1d6 damage, and falls. 5 bandits against cleric and MU. There are two few combatants to keep using 20:1, and at this point I'm guesstimating. Could go either way, but it seems PCs are doomed.

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So, 3 PCs were not enough to win this battle decisively. An additional warrior (or just another fireball) would certainly change things.

Still, the PCs made a significant difference. Instead of 80 bandits, now only a few will remain. In practice, repeated morale rolls (that I skipped) could win the day for the PCs.

Took me a bit more than an hour to write this and took some abstractions, rulings, etc. Seems that dwarves had little chance, even with better armor and weapons, after losing initiative. Even with the PCs, it was basically 100 HDs against 78, and the loss of initiative was a huge big deal.

It was a fun exercise, but probably would be more fun in an actual table with friends. Definitely deserves a few tweaks. I need to give it a try...