Split your army into “forces”, where a force is a mixed group of attackers working together towards common goals. These forces are somewhat fluid, but it takes a little bit of accounting to turn creatures into forces, so you’ll mostly figure out what happened to individual creatures in the aftermath. Sometimes, individual creatures can be a force unto themselves, but numbers get a pretty big “lift”, so you’ll usually not want that. Forces can — should! — be made of disparate types of creatures at whatever scale you’d like, though you’ll generally want to abstract things, so the scale should include at least one side of at least dozens and ideally hundreds of creatures.
This engine is an “offline” engine: it doesn’t try hard to model the actual effects of which creatures are strong against which other creatures, and just generally gives somewhat reasonable results. If PCs are involved and fighting at the front lines, this engine will generally not produce interesting combat, but instead fast forward to the next scene with everyone having taken a little damage and the question of who proves victorious decided.
A force has statistics: it has a Strength (the sum of the challenges of creatures that make it up, which is sort of its hit points), and its damage bonus which is its Strength to one significant digit, divided by 10 (so for instance, a strength of 11 and of 19 both have a damage bonus of +1; strength of 25 and 28 are both +2, 111 is 10, 999 is 90, and 1024 is 100). It also has a magnitude which is just the number of digits in its strength (a strength of 200 would be a magnitude of 3, a strength of 8 would be a magnitude of 1).
The force also has statistics unrelated to its numerical composition: Morale threshold, which is the percentage of the starting strength value at which the force will rout, attempting to flee the combat. This is derived from the wisdom saving throw modifier of its commander. If the forces are substantially immune to fear, use the +10 line; if the forces are substantially resistant to fear, add +5 to the commander’s wisdom saving throw modifier:
Adjusted wisdom saving throw modifier: Morale Strength percentage:
+10 or higher: 0% (only total defeat can cause a rout)
+3 to +9: 50%
+1 or +2: 66%
-1 or +0: 75%
-3 or -2: 80%.
-5 or worse: 95%
For instance, let’s consider a force of a thousand goblins led by a goblin, and a force of a hundred hobgoblins led by a hobgoblin. The thousand goblins are individually Challenge 1/4, which makes them a Strength 250 (magnitude 3, damage 20, morale 187); the hundred hobgoblins are Strength 50 (magnitude 2, damage 5, morale 37). If we were to declare that hobgoblins are fearless (… why aren’t they?) or their commander were particularly bold, the morale threshold at which they route might be decreased to 50%, 25 strength.
A force is also somewhat described by its composition: pikes have vulnerability to damage from archers, archers from cavalry, cavalry from pikes; forces composed of dark-seeing units can see in the dark themselves, and so forth. Combat and damage below will discuss how these are used.
If a force holds a defensive point or piece of machinery, the asset has rules which can modify these, so see below. PCs wishing to aid the war effort will likely be involved at this level, taking and destroying assets on an individual level.
Combat and Damage.
Each exchange of combat represents ten minutes spent getting into position, maneuvering lines of contact, and so forth. Each force rolls for initiative, adding their magnitude as a bonus, then acts in order.
On its turn, a force atomatically makes 1d10 attacks each of which automatically hit, dealing damage to the attacked forces with each hit. Forces take double damage from attacks against which they are vulnerable or in which the attack has advantage, and half damage from attacks against which they are resistant or in which the attack has disadvantage, and none at all against attacks to which they are immune. Each hit automatically cleaves if the strength of a force is reduced at or below its morale threshold.
Named characters in a force which are hit take this damage as hit point damage and expend a spell slot of at least the magnitude of the attacker (or their highest level remaining if there aren’t any of the magnitude of the attacker). Named characters who make up at least 50% of the strength of their force take five times the hit point damage.
If a force wishes to withdraw, it does so instead of attacking, leaving at the end of the round. Routed forces automatically withdraw.
To determine the fate of the individual creatures which had made up a force, simply divide the force’s new (lower!) strength back into individual creatures. If it was a rout, reduce the strength to 1d100% of its value first to reflect additional casualties in the retreat.
Assets: Fortifications and Machinery.
Seige equipment, vehicles and foritications are all basically monsters requiring a crew (often of commoners albeit ones with particular skill) to operate.
The challenge values of an asset (unless otherwise noted) don’t add to the strength of the force it’s a part of as a creature’s would. Instead, it functions somewhat similarly to temporary hit points for a character: a separate pool of ablative damage which can be used to absorb hits. Vehicles and fortifications are generally resistant to non-siege damage, which acts as an additional defensive measure. Half of the damage taken by a fortification is also dealt to the inhabiting force. Remember to calculate the morale threshold of each asset, because a fortress doesn’t have to be destroyed to fall!
If the asset isn’t fully crewed, it cannot be used.
Siege Weaponry. It’s slow and requires subsumption of a crew to operate it. Siege weapons function as creatures instead of as fortifications, adding to the Strength of the force directly. Siege weapons all deal siege damage, that is, full damage to fortifications. To be clear: siege weapons don’t have resistance to non-siege damage.
- Ballista (crew 3, challenge 1)
- Cannon (crew 3, challenge 2)
- Cauldron, Suspended (crew 1, challenge 1/8)
- Mangonel (crew 5, challenge 1)
- Trebuchet (crew 5, challenge 3)
Vehicles. Vehicles are, unless otherwise noted, resistant to non-siege damage. Often they will include siege weaponry to boost their challenge further. Also, they can move around, which is usually considered a perk. Their crew is the minimum number of creatures required to operate and, if not listed, is 1. Remember, these challenges form a separate “pool” of strength beyond that of the
- Airship (crew 10, challenge 6)
- Carriage (challenge 1/4)
- Cart (does NOT resist mundane weaponry, challenge 0)
- Chariot (does NOT resist mundane weaponry, challenge 1/2)
- Galley (crew 80, challenge 7)
- Keelboat (challenge 4)
- Longship (crew 40, challenge 5)
- Ram (crew 4, deals siege damage, fortifications are vulnerable, challenge 1/2)
- Rowboat (does NOT resist mundane weaponry, challenge 1/8)
- Sailing ship (crew 20, challenge 5)
- Siege Tower (crew 4, attacks using a siege tower circumvent fortifications entirely, challenge 4)
- Sled (does NOT resist mundane weaponry, challenge 0)
- Wagon (challenge 1/8)
- Warship (crew 60, challenge 7)
Fortifications. Fortifications are resistant to non-siege damage and likely have mounted siege weaponry. Additionally, a fully crewed fortification doesn’t consume the strength of its crew: they still count towards the strength of the force they’re acting as a part of.
- Abbey (crew 5, challenge 9)
- Guildhall (crew 5, challenge 4)
- Keep/small castle (crew 50, challenge 9)
- Manor (crew 3, challenge 7)
- Outpost/fort (crew 20, challenge 6)
- Palace/large castle (crew 200, challenge 22)
- Temple (crew 10, challenge 9)
- Fortified tower (crew 10, challenge 6)
- Trading post (crew 4, challenge 4)
- Civilian Structure (crew 1, challenge 1/8)