Handling Warfare In Core Rules Combat

Military Swarms

I wanted to find a way to represent groups of soldiers moving around a battlefield and clashing with each other while also being able to represent individual creatures in the middle of said conflict. For example, an adventurer standing in a battle hammering his way through heaps of soldiers, or mobs of peasants revolting with only one squad of guards to control the chaos. I thought long and hard on this and got an idea: Giant swarms.

Swarms are a type of mundane creature found in the MM on pp.337-339. All of them are composed of tiny creatures which have their own individual statblocks. All swarms have properties in common with other swarms, and each swarm has properties in common with its base creature. Thus, it is possible to extrapolate the rules by which theoretically any creature can be turned into a swarm... even Tarrasques. (Rules pending on flocks of ancient dragons, friends. Their wings shall blanket the sun!!)

There are pregenerated statblocks for generic NPC types in the MM starting on pp.342. By making swarms out of NPCs, you can represent large groups of people acting together with a mob mentality or as an organized combat unit. Using these inferences and a bit of brute-force creativity, I was able to make a number of generic combat groups and run tactical combats involving them in a white-room theoretical encounter. I also ran them up against some white-room generated PCs (lacking magic gear weapons of course) to fine-tune the estimated challenge rating.

To Make A Swarm:

• AC remains the same
• A swarm is at least 2 size classes larger than the base creature. (If this increases the size beyond gargantuan, simply increase the occupied space by the gargantuan creature.)
• Multiply HP by estimated count of creatures (The number that can fit or squeeze into new size class floor area.)
• All abilities remain the same except STR, which typically increases by an arbitrary value. I will keep STR close to the same, because at medium size the only meaningful change is carrying capacity, which is already covered by the size category increase.
• A swarm can occupy the same space as other creatures and can pass through an opening large enough for one of its constituents.
• A swarm's melee attacks can target creatures occupying the same space as the swarm.
• A swarm's attack is generalized to randomly determine the damage with an even or peaked distribution maxing out at half damage, with half the damage dice when the swarm is reduced to half health. (For example, a swarm of 24 rats, dealing 1 damage apiece, could deal a maximum of 12 damage in a single melee attack, with the other 12 rats running around. A peaked distribution is achieved with 2d6. The attack deals 1d6 when HP<50%.)
• Swarms have Damage Resistances to bludgeoning, piercing, slashing
• While the swarms of tiny creatures have a bunch of condition immunities, all of these seem to be more because it's a whole bunch of tiny things, not because it is a swarm.

Building Armies

While planning all of this, I did a little research and put together this information, for those who want to represent actual military engagements.

A squad consists of 9 men; 8 privates in two sections, and a corporal to lead them. One of the privates may be promoted to lieutennant corporal to act as an assistant and replacement to the corporal. Thus, a unit is a swarm consisting of 9 medium creatures; a huge creture. If mounted, a squad's movement speed increases to 60ft and their size class becomes gargantuan.

A platoon consists of 2 squads and is lead by a sergeant.

A company consists of 2 platoons and is lead by a captain.

A battalion consists of 4 companies and is lead by a captain.

A regiment consists of 2 battalions and is lead by a Major.

A division consists of 3 regiments and is lead by a Commander.

A corps is 2 divisions and lead by a Colonel.

An army is 2 or more corps and lead by a General.

Mob (Swarm of Commoners)

Huge swarm of medium humanoids, any non-lawful alignment

AC 10
HP 36
Speed 30ft

STR 10
DEX 10
CON 10
INT 10
WIS 10
CHA 10

Damage Resistances bludgeoning, piercing, slashing
Senses Passive Perception 10
Languages Any one language
Challenge 1/2 (100xp)

Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a medium humanoid. The swarm can 't regain hit points or gain temporary hit points.

Actions
Club Melee Weapon Attack: +2 to hit, reach 5ft, one target, Hit: 8 (4d4) bludgeoning damage, or 4 (2d4) if HP<50%

Band (Swarm of Bandits)

Huge swarm of medium humanoids, any non-lawful alignment

AC 12
HP 99
Speed 30ft

STR 11
DEX 12
CON 12
INT 10
WIS 10
CHA 10

Damage Resistances bludgeoning, piercing, slashing
Senses Passive Perception 10
Languages Any one language
Challenge 5 (1800xp)

Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a medium humanoid. The swarm can 't regain hit points or gain temporary hit points.

Actions
Scimitar Melee weapon attack: +3 to hit, reach 5ft, 1 starget, Hit: 20 (4d8+4) slashing damage, or 10 (2d8+2) if HP<50%.
Light Crossbow  Ranged weapon attack: +3 to hit, range 80/320ft, 1 starget, Hit: 20 (4d8+4) piercing damage, or 10 (2d8+2) if HP<50%.

Guard Squad (Swarm of Guards)

Huge swarm of medium humanoids, any alignment

AC 16 (Chain shirt, shield)
Hit Points 99
Speed 30ft

STR 15
DEX 12
CON 12
INT 10
WIS 11
CHA 10

Skills Perception+2
Damage Resistances bludgeoning, piercing, slashing
Senses Passive Perception 12
Languages Any one language
Challenge 5 (1800xp)

Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a medium humanoid. The swarm can 't regain hit points or gain temporary hit points.

Actions
Spears Melee or Ranged weapon attack: +5 to hit, reach 5ft or thrown range 20/60ft, 1 target. Hit: 16 (4d6+4) piercing damage, or 8 (2d6+2) if HP<50%.

Miltary Squad (Swarm of Veterans)

Huge swarm of medium humanoids, any alignment

AC 17 (splint)
Hit Points 522
Speed 30ft

STR 16
DEX 13
CON 14
INT 10
WIS 11
CHA 10

Skills Athletics+5 Perception+2
Damage Resistances bludgeoning, piercing, slashing
Senses Passive Perception 12
Languages Any one language
Challenge 8 (3900xp)

Swarm. The swarm can occupy another creature's space and vice versa, and the swarm can move through any opening large enough for a medium humanoid. The swarm can 't regain hit points or gain temporary hit points.

Actions
Multiattack The brigade makes two longswords attacks. If they have their shortswords drawn they can also make a shortswords attack.

Longswords Melee weapon attack: +5 to hit, reach 5ft, 1 target. Hit: 28 (4d8+12) slashing damage, or 14 (2d8+6) if HP<50%, or 32 (4d10+12) slashing damage if used with two hands, or 16 (2d10+6) if HP<50%.

Shortswords Melee weapon attack: +5 to hit, reach 5ft, 1 target. Hit: 24 (4d6+12) piercing damage, or 12 (2d6+6) if HP<50%.

Heavy Crossbows Ranged weapon attack: +5 to hit, range 100/400ft, 1 target. Hit: 20 (4d10) piercing damage, or 10 (2d10) if HP<50%.

Results

A single band can wipe out a guard squad with ease. Though they have a lower hit rate, they deal much more damage at a time. However, their success is highly dependent on the initial few rounds. Once the band starts winning, it sets off a death spiral for the guard squad that is hard to climb back from. The result is that a guard squad will sometimes smash a band, but a band will usually win at heavy loss. Two bands is enough to eliminate a single guard squad with ease, and two guard squads will do the same to a single band. Neither is meaningfully threatened by a single mob. It would take many, many villagers to overwhelm a raiding group or an oppressive militia. A military squad, however, will wipe out all of the above with ease. They have phenomenal HP making them very hard to slog through, good attack bonuses, extra damage output, and high damage per attack even after being reduced to half power. Based on CR, a single unmagical character needs to be at least level 12 before they can meaningfully threaten a military squad, and even this is approaching a deadly encounter for them.

This all feels about right for a low-magic military type campaign. I'm satisfied with the results.

There is one weird thing though: swarms create a loophole in the rules regarding unit positioning in grid combat. Because there is no rule controlling unit layering for units that defy the "one unit per space" rule, there is no limit to how many swarms can occupy a single space! I guess they figured no DM would be savage enough to drop more than one swarm at a time on a single PC. However, once you have swarms that occupy multiple grid spaces, overlapping becomes common. I'm fine with single-layer overlapping, it really gets across the idea that the soldiers are all crammed in together in a chaotic mess. Beyond that though it gets a little ridiculous. So, I have a variant rule for those who would use these creatures:

Corporeal creatures which can occupy the same space as other creatures fill the remaining occupied space completely, preventing other such creatures from occupying the same space. You may only have a maximum of two corporeal creatures occupying the same space at a time.

So you could do things like cram 2 squads on top of each other, packing your soldiers shoulder to shoulder to make a group that can't be infiltrated by an attacking squad. Or if a band was being attacked by squads from two sides, the two squads could both overlap part of the band but no part of either squad could overlap each other and the band at once.