D&D 5E Help me make a mass combat system that does what I want

[Sword of Spirit]

WotC gave it 2 or 3 tries years ago in UA articles, but none of the attempts were quite good enough to make it to prime time. While I'd love to see them put out Birthright and include mass combat and domain management rules, I would be mildly surprised if that happens any time soon. It could be one of the classic settings for next year, but probably not. In the mean time, my creativity has started flowing towards mass combat for some reason, and I want to see what I can come up with.

I know there are 3PP mass combat systems, but I doubt any of them will do what I want it to do, for a couple of reasons.
-Most of them are probably extensive affairs in largish books
-Most of them probably don't "fit" 5e terribly well.

I'm not really looking for a giant book on realm management and warfare that makes a lot of assumptions about the world and requires a lot of effort to use. And when people make 5e material, they often make stuff that isn't like official material. When I'm using someone else's 5e material, I want it to feel like it could have come out of WotC, not like someone is taking an incompatible thing and squishing it into 5e mechanics. Now, if someone knows of a 3PP that will do what I want, feel free to send a link.

On to what I am looking for.

Basically, I want there to be two types of rules. The first is a tactical scale where you are controlling forces moving around on a battlefield, etc. The other is a larger more abstract system like the old BECMI War Machine. I'd also like it if actions by characters (whether by running parts of the battle at the tactical scale, or by regular adventuring stuff during or prior to the conflict) can affect the abstract resolution level.

But I need it to do and not do certain things.
1) It needs to provide a close approximation of the results you would get if you actually ran these massive battles using normal D&D rules. One of the issues I have with the BECMI treatment is that it doesn't do that. It overvalues training and equipment of typical humanoid soldiers, and undervalues the raw monstrous power of monstrous opponents. Some good gear and training shouldn't make a normal human with an average of 3.5 hit points a superior combatant to a hulking hill giant. Whether battles were run with standard D&D combat, at the tactical scale, or as a strategic abstraction with a couple rolls, I want it to produce very similar results.
2) The tactical scale needs to be designed to balance setting consistency with large units. For example, I would like it if each unit were 100 (or even more) Medium creatures. But I also need to allow for units of other sizes, that can properly face off against a unit of Medium creatures. It seems a bit absurd to have units with multiple Gargantuan creatures, so that limits the maximum size of my units. Each unit needs to be appropriate to pair off against a single Gargantuan creature. By appropriate, I mean that tough creatures should still feel tough. So if you've got a unit of typical baseline Medium troops (maybe the guard statblock with a special trait for their unit type) a unit of Large ogres, or Huge giants, or a Gargantuan anything should destroy them. It should take at least 2 or 3 units in succession, a PC or powerful NPC led unit, or a group of more elite troops to defeat such a threat. At the same time, the numbers of creatures in such other units should make sense in the world, and on the battle field as far as dimensions. 50 ogres isn't believable. Half a dozen is. 12 is maybe/iffy/depends on how well all the other moving parts fit. So the different numbers of Medium (or Small), Large, Huge, and Gargantuan (should be 1) combatants that should be the standard for a unit needs to be devised to give good results, where monsters feel scary but don't congregate in unreasonable numbers.
3) There should be a few different basic troop types (heavy infantry, light infantry, heavy cavalry, light cavalry, etc), but it would be nice if I can avoid having to mess with stats for most of the monsters. So maybe hobgoblins could just be set up in a heavy infantry melee unit by choosing to use their shield and sword, or a ranged unit by putting away their shield and using their bow. When it comes to using the stock NPC stat blocks, the average soldier would probably use the guard stats (seems standard in 5e), but the different unit types could make slight changes to gear and provide unique features based on race (maybe elves get Advantage on ranged attacks and ignore half and three-quarters cover, so that hobgoblins don't totally own archer supremacy by virtue of their Martial Advantage). Probably worth having the troop types give the guard statblock a bit of boost as well as the race to get it to CR 1/4. It just seems like a typical soldier should be able to take on a typical goblin warrior. The soldier statblock from the Ravnica book might be a good pattern for elite heavy infantry, but making it standard just throws stuff off by being a bit too good.
4) There should tactics, but they should be simple. I probably don't want a dozen different types of formations, but I would want a few. For example, maybe infantry have standard, defensive, and aggressive. Flavor as desired. Or maybe they need a few more for it to cover everything that needs covered. (We're at the broad strokes level here.) Units are being controlled as a unit, not as individual members, so the exact way the individual troops would be configured isn't going to make a difference. If miniatures were used, one miniature would equal one unit, not one troop.
5) Morale and winning by routing like real battles should be a thing rather than everyone fighting to the death, but since some creatures are immune to morale concerns (an army of mindless undead, for instance), the rules also need to be able to run battles that destroy units to the last creature.

Some thoughts I've been having include:
-Powerful leaders and bigger creatures could perhaps be accommodated by having some sort of simple rule for a mixed creature unit. So maybe a standard unit needs 4 Huge creatures, but a Huge mixed unit might have 2 Huge creatures and X Medium or X Large creatures. So maybe you have 2 frost giants as half of the unit and a bunch of orcs as the rest most of the time to get a more believable unit. And maybe the same thing happens with a PC/NPC led unit, where they count as "half" of the unit (even if it's assumed that there are actually a couple dozen troops or so as their personal guard so they don't throw off the dynamics). If there was only one frost giant that was a leader of the orcs, they could also count as half of the mixed unit, and it's assumed there are extra orcs (and/or generic whatever troops) as part of their half.
-There needs to be some way to take account of the fact that a well-placed fireball can probably take out most of a unit, without running it in actual 6 second rounds. I'm not sure what the length of tactical rounds should be. There also needs to be some way of handling the fact that if you don't run it in 6 second rounds you could cast all your mass damage spells in one or two longer tactical rounds, and a dragon could be using their breath perhaps even more than once per tactical round. It's less of a concern with spellcasters. You might even go so far as to say you can just straight up cast as many spells as you have slots for. Throw out 8 fireballs, and annihilate the nearby units on your turn. Then you're out. Wouldn't work so well with a dragon's recharging breath though.
-Needs to be some way of handling powerful solo creatures that aren't Gargantuan. For many, they could just be a mixed unit with other troops, but for flyers, like a Huge dragon, for instance, that doesn't work. Some high level PCs could also solo a unit or two of troops without any help before going down. That could be run as a normal fight though, whereas you wouldn't want to zoom in the battle to regular D&D creature combat rules just because the dragon involved is Huge instead of Gargantuan.
-There needs to be some way to determine how to deal with transitioning different scales. So let's say your high level fighters unit gets destroyed, but he survives and wants to go try to get to the enemy commander (who still has some of his unit left). There should probably be a way to pause the larger battle and go to standard D&D rules to run it. This also ties into how the more zoomed in scales can affect the larger ones. After doing that, you might go back to the tactical scale, and lets say you're only running part of the overall battle this way, so after you finish it up, then you take the results and plug them into the abstract "War Machine" kind of rules to see how the overall battle turns out after accounting for the results of the parts you played out in more detail.
-The various formations and troop types should all take up the same space on the tactical field, and the various pros and cons of formations and troop types should be represented by standard 5e things like Advantage/Disadvantage, reduced movement, cover rules, etc. While close formations would realistically pack more troops into the same space, I think it would make them too good to actually say two or three of them can fight against a single loose formation unit. It would also undesireably penalize forces like a typical horde of orcs who are all going to be in an irregular formation but should still be powerful. That being said, these sorts of differences should be meaningful. If you played out troop movement in standard D&D with everyone packed together in adjacent 5' squares, they would end up moving slower than normal due to difficult terrain unless it was a completely flat field; if the individuals were spaced out with an empty 5' square between them, they wouldn't be slowed down as much because they could better maneuver around difficult terrain. So it makes perfect sense and sticks to thing #1 I want to say that in the tactical warfare scale close combat formations have reduced movement. Maybe a close defensive formation gives everyone three quarters cover instead of the normal shield bonus, but each space of movement costs 3 movement instead of 1. That sort of thing.
-Hit points of units should probably just be the combined total of the troops in the unit. Damage of a unit should be the combined average damage total of all of the attacks of an individual creature, times the number creatures that can be brought to bear. The standard unit rules would determine this most of the time. So if the rule ended up being that a Medium unit is about 50 troops, with 4 ranks of 12 troops, then the damage for typical guards (4 damage average) is 48, since 12 troops can attack at once. Maybe for ogres it's 12 in a unit, and 6 of them can attack at once ( or 8 in a unit and 4 can attack at once, or however it works out). I'm not at all sure how to make that fit with things like swarming around your foes, or even a loose melee where everyone wades into and no one is holding a formation. Most of those sorts of things should be dealt with by bonuses and penalties of some type, rather than changing the position of units on the map. On the map, they should each just take up a single space.
-One way of doing attacks might be that if you hit you do the full damage, and if you miss you do half damage. Crits might do double and 1s might mean you failed to do any damage. There could be better ways to do that. It's generally hard for one force to attack in melee without getting counterattacked during that attack, but I'm not sure what the rule should be for that.

As you can see, most of the thought has gone into the tactical scale, probably because that's harder to do. The abstract scale is a lot easier, because you can reduce the battle to a series of a rolls for each clash (just roll until one side retreats, gives up, or captures or destroyed). You just have to figure out how all the math works to match up properly. Probably things like good tactical choices could just provide certain modifiers to these rolls. Could be 1d20 or 1d100 rolls, and each one might have a sub-roll or two to determine the actual casualties and such.

Suggestions? Thoughts? No idea is too specific or too general to potentially be useful at this early brainstorming stage.

 

[Ath-kethin]

Did you ever check out the 3.x Miniatures Handbook? That was the point (just prior to 3.5) where WotC decided to go full-bore on making D&D a tabletop boardgame instead of just an RPG, and it had most do the features you describe. It's not 5e, obviously, but could be easily adapted.

 

[Lanefan]

I dreamed up a homebrew system for this a while back. It's not for 5e (I think 3e was still brand new at the time!) but the general idea in it that might be of use to you is that it's unit-based, with 4 types of units:

Specials - this includes all PCs and any other named or significant individuals (generals, major monsters, etc.) in the battle. Unit size is almost always 1 and damage etc. is tracked for these by hit points as usual.
Elites - these include special forces, flying squads, scout or stealth groups, groups of elite warriors or noteworthy monsters, etc. Unit size varies, usually in the 5-10 range but could be more, depending on the situation.
Regulars - these are the common soldiers. Unit size varies; for big armies it's often simplest just to take the larger army and say it has 20 units each of size [total regulars/20]; then take that same unit size and apply it to the smaller army to see how many units it has. In other words, the larger army will always start with 20 units worth of regulars no matter how big that army actually is. If both armies are quite small (e.g. the largest has less than about 200 regulars) then just set the unit size as 10 and divide normally to see how many units each side has.
Irregulars - these are levies, peasants, camp followers, mundane field medics, and other untrained types. Easiest just to use the same unit size as for regulars.

All units are assumed to be comprised of similar-grade individuals; there's no provision for "mixed" units. For example, if an army consisted of 1 Stone Giant, 20 Ogres and 500 Orcs the Orcs would count as regulars (at 25 per unit if they were the larger army) and I'd make the Ogres into maybe 3 elite units even though realistically the Ogres would probably be scattered among the Orcs on the field. The Stone Giant would be its own "special" unit; there's no irregulars here, thus this army would have 24 units total.

A couple of common types of warrior can fall into different categories depending on the battle:

Mounted cavalry - in a real-world battle these would always be elites; in a fantasy battle with lots of magic and flight etc. they might just count as regulars with better move speed.
Archers - these can fall under regulars or irregulars, again depending on the battle.

I've got several pages of rules on how these all interact during a battle, and on what effects magic might have. The very short summary is that every unit in the field gets an attack roll against one other unit it can reach; then the effects are sorted out (unit by unit though it's all simultaneous in the scene), then units are recombined or disbanded etc., then mobile or disengaged units can move, then it's all done over again.

I don't worry about formations; that's up to the players/DM to decide. Terrain can give a bonus or penalty to individual units based on where they are.

 

[Numidius]

Just describe what troops, monsters, magic, do, or want to do, on the battlefield, detailing as much as needed, in plain language.

Dm adjudicates using logic, players of course will advocate for their side, then reach consensus, otherwise:

Roll opposing D20s plus proficiency dice as per variant rule in the DMG, apply dis/advantage.

Adjudicate results of rolls.

Zoom in and out of every situation among the battlefield on demand.

Disposition, morale, ecc, use 2D6, or 3D6 if you want less likely extreme results, in case even as opposed rolls w dis/adv.

You're done.

My two cents

 

[Tonguez]

Have you seen the Pathfinder system? It uses Army CR based on creature cr adjusted by army size so a Medium army is 100 humanoids, a Large army is 200 and a Gargantuan army =1000 humanoids.

The ARC number then becomes your base modifier to is then used to determine combat stats Eg Army HP = ARC x average HP of creature
The ARC allows you to balance armies and also use single monsters (eg you can drop a fine army of one Tarrasque and determine its ARC = 17

As to Abstract systems, since watching the Dynasty Warriors movie I’ve been thinking about using the idea of Lair Actions to model Armies on the Battle Field. The PCs play the game as normal and are given a set of onjectives (defend the bridge, kill the enemy general, save the princess etc) and the Battlefield is the background that the PCs are moving through,

The game focusses on the PC actions using normal rules but with the option of triggering Platoon Actions for nearby units eg a PC can trigger archers to provide suppressing fire against enemies which then provides cover for the PCs to dash forward to the next objective or a unit can be summoned to reinforce the bridge defence.

Again ARC could be used to trigger Unit Actions here too

 

[Ancalagon]

There was a great post on this topic by explorerwizard: D&D 5E - Tools for Running Larger Battles Efficiently

It was so good that I felt the need to copy it 6 years ago and remember it to this day!

 

[LuisCarlos17f]

My suggestion is to add an idea from Pathfinder: the troop monster subtype. It is like swarn but for humanoid and bigger creatures.

You can find it in the SRD.

 

[Dausuul]

I have thought a lot about this, and taken various stabs at it over the years.

Ultimately, what I realized is that the tactical element is a huge stumbling block to designing a system that plays well with D&D. If you try to build out combat rules to that level of detail, you end up flipping awkwardly back and forth between a miniatures wargame and a D&D adventure, with endless friction points as you convert "D&D scale" to "wargame scale" and back again, and a ton of new rules to keep track of.

BECMI was on the right track with the War Machine--BECMI's implementation was a mess, but the basic idea to keep mass combat at a highly abstract level was sound. I believe the ideal approach would be a system that uses mass combat as a backdrop, and generates a range of possible outcomes for a given battle. Then it helps the DM to create "flash points," where the PCs can intervene personally at pivotal moments. Each flash point is a regular combat encounter, where the PCs have a certain goal or goals (hold back the enemy for X duration, etc.).

At the end of the battle, you'd go back to that range of possible outcomes; look at how many of the "flash point" goals were achieved; and select an outcome from the list based on that. So, if the PCs hit all of their goals, they get the most favorable outcome possible for that battle, like rolling a natural 20. If they miss all of their goals, they get the worst outcome, like rolling a 1.

As I recall, "Red Hand of Doom" had a system very much like this for defending the city against the hobgoblin horde. The challenge would be to create a generalized version.

 

[NotAYakk]

Adding up CR does a decent job of how beefy each side is. But fate and fortune is important; baseline 5e combat rules are not swingy enough to handle how a large battle could swing.

The things that make a huge battle swing away from "best army wins" are things like a force breaking and fleeing, mispositioned troops, a commander doing something really smart, dumb, lucky or unlucky, etc.

And even a force breaking and fleeing is going to be based off of a lot of chaos; they won't know if they are winning or not, they just have their local information about it.

In any case, I'd start with slightly modified CR, like I do for encounter building

For mass combat, I'll make weak creatures a bit weaker than they are in encounter building, with the assumption that they are a bit less able to "fully engage", and because it makes the math easier.

For a creature up to CR 20, the power per creature is equal to its CR. For a creature above CR 20, add twice its CR over 20.

So a CR 30 creature has 30 + 2*(30-20) = 50 power.

A unit of 100 basic trained troops (CR 1/4) has 25 power.

A unit of 10 knights on warhorses has 35 power.

For such units, add up all their save modifiers and divide by 5 to give a generic "save" bonus. If the unit has a mix of creatures, take the weighted average. So the knights have a +11 total (so +2 average), the warhorses a +0, so the unit has a +1 total save modifier.

Make combat take place on a scale of minutes, not rounds.

When hit by something epic, like a dragon's breath against knights or troops, roll a save against it. On success, it loses 25% power, on failure it loses 50% power. (a sufficiently large breath might up this to 50%/100%).

Dragon breath weapon, reroll on scale of minutes; the reroll includes the chance you get a great chance to use it offensively. "Regular" use of dragon's breath is assumed to happen, just not an epic wipeout chance.

When two units clash, compare their power. For every doubling of one side's power over the other, they get a +1 to their roll and the other gets -1. Roll 1d4 for each side; each does 1d4 times (power/10) damage to the other side.

If one side has a tactical advantage, double its damage and give it a +1/-1 on the conflict roll.

So the knights engage 100 troops equipped with pikes.

Neither side is 2x the other. So even rolls. Pikes are anti-knight weapons, so +1/-1. Knights engage the troops.

Knight rolls 2-1 for 3 damage, Pikes roll 4+1 for 25 damage. Knights are reduced to 10 power, pikes are at 22 power.

Oops, don't charge into pikes.

A force of 10 stone giants charges in at the pikes. 70 power; so 7 damage. Pikes have no real advantage against giants. Giants roll 4, pikes roll 1. Giants deal 28 damage, pikes deal 2.

Bye bye Pikes.

---

You can probably codify how "AOE" attacks work, as they are pretty common, by looking at the HP of each piece of the unit.

 

[Dausuul]

One other thing to note: Morale is largely ignored in D&D combat. But in mass combat, morale is everything.

In principle, a couple of thousand commoners can shoot an ancient red dragon out of the sky without a single casualty--give them longbows, ready an attack as soon as the dragon is within 150 feet, and down it goes*. But how many commoners have the courage to stare down a hundred-foot dragon plummeting toward them with fire boiling out of its throat, holding their arrows for the signal? And if they break, or even hesitate, the dragon gets close enough to use Frightful Presence or its breath weapon, and destruction ensues.

Two thousand commoners versus an ancient red results in fiery death. Two thousand commoners, plus one really good bard, results in flawless victory. A good mass combat system should reflect this. (Conveniently, this gives the system a reason to care--a lot!--about PC battlefield heroics.)

*150 feet is short range for a longbow, but too far for the dragon to use any of its abilities. 5% of them will roll natural 20s and crit for 2d8 damage apiece. It takes 1214 commoners to average more damage this way than an ancient red's hit point total; 2000 gives you plenty of buffer in case they roll badly.