Building a Mass Combat
In a mass combat, the party is in command of a large army and opposed by another, similarly large army. The mass combat is played on a hex grid, each unit occupies one hex, and in general the size of a unit is about four hundred soldiers of medium size, or half that for each size larger and half again that for each size smaller. This is a rough estimate. Some indescribably powerful creatures, like ancient red dragons or the mighty Tarrasque, can serve as a unit unto themselves, and some creatures of small or medium size tend to form swarms or hordes of larger than average size.
Each unit has five primary stats, those being morale, attack, defense, speed, and range. Speed and range are the easiest. Each unit has one speed for every fifteen feet of movement in skirmish combat (i.e. the standard combat rules provided in the Player’s Handbook). A unit has one range by default, plus one extra for every full 200 feet of its maximum range (so shortbows have range 2, heavy crossbows have range 3, and longbows have range 4).
Morale depends on what the troops under your command are fighting for. Morale 1 units are conscripts. They have no stake in winning or losing the war at all and are there for no other reason except that there are penalties for deserting. Morale 2 units are either professional soldiers or else have been incentivized to stay and fight somehow, but not so much that they’ll face certain death for it. Most mercenaries and raiders are morale 2. Morale 3 units are genuinely dedicated to whatever cause their army is fighting for. Militias raised to defend their own lands are usually morale 3, as are elite units vetted for dedication and zeal. Finally, morale 4 units simply will not run away no matter how savage the fighting gets nor how certain their death is nor even how insignificant their sacrifice would be. While some units can occasionally manage this just on the extremes of sheer zeal and dedication, the vast majority of morale 4 units are mindless undead or golems. Morale is added to all attack and defense rolls, and is reduced whenever the unit is successfully attacked. If morale reaches zero, the unit breaks and flees the battlefield.
Attack is a sum of three other factors: Training, gear, and power. A unit that’s been trained and drilled to fight as a unit adds one die to attack power, whereas untrained units add none. Gear provides a -1 penalty for peasants with simple weapons like shortbows and wood axes or light weapons like scimitars or short swords, a +0 for standard martial weapons like long swords, pikes, halberds, longbows, and so on, up to +1 for heavy weapons, and a +2 if the entire unit is equipped with magic weapons (whether they’re martial weapons, light weapons, or what). Masterwork weaponry has a +1 over its normal bonus, so a unit equipped with masterwork short swords would be +0 rather than -1. A unit may have two different gear bonuses listed for attack, the first for melee and the second for range. In this case, the unit must use the melee bonus at melee and the ranged bonus at range.
Finally, power refers to the raw physical power of the creatures who make up the bulk of the unit. Small or weak creatures like goblins and halflings have a -1 to attack, standard creatures like humans, hill dwarves, or elves have a +0, creatures stronger than normal like orcs and mountain dwarves have a +1, larger creatures like ogres or trolls get a +2, and the most monstrously powerful of enemies like hydra cavalry or frost giant units have a +3. The bonuses for training, gear, and power are added up to make the total attack score of the unit. A unit’s attack score cannot be lower than 0 no matter how many penalties they take. When making an attack, a unit will always roll their attack score plus their morale score, unless otherwise noted.
Defense is also a sum of three other factors: Discipline, gear, and durability. Units with a +0 to discipline have no experience fighting as a unit at all, and are probably skirmishers or raiders used to splitting up and fighting many small battles or else brand new recruits. Units with a +1 to discipline are the most common, representing men-at-arms who’ve received some basic training to fight in formation but are still easily intimidated by powerful opposition and easily wearied by long campaigns. Units with a +2 to discipline particularly well-drilled, professional soldiers, and many standing armies and mercenary companies have +2 discipline. Finally, units with +3 to discipline are trained and commanded by a skilled officer corps and live and breathe not just for war, but for organized warfare with one another specifically. A +3 discipline unit is usually the product of a large and powerful empire’s elite shock troops, like the Roman legions.
Gear ranges from -1 for armor with base AC (including shield bonuses) no higher than 11, +0 for AC of 12 to 16, a +1 for 17 to 19, and a +2 for 20 or higher. Soldiers equipped with a reach weapon have their gear bonus determined as though they had a shield so long as their discipline bonus is at least +1. For example, a pike formation with chain mail has AC 16, which would normally be +0 to gear for defense, but if their discipline is +1 or higher, they can use their pikes to keep enemies at bay and make up for their lack of a shield, thus allowing them to count their gear as though they had a shield and were AC 18, giving them +1 to gear. This does not change their actual AC if they’re encountered in skirmish combat.
Physical toughness counts for relatively little because at the end of the day, very few creatures are so tough that being stabbed or hacked with swords and axes and arrows won’t incapacitate them. For the overwhelming majority of creatures, the armor they wear counts for more than the thickness of their skin. Some creatures are particularly frail, like elves or halflings, and take a -1 penalty to toughness. Most creatures are average, like humans or orcs, and receive +0. Some are particularly tough, like dwarves or giants, and get a +1.
Just like attack, defense is a sum of these three factors, and just like attack, that sum cannot go below 0, and just like attack, the defense score will always be rolled with the morale score added to it unless otherwise noted.
Mass Combat Actions
A mass combat turn is divided into the skirmish and melee phases. During the skirmish phase, a unit can move up to its speed in hexes, make a ranged attack, make a flanking attack, or disengage from melee. A unit can also change facing during the skirmish phase even if they take no actions at all. A unit cannot continue moving after making a ranged or flanking attack, nor after moving adjacent to an enemy unit facing towards you. In the latter case, the unit is now engaged in melee with the enemy unit. A unit that ends its movement without making any attacks may face in whichever direction they like at the end of the movement. A unit who ends their movement by making an attack must face directly towards their attack, with the frontward face of their hex aligned facing towards the enemy hex. A unit who ends their movement by engaging in melee must be facing in the general direction of the enemy, with any one of their front three hex faces pointing towards the hex occupied by the enemy unit.
The target of a ranged attack must be a unit that is not adjacent to the attacking unit and must be within range of the unit’s ranged weaponry. The attacking unit rolls its attack, the defending unit rolls its defense. For each 4-6 on the attacking unit’s roll, the attacker scores one hit. For each 4-6 in the defending unit’s roll, the defender can soak one hit. Every unsoaked hit in the attack roll reduces the defender’s morale by 1. Extra hits on the defense roll do nothing.
The target of a flanking attack must be an adjacent unit that is not facing towards the attacker. This means the attacker is only adjacent to one of the back three faces of the hex the defender is occupying. In this case, the attacker does not have to immediately stop and engage in melee. If they make a flank attack, their attack dice (but not their morale) are doubled for the attack. Just like in ranged attacks, the attacker rolls their attack pool and any rolls of 4-6 are a hit, and the defender does the same with their defense pool, with any rolls of 4-6 soaking a hit, and then the defender loses one morale for each unsoaked hit in the attack. If the flanked enemy survives the attack, they may turn to face in the general direction of the flanking attack immediately and at no cost. Just like engaging in melee, when turning to confront a flank attack, the unit must align any of its frontward three hex faces towards the enemy’s hex, but it doesn’t matter which. If the unit has turned away from an enemy it was previously engaged in melee with such that none of its three frontward faces are now in contact with the enemy’s hex, that enemy is no longer engaged in melee and can move away freely (they can also make flank attacks of their own instead).
A unit who is currently engaged in melee can disengage, moving a single hex away from melee and being unable to make any ranged or flanking attacks after doing so. However, this is the only way a unit can leave melee short of wiping out the enemy unit.
After the skirmish phase comes the melee phase. In the melee phase, all units in melee automatically attack one another. If a single unit is in melee with more than one other unit, they must pick one and only one unit to attack. All melee phase attacks are simultaneous. If two units are in melee with one another, you make an attack roll for one of them and the other rolls defense just like with a ranged attack, however the defending unit doesn’t remove any morale until after they’ve made their own attack roll. Once all units in the melee have made their attacks, then and only then is morale removed. This is true even if a unit has suffered an attack that will remove all of their morale and rout them completely. They still get to make their attack roll for the melee phase before routing.
Whenever a unit runs out of morale and routs for any reason, any adjacent friendly units with equal or lower discipline scores automatically lose one morale. This can lead to a domino effect where a frontline loses one unit, which causes the two to either side to rout, which causes the two to either side of them to rout, and the whole thing crumbles from a single hole in the line. For this reason it is extremely unwise to have conscript units form a line by themselves. Interspersing them with more disciplined mercenaries or professional soldiers will stop this cascade from happening. Additionally, if you have a second line of soldiers (and if at all possible, you should), swapping a fatiguing unit out for a fresh one will prevent fatigue chaining. If playing in a military campaign, it will also allow a fatiguing unit to be safely retreated off the edge of the map rather than risking its total destruction at the hands of the enemy (in a one-off mass combat it is technically true that a unit that retreats and a unit that gets destroyed are the same, but there’s certainly a difference in the narrative between an overwhelming victory and a Pyrrhic one). On a similar note, while neither side has any mechanical incentive to retreat during a one-off battle, for reasons both of verisimilitude and pace an enemy who has clearly lost the fight should begin retreating units to safety to live to fight another day (and if the party is losing badly, any advisors they have should recommend they do the same, although the final decision is theirs if they are the army’s grand commander).
Commanding a large army is difficult and the larger an army gets, the more impossible it will be to keep the entire thing under control. Generally speaking, each unit in an army will have a leader (sometimes armies or units particularly dense with command talent will have more than one). That leader has a leadership score equal to one half their INT save, rounded down. Whoever has the highest leadership score in the army is, by default, the army’s grand commander (the narrative might demand that someone less competent be calling the shots). The army can activate a number of units each round equal to their grand commander’s leadership score. Each unit can be activated only once, and any units that aren’t activated cannot act in the skirmish phase. They don’t move and can’t make ranged or flanking attacks. They still fight in the melee phase if they’re engaged in melee, they can still change facing during the skirmish phase, and they can still change facing automatically if hit by a flanking attack.
If the grand commander’s unit becomes engaged in melee, they cannot act as grand commander until their unit is back out of melee. By default, the designated successor will be whoever has the second highest leadership score in the army (though again, the narrative might see the grand commander designating someone less competent to act on their behalf should they be unable to command).
Additionally, a leader contributes one extra point of morale to their unit for every four points of their WIS or CHA save (whichever is highest), rounded down. So, a leader with a WIS save of +7 (and a CHA save that’s equal or lower) grants a +1 bonus to morale, but one with +8 would grant a +2 bonus to morale. This morale bonus can allow a unit to continue fighting when they otherwise would’ve routed, however if the leader is the only thing keeping his unit together, they will rout immediately after that leader is killed in battle (or assassinated).
Whenever a unit is routed, the unit’s commander must make an INT save against DC 10, +1 for every additional unsoaked hit past the hit that knocked off their last point of morale. If the save succeeds, the unit is routed but will regroup after the battle, If the save fails, the unit has been completely destroyed. If the unit hasn’t been destroyed, the commander may attempt a CHA save against DC of 15, +1 for every unsoaked hit past that required to reduce morale to zero (the same bonus applied to the DC for the INT save). If the commander succeeds, the unit rallies. It returns to the battlefield in a hex that is its full speed distant from the hex where it was routed, with one morale, plus one more for every five points the commander beat the DC. On the following turn, the unit may be activated again as normal, however the bonus to to the DC for the INT and CHA saves is retained, increasing the odds the unit will be annihilated or, failing that, fail to rally if they are routed again. If the unit has no commander, the save versus annihilation is made at a +0 bonus and the CHA save to rally fails automatically.
If a routed unit cannot reach the friendly edge of the battlemap (including situations where there isn’t one to reach) without passing through any enemy units, then they cannot rout. There is nowhere to run, and the unit must fight to the death. In this case, the unit is on deadly ground. Their morale bonus to attack and defense is always three (they are fighting for their lives), however the unit’s morale is zero for purposes of absorbing hits. Every time the unit is hit, they immediately rout again and the commander must make a new save against the DC. Because there is no more morale to chew through, every unsoaked hit will raise that DC by 1. The growing DC does not reset to 10 until the end of the battle. Additionally, if the unit is hit and a path to safety has opened up, they are immediately discarded as a casualty as normal (the commander must still make an INT save to see if they are annihilated or if they regroup after the fight).