I'm currently running a heavily modified low fantasy version of 3.5, and some large scale battles are on the horizon. I poked around online for some mass combat systems, but haven't really found anything useful so far, so I thought up some rules on the fly. It focuses on squad/groupings. These might be too fiddley for core mechanics, but let me know if you have any input. I would really like to see mass combat acknowledged in the next edition!
- Squads/units can be any amount of men, but should all be roughly same level, class, and weapon type (except for commander)
- Initiative is -1 for every 10 men in a squad.
- Squad speed is 25 feet (double for cavalry)
- Squads move like regular units, except that they share spaces with other squads they are fighting.
- Map size varies depending on scale of battle, but 25 ft hexes (or squares) is default
- Every soldier's hit points are pooled into the squad's total
- When two squads engage in melee, they roll opposed attack rolls, modified by advantages, numbers, skill level, commander charisma rating, etc.
- The winner rolls 1d6 (if squad is using short swords, for example) for each soldier to a maximum of 9. If there are 10 soldiers, then he multiplies 5d6 by 2. If there are 20, he multiplies 5d6 by 4, etc. For odd numbers simply add an extra d6
- Commander may roll his own damage in addition
- The loser does the same, but his damage is reduced by 75%, 50%, or 25% depending on how much he lost by. If he lost by 5 then 75%, if 10 then 50%, if 15+ then 25%
- If average hit points are 5, then for every 10 hp the squad loses, someone dies, until squad reaches 50% hp, after which someone dies for every 5 hp lost, until squad reaches 25%, at which point someone dies for every 3 hp lost.
- Squad takes a morale check at 50% and 25% hp to avoid routing
- Morale check is 1d20+(1 for every 5 units they are outnumbered) against 10+commander's charisma
- If the squad hp are ever down to half of the commander's hp, he is the only one left and is bloodied.
- Archers work same way except ranged
- If firing into a melee, their damage is divided between their own troops and the enemy
- If firing while their own units are adjacent an enemy, their own troops take a quarter of the damage
- Ranged attacks only do half damage if squad all have shields
Higher ground +5
Polearms vs cavalry +10
Cavalry vs regular infantry +10
Melee vs archers +15
Outnumbering (+2 for every 10 units extra)
Adjacent friendly squad +5
Wounded (-5 at 75% health, -10 at 50%, and -15 at 25%)