Information Rich Combat Mechanics

June 13, 2017

The Modiphius 2d20 system is one I have used a couple of times to run convention games based around the Conan roleplaying game. I am thinking of adapting it for use in a Megagame.

First, a Quick summary of the 2d20 system:

  • You always roll at least 2d20.
  • You can roll up to three more d20s for situational modifiers, such as other players assisting you, to a cap of 5d20.
  • The roll is compared against an Attribute (usually in the 8-15 range) and a Skill (usually in the 1-5 range), potentially generating 0, 1 or 2 successes for each d20 roll
  • For example if you have an Attribute of 12 and a Skill of 3, and you roll 2d20 and get a 12 and a 2, you have three successes
  • If the number of successes equals the task difficulty, you succeed, and for each extra success you gain a point of Momentum
  • You can then spend Momentum to cool stuff in the game
  • Weapon damage is handled by rolling d6s
  • A damage roll of 1 or 2 inflicts damage equal to the roll, a roll of 3 or 4 does nothing, but rolls of 5 and 6 trigger special effects based on the weapon type (e.g. bypassing armour, or extra damage).

It recently occurred to me that I could adapt this as a mechanic for handling Army/Front level combat in Megagames. Traditional wargame mechanics often involve a lot of counting of various factors, followed by some maths as you try and make sure you reach the golden 3:1 ratio considered the minimum to ensure success in land warfare. In a Megagame there is no time for all this counting, you need to be able to take in the situation at a glance and get on with resolution. At the same time I want rich information from the combat result – if we are only doing a few combats each turn, then they need to actually move stuff around on the map and add to the game narrative.


The situation in Army Group Center’s sector of the Eastern Front on 6 December 1941. This is a German map, the Soviet reinforcements that are about to launch a counteroffensive are not on the map. Sourced from the Dupuy Institute blog.

Generally speaking, formations of Army/Front size are rarely destroyed in combat – the exceptions being encirclement (e.g. destruction of Army Group Center in 1944) and/or running out of space to retreat (e.g. British at the Fall of Singapore in 1942). What is important is how ready is the unit for further combat operations, and what is the momentum on the front.

So I am thinking of a mechanic where we are rolling d10s, and the important factors about a combat formation are readiness, on a 1-10 range, and quality, on a 1-5 range. A rested unit at full strength with brand new equipment would have a readiness of 10 (so most units would be rated nine or less). Quality is something that can be worked out based on historic performance (for World War Two, based on effectiveness scores from post-war quantitative analysis, I would put German units at 5-6, the  UK at 3-5, the USA units at 4-5, and the Russians at 2-3). Units roll a base 2d10, then +1d10 for each supporting unit flanking the enemy. Units then roll 2d6 for damage, but can spend supply points (or play special capability cards) to boost that up to 5d6 (I will have to playtest that cap, or perhaps allow it to be exceeded by special limited use cards).

The force being attacked also rolls for its defence, and the force with more successes is the force that gets Momentum points to spend. Units that are defending get bonus Momentum for defending river lines, urban terrain, mountains and prepared/fortified positions.

So we also rolled some d6 for damage, and while we throw away the 3-4 rolls as in 2d20, in this 2d10 system, the rolls of 1-2 are used for Attrition Effects and the rolls of 5-6 are used for Maneuver Effects.

Attrition Effects

Spend your Momentum points to reduce the targeted unit’s Readiness score by 1-2 points. The defender can also spend Momentum to hold the ground the occupy (the default assumption is that the attack does move the defender backwards) at a cost in Readiness.

In theory with 5d6, if you roll enough 2s you can take a unit from Readiness 10 to Readiness 0 in one attack, in practice its likely to take a while to grind forces down. At a glance in the European Theatre in World War Two, it was pretty hard for any force to sustain continuous operations with land forces for longer than a couple of months (the US/UK tended to run out of supplies first, the USSR to run out of tanks).

Maneuver Effects

This is where it gets more interesting and you can spend Momentum to:

  • reduce your own Readiness losses
  • reduce enemy Political Will (i.e. capture a large number of prisoners, or a city or other vital objective)
  • gain initiative for your side next turn
  • exploit the breakthrough (deep penetration and/or forcing flanking formations to retire)
  • capture enemy supplies that you overrun.

Using the two sets of dice, lets the game create a rich tapestry of potential game information. The downside is getting the players to make those decisions around spending Momentum quickly. This would be the key thing to stress test in playtesting the design.


One way of representing historic doctrine is to programme the first choice a side makes (or perhaps even the first two choices). For example, UK forces could be required to spend their first Momentum effect on reducing their own Readiness losses, Soviet forces on getting a breakthrough, and US forces on maintaining the initiative.


I used to own a copy of a game called Renegade Legion: Prefect, which focused on hover tank battles on a planetary scale. The side that had initiative did nearly all of the movement and combat, while the side without basically sat there and hoped for a counterattack to give them the initiative. That concept bubbled to my head while thinking about this hack.

So my plan for this 2d10 system is that the side which starts the game on the attack holds the initiative. The initiative allows you to attack as many times as you like (up to one per Army formation). The side without the initiative gets a limited number of counterattacks. Both sides can spend Momentum on initiative, with a cumulative penalty for any side holding on to the initiative for consecutive turns. Another way of doing that might be to have an escalating supply cost, so you could hit a point where one side runs out of puff, no matter how well they are doing on the map. Frustrating, but a representation of Clausewitz’s theory of the culminating point.

A zero score for initiative could be taken as both sides are temporarily exhausted and spend a couple of weeks (or longer) resting or maneuvering before one side resumes offensive operations. Maybe both sides would be limited to a small number of attacks, like counterattacks.

Recovering Readiness

Units should recover Readiness quickly. Fifty percent of lost Readiness per two week turn seems okay as a starting position for playtesting. In this system I would just about never remove a unit from play, but at Readiness One I would not allow it to initiate attacks. Front lines would also be continuous – if you run out of actual Army formations, you would just deploy a Readiness One Battlegroup counter.

While Readiness should bounce up and down, quality would change only rarely – perhaps reflecting a unit gaining an elite reputation, or being issued with state of the art equipment in sufficient numbers to have an impact on operations (one Super Pershing does not a +1 Quality increase make).

…and now I really need to get back to revising The Colossus of Atlantis. GENCON is only 63 days away.