The simpliest solution I can think of is fixed ratio of units (hardcoded). For example the army should consist of 40% infantry, 10% tanks, 15% artillery, 5% selfpropelled-artillery.

But that's a very unappealing solution, the player would just calculate the ideal ration all the time and try to match it... Without any logic or reason behind it.

The reason behind it is to find the ideal solution. The logic behind it is to win. You have declared a desire to express one strategy, or category of strategies as superior to other strategies. The players will pit one strategy against another strategy until the winner or winning group is found.

"diversity is essential to victory" - This is a procedural rhetoric that the developer wishes to convey. This is a type of artistry, a design about the way this universe works; it is essentially engineering a moral for the game. "Variety is good, uniformity is bad."

"diversity is essential to victory" - This is a procedural rhetoric that the developer wishes to convey. This is a type of artistry, a design about the way this universe works; it is essentially engineering a moral for the game. "Variety is good, uniformity is bad."

I'm willing to sacriface variety :) I want it like a real military. Sure, there are some differences in armies but all of them have infantry and tanks and artillery and hellicopters. There is not such thing as an army without one of these components in real world. Real armies do not specialize by not having any artillery for example :) I want to model this.

I think it is a question of scoring. You have to have an elaborate scoring algorithm but it shouldn't be too hard. A simple way of doing it would be to calculate combat contribution not by the number of units of a type but of the root (or log) of said number. That way an army with more types with low numbers achieves much higher scoring than an army with few units and high numbers. Also you can easily add in bonus multipliers for attacker/defender, terrain, doctrine etc on a per unit basis.

Other options are more work, like creating a small fighting simulator that lets unit types attack other unit types in a preference order that does not reflect the efficiency order. Like everyone attacks tanks first but tanks are resilient vs most guys. If no tanks are present (killed or you didn't bring any) dmg hits the more squishy backline. Bring too many tanks and you have no fire power, to few and you lose as well.

Here you can also make an target order, an efficiency table and additionally work in terrain bonus etc. Also this system is easier to visualize/describe ingame. So it seems to be more work but easier to get an intuition for than the above simple calculation.

I think a fighting simulator would be better... Probably something along the lines what powerneg and Orymus3 wrote. As you wrote the key would be representation (the battle "logs" should give enough information to determine what's wrong with your army setup and can't be too confusing).

... the the player wants to build various units at the same time... as combined forces, not just "only tanks" or "primarily artillery", balanced forces shall be the most efficient...

...

The whole idea is the concept of "combined arms". The requirement of different types of units working together and that the diversity is essential to victory (no specialization to certain units, at least not to a total degree). That's what I want to convey in this mechanic.

...

I'm willing to sacriface variety ... all [armies] have infantry and tanks and artillery and hellicopters. There is not such thing as an army without one of these components in real world. Real armies do not specialize

The "real armies" thing doesn't seem to mean what is going on in real life on planet Earth.

The Bangsomoro Armed Forces currently fighting a war in the Phillipines over the rich oil assets in that region have only troops with light armament; assault rifles, mortars, rocket-propelled grenades and machine guns. They don't have tanks and helicopters.

And what about the battle raging in Syria, a competition between a Syrian government army and USA-backed rebel forces? The USA was going to use an aircraft carrier loaded with fighter/bombers against a government that was said to be using chemical-weapon rockets. Syria doesn't posess an aircraft carrier, and the USA doesn't use chemical weapons.

It looks like the concept of "Reality" is being used as a sort of authority or credence to a desired plan. You're the designer, you don't need a reason -- do what you like!

It looks like the concept of "Reality" is being used as a sort of authority or credence to a desired plan. You're the designer, you don't need a reason -- do what you like!

Also I was thinking along the lines of WWI - WWII - cold war era military (I'm not interested in the very modern assymetric warfare).

OK, back on topic. About the combat simulator.

I thought on the concept of "combat/front width" which is used in some heavier wargames. Actually, I'm not sure how it works in detail but it's used to limit the number of units that fight each round.

I was also thinking of phases. Like:

* first bombers try to bombard enemy lines with interceptors and AA trying to counter it

* then artillery starts shooting (you get a bonus if your recon airplanes passed a recon test)

* next fast units (light tanks and other light vehicles) do their action, they could for example quick strike artillery, acquire a better tactical bonus for the whole army (by attacking some weak spot, countering maneuver of infantry)

* the second round of artillery fire (some will be disabled due to action of fast units in previous phase)

* next tanks rush to break enemy lines (hellicopters and anti armour can counter it)

* mortars starts firing (vs infantry only)

* then clash of infantry

If at any point infantry get's demolished (not necessarily fully destroyed) then battle is automaticly lost no matter how many other uinits are stil capable of fighting.

Then you can have "special stuff" like if you invent and apply "paratroopers doctrine" you can use some air transporters to drop infantry behind enemy lines and disrupt it (you would get another phase), or you could send commandos, or use electronic warfare to disrupt communication. All these would grant you a new phase (which emans the game will become more complex as it progresses, which is good I think).