First one.

In game mechanics terms, if an LT unit is attacking an AT unit, the LT unit uses its "attack against infantry type" value to determine hit points lost by the AT gun, and the AT uses its "defense against armor type" value to determine hit points lost by the tank. Hit points lost are then simultaneously deducted from both sides.

Combat values are obviously adjusted for many factors like terrain, morale, forts, etc etc.

Yeah, that's a source of a lot confusion. The armor class is NOT determined by the tab at which the unit is produced. Instead, it is shown by the little icon in the terrain line of the unit desciprion. Go to the unit details page, and check the icons by the side of the terrain. For AT, you see four "green man" icons there (the fifth, an anchor, applies when it is loaded aboard a ship). This means that the "armor class" of this unit is infantry, NOT armor.

To simply add a few pictures to Roko's answer




In this simple example I am going to take my light tank and attack an infantry in a city. The infantry will defend, and my tank will attack it.

When preparing for a battle First identify the terrain where the battle will be. Very important.
Select the province > terrain is shown in the upper right corner
In this case a city.





Second: Define the target - In that location.
look at the unit's stat sheet. Click the unit's "icon" in the box.
Also make note of any fortifications/bonus



So I follow the red arrows. We defined the battleground as city so the target is:
15 hit points
infantry class (see terrain can matter - on the water it would be ship class, Planes refueling or in convoy are infantry class instead of air)
Pause there for a second, because we have to define our attacking force. Look at the next section for clarification:



Third: Define attacker
One light tank

Again follow the red arrows
Terrain: City
Hit points: 10 - Yes, the hit points are reduced in cities. armored units in cities are fragile
Armor class - armor
Strength: -50% - That means that the published value of attacking or defending is cut in half
Damage to the enemy: 1.5 points - We are attacking an infantry class unit, normally a 3.0 attack value, but the -50% urban penalty drops that to 1.5.



Now that we know the attacking force is armor class we can return to the blue arrows in the defending infantry
Defending against armor: 1.5 points



Fourth - Calculations:
So here is how that battle will go: Each round takes one hour.
Round 1: Tank whacks infantry to open the battle. Infantry takes 1.5 damage reducing it's hit points from 15 to 13.5. Infantry defends itself against the tank, and returns 1.5 damage to the tank reducing the tank to 8.5 hp.

Round 2: Again each side hits the other for 1.5. Results after round 2: Infantry 12 hit points, tank 7 hit points

Results after round 3: Infantry 10.5 hit points, tank 5.5 hit points

Results after round 4: Infantry 9 hit points, tank 4 hit points

Results after round 5: Infantry 7.5 hit points, tank 2.5 hit points

Results after round 6: Infantry 6 hit points, tank 1 hit point

Results after round 7: Infantry 4.5 hit points, tank destroyed.

Now I question that round 6 to 7 results in my mind. I am thinking as the tank gets that weak it doesn't hit as hard, but I have not studied that closely. Also it may be that if the tank is destroyed in round 7 that it will not actually damage the infantry that round. That is a game nuance question for @DxC or @Restrisiko or equivalent expert.



Fifth - Variations
Three important factors were left out of the calculations above

X-factor: There is a random value in each attack to account for the randomness of real battles. Attacks can vary from zero to 100% effectiveness.

Fortifications: If the infantry had a fort, for example 33% fort value that means the tank's attack of 1.5 would be split into 1 point damage to the infantry and .5 damage absorbed/deflected by the fort

What if both sides attack: That is a possibility. In most cases it is better to defend than to attack. But if I am controlling the infantry in this case I *might* want to counter attack the enemy tank. in that case the infantry will attack the tank with 1.0 points and the tank will return 1.5 hp damage to the infantry. Not a wise choice here, so I won't. Other cases might be different. If the infantry did counter-attack there would be two hourly battle calculations, each on their own timer.

No, this is not completely correct. As the units take damage, they are no longer functioning at full effectiveness. This ranges from 40% effectiveness for a (theoretical) 0% health unit to (duh) 100% for 100%. This means for example that a unit at 50% strength infilicts 70% of its listed damage (halfway from 40 to 100). Thus in the above example, both units inflict less and less damage as they lose hit points themselves.

Thank you Roko. Always more to learn.





I intended to link to the battle calculator created by @DxC

dxcalc.com/cow

I use this for complicated battles. It takes a bit of concentration to figure out, but it is the key to success in many battle situations for me. Not so much now, but I used it extensively for a few weeks to learn the game early on.

Example: Artillery. Due to its weaker defense value, if it gets into melee combat, it is best to set it to attack to maximize damage caused to the enemy.

Yes, that is fundamental and is the whole concept of SBDE. In the first round of this battle the LT would hit at 1.5 * 0.9 = 1.35 power and the INF would defend at 1.5 * 0.69 = 1.035 power. Power would decrease for both in each round as SBDE decreases.

Another thing in this example that may confuse people is that it assumes both units start with 100% hitpoints given the terrain, but that is not right. Furthermore, in this particular battle the tank is expected to win.

@DxC. To be honest I just grabbed a couple images instead of tailoring them to my example. I will attempt to fix that during the blizzard tomorrow. I will take the time to run it through your calculator as well instead of using my head before my morning coffee. Thanks for the feedback.

No problem. It was a great explanation, but there were some things that might have been confusing.

how goes damages if examples 3x tactical bomber lvl 4 attack province where is lvl 4 lt and lvl 4 infrantry and terrain is hill or forest

how then went damages

Im wondering how does submarine attack and deffend damage is calculated.
Is my sub using deffending stats when enemy ship "runs over" it? Since sub is hidden if not attacking

It is likely in that case that the sub is doing an attack each hour and the ship that runs over it is doing an attack each hour. That isn't always true, so watch each units combat timer to see.

If both naval units are engaged in a close combat fight, both units will do both attack and defense damage.

lets say that they both have single attack time. Does that means that they actually strike twice? Once for attack and once for deffense?

If you want to call it that, yeah. They strike at their own timer tick (and recieve defensive fire from their enemy), then they take damage at the enemy tick (and inflict damage ion their enemy again), both within one hour.

That is assuming that both stacks are within attack range. If a ranged naval vessel attacks another stack that has a shorter range, it is possible to have one side attacking and the other only defending.