Combat efficiency modifiers
This is a not entirely compete list of what affects combat efficiency. It is a list of information I picked up while playing the game. If you have more or better information on this please add.
Base efficiency is 100. An A means that the modifier applies to the attacker, a D to the defender
Topology (A) Mountain -40 Hills -20 Broken lands -10 Marshes 0 Vegetation (A) Woodland -15 Forest -30 Clear 0 Frozen ? Steppe 0 Desert 0 Climate (A and D) -101 Entrenchment (A) -1*(average level of entrenchment)2 Fortification (A) -10*(fort level) Infrastucture (D) +20 (if a RR is present, no matter the level of RR) Landing (A) -20 (attacking from a ship) Encircled (D) -20 (no friendly province to which the unit can retreat) Enveloped (D) -10*(n-1) (where n is the number of sides from which the unit is attacked) Artillery (A or D) +SQRT[ART(D)-ART(A)] (the bonus is given to the side with the most arty brigades) Experience (A and D) +[unit experience]-10 Gas: one side (A or D) +503 Gas: both sides (A and D) +203 Shore bombardment (A or D) -10*SUM[shorebombardement values of enemy ships] Stormtrooper bonus (A and D) +1204 Tank bonus (A and D) +150 (only applies to the unit with tank attachment I believe)4
- I don't know to what climate is related, it seems to usually show up in the tropics.
- If a province with 4 division entreched at 100 and 3 at 20 the attacker will get an entrenchment malus of ((100*4+20*3)/7)=65.71. Would this battle be inforced by 10 divisions the entrenchment malus would be ((100*4+20*3+10*0)/17)=27.06
- If one side has had the two gas inventions, gas attack and gas defence, that side gets a +50 bonus. If both sides have both inventions both sides get a +20 bonus. I'm unsure what happens if you only have the attack capability.
- The stormtrooper bonus (+120%) and tank bonus (150%) show up after certain inventions. It's not sure what their function is, some say it is to negate the effect of entrenchment.