Tactical turn based combat is the heart of Battle Brothers. The battlefield is a hex grid, with elevation, obstacles/terrain considerations and zone of control mechanics, where an initiative-based system is used to determine the order in which combatants can act out their turns.
The character with the highest initiative will start first in a battle round, followed by characters with lower initiative. As initiative is lowered when a character builds up fatigue or has a penalty to max. fatigue (due to armor/weapons or other effects), his turn may move from first to last very quickly, if he gets fatigued too fast and the enemies do not.
All weapon strikes and moves cost fatigue to execute, therefore a fully fatigued character can neither strike nor move. Every character recovers 15 fatigue at the start of his turn. As per full release version 1.1, dodging blows also increases Fatigue by 2 and getting struck by a blow increases Fatigue by 5.
Base chance to hit (shown after selecting a skill and mousing over a target) is essentially: melee skill of brother subtracted against base melee defence of target. 
This is further modified by various factors listed below.
- Gear, elevation and surround bonuses are factored in additively. (ie an attacker with Melee Skill of 70 striking a defender with Melee Defense of 0 will have 70% hit chance. If said attacker had another friendly unit adjacent/surrounding the defender, he would get +5% or in other words his hit chance would be 75% instead)
- Morale bonuses/penalties and injury penalties are factored in multiplicatively (ie an archer with 86 Ranged Skill at Steady will have effectively 94 Ranged Skill at Confident (+10%))
- Weapons with hit bonuses include, for example, pitchforks, pikes and the Battle Standard with a +10% chance when using the "Impale" skill.
- Weapon skills like Slash (+10% hit chance, available for swords) or Thrust (+20% hit chance, available for spears)
- Shields confer strong defense bonuses which significantly lower the hit chance of anyone attacking someone who has a shield equipped. Examples of standard shields:
|Buckler||Wooden Shield||Kite Shield||Heater Shield|
| +10 Melee Def.|
+5 Ranged Def.
| +15 Melee Def.|
+15 Ranged Def.
| +15 Melee Def.|
+25 Ranged Def.
| +20 Melee Def.|
+15 Ranged Def.
The Shieldwall skill (not available to mercenaries using a Buckler as it is not a "normal" shield) can be used in combat to double shield defense with a additional bonus for each adjacent ally also using the Shieldwall skill. This tactic can be used to give your front rank mercenaries a big boost to defense when taking a large amount of damage is otherwise inevitable (e.g. needing to advance while under fire from enemy ranged troops).
Height levels are used as ground elevations (hills) on the battle map. When standing on them, you gain a bonus to hit chance while enemies suffer a penalty to their chance to hit you.
Changing height level costs more action points and costs more fatigue than walking on the same height layer. The Pathfinder perk eliminates these penalties. The Pathfinder perk is especially useful for polearm or 2H weapon users, as it allows them to change height level and still attack. It is also extremely useful for ranged mercenaries as they gain significant bonuses from having a higher elevation than their targets and the Pathfinder perk facilitates easy repositioning.
There are the following types of height level in-game:
When standing on a higher height level than your opponent, you gain a +10% chance to hit and they suffer a -10% penalty to hit. It is always advantageous to have the high ground in any battle and the AI will try to occupy the high ground whenever possible, especially their ranged units.
Ranged weapons gain an additional hex of range for each level of height. They also gain increased damage as well as improved hit chance versus targets at a lower height level.
You only count as being in melee attack range if there is a one level difference of height between opposing characters standing in adjacent hexes. If there are two or more levels of height difference between the hex a character is standing on and an enemy in an adjacent hex, you do not count as being in melee attack range or being in each other's Zone of Control.
- Surrounding an enemy with your mercenaries gives a +5% melee hit chance per ally (your own mercenaries or friendly AI) standing adjacent to the enemy not counting the character currently acting (if he is adjacent to the enemy).
- Your own mercenaries are vulnerable to the same surround mechanic as enemies. The Underdog perk makes it so that opponents can only gain a bonus chance to hit if the character with the Underdog perk is in base contact with 4 or more enemies. The first 3 are discounted for the calculations. This makes Underdog an extremely valuable pick for frontline mercenaries, especially those on the flanks of the main battle line as they will almost always be at least partially surrounded.
- The Backstabber perk doubles the +5% hit chance bonus to a +10% hit chance bonus for each ally adjacent to an enemy for the character who possesses the perk not counting the character currently acting (if he is adjacent to the enemy).
- Wardogs count as allies for the purposes of calculating surround mechanic hit chance bonuses.
- Example: A Brigand Raider is surrounded by Diethelm, Tostig and Erik, all of whom are mercenaries in your company.
Tostig is the currently acting character in the turn order. He gains +5% chance to hit for Diethelm being in base contact with the Brigand Raider and another +5% chance to hit for Erik being in base contact with the Brigand Raider. This creates a total of +10% chance to hit as Tostig is not counted for the purposes of the surround mechanic as he is the currently acting character. If Tostig had the Backstabber perk, he would have a total bonus of 20% chance to hit in this scenario. Backstabber can be very useful for mercenaries with low melee attack skill, like tanks or "cannon fodder" mercs that you plan to replace with superior quality hires at a later time.
- Another example:
- Dodge gives a bonus equal to 15% of current Initiative to both Melee Defense and Ranged Defense. Note that Dodge loses effectiveness due to certain injuries which affect Initiative and as a mercenary builds up fatigue during battle (accumulated fatigue lowers Initiative). Dodge is also less effective on characters that are wearing heavier types of armor and using heavy weapons (e.g. Fighting Axe) and even shields as your Initiative is lowered based on the fatigue penalty of equipped weapons, shields, armor and by what is being carried in your bags if it has a fatigue penalty (although this penalty is reduced by 50% while said items are in your bags).
- Shield bonuses to Melee Defense and Ranged Defense can be increased further by using the Shield Expert perk which increases the base defense bonuses of the currently equipped shield by 25%. Unique shields with higher bonuses to defense values make this perk even more potent.
- Some weapon masteries increase the to-hit chance of particular attacks of the related weapon (e.g. Sword Mastery gives the Split and Swing attacks available when using a Greatsword or Warbrand a +5% chance to hit).
- Some other perks give bonuses/maluses to hit chances under specific conditions. They are described in more detail on the Perks page.
Battle Brothers uses a day/night cycle, going through the following phases
- Dawn - Morning - Midday - Afternoon - Evening - Dusk - Night
Battles fought during the night give combatants the Nighttime debuff which gives them penalties of -2 Vision, -30% Ranged Skill and -30% Ranged Defense (if not immune to the effects - e.g. having The Fangshire helmet equipped). As Ranged Skill for both AI ranged troops and human-controlled mercenaries generally tends to be significantly higher than Ranged Defense in most cases, this usually works out in favor of the defender. Thus it is advantageous to attack enemies which have ranged superiority during Nighttime.
Ranged To-Hit ChanceEdit
Ranged to-hit rolls operate in the same manner as melee to-hit rolls, where to-hit = Ranged Skill of brother subtracted by base Ranged Defense of target. A few additional factors come into play though, besides the usual gear and perk considerations, namely:
- 1. Distance and base accuracy bonus of strike
- Regular bows suffer -4% accuracy per hex with Quickshot (no base accuracy bonus)
- Regular bows suffer -2% accuracy per hex with Aimed Shot (offset by a +10% base accuracy bonus)
- Crossbows suffer -3% accuracy per hex when using the Shoot Bolt skill (offset by the standard +10% base accuracy bonus for crossbows or +5% base accuracy bonus if using a Spiked Impaler + 15% base accuracy bonus for the Shoot Bolt skill)
- The first hex from the bowman is NOT counted and does not give penalties for the purposes of to-hit chance calculations.
(a.) Aimed Shot by a Ranged Skill 50 bowman on a Bandit Thug with a Ranged Defense skill of 0 who is 7 hexes away, will have 50% + 10% (Aimed Shot) - 12% (accuracy degradation of 2 for 6 hexes of distance) = 48% to-hit chance.
(b.) Shoot Bolt by a Ranged Skill 50 crossbowman on a Bandit Thug with a Ranged Defense skill of 0 who is 6 hexes away using a Light Crossbow, will have 50% + 10% (basic accuracy bonus for crossbows) +15% chance for Shoot Bolt - 15% (accuracy degradation of 3 for 5 hexes of distance) = 60% to-hit chance.
- Thrown weapons (e.g. Bundle of Javelins) suffer a penalty of -10% accuracy per hex (offset by a +30% base accuracy bonus). Note that, unlike bows and crossbows, thrown weapons DO count the first hex from the attacker for distance effects on accuracy.
- Regular bows suffer -4% accuracy per hex with Quickshot (no base accuracy bonus)
- 2. Cover (shown as "Line of fire blocked" with it's own unique icon of a shield with an arrow) reduces overall to-hit chance by 75%. This penalty can be reduced to 50% by the Bullseye perk. In the above example (a.), the bowman would only have a 12% to-hit chance on the Bandit Thug if he had cover (e.g he was standing behind another enemy unit or was behind one of your own units. This chance would be improved to 24% with the Bullseye perk making it a core pick for ranged mercenaries.
The initial roll on whether the shot hits the intended target or its 'Cover'(which could be another unit or an inanimate obstacle) is NOT shown on the battle log though as of release 1.1. The battle log ONLY displays the to-hit roll for the intended or unintended target, without factoring in Cover a second time.
- Ranged attacks now confer the debuff granted by the Overwhelm perk to any target struck even if it is not the intended target (e.g. hit on another target due to the scatter mechanic for ranged attacks) or even by a miss on the intended target.
- As with Melee Defense, the Dodge perk and shields also affect Ranged Defense, as does height advantage/disadvantage. The Anticipation perk confers a bonus to Ranged Defense based on the distance from the attacker and on the base Ranged Defense of the defender. The farther the distance from the attacker, the bigger of a bonus Anticipation provides to Ranged Defense. Some enemy units have access to these perks as well (e.g. Goblin Ambushers have the Anticipation perk).
- 3. Scatter is a mechanic whereby a missed ranged attack has a chance to strike an adjacent target, friendly or enemy. Because of scatter, it can be effective to fire into a block of enemy units even if your hit chance on your intended target is low for whatever reason (e.g. due to the line of fire being blocked, due to low ranged skill or due to distance). In this circumstance, you have a reasonable chance to hit something (hopefully an enemy!).
- Ranged attacks via the scatter mechanic can actually strike unintended targets one hex beyond the normal maximum range of the attack in question.
HP and Armor DamageEdit
A regular d100 roll (a procedure to get a random number in the range of 1 to 100) is made. If number is lower than to-hit % chance,then this is a hit, a 2nd d100 roll is made to see if it the attack hits the head. 
Head hits are critical hits which do +50% damage to HP, but no added damage to head armor. Base chance to hit the head is 25%, modifiable by weapons (i.e. flails, billhooks, etc), perks (Head Hunter) and Character Backgrounds(Killer on the Run, Juggler).
- If no armor is present (or armor has 0% condition) and a strike hits, then the damage will be subtracted from HP. This will be the base weapon damage plus any damage modifiers (i.e. Drunkard trait).
- When armor is present, armor takes damage first (regular damage x armor modifier) and HP takes damage subsequently ((regular damage x ignore armor modifier) - 10% of current armor).
- If armor is destroyed by a blow whose armor damage would exceed the previous durability of the former, HP damage is calculated partly due to the "ignore armor modifier" mechanic and party as a direct subtraction of the base weapon damage. The math is done by applying the "ignore armor modifier" of the base weapon damage only for the fraction of base damage that is required to destroy the armor, the rest of base damage actually damaging HP directly [5: reference "Damage Mechanic Explanation" on guide section - https://steamcommunity.com/app/365360/discussions/0/135512133547682981/].
- Billhook (70-100 base damage)
- Orc Warrior is hit in the head (critical hit), resulting in +50% HP damage
- 30% ignore armor [range: 21-30 hp damage]
- 130% vs armor [range: 91-130 armor damage]
- We roll 120 on armor damage, 27 on hp damage (which, because of the +50% bonus of critical hit, truly equals 40 hp damage).
- Result: Looted Plate takes 120 damage. 280 armor remains.
- Orc Warrior takes 40 - 28 (10% of remaining armor) = 12 hp damage
"Split Man" damage mechanics: Edit
The split man will hit the target twice in one attack.
The first hit is the same as common weapons and do 100% of weapon damage. It will roll to determine if the hit is on the head or body just like normal weapons. If it hits the head, it will do critical damage as well. The second hit will be on the other part (if first hit on body, the second on head and vice verse). This damage is 50% of the weapon damage and NEVER crit.
The raw damage can be considered as 150% weapon damage if not crit and 200% if crit (with no other crit damage bonus). But as the damage will be subtracted by armor twice (once per hit, it does less health damage than a weapon with 150% damage, while the total damage on armor is the same as 150%. [6: reference "Split Man" damage mechanics explanation" on guide section - https://steamcommunity.com/app/365360/discussions/0/135512305398270178/]
Weapon durability is important, as when a weapons or shields durability reaches zero, the weapon or shield will break.
- Melee weapon durability is lowered by 4 when it strikes metal (or other hard) armour, it doesn't lower when it hits flesh (Hitpoints).
- Shield durability is lowered if it is hit by certain Throwing Weapons (like Javelins and Throwing Axes), by being hit with the Split Shield skill of a wepaon (the shield damage will vary based on the weapon doing the splitting) or by randomly being hit with any other weapon when the attempted attack fails but doesn't miss and hit the shield instead (-1 durability for each hit, regardelss of weapon).
The Shield Expert Perk reduces the incoming shield damage by half (50%) to a minimum of one.
- Bow or Crossbow durability is lowered by 4 with each shot.