Collateral damage is an ability certain military units have which allows them to inflict damage on multiple enemy units in a defending stack. Collateral damage is often referred to by players as just "collateral". Units which inflict collateral damage include most siege units, bombers, and some naval units; these units are referred to collectively in this article as "collateral units".
Implementation 
Edit
When a unit with the collateral damage ability attacks a stack (that is, 2 or more enemy units in the same tile), it will face one particular defender -- whichever defender is strongest against it. That attack is computed normally. But regardless of which unit wins the main battle, or how many rounds the battle goes, the attacker gets an extra damage round applied to 5-8 other defenders in the stack. The damage done is 50% of normal, so it tends to be around 10 hitpoints of damage.
Units which can inflict collateral damage have a maximum level of damage they can inflict on the attack. This collateral damage cutoff applies to all collateral attacks. If a defending unit is assigned collateral damage in the collateral portion of the attack which would lower its hitpoints below the cutoff, it only takes enough damage to drop it to the cutoff. Units which are at or below the cutoff will not be chosen for collateral damage infliction; it will go instead to some other healthier defender in the stack.
Some units also have a damage cutoff that applies to their main attack. Enemy units which are already damaged to a unit's primary attack damage cutoff cannot be attacked by it. If the main defender drops below the cutoff level during its battle with the attacking unit, the battle ends immediately; this effect is similar to withdrawal. If no defender in a stack is above a unit's primary attack damage cutoff level, then the unit cannot attack that stack.
Units with Collateral Edit
The following units can inflict collateral damage. Their strength and maximum damage cutoff is also given.
- Catapult (5) 75%
- Hwacha (5) 75%
- Trebuchet (4) 75%
- Cannon (12) 80%
- Artillery (18) 85%
- Mobile Artillery (26) 85%
- Bomber (16) 50%
- Stealth Bomber (20) 50%
- Battleship (40) 60%
- Missile Cruiser (40) 60%
Other units:
- Cho-Ko-Nu (6) 60%
