Collateral damage (Civ4)

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 ==
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 hit points 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 hit points 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 ==
The following units can inflict collateral damage. Their strength, maximum damage cutoff, collateral damage cutoff, and number of units affected is also given. For siege and air units, their full strength is converted to collateral damage. For naval and other units, half their strength is converted to collateral damage.
* Siege weapons:
** Catapult (5) 75% max, 50% from collateral, to up to 6 units
*** Hwacha (5) 75% max, 50% from collateral, to up to 6 units
** Trebuchet (4) 75% max, 50% from collateral, to up to 6 units
** Cannon (12) 80% max, 60% from collateral, to up to 7 units
** Artillery (18) 85% max, 70% from collateral, to up to 8 units
** Mobile Artillery (26) 85%, 70% from collateral, to up to 8 units
* Air units:
** Bomber (16) 50% max, 50% from collateral, to up to 5 units
** Stealth Bomber (20) 50% max, 50% from collateral, to up to 6 units
* Naval units:
** Battleship (40) 100% max, 60% from collateral, to up to 5 units
** Missile Cruiser (40) 100% max, 60% from collateral, to up to 5 units
* Other units:
** Cho-Ko-Nu (6) 100% max, 60% from collateral, to up to 5 units
== Using Collateral Damage ==
Collateral damage is extremely useful if you're trying to attack a tile that's occupied by a large number of units. This situation happens most commonly when attacking a city. A good strategy when attacking a city is to first soften up the defenses with bombers, siege units, or naval units, then use siege units to attack to inflict collateral damage to the defenders remaining inside the city. Then, follow up with melee, gunpowder, mounted, ranged, or armored units, as appropriate.
The same strategy can also be used if you're trying to defend a city that's being besieged. Engage the enemy with siege units, then send your defenders on a sortie to defeat the now weakened attacking force.
== Preventing Collateral Damage ==
If you're trying to survive a siege, collateral damage can severely weaken your defenders and make them very vulnerable. A partial solution is to put siege units inside your own cities, as they're immune to collateral damage from other siege units, though they tend to be rather weak at defense, so they may be better suited to inflicting collateral damage on the besiegers. Another solution is to build several mounted units with the Flanking promotion and attack the attackers. Even if your opponent has guarded their stack well against such attacks, the mounted units don't have to win - they just have to not be killed. This will enable them to flank attack the siege units, potentially even destroying some of them.
If you have a belligerent neighbor, consider researching the Railroad technology as soon as possible and placing many Machine Guns inside any vulnerable city. Machine Guns aren't vulnerable to collateral damage from siege units, though they are vulnerable to bombers, so you will want to support them with SAM Infantry.
Category:Combat (Civ4)
Category:Game concepts (Civ4)