• Preamble
• Combat properties
• The Attack Value
• The Defense Value
• Critical hits
• Doing damage
• Additional effects
• Defense mode
• Covers

Combat is obviously the most important part of the game. Understanding the combat mechanics in detail is one of the key steps towards developing a good battle strategy. It is highly advised to carefully read this chapter even if you're not really into numbers. On the other hand, none of this information is required to be able to equip a squad and start experimenting with how things work – in real action!

The USC combat system uses many different variables to evaluate the result of an attack. As there's always an attacker and a target (defender), combat variables can be divided into attack and defense properties, the latter being reasonably fewer.

Defense properties are (properties of target/defender):

• (link GG armor)current Armor Rating [AR]
• (link GG defv)Defense Value [DV] (in melee)
• (link GG defv)Static Defense Value[SDV] (when being a ranged target)
• (link GG defv)Dynamic Defense Value [DDV] (when being a ranged target)
• (link UIT skill7)Stamina %

Attack properties form two major groups, one being the attributes of the attacking unit (attacker properties), the other the properties of the weapon / ammo / attack mode used (weapon properties).

Attacker properties are:

• (link GG attv)Precision (in melee; also called Base Attack Value, BAV); may incl. modifier from attack mode
• (link GG attv)Static Precision [SP] (in ranged combat); may incl. modifier from attack mode
• (link GG attv)Dynamic Precision [DP] (in ranged combat)

<*(link UIT skill6)Reaction %

Weapon specific attack properties are:

• (link GG damage)Critical Chance [CC] (also called Critical Threshold, see later)
• (link GG damage)Critical Damage Factor [CDF]
• (link GG damage)Maximum damage [maxDmg], from which the Minimum (base) damage [minDmg] is also calculated; may incl. modifier from ammo

Attack mode /+ ammo specific attack properties are:

• (link GG ARP)Armor penetration [ARP]
• (link GG IF)Impact force
• (link GG TQ)Tranquilization
• (link GG inc)Ignition chance (hidden on ATAC)
• (link GG cb)Corrosiveness (hidden on ATAC)
• (link GG cb)Biohazard (hidden on ATAC)

Although not a property, but worth listing:

• (link GG damage)Damage Factor: multiplier of the base damage
• (link GG attv)Target range (in ranged combat): a modifier for Static Defense Value
• (link GG defv)the To-Hit Value and the result of the Attack (To-Hit) Roll

The AV is a complex variable that represents the ability of the attacker to hit the target. Doing so in melee combat or from a distance is totally different, thus the calculation of the AV is not the same. AV is then subtracted from the target's Defense Value to get the To-Hit Value, against which the result of a 20-sided die roll (1-20) is tested to determine whether the attack was successful or not. This means that even under the exact same circumstances attacks have a chance to be “more or less precise”, to hit or to miss.

Melee Precision (Base Attack Value) = Melee combat %/20 (0-5) + Reaction %/20 (0-5) + attack mode (weapon) precision (0-5).

Ranged Precision has two components. Static Precision measures the basic accuracy with the weapon, based on proficiency and “static” circumstances, such as target range, light level, or obstacles in the way. Dynamic Precision refers to the attacker's ability to aim at moving or otherwise “erratic” targets, where very quick adaptation is required. The values are independent of each other per se; i.e. having good reflexes doesn't help to hit a faraway target, while being able to aim precisely at a static target doesn't necessarily mean an ability to hit fast, moving ones. (Note: the latter ability is less important, generally speaking, as the top speed of units is limited.)

Ranged Static Precision = corresponding Small/Heavy arms %/20 (0-5) + attack mode (weapon) precision (0-5) {+ bonus from targeting computer (4/8)*}.

* If enabled, gives +4 SP under normal circumstances and +8 SP in darkness or against a cloaked unit (~ counters target's Static Defense Value only from these sources).

Ranged Dynamic Precision = Reaction %/20 (0-5).

It measures the target's ability to defend itself against the attack by means of dodging, evading, or deflecting. DV does NOT protect against damage but gives a chance to avoid being hit. Defense is successful if the To-Hit Value (DV decreased by AV) is the same as or higher than the To-Hit (Attack) Roll and the attack was NOT a critical hit (see later).

Melee Defense Value = Melee combat %/10 (0-10) + Reaction %/20 (0-5) + current speed (0-5) + cover (0-6) {+ Defense Mode (0-27)} {+ cloaking (8)}.

In ranged combat, the attacker's Static Precision is subtracted from the SDV, and the Dynamic Precision is subtracted from the DDV (both are clamped at 0), then these two results are added together to get the To-Hit Value.

Static Defense Value (SDV) = range (1/grid) + cover (0-10) + darkness (0-10) {+ cloaking (8)}.

Dynamic Defense Value (DDV) = Reaction %/20 (0-5) + current speed (0-5, capped at range).

As stated above, by standard an attack is considered a successful hit if the result of the Attack Roll (1-20) is greater than the To-Hit Value, which is the target's Defense Value decreased by the attacker's Attack Value (Precision).

There is a very important exception, though. Every attack has a chance to score a “critical hit”. Critical hits are by definition considered successful hits, absolutely irrespective of the To-Hit Value. This chance is determined by the Critical Threshold, a value that is based on the actual weapon's own Critical Threshold attribute and a few modifiers (proficiency, active mods, etc). The value of the Critical Threshold is generally between 13 and 20. If the Attack Roll is equal to or greater than this, the attack is a critical hit. Critical Chance is the exact same thing, just expressed in the other way: a CT of 20 means a CC of 5% (1:20), 16 means 25% (5:20), and so on.

Beside being a granted hit, critical hits have other bonuses. They multiply the Damage Factor (default 1.0×) of the hit by 2.0 (martial & small arms) or 1.5-4.0 (heavy arms), which results in increased damage. (Prototype weapons may have a further bonus.) In addition, a critical hit always damages the target's armor by 2.

Critical hits cannot be fully averted, but (link GG specializations)Melee combat mastery decreases the attacker's chance in close combat by 5%, and the usage of a cloaking device reduces their Total Damage Factor to 0.35× (0.6× against heavy arms). Also, on lower difficulty levels lesser aliens have no chance of scoring a critical hit.

Critical hits have a chance to return some APs to the attacker. This effect is called critical AP-rebound. It symbolizes situations where the attack could be conducted faster than it was expected or where the result of the attack altered the combat situation in a sudden, but positive way. The chance for AP-rebound is Reaction % per hit (area attacks thus have good AP-rebound effectiveness). Only hitting units can confer bonus APs. The amount of APs returned per unit can be 1-4, based on luck and the (link GG skill6)Reaction skill.

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