Defense

Defense is both a unit attribute and a gameplay mechanic in XCOM: Enemy Unknown.

Overview

Defense directly decreases an enemy's chance to hit the unit with most weapons. It does not reduce the damage sustained when hit. Note that melee attacks, area of effect weapons (such as grenades and rocket launchers), and offensive abilities ignore a unit's Defense attribute and always hit.

Chance to Hit

A unit's chance to hit is:

Shooter's Aim - Target's Defense ± Weapon Range Modifier

The game mechanic adds the shooter's Aim attribute to any applicable Aim modifiers (abilities, items, etc.), subtracts the target's Defense attribute and modifiers, then adds or subtracts a weapon range modifier (if applicable), to determine the chance to hit.

For example, an enemy with 65 Aim has a 65% chance to hit (without taking into account weapon range and other modifiers). A soldier in full cover is granted 40 Defense, giving the shot a 25% chance to hit.

When aiming a shot, the player can select "More Info" to see a list of modifiers that are currently being applied.

Units

XCOM

XCOM soldiers have an innate Defense attribute of 0.
MEC Troopers are granted 10 Defense via their MEC.
S.H.I.V.s have 20 Defense.
Alloy S.H.I.V.s have 30 Defense.
Hover S.H.I.V.s have 40 Defense.

Alien

Aliens have an innate Defense attribute that is determined by their species and the game difficulty:

Alien Defense
Species	Defense	Species	Defense
Berserker	20 · 20 · 20 · 20	Muton Elite	20 · 20 · 30 · 30
Chryssalid	10 · 10 · 10 · 10	Outsider	0 · 0 · 10 · 10
Cyberdisc	10 · 10 · 10 · 10	Sectoid	0 · 0 · 0 · 0
Drone	10 · 10 · 10 · 10	Sectoid Commander	20 · 20 · 20 · 20
Ethereal	40 · 40 · 40 · 40	Sectopod	30 · 30 · 30 · 30
Floater	0 · 0 · 0 · 0	Seeker ^EW	10 · 10 · 20 · 20
Heavy Floater	10 · 10 · 10 · 10	Thin Man	0 · 0 · 0 · 0
Mechtoid ^EW	10 · 10 · 10 · 10	Uber Ethereal	40 · 40 · 40 · 50
Muton	10 · 10 · 10 · 10	Zombie	0 · 0 · 0 · 0
Easy · Normal · Classic · ImpossibleSource: DefaultGameCore.ini, XCOM: Enemy Within

EXALT

All EXALT members have an innate Defense attribute of 0.

Cover

Main article: Cover

Using cover increases a unit's Defense. Conversely, units receive a +50% critical chance bonus when targeting an exposed enemy. These factors combine to make cover the most frequently used method of boosting a unit's Defense. There are two types of cover available, full and partial:

Full cover: +40 Defense
Partial cover: +20 Defense

All EXALT units and most alien species can use cover for Defense bonuses equal to XCOM's. Chryssalids, Cyberdiscs, Drones, Ethereals, MEC Troopers, Mechtoids, Sectopods, Uber Ethereals, Zombies, and all varieties of S.H.I.V.s cannot use cover.

Bonuses and Perks

Beyond the use of cover, there are a substantial number of ways to increase a unit's Defense.

Basic Abilities and Traits

Ability / Trait	Description
Evasion	+20 Defense when airborne. XCOM: Soldiers equipped with Archangel Armor Enemies: Cyberdisc, Drone, Floater, Heavy Floater, Seeker
Head Down	+10 Defense, even when not in cover. XCOM: Civilians only Enemies: None
Hunker Down	Doubles the cover Defense bonus. XCOM: Assault, Heavy, Sniper, Support Enemies: All Muton species, All EXALT units

Class Abilities

Class	Ability	Description
Assault	Tactical Sense	+5 Defense per enemy in sight (max +20).
MEC ^EW	Automated Threat Assessment	Confers +15 Defense when in Overwatch.
MEC ^EW	Distortion Field	Nearby allies in cover receive +10 Defense. (Support-based MEC Troopers)
Psionic	Telekinetic Field	Grants +40 Defense to all units within the field.
Sniper	Damn Good Ground	Confers +10 Aim and +10 Defense against enemies at a lower elevation.
Sniper	Low Profile	Makes partial cover count as full.
Support	Dense Smoke	Smoke Grenades increase Defense by +40 instead of +20.
Support	Smoke Grenade	Confers +20 Defense to all units in the smoke cloud.