Perks

Perks are modifiers in multiplayer only that affects game play, allowing further customization of classes. They can affect available equipment or player's properties such as speed. Elite title of the Perk has been added only to Tier 1 perks. Perks are upgraded when "leveled up".

Tier 1 Perks
They're most notable because they change the player character models.
 * Hardline: Killstreaks are earned by one less kill.
 * Hardline (Pro): You can now change the contents of a care package and flinch less when shot.
 * Hardline (Elite): HOT (Healing Over Time) has been shortened, each 2 assists will be counted as a kill and can revive himself after killing an enemy while Last Stand.
 * Scavenger: You can earn ammo by taking blue backpacks that players drop when they're killed.
 * Scavenger (Pro): You start with max ammo, earn lethal and frag grenades while scavenging.
 * Scavenger (Elite): Now you can refill your equipment when taking blue backpacks.
 * Lightweight: You can move faster.
 * Lightweight (Pro): You take no fall damage.
 * Lightweight (Elite): You can do now a power slide instead of a quick prone position.
 * Juggernaut: You can take more damage (health is increased by 25%) and throw back grenades safely.
 * Juggernaut (Pro): You can carry heavy weapons without losing your normal speed.
 * Juggernaut (Elite): Inmunity to explosives and fire by 50% and increased bullet damage.
 * Ghost: Undetectable by UAV.
 * Ghost (Pro): Undetectable by Pave Low, Attack Helicopters and Sentry guns.
 * Ghost (Elite): Undetectable by thermal scopes, no red crosshair or name shown when targeted and undetectable by Predator Missiles.

Tier 2 Perks

 * Predator: Increased bullet penetration.
 * Predator (Pro): Extra damage to enemy equipment and aircraft.
 * Sharpshooter: Hold the breath longer.
 * Sharpshooter (Pro): Switch weapons faster.
 * Steady Aim: Increased hip fire accuracy.
 * Steady Aim (Pro): Recover faster from knife lunges and faster ADS after sprinting.
 * Sleight of Hand: Faster reloading.
 * Sleight of Hand (Pro): Faster ADS. (Aiming Down the Sights)
 * Warfighter: You can equip 2 attachments to your primary and secondary weapons.
 * Warfighter (Pro): Start with more grenades and can equip two primary weapons.

Tier 3 Perks

 * Running Back: You can sprint for a longer time.
 * Running Back (Pro): Unlimited sprint.
 * Shadow Man: Quiet Movement by 75%.
 * Shadow Man (Pro): Hear enemies louder. Player become completely silent.
 * Second Chance: Survive lethal damage and use a pistol to defend oneself. Cannot be revived.
 * Second Chance (Pro): Survive lethal damage and use a pistol to defend onself. You can revived by a teammate.
 * Hacker: Detect enemy equipment.
 * Hacker (Pro): Hack enemy equipment, sabotage enemy care packages, turn enemy turrets into friendly ones.
 * Gas Mask: Inmune to Nerve Gas.
 * Gas Mask (Pro): Reduces the enemy flashbangs, concussion grenade effects and reveals the positions of stunned enemies.

Special Perks

 * Blood Rage: Damage increased by 40% when you're hurt. Auto-reviving when lethal damage is dealt.
 * Adrenaline Rush: Speed increased by 15% when you're hurt.
 * Combat Intuition: Allows you to sense if an enemy is aiming to you (If they're near, so it's almost useless for campers and snipers).
 * Supply Commander: Allows you to share part of your ammo with your teammates.

Perk Unlocking (14/10/12)

 * Hardline is unlocked after reaching the rank 'Sergeant' (Level 13).
 * Scavenger is unlocked after reaching the rank 'Sergeant II' (Level 15).
 * Lightweight is unlocked after reaching the rank 'Private First Class' (Level 4).
 * Ghost is unlocked after reaching the rank 'Specialist I' (Level 8).
 * Juggernaut is unlocked after reaching the rank 'Staff Sergeant' (Level 16).
 * Predator is unlocked after reaching the rank 'Master Sergeant' (Level 22)
 * Sharpshooter is unlocked after reaching the rank 'Corporal' (Level 10)
 * Steady Aim is unlocked after reaching the rank 'Specialist' (Level 7)
 * Sleight of Hand is unlocked after reaching the rank 'Private First Class I' (Level 5)
 * Warfighter is unlocked after reaching the rank 'Sergeant Major' (Level 28)
 * Running Back is unlocked after playing once with a Recruit class.
 * Shadow Man is unlocked after reaching the rank '2nd Lieutenant' (Level 34)
 * Second Chance is unlocked after reaching the rank 'Captain' (Level 40).
 * Hacker is unlocked after reaching the rank 'First Sergeant' (Level 25).
 * Gas Mask is unlocked after being flashed, stunned or poisoned with gas for the first time.
 * Blood Rage is unlocked after completing the Hardline Contract.
 * Supply Commander is unlocked after completing the Scavenger Contract.
 * Adrenaline Rush is unlocked after completing the Lightweight Contract.
 * Combat Intuition is unlocked after completing the Ghost Contract.
 * Jugg Walk is unlocked after completing the Juggernaut Contract.
 * One Man Army is unlocked after completing all the five contracts and reached the rank 'Commander' (Level 70) for the second time (by Re-Setting, as there is no Prestige Mode).