Perks

Perks (referred as Specialties) are multiplayer modifiers in Call of Duty 4: Modern Warfare, Call of Duty: World at War, Call of Duty: Modern Warfare 2, Call of Duty: Black Ops and Call of Duty: Black Ops (Nintendo DS) that passively affect game play, allowing further customization of classes. They affect available equipment, effectiveness of the player's equipment, the usefulness of the enemy's equipment, and the physical properties of the player's character.

Call of Duty 4: Modern Warfare Perks
Some perks are available initially while others are unlocked as the player progresses through multiplayer ranks. Up to three perks, one of each tier, can be equipped at one time. The tiers are color coded blue, red, and green and therefore only one of each can be equipped. 

First Tier
These perks deal with a player's equipment and/or explosives. First tier perks are colored blue.

Second Tier
These perks modify player's or enemy weapons effectiveness. Second tier perks are colored red.

Third Tier
These perks give the player various abilities. Third tier perks are colored green.

Call of Duty: World at War Perks
Like in Call of Duty 4: Modern Warfare, the perks are divided into equipment, weapon and ability tiers.

First Tier
Special Grenades x3
 * Gives the player 3 special grenades excluding smoke grenades.

Satchel Charge x2


 * Similar to the C4 x2 in Call of Duty 4.

M9A1 Bazooka x2
 * Similar to the RPG in Call of Duty 4

Bomb Squad
 * Same as it was in Call of Duty 4, you can see where enemy Satchels and Bouncing Betties are located.

Bouncing Betty x2
 * Similar to the Claymore x2 in Call of Duty 4, mines that are planted in the ground (Bouncing Betties are more powerful).

Bandolier
 * Increases initial ammo for your selected weapons.

Primary Grenades x2
 * 2 frag grenades, sticky grenades, or Molotov Cocktails.

M2 Flamethrower
 * The player is equipped with a flamethrower.

The following attachments replace Perk 1:

Rifle Grenade Foregrip
 * Attaches a high-velocity impact grenade launcher to a semi-automatic or bolt-action rifle (it is always armed unlike in Call of Duty 4: Modern Warfare and Modern Warfare 2.
 * Decreases the recoil of shotguns.

Second Tier
Stopping Power
 * Each bullet does 40% more damage and is canceled out by the "Juggernaut" perk.

Fireworks
 * Explosive damage is increased by 40%.

Flak Jacket
 * Reduces incoming explosive damage by 25% and caps damage at 3/4 of the player's health. Canceled out by the "Fireworks" perk.

Gas Mask
 * The effects of Tabun gas are decreased.

Juggernaut
 * Reduces incoming damage by 25% and is canceled out by the "Stopping Power" perk.

Camouflage
 * The player doesn't get exposed by recon planes. Identical to UAV Jammer.

Sleight of Hand
 * Reloading is quicker.

Shades
 * Reduces the effect of signal flares on the player's vision. (This perk changes the character model.) Not available on the Wii version.

Double Tap
 * Decreases time between bullets by a third.

Overkill
 * Allows the player to wield 2 primary weapons (meaning no pistols). Same as Call of Duty 4.

Third Tier
Deep Impact
 * Gives the user's weapon more penetration power.

Extreme Conditioning
 * Gives the player the ability to sprint longer.

Steady Aim
 * More accuracy when firing from the hip. Note: this does not help with aiming down the sights.

Toss Back
 * When tossing back a grenade, it resets the grenade fuse.

Second Chance
 * Almost the same as Last Stand in Call of Duty 4 except the player survives for 30 seconds and another player who has Second Chance will be able to revive the player.

Martyrdom
 * When the player is killed, they drop a live grenade.

Fireproof
 * Damage from fire done to the player is reduced to 55%.

Dead Silence
 * The player barely makes noise when walking or sprinting.

Iron Lungs Reconnaissance
 * Gives the user the ability to hold their breath with a sniper rifle for 10 seconds instead of 4. Not available on the Wii version.
 * Gives the player the ability to see all artillery, dogs, and tanks on the map. Not available on the Wii version.

Vehicle Perks
Water Cooler
 * Decreased turret overheating.

Greased Bearings
 * Increased turret rotation speed.

Leadfoot
 * Increases the speed of the tank.

Ordnance Training
 * Boosts the firing rate of the tank's main firing cannon.

Coaxial Machine Gun
 * Allows the driver to use a coaxial machine gun only in the front of the tank.

Shades, Reconnaissance, Iron Lungs, and Vehicle perks are not available on the Wii version of Call of Duty: World at War.

Call of Duty: Modern Warfare 2 Perks
In Call of Duty: Modern Warfare 2 the perks are divided into tiers in different way than in Call of Duty 4 and World at War Along with standard perks, players will now be able to unlock improved "Pro" versions of certain perks by fulfilling certain requirements while using them. These "Pro" versions include the original abilities of the perk, but also add new benefits. Many of the perks that were in Call of Duty 4 or 5 that are missing are now either part of a Pro perk, available as weapon attachments, or are now deathstreaks, such as Deep Impact (FMJ), Martyrdom and Double Tap (Rapid Fire). The Overkill perk has been replaced partially by the inclusion of Machine Pistols, Shotguns, and Launchers as secondary weapons and also by the One Man Army and Bling perks. Interestingly, if a Perk Challenge IV is achieved mid-game the "Pro" version will take effect immediately for all classes equipped with that perk. However, the effect of the Pro version is granted after respawning.



First Tier
This tier affects players in terms of Movement Speed (Sleight of Hand/Marathon), Ammunition (Scavenger, One Man Army).

Marathon (Unlocked at level 1)
 * Unlimited sprint. (Replaces Extreme Conditioning)
 * Marathon Pro: Climb ladders and objects faster.
 * Unlock Pro: Run 26 miles using marathon.
 * Unlock Emblem: Run 104 miles using marathon

Sleight of Hand (Unlocked at level 1)
 * Faster reloading.
 * Sleight of Hand Pro: Faster aiming down the sight or scope.
 * Unlock Pro: Get 120 kills using Sleight of Hand.
 * Unlock Emblem: Get 750 kills using Sleight of Hand.

Scavenger (Unlocked at level 13)
 * Resupply from dead bodies.
 * Scavenger Pro: Extra mags upon spawning. (Replaces Bandolier)
 * Unlock Pro: Resupply from 100 dead bodies.
 * Unlock Emblem: Resupply from 500 dead bodies.

Bling (Unlocked at level 21)
 * Allows two attachments to primary weapon.
 * Bling Pro: Allows two attachments to secondary weapon.
 * Unlock Pro: Get 200 kills using two weapon attachments
 * Unlock Emblem: Get 900 kills using two weapon attachments.

One Man Army (Unlocked at level 45)
 * Allows class switching ingame. (Replaces secondary weapon)
 * One Man Army Pro: Faster class switching (from 5 seconds to 3).
 * Unlock Pro: Get 120 kills using One Man Army
 * Unlock Emblem: Get 750 kills using One Man Army

Second Tier
This Tier deals with the effects on Damage (Stopping Power/Danger Close), Movement (Lightweight) and bonus effects on Killstreaks (Hardline/Cold-Blooded).

Stopping Power (Unlocked at level 1)
 * Increased bullet damage by 40%.
 * Stopping Power Pro: Increased damage versus vehicles.
 * Unlock Pro: Get 250 kills using Stopping Power
 * Unlock Emblem: Get 1000 kills using Stopping Power

Lightweight (Unlocked at level 1)
 * Move 7% faster.
 * Lightweight Pro: Quicker aiming after sprinting.
 * Unlock Pro: Run 30 miles using Lightweight.
 * Unlock Emblem: Run 250 miles using Lightweight.

Hardline (Unlocked at level 9)
 * Killstreaks require 1 less kill.
 * Hardline Pro: Deathstreaks require 1 less death.
 * Unlock Pro: Get 40 killstreaks while using Hardline.
 * Unlock Emblem: Get 250 killstreaks while using Hardline.

Cold-Blooded (Unlocked at level 25)
 * Makes the user invisible to enemy thermal optics, and enemy killstreaks. (replaces UAV Jammer and Camouflage)
 * Cold-Blooded Pro: No red crosshair or name when targeted.
 * Unlock Pro: Destroy 40 killstreak rewards using Cold Blooded.
 * Unlock Emblem: Destroy 250 killstreak rewards using Cold-Blooded.

Danger Close (Unlocked at level 33)
 * Increased explosive damage. (replaces Sonic Boom and Fireworks)
 * Danger Close Pro: Increased damage from killstreak rewards.
 * Unlock Pro: 100 kills using explosives while using Danger Close.
 * Unlock Emblem: 500 kills using explosives while using Danger Close.

Third Tier
This tier effects the enemy players equipment (Sitrep)and gives players a tactical advantage in combat (Scrambler/Ninja/Steady Aim/Commando/Last Stand).

Commando (Unlocked at level 1)
 * Increased melee lunge distance.
 * Commando Pro: No falling damage.
 * Unlock Pro: 20 melee kills using Commando
 * Unlock Emblem: 100 melee kills using Commando

Steady Aim (Unlocked at level 1)
 * Increased hip-fire accuracy.
 * Steady Aim Pro: Breath can be held longer while aiming down a sniper or thermal scope. (Replaces Iron Lungs)
 * Unlock Pro: 80 hip fire kills using Steady Aim.
 * Unlock Emblem: 500 hip-fire kills using Steady Aim.

Scrambler (Unlocked at level 17)
 * Jams the enemy radar when they are close enough.
 * Scrambler Pro: Delays enemy claymore explosions.
 * Unlock Pro: 50 close range kills using Scrambler.
 * Unlock Emblem: 250 close range kills using Scrambler.

Ninja (Unlocked at level 29)
 * Makes Player invisible to the Heartbeat Sensor.
 * Ninja Pro: 4x quieter footsteps. (Replaces Dead Silence)
 * Unlock Pro: 50 close range kills using Ninja.
 * Unlock Emblem: 250 close range kills using Ninja.

SitRep (Unlocked at level 37)
 * Detect enemy explosives (Claymores, C4, and Grenades) and Tactical Insertions. (Replaces Bomb Squad)
 * SitRep Pro: 4x louder enemy footsteps (Cancels out Ninja Pro users, whose footsteps remain at 1/4x regular volume).
 * Unlock Pro: Destroy 120 enemy explosives using Sitrep.
 * Unlock Emblem: Destroy 750 enemy explosives using Sitrep.

Last Stand (Unlocked at level 41)


 * Use a pistol while bleeding out prior to death.
 * Last Stand Pro: Use your equipment and knife in Last Stand.
 * Unlock Pro: 20 kills while in Last Stand
 * Unlock Emblem: 100 kills while in Last Stand

Deathstreaks
Copycat (Unlocked at level 4, although is available in default classes) Painkiller (Unlocked at level 6, although available in some default classes) Martyrdom (Unlocked at level 27) Final Stand (Unlocked at level 39, although available in some default classes)
 * Copy the loadout of the person who last killed you during the killcam/second after death
 * Unlock Emblem: Kill the person who last killed you with their loadout
 * 4 deaths without kill
 * Divide all incoming damage by 3
 * Unlock Emblem: Survive over 100 damage
 * 3 deaths without kill
 * Drop a live frag grenade upon death
 * Unlock Emblem: Get one kill with Martyrdom grenade
 * Note: Grenade acts like a normal frag and will roll/be thrown
 * 4 deaths without kill
 * Survive after lethal amount of damage (not headshots, knives or explosions) and use primary/secondary weapons and equipment
 * Unlock Emblem: Survive long enough to stand back up
 * 4 deaths without a kill

Black Ops
Perks are going to return back in Call of Duty: Black Ops. There will be no return of the perks Commando or One Man Army.

Scavenger will return, but it will not replenish Equipment.

It is confirmed that Lightweight, Steady Aim and Sleight of Hand return. Also, there will be no Stopping Power or Juggernaut.

Tier 1 Perks change your appearance:

Tier 1: Lightweight, Scavenger, Ghost, Flak Jacket, Hardline

Tier 2: Hardened, Scout, Steady Aim, Sleight of Hand, Warlord

Tier 3: Marathon, Ninja, Second Chance, Hacker, Tactical Mask

Black Ops (Nintendo DS)
Perks are going to be featured in Call of Duty: Black Ops (Nintendo DS).

Trivia

 * There were rumors on the internet of a "monkey man" perk on Call of Duty: World at War, allowing the ability to climb trees, although there has never been any evidence of the perk. This rumor likely started because you can see someone climbing a tree in this video: http://www.gametrailers.com/video/exclusive-debut-call-of/35340
 * The monkey man perk was even more convincing after a glitch on Makin was found, allowing the player to jump on top of a tree.
 * If a player unlocks the Pro version of a Perk in Call of Duty: Modern Warfare 2, the Perk will change automatically during the game and so the player won't have to change the perk in the Create-A-Class menu.
 * Pro Perks of Call of Duty: Modern Warfare 2 all have stars as the background of the perk's icon, superimposing the graphic on top of it.
 * If spectating someone in Call of Duty: Modern Warfare 2, the text by each perk will not say that the perk is pro unless you have the pro version yourself. However the pictures have the star background showing that the perk is pro.
 * A glitch was found for getting Cold-Blooded Pro, in which if a helicopter is shot down by bullets causing it to spin down, every bullet that is shot into the falling helicopter will count as a killstreak destroyed. In order for this to work, the player must have Cold-Blooded while shooting the falling helicopter. This is demonstrated in this video: http://www.youtube.com/watch?v=ne-ECiZYiyk