Perks

Perks (also known as Specialties) are modifiers in multiplayer only 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.

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.


 * Vehicle perks, shades, and reconnaissance 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.

Call of Duty: Black Ops
All Perks are unlocked for purchase at level 4. Unlocking Pro Perks will require either one, two or three sets of challenges related to the standard version, as well as the purchase of the ability for 2000 cp.

First tier perks designate player appearance and provide constant passive effects. Second tier perks enhance weapon performance. Third tier perks are either active or passive and are generally more context-sensitive than first tier perks. The perks featured in Call of Duty: Black Ops are as follows.

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

Trivia

 * In Call of Duty 4, the Tier 1 perks originally appeared after Tier 3 perks.
 * Tier 1 perks in Call of Duty: Black Ops affect the user's third person player appearance.
 * 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 someone climbing a tree in this video can be seen:
 * 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. Although your perk changes in game, it will only affect the class you got pro on, you'll have to go to the menu to change to the pro perk in another class.
 * 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 watching someone in the Killcam in Call of Duty: Modern Warfare 2, the text by each perk will not say that the perk is pro unless one has the pro version of each and any respective perk. However the pictures have the star background showing that the perk is pro.
 * Call of Duty: Black Ops for the Nintendo DS will be the first Nintendo DS game to feature perks.
 * 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: [2]
 * Modern Warfare 2 and Call of Duty: Black Ops are the only Call of Duty games to feature pro versions of perks.
 * In World at War Tier 1 perks were originally green-colored. The green color for early World at War perks is brighter than color of Call of Duty 4 Tier 3 perks.