Hardline

Hardline is a Tier 2 perk available in Call of Duty: Modern Warfare 2 and a Tier 1 perk going to be featured in Call of Duty: Black Ops. It reduces the amount of kills required to gain a Killstreak reward by one.

Call of Duty: Modern Warfare 2
In Modern Warfare 2, it allows the player to gain their killstreak rewards with one less kill. For instance, if the player had UAV Recon, Care Package and Sentry Gun as killstreak rewards, rather than needing 3, 4 and 5 kills respectively, they would only need 2, 3 and 4 kills. It is useful with all classes, although especially useful with classes with guns which carry little ammo, or ammo which is used up quickly, such as the Vector, because it means fewer bullets are needed to gain killstreak rewards. Hardline Pro is unlocked after obtaining 40 killstreak rewards (not getting at least a 2 kill streak 40 times, as many may think), the easiest way to do this is set the player's killstreak rewards to require 3, 4 and 5 kills. The Pro version of the perk allows deathstreaks to be activated by one less death. For example, if the player has Final Stand as a deathstreak, requiring four deaths, with Hardline Pro the player only needs to die three times before the deathstreak is activated.

Call of Duty: Black Ops
Hardline is set to return in Call of Duty: Black Ops, this time as a Tier 1 perk. Like the Modern Warfare 2 version, Hardline will decrease the number of kills needed for a killstreak by one. The Pro version of this perk allows you to get a second chance on the result of care packages.

When this perk is chosen, a belt, appearing similar to a sash, is added to the player's character model.

Utility
The utility of this perk in improving kill/death ratios is debatable. Depending on the killstreak the perk will decrease the kills needed for the killstreak by 33% of what is required (UAV, for instance) to only 4% for the Tactical Nuke. This means that builds featuring killstreaks that require fewer successive kills receive more benefits from Hardline. On one hand: Stopping Power, Danger Close, or Cold-Blooded allow the player an excellent chance of getting the necessary kills for a killstreak reward while simultaneously allowing the player the freedom to improve their kill-death ratio gradually without relying on the "magic numbers" needed for a kill streak (since these numbers can be difficult to attain on certain maps or against certain teams). On the other hand, killstreaks can cause dramatic spikes in a player's kills without undue risk to a player, potentially increasing a player's kill/death ratio substantially (in addition to suppressing the enemy team: it's very hard to move about and secure objectives with an AC-130 overhead).

On the other hand, the killstreaks with the greatest degree of utility (AC-130s, Chopper Gunners, Pave Lows, Harriers, and Attack Helicopters) can be countered by launchers with surprising ease, whereas "unstoppable" killstreaks (such as Predator Missiles, Precision Airstrikes, Stealth Bombers, Tactical Nukes, and EMPs) are either much more random in their effectiveness (Predator Missiles, Airstrikes, and Stealth Bombers are quite capable of failing to achieve even a single kill for the player using them or incapable entirely, such as with EMPs) or very difficult to acquire, regardless of the presence of Hardline. Lastly, Hardline's utility depends on the killstreaks the player has equipped.

Instead of being used to directly improve a player's kill/death ratio, Hardline can be considered a "support" perk: with the right killstreak rewards, a player can use Hardline to consistently deploy killstreaks that benefit the whole team: UAV Recon, Care Package, Counter-UAV, and Sentry Guns are all killstreaks that both receive substantial benefits from Hardline and provide support for the entire team, allowing them to pursue mission objectives and take down opposition with greater ease. This can be exceptionally useful in game modes like Domination, in which a succession of these killstreak rewards can help take the pressure off friendly players.

Hardline is a very useful perk in Search and Destroy where killstreaks are often short, and become much more valued.

Trivia

 * Politically, a "hardliner" is any extreme, militant, and uncompromising doctrine.
 * Hardline could also be a computer reference where equipment is directly plugged into servers for optimal performance.
 * The Perk emblem resembles the screen of an EKG machine.