Call Of Duty : Modern Warfare 2
Hardline is a perk available in Modern Warfare 2. It is a Tier Two Perk which is unlocked at Level 9, and 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 your killstreak rewards to require 3, 4 and 5 kills. The Pro version of the perk allows deathstreaks to be activated after 1 fewer death, with the exception of Painkiller.
The utility of this perk in improving kill/death ratios is debatable. On the 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 asPredator Missiles, Precision Airstrikes, Stealth Bombers, and Tactical Nukes) 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 very difficult to acquire, regardless of the presence of Hardline. Lastly, Hardline's utility depends on the killstreaks the player has equipped. In terms of percentages, UAV Recon requires 33% fewer kills to achieve with Hardline, whereas a Tactical Nuke is only 4% easier to achieve with Hardline. This means that builds featuring killstreaks that require fewer successive kills receive more benefits from Hardline.
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.
Call Of Duty : Black Ops
Below is a table showing the default Care Package probabilities compared to the re-roll probabilities. As can be seen re-rolling favors middle killstreaks much more than Care Packages, while higher killstreaks are almost unchanged.
Reward Default % Re-Roll % Ammo 20% 9% Spy Plane 15% 9% Counter-Spy Plane 15% 9% RC-XD 9% 9% Valkyrie Rockets 5% 9% Mortar Team 5% 9% Sentry Gun 5% 9% SAM Turret 5% 9% Rolling Thunder 3% 4% Grim Reaper 3% 4% Napalm Strike 3% 4% SR-71 Blackbird 3% 4% Attack Helicopter 3% 4% Death Machine 2% 3% Chopper Gunner 2% 3% Attack Dogs 1% 1% Gunship 1% 1%