Tactical Knife

The Tactical Knife is a weapon attachment featured in Call of Duty: Modern Warfare 2, Call of Duty: Modern Warfare 3 and Call of Duty: Black Ops II for handguns.

Call of Duty: Modern Warfare 2
The Tactical Knife attachment allows the character to hold both a pistol and a knife at the same time, letting the player stab about twice as fast. The Tactical Knife can be used with all handguns, although in the single player campaign it is only used with the USP .45 by default. The ability to knife faster and more frequently is advantageous in close quarters combat. The Tactical Knife attachment seems to offer no downside whatsoever versus the base weapon, with the exception of increasing visual recoil on USP .45 and M9, which may disturb the player's performance.

Call of Duty: Modern Warfare 3
The Tactical Knife attachment returns in Call of Duty: Modern Warfare 3, being functionally the same, and once again, exclusive to Pistols. It is unlocked at weapon level 7. On the 2 revolvers in MW3, unlocking The Tactical Knife brings the weapon level to 10, the maximum for the normal pistols, since extended mags isn't available.

Call of Duty: Black Ops II
The Tactical Knife attachment returns in Call of Duty: Black Ops II. However, the model of the knife is not the same as from the previous games.

Trivia

 * The Tactical Knife in Modern Warfare 2 and Modern Warfare 3 uses the same model as the throwing knife.
 * In early demonstration videos, such as the "Cliffhanger" video, the knife user slashed with it. In the final version, the user stabs with the knife.
 * In Modern Warfare 2 Singleplayer, the USP .45 always appears with a Tactical Knife, although never identified as such.
 * In Multiplayer, the Tactical Knife has no third person model. Players will look like they're holding a pistol with no attachments. Also, the Tactical Knife uses same melee animation as generic melee in third person. However, in Black Ops II this was fixed.
 * The .44 Magnum has a different reload animation when equipped with the Tactical Knife.
 * When the M9 is equipped with the Tactical Knife in Multiplayer, the reload animation doesn't show a magazine.
 * Kills with the Tactical Knife do not count towards the Veteran challenge for the gun, only kills by shooting will count towards the challenge. However, kills with the Tactical Knife do count towards the Marksman challenge for the weapon.
 * There is a visible recoil decrease when using the tactical knife on the .44 Magnum.
 * When using the Tactical Knife on the Desert Eagle in Call of Duty: Modern Warfare 2, its sights become correctly aligned. In Call of Duty: Modern Warfare 3, equipping the tactical knife on the Desert Eagle will reduce its vertical visual recoil somewhat.
 * The MP412 equipped with a Tactical Knife has a shorter reload animation, as the player doesn't rotate the cylinder.
 * The MP412 has a much slower draw time with Tactical Knife.