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. It does, however, correctly align the Desert Eagle's iron sights when attached.
Tactical Knife, as shown in an early demonstration of Cliffhanger.
The final version of the tactical knife. Note the angle the knife is held at.
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 two 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.
The Tactical Knife attachment returns in Call of Duty: Black Ops II. The tactical knife is unlocked at weapon level 9 for the pistols. It performs similarly to Combat Knife (in fact, the knife held is the Combat Knife) as it has a little lunge and can be used more rapidly than the standard knife.
The Tactical Knife returns in Ghosts. Unlike the regular Combat Knife, the Tactical Knife does not immobilise the player for a few seconds when stabbing a target, generally making it a preferable choice over the standard Combat Knife.
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 the same melee animation as generic melee in third person. However, in Call of Duty: Black Ops II this was fixed.
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.
In general, most guns equipped with the Tactical Knife are held farther away from the player. This causes iron sights to appear smaller, but does not change weapon zoom in any way.
While aiming with the Tactical Knife equipped, the sights can be seen shaking slightly. In Call of Duty: Black Ops II, this seems to be much more noticeable, as it can be seen easier with the Tactical Knife combined with the Reflex Sight. Although this may hinder aiming, it adds no weapon sway or accuracy reduction.
In Call of Duty: Black Ops II, after knifing while in ADS with the Tactical Knife, the player will be instantly reverted to aiming again.
In Black Ops II, the camouflage on the players Combat Knife will be the same as the Tactical Knife.
In Black Ops II, getting a kill with the tactical knife will count towards a bloodthirsty for Skulls Camouflage, however, if a normal knife is used, it will not count.