An attachment is an optional enhancement, modification or accessory for a weapon. In the first Call of Duty games, there was a lot less customization available to the player, meaning attachments were limited to the basics such as Sniper Scopes. In Multiplayer, attachments were introduced in Call of Duty 4: Modern Warfare, and since have been available in every game released afterwards.
Optical Attachments are the most common attachments and replace the standard Iron Sights that all guns possess (with the exception of sniper rifles, which include a high-power scope). All gun-sights improve the view of the player while aiming, either by enhancing the zoom-in effect or allowing for greater visibility of the battlefield, especially underneath the point of aim where the firearm itself usually obscures the view from iron sights. Some scopes, however, can cause certain detriments to balance their benefits: they can lengthen the time it takes in the transition from hip-firing to ADS (simulating the adjustment that the eye must make), and some block out all peripheral vision, allowing the player to see only through the comparatively small gun-sight window while aiming. Even with Bling, Warlord, Attachments, Primary Gunfighter, Extra Attachment or Primary Expert, only one optical attachment can be used at one time, and none of the sights can be used with Akimbo most games. The types of gun-sights are:
Red Dot Sight (RDS): (Modern Warfare series, Black Ops, Black Ops II, Ghosts and Advanced Warfare) These are very common sights due to the ease of unlocking them and their general versatility. It is a small glass sheet surrounded by a very thin metal frame that uses optics technology to display, as the name implies, a red dot over the point of aim. While the sight's accuracy is very good even at extreme range, the dot does not follow the player's movements instantly - there is a moment after a drastic motion during which the point of aim will not be the point of impact until the red dot settles. In Call of Duty: Black Ops, the player is able to customize the color of the lens and dot, whilst also being able to choose the shape of the dot itself. In all subsequent games, the reticle can be changed.
Reflex Sight: (Call of Duty: Black Ops, Black Ops II, Black Ops III and Infinite Warfare) An variant of the RDS, there is little difference between the two sights.
ELO: (Call of Duty: Black Ops III and Infinite Warfare) A Red Dot Sight variant, but has a much less obstructive frame and an orange/yellow floating reticle.
MARS Sight: (Call of Duty: Modern Warfare 2) A variant of the RDS, it automatically replaces it when the RDS is equipped for the TAR-21. Its viewing window is circular rather than square, and while it allows for better and easier observation of other attachments such as the Heartbeat Sensor while in ADS, the opaque body of the sight that surrounds the viewing window is much larger and therefore obscures more of the view. It is referred to in singleplayer as the MARS Sight, but is just labeled as a Red Dot Sight in multiplayer.
F2000 Red Dot Sight: (Call of Duty: Modern Warfare 2) This sight is unique to the F2000, resembling a stockier, thicker variant of the single player sight for the G36C. Due to is being very long, the view down the sight is often very dark and ineffective, only possessing lower zoom and a smaller viewing area than any other scope, thus it is rarely seen or used. However, it does not become disabled when an EMP is deployed.
Aperture Sight: (Call of Duty: World at War) It consists of a circular glass sheet encased in metal containing two black lines to form a cross-hair. It is unlocked after getting 75 kills with a weapon, and offers a slight magnification.
Holographic Sight: (Modern Warfare series, Black Ops II and Ghosts) Similar to the RDS in most respects, and is unlocked by getting kills while using the RDS. The very small red dot in the center of the viewing window is the point of aim/impact, but a larger red circle surrounds the dot, which can tend to obscure details or even the target from long ranges. Both the dot and circle are translucent, however, unlike the RDS's dot. While the RDS is almost perfectly accurate in its point of aim vs. impact, the Holographic Sight is in fact perfect in this regard, simulating its parallax-adjusting optics technology, nor does it have to settle after turns or other adjustments like the RDS does. The body of the sight is slightly larger and therefore obscures slightly worse than the RDS, but the sight overall sits much higher on the weapon than the RDS does, and so the weapon itself obscures significantly less of the shooter's view while aiming. In Ghosts, it gains a tracker on the left side to indicate how much damage the gun will deal at that range.
VMC: (Call of Duty: Infinite Warfare) The VMC is an optical attachment featured in Call of Duty: Infinite Warfare. It looks similar to the Holographic Sight from previous games, except the reticle is different, and is an engage zoom sight, but only with non-hybrid weapons.
ACOG Scope: (Modern Warfare series, Black Ops, Black Ops II, Ghosts and Advanced Warfare) They are the last sight to be unlocked by getting a set amount of kills in Modern Warfare titles. While the ACOG is perfectly accurate and enhances zoom during aiming much more than the RDS or Holographic, it increases recoil. As a result, the weapons that it is ideal for are those with low base recoil and/or very large initial damage output, and it is tailored overall for long-range engagement (but not as long as with true sniper scopes). It also lengthens the transition time from hipfire to ADS considerably, and the large body of the sight surrounding the view-port obscures a considerable portion of the screen around the targeted area. In Modern Warfare, the area around the sight is blocked off, similar to the style of a Sniper Scope. In Modern Warfare 2, the player now has peripheral vision, however the bulkiness of the sight still considerably blocks some of the screen. The case remains the same in Call of Duty: Black Ops; however, the optic is less bulky. In Call of Duty: Black Ops II, the ACOG Sight features a faster aiming time and decreased recoil.
SUSAT Sight: Identical to the ACOG except in that the fiber-optic and tritium-illuminated reticle is replaced by a post, meaning the sight still works under an EMP. It is found on the L86 LSW, the Enfield, and the L96A1. It is also simply referred to by the game as an ACOG sight, similar to how the MARS sight is referred to as RDS. The sight has more peripheral vision than its ACOG counterpart and a somewhat more manageable zoom, however still increases recoil on the gun.
Telescopic Sight: (Call of Duty: World at War) The equivalent of the ACOG from Call of Duty 4, with the main difference being that the aiming chevron is black, rather than red. Again, the peripheral vision is severely reduced to allow only viewing down the sight.
Swarovski Scope: This is an attachment that appears in Call of Duty: Modern Warfare 2 and Call of Duty: Black Ops. The Swarovski Scope is integral 1.5x optical sight exclusive used on the AUG series of weapons. The Modern Warfare 2 version is essentially a sniper scope with the zoom of an ACOG, similar to the original ACOG, while the Black Ops version uses two black lines to form a cross-hair with a circle in the middle and the zoom of an ACOG scope also, acting much more similarly to the ACOG from Modern Warfare 2.
Scout/Scout Hybrid: (Call of Duty: Infinite Warfare) The Scout/Scout Hybrid is an optical attachment featured in Call of Duty: Infinite Warfare. It adds a rectangular sight with a holographic ammunition counter onto the weapon, similar to the ACOG Scope. It focuses onto a target with a floating reticle in the center that can be customized. This attachment also features a unique feature by Y/Triangle (by default) to flip up another iron sight similar to the ELO Sight, in the right side of the weapon for reduced zoom and better close range performance. This feature acts more like the Hybrid Sight. Weapons with a secondary function and all Sniper Rifles (except the M1 Garand) cannot use this sight, the regular Scouttakes its place.
Thermal Scope: (Modern Warfare 2, Modern Warfare 3, Ghosts and Advanced Warfare) Unlocked by getting a set amount of kills while using the ACOG. Behaves as a modified telescopic sight, as it has a powerful zoom, it can be steadied by breath-holding, and it obscures all peripheral vision. It is the only sight that actually modifies what the player is seeing in a way other than simply zooming in on it. Players and other sources of heat glow a distinctive solid white in the sight's picture, while everything else is seen in shades of gray. This makes the thermal sight extremely useful for scanning distant terrain for enemies, as any exposed enemy body part will be readily noticeable. Friendlies also glow white, but their brightness strobes, IE blinks rapidly, to simulate the effect of an IR IFF device that they would carry. When viewing a player using the Cold-Blooded perk through a thermal sight, however, they will appear in shades of gray in exactly the same spectrum as the rest of the terrain, which can easily cause them to be overlooked if the shooter is expecting the trademark white glow. Smoke, even the thickest smoke generated by a Smoke Grenade, is completely transparent through a thermal sight, which makes a smoke grenade an ideal complement to the thermal scope.
Infrared Scope: (Call of Duty: Black Ops) Similar to the Thermal Scope from Modern Warfare 2, and is the same generalized principal, however the scope turns everything blue or white, rather than various shades of gray. Furthermore, instead of being a straightforward cross-hair in the center, there is a chevron, similar to the ACOG Scope from the first Modern Warfare.
Sniper Scope: (Call of Duty: World at War) Despite being the default sight in the non-WWII games, it is actually an attachment in World at War, and it is unlocked by completing Marksman challenges for the M1 Garand and for the Bolt-Action Rifles (though the PTRS-41 comes with a sniper scope by default. This sight is also seen as an attachment in the campaign modes of Modern Warfare 2 and Modern Warfare 3 (for the M14 EBR) and Black Ops (for the Mosin Nagant), and in the Zombies mode of Black Ops (for the Kar98k).
Variable Zoom Scope: This is a scope attachment in Call of Duty: Black Ops, Call of Duty: Modern Warfare 3, Call of Duty: Black Ops II , Call of Duty: Ghosts and Call of Duty: Advanced Warfare. It allows the user to have three levels of zoom (two levels of zoom in Black Ops II), switched by using the melee button. It costs 2000.
Upgraded Iron Sights: An attachment for pistols in Black Ops, adding it will result in small dots of tritium being placed on each post, making aiming down the sight easier. The attachment is the cheapest attachment in-game, costing only 250.
Hybrid Sight: An attachment for assault rifles in Modern Warfare 3, the Ripper in Ghostsand most weapons in Advanced Warfare. It is an EOTech sight with a 4x magnifier. The Hybrid Sight is usually looked down upon, due to the fact that it increases recoil. In Ghosts, it is used on the Ripper to switch between SMG mode and AR mode with SMG mode as the default iron sights and the AR mode to have a unique Interface Sight with a Green Dot. In Advanced Warfare, It is two red dot sights, the closer being a square dot sight while the other is just a red dot.
HAMR Scope: Appears as such in Modern Warfare 3, and as Hybrid Optic in Black Ops II. Very similar to the Hybrid Sight, the HAMR Scope is the SMG variant. It consists of a 3x zoom scope, with a regular Red Dot Sight on top op it. The 3x scope also increases recoil, and it is rarely found in Multiplayer. A variant in Call of Duty: Ghosts is used on the Assault Rifle mode of the Ripper.
Hybrid Optic: Appears in Black Ops II, the Hybrid Optic is similar to its HAMR Scope counterpart. It can be mounted on Assault Rifles and Light Machine Guns.
Target Finder: Appears in Black Ops II, it highlights enemies without Cold-Blooded in bright red diamonds, but the player will suffer from extreme tunnel vision.
Millimeter Scanner: Appears in Black Ops II, it reveals enemies behind cover or concealed by smoke every several seconds, but increases recoil.
Trojan: (Call of Duty: Infinite Warfare) The Trojan is an optical attachment that tracks and outlines enemies, even through smoke.
Dual Band Scope: Appears in Black Ops II, it is similar to Thermal/Infrared Scope, but highlights enemies in orange rather than white. The Dual Band can be combined with the Variable Zoom, creating a hybrid optic.
VMR Sight: Appearing in Call of Duty: Ghosts, the VMR Sight is similar to the Hybrid Sight from Modern Warfare 3, albeit with less tunnel vision. It can be used on Assault Rifles, Submachine Guns, and Light Machine Guns.
Tracker Sight: Appearing in Call of Duty: Ghosts, the Tracker Sight can be switched between an advanced optic and integral iron sights. The advanced optic highlights and tracks enemies for the player. A scoped variant appears on the Maverick-A2.
Thermal Hybrid Scope: Appearing in Call of Duty: Ghosts, the Thermal Hybrid Scope can switch between an integrated Holographic Sight and a Thermal Scope.
Auto Focus Sight: Appearing in Call of Duty: Advanced Warfare, the Auto Focus Sight zooms in if the player is standing still for a short amount of time.
Target Enhancer: Appearing in Call of Duty: Advanced Warfare, the Target Enhancer highlights enemies who are viewed through the sight.
RW1 Scope: Appearing in Call of Duty: Advanced Warfare exclusively for the RW1, the scope offers the weapon an increased zoom level.
Crossbow Scope: Appearing in Call of Duty: Advanced Warfare exclusively for the Crossbow, the scope offers the weapon an increased zoom level.
Smart Shot: (Call of Duty: Infinite Warfare) The Smart Shot is an optic exclusively for shotguns that when aiiming down sights guides all pellets to the target.
Some attachments modify the use and properties of the weapon besides the sights used to aim. They are:
Suppressor: Included in all games after Modern Warfare; commonly referred to as a silencer. By capturing and compressing escaping gasses, it reduces overall noise emanating from the barrel during a shot. While a player's location is marked by a bright red dot on the mini-map to all their enemies when they fire a non-silenced weapon, a silencer allows them to fire at will without being revealed in this way. This is particularly advantageous for players that prefer to find an ideal fighting position and stay there picking off targets of opportunity until they are noticed. The silencer also causes less tracer rounds to be fired, making it far harder for an enemy to deduce the shooter's location by observing the impact of their rounds. Naturally, the drastically reduced sound of their firing also makes it harder for observant enemies to locate them from it. Finally, the suppressor almost completely eliminates muzzle flash, allowing the user to keep track of their targets more consistently, at the expense of damage over longer range, which decreases much quicker than without. It should be noted that silencing Light Machine Guns and Sniper Rifles comes at a much larger cost, since these guns do not suffer damage drop-off, they simply have lower overall damage (10 point drop in damage for LMGs, 20 for sniper rifles).
Flash Suppressor: Appears in Call of Duty: Ghosts, reducing muzzle flash for the weapon it is attached on.
Grip: Included in the Modern Warfare series, World at War, Black Ops, Black Ops II, Ghosts and Advanced Warfare. Sometimes known as "Foregrip", it is mainly found on Light Machine Guns and Shotguns, as these weapons naturally suffer from the greatest recoil. The foregrip increases the rate at which aim recovers from the recoil after shooting, allowing bursts of fire to stay accurately on target during a much larger firing time. In Black Ops, however, it can only be used on one assault rifle (the M14), the M60, most SMGs and the Stakeout shotgun. In Black Ops II, the Grip returns but has a much less noticeable effect compared to previous versions.
FMJ: Abbreviation for Full Metal Jacket. it appears in Modern Warfare 2 and Black Ops II. Contrary to many players' belief, FMJ does not increase the damage of weapons in any way; the attachment only reduces the amount of damage lost while shooting through cover (walls, sheet metal, etc.), in the same way as the perk Deep Impact or Hardened (perk). FMJ also has the added effect of increasing damage towards scorestreaks in Black Ops II. The MG4 from Modern Warfare 2 is incorrectly stated as "Explosive Rounds" when equipped with FMJ.
Extended Magazines: These appear in World at War, Modern Warfare 2, Black Ops, Modern Warfare 3, Black Ops II, Ghosts and Advanced Warfare. In Modern Warfare 2 they are unlocked for primary weapons after a set amount of kills that are made not only with FMJ equipped, but where the killing round penetrates some solid material to reach the target. As such, they are widely considered the hardest attachment to unlock, especially with weapons that do not lend themselves to blind-firing through cover, such as sniper rifles. On Secondary Weapons however, Extended Magazines can be unlocked simply with enough kills, and is always the last achievement unlocked. As the name implies, Extended Magazines significantly increase the number of rounds that a weapon can have loaded in a single magazine, allowing for more shots to be fired before reloading. The increase varies by weapon from 50% to 100%. However, it is important to note that in all games prior to Modern Warfare 3, the total amount of ammunition isn't increased in any way when using Extended Magazines; as magazine size changes, so does the amount of magazines the player carries on spawn. For example, a SCAR-H without the attachment will contain 2 reserve magazines each containing 20 bullets, yet with Extended Magazines containing and 30 bullets, only one spare mag is given. However, in Modern Warfare 3, while each magazine still contains more bullets, the number of magazines provided on spawn isn't decreased. So, if you have an M4A1 with 45 rounds a clip and 2 extra magazines, this equals 135 total rounds, versus 90 without the attachment. In Modern Warfare 2 and Modern Warfare 3, Extended Magazines are often used with Rapid Fire on Submachine guns, to counter the faster fire-rate. In World at War, they are simply unlocked after enough standard kills with any gun of choice, and like above, is normally used with Double Tap. However, there are several variations, all of which do the same job:
In Black Ops, the attachment returns without needing any special challenge to unlock, instead requiring CODPoints to purchase. Like in World at War, adding Extended Magazines changes the shape of the magazine, excluding certain weapons, like the M14 . The attachment costs 1000.
Dual Wield/Akimbo: Appears in Black Ops, Modern Warfare 2, Modern Warfare 3, Black Ops II, Ghosts and Advanced Warfare, and causes the player to wield one of the equipped weapon in each hand, replacing the ADS button as the trigger for the left-hand gun. In addition, the hipfire accuracy of the weapons is also significantly reduced. SMGs, Handguns, Machine Pistols and the Model 1887 & Ranger shotguns can be wielded akimbo. This attachment is popular with players that emphasize speed to close with their enemies as fast as possible. Akimbo cannot be used with Tactical Knife since both attachments take the left hand. It also cannot be used with any optical attachments since the player cannot aim down the guns' sights. The attachment appears again in Black Ops, under the name of Dual Wield and does essentially the same thing as before. In Black Ops, however, the player is much more limited in terms of attachments that can be used with Dual Wield and Warlord. No attachments can be used with Dual Wield in Black Ops II.
Rapid Fire: Appearing in Modern Warfare 2, Black Ops, Modern Warfare 3, Black Ops II, Ghosts and Advanced Warfare, it acts as a replacement for the Double Tap perk of Call of Duty 4 and World at War. In Black Ops, it increases fire rate by 33%. It is the first attachment unlocked for SMGs, and is one of their exclusive attachments. However, it is worth noticing that recoil kicks in sooner when used in a long burst and consequently lowers the effective range of the weapon. It also depletes the magazine faster allowing less fire time between reloads and drains ammunition faster. With Bling or the Attachments proficiency, the attachment is often used in conjunction with Akimbo for fast mid-range kills, or Extended Magazines to allow more firing time between reloads. In Black Ops, it is often used to compensate for the lack of Stopping Power, as it is the only way to increase the damage per second of a weapon.
Select Fire: Originally planned to appear in World at War exclusively for SVT-40 and STG-44, it allowed to switch fire mode between semi-automatic and full-automatic. This was cut from the final game's release. It appears in Call of Duty: Black Ops II, allowing fully automatic weapons to utilize burst firing and semi-auto and burst fire weapons to fire automatic.
Full-Auto Upgrade: An attachment exclusive to the CZ75 in Black Ops, it allows the pistol to fire full-auto. However, the rate of fire is lower than the normal firecap without this attachment, and damage is reduced.
Bipod: Appearing in World at War, the attachment appears on machine guns only, and is the first attachment unlocked for them. It increases accuracy of the gun when it is mounted on solid surfaces by eliminating recoil and weapon sway, but at the expense of the player not being able to move and not being able to rotate the gun in a full 360 degrees range. Also, a white cross will replace the standard cross-hair, with the cross even appearing in hardcore modes. In short, when in use, this essentially turns the machine gun into a turret, like the mounted M249 SAW from the Modern Warfare series.
Dual Magazines: in Black Ops and Advanced Warfare, this attachment decreases the reload time of every odd-numbered reload (1, 3, 5, etc.) by taping two magazines side-by-side. After every second reload, a new group of magazines must be used, thus every second reload is the same speed as a normal reload. In Black Ops, the player also receives two extra magazines, or 66.6% more ammunition.
Speed Reloader: An attachment exclusively for the Python in Black Ops. As the name suggests, it decreases the time taken to reload the gun by reloading all six bullets at once, rather than one by one when not using the attachment. When Pythons are Dual Wielded, however, Speed Reloaders are automatically given, as they are to all Revolvers outside of Black Ops except for the Executioner.
Fast Mag: An attachment in Black Ops II that reduces player's reload time, it is essentially Sleight of Hand as an attachment.
Some attachments do not actually alter the weapon they are attached to in any way, but rather alter another capability of the player or add a new capability entirely. They are:
Grenade Launcher: Appears in Call of Duty 4, Modern Warfare 2 and every game after, it can be mounted on most Assault Rifles, and in Black Ops, the AK74u SMG. They are under-slung, meaning that they attach to the rifle along the bottom of its barrel over the handguard, and are designed for the shooter to pull their trigger while holding the weapon's magazine as if it were a pistol grip (The launcher for the AK74u has its own pistol grip). It loads and fires only one grenade at a time, and must be drawn as a separate weapon before use. The grenade that it fires is identical to a thrown grenade except for the fact that it explodes instantly upon any impact with a non-breakable entity, unless it impacts something so soon after being fired that its explosion would harm the shooter, in which case it does not explode at all. Even a grenade that does not explode in this way, however, will kill any opponent it hits directly. The flight trajectory of the fired grenade follows an arc that must be accounted for when firing from a distance. While it only comes with two rounds upon spawning, the Scavenger perk allows a player to replenish their grenade ammunition very effectively. It is identical to the Thumper except for the fact that there is no ADS for it. The slang term 'noobtube' has arisen to criticize the grenade launcher and its users as 'noobtubers', to such an extent that the latter is a title that can be earned by using it. This attitude arises from a popular sentiment that relying upon the grenade launcher and/or Thumper is a way to compensate for poor aiming reflexes with firearms. The Grenade Launcher cannot be used with the Masterkey Shotgun or Flamethrower since they are all under-barrel attachments, nor can it be equipped with the Hybrid Scope, as both require the left directional button to operate and are also physical impossibilities.
Shotgun (in some cases a Masterkey): Appearing for Assault Rifles in MW2, BO, MW3 and Ghosts; unlocked after getting 20 kills with an attached grenade launcher. It has a better range than any standalone shotgun. However, it possesses several drawbacks. Each of its shells only fires 6 pellets, compared to most other shells' 8, amounting to 75% of their damage output per shot. In Black Ops, it now fires 8 pellets similar to the Stakeout shotgun, but with less damage. Its firing rate is also very slow and its breech capacity (the equivalent of magazine size) is only 4 shells, making it very hard to actually kill someone at the weapon's max range. The Masterkey Shotgun cannot be used with the Grenade Launcher or the Flamethrower since they are all under-barrel attachments; additionally, as it is an under-barrel attachment, it cannot be accompanied by a second attachment in Black Ops multiplayer when using Warlord.
Flamethrower: The Flamethrower is an under-barrel attachment for assault rifles, appearing in Call of Duty: Black Ops. It has a limited amount of fuel in one tank, and after the fuel runs out, it can be reloaded, similar to a Grenade Launcher. The player cannot keep partial fuel tanks, however.
Rifle Grenades: Found in Call of Duty 3 and Call of Duty: World at War, this explosive is only available when a player has the M1 Garand, the Gewehr 43, or any bolt-action rifle except the PTRS-41, and is basically the equivalent to a grenade launcher, and although slower, have a larger blast radius. Also, because they can only be found on a few select weapons, and are normally the last attachment unlocked for them, they are not nearly as frowned upon as grenade launchers. They also do damage against tanks, but are not as effective as the bazooka.
Heartbeat Sensor: Appears in Modern Warfare 2 and Modern Warfare 3, and is only available on the larger Primary Weapons and the AA-12 shotgun; unlocked after 15 kills while using the suppressor on a given weapon. The sensor displays as a small screen at the bottom left of the HUD extending from the weapon. There is a white dot in the middle of the bottom of the sensor that represents the player, and a pulse is shown to periodically emanate from the player every few seconds. The pulse scans the 180 degrees to the front of the player up to a moderate distance ahead of them, and displays friendlies as green dots and hostiles as red (In Singleplayer friendlies are blue and 'unrecognized' contacts are white dots). No features other than the locations of other players are displayed on the sensor, and their displayed locations are only refreshed every several seconds during each sensor pulse.
Tactical Knife: Only available on handguns in Modern Warfare 2, Modern Warfare 3, Black Ops II, Ghosts and Advanced Warfare. This attachment causes the player to hold their knife at the ready in their offhand (left) while their handgun is drawn, doubling the speed with which the player stabs using the normal stab command. Useful both for stabbing an enemy just before they would otherwise stab the player, as well as for recovering from a stab to attempt another or to move on to another enemy within stabbing distance. Tactical Knife cannot be used with Akimbo.
Bayonet: The Bayonet is a sword used to stab or slash enemies with mounted onto the barrel of a gun. Appearing in World at War, this attachment is only available on all bolt-action rifles (except the PTRS-41), the Type 99, the M1897 Trenchgun, the M1 Garand and the M1A1 Carbine. While it and the Tactical Knife both affect melee combat, the bayonet affects melee range, and decreases speed. In Modern Warfare 2, the attachment was replaced with the Commando perk, and the Tactical Knife was added in its place.
Laser Sight: Appears in Black Ops II, Ghosts and Advanced Warfare. It increases hip-fire accuracy by emitting a beam of light where the weapon is facing, and is essentially Steady Aim as an attachment.
Ballistics CPU: Appears in Black Ops II, it reduces the idle sway on the scope. The Ballistics CPU cannot be paired with the ACOG Scope.
Although classed as an attachment, part of the gun has been removed, so it can be considered a "detachment". Also, these attachments generally radically reduce one of the gun's stats, such as range, to increase another, such as damage. There are currently three versions of these:
Sawed-Off: Appears in World at War on shotguns and, as the name suggests, the top end of the barrel is cut off. This increases the damage of the gun, but at the expense of both accuracy and range. It is not present in Call of Duty 4 or Modern Warfare 2, however there is the Ranger shotgun, which has already had the barrel sawed off.
Snub Nose: An attachment available for use on the Python in Call of Duty: Black Ops, the barrel of the revolver is shortened. This decreases the recoil of the gun, but at the expense of short range damage. It can be seen as the polar opposite of the above Sawed-Off attachment in World at War.
In Call of Duty: Advanced Warfare, the SAC3 and the XMG have Akimbo integrated by default (except for five supply drop variants of the SAC3), and the MAAWS once again has an integrated Laser Sight to guide the rockets. Additionally, certain variants of weapons earned from supply drops will have integrated attachments. These attachments do not use a Pick 13 point when used, but do take up one attachment slot on the weapon.