The ACOG Scope (Advanced Combat Optical Gunsight) is a reflex optic available in Call of Duty 4: Modern Warfare and Call of Duty: Modern Warfare 2. The ACOG scope is a series of telescopic sights manufactured by Trijicon. The ACOG scope is designed for use with the M16 and M4 series, but Trijicon also develops ACOG accessories for other types of firearms. Models of the ACOG scope provides magnification levels between 1.5x and 6x. ACOG scopes don't require battery power, unlike some other gunsights, because the sight isn't powered by electricity. The superimposed reticle is available in a variety of patterns and colors. It is illuminated by an external fiber-optic light gathering rail when light is plentiful;during low-light conditions it is illuminated by an internal tritium lamp.

The ACOG scope can be used on any Assault Rifle (excluding the MP44), Light Machine Gun, Sniper rifle or Submachine Gun after the player has unlocked all Marksman challenges for it (150 kills). It can also be used on a Sniper Rifle in lieu of its standard telescopic sight after 100 kills. Equipped as the weapon attachment, it replaces the iron sights or sniper scope and provides a 2x zoom. The increased zoom improves visibility over range, but increases idle sway - reducing accuracy. Effective bullet range is not actually affected by this attachment (all guns except shotguns have infinite range). The reticle is a red chevron

The ACOG scope attachment in Call of Duty: Modern Warfare 2 is unlocked by completing the Marksman IV challenge (150 kills) for all primary weapons (except for Sniper Rifles; completing the Marksman II challenge of 25 kills with a sniper rifle unlocks the ACOG scope for that rifle).

Many players consider the ACOG greatly improved and can be used on many weapons effectively. The different types of ACOG scopes are:

• Trijicon ACOG
• SUSAT (only available on the L86 LSW)

In Multiplayer, the ACOG scope remains the same on all weapons except the SUSAT on the L86 LSW.

20 kills aiming down the ACOG scope will unlock the Thermal Scope. This can be difficult when using weapons with high recoil. By usingstopping power or playing in Hardcore, this will be less of an issue.

The ACOG causes a considerable increase in recoil, making it fairly difficult to use on guns that do not have very low recoil to begin with.

The standard ACOG's appearance has changed slightly since Call of Duty 4's version and its real-life counterpart. The old chevron crosshair is replaced with a more standard cross style crosshair with mil dots which are completely decorative as there is no wind or bullet drop. A red dot in the middle of the cross serves as the aim point.

The ACOG scope is very useful when an enemy triggers an EMP, as even though the red dot and surrounding lines disappear, the black, hair-line crosshairs remain. Some players actually prefer the ACOG without red lit markers because it is more precise and easier to make pinpoint headshots without the red dot in the way.

The ACOG in MW2 differs from the previous game in that there is a further eye relief, improving peripheral vision. However, players still usually opt for the Red Dot Sight orHolographic Sight over the ACOG, or only use it until they unlock the Thermal Scope. Using the ACOG scope on any weapon adds a slight delay when zooming, in comparison to Red Dot Sight, Holographic sight, or iron sight.

If the ACOG is used in third person, ADS will zoom in farther. If used on a sniper rifle in third person, there will be no scope, but instead the hipfire crosshairs will join together to form a "+."

In general, the scope is smaller and more cluttered than the variants in previous games. ACOG's lack idle sway which was present in previous games, but the scope's magnification still increases recoil, and the time it takes to aim down sight is also longer than in Modern Warfare 2.