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The M4 Carbine is an American-made carbine assault rifle chambered in 5.56×45mm NATO. A lighter, more compact development of the venerable M16, the M4 carbine is in heavy use with the United States Armed Forces and is currently replacing the M16 rifle in most United States Army and United States Marine Corps combat units.
After the adoption of the M16, it was then decided that a carbine variant was to be produced for close quarters operations. The first attempt at such a weapon was the CAR-15, however this early variant had a variety of different flaws. Since 1988, Colt has worked on a newer and more improved weapon. By the 1990s, the weapon known now as the M4 Carbine was introduced. Several variants have been produced, capable of differing fire modes and with an assortment of barrel lengths.
In Aliens vs. Predator: Requiem, the National Guardsmen dispatched to Gunnison are armed with M4A1s fitted with foregrips and various optics. Some also have M203 grenade launcher attached. Dallas Howard and Kelly O'Brien both take M4A1s from the armory aboard the Stryker armored fighting vehicle and use them for the rest of the film.
- Contrary to popular belief, the compact AR-15 variant used by Mike Harrigan in Predator 2 is not an M4 Carbine — the M4 did not enter production until some 4 years after Predator 2 was released, and did not start appearing in films until the late 1990s. Harrigan's carbine is an as-yet unidentified earlier AR-15 variant.