Colt CAR-15-earliest version.
The Colt Automatic Rifle-15 Military Weapons System or CAR-15 was a family of AR-15 and M16 rifle based firearms marketed by Colt in the late 1960s and early 1970s. It uses the 5.56x45mm of the M16. Due to their compact size, the short-barreled Colt Commando and XM177 versions of this family continued to be issued to the US military after the Vietnam War.
The CAR-15 name was an attempt to re-associate the AR-15 name with Colt, since the AR initially stood for ArmaLite Rifle, the original manufacturer. Colt later abandoned the CAR-15 concept, but continued to make variations, using the M16 brand for military oriented models and the Colt AR-15 brand for law enforcement and civilian models. However, in present usage, CAR-15 is used as a generic name for carbine length M16 and AR-15 variants.
Specifically, "Colt Commando" currently refers to the ultrashort 11.5 inch barrel assault rifle of the Model 733 series. By comparison, the M4 Carbine has a 14.5 inch barrel, while the M16 assault rifle series has a 20 inch barrel.