The CAR-15 XM177 or CAR-15 Commando was a part of the CAR-15 Military Weapons System designed in 1966 in response to the US military's desire for a compact M16 variant to improve on the inadequacies of earlier shortened M16 types.

Although the United States had already tested the CAR-15 Model 607 submachine gun in Vietnam, it had a number of shortcomings, including overwhelming muzzle blast and an overly complicated, unreliable collapsible stock. Colt came up with the XM177, which featured a number of improvements, to address the shortcomings.

The triangular collapsible stock was replaced with a simpler two-position telescoping tubular aluminum buttstock, while the fragile improvised handguards of the Model 607 were replaced by reinforced round handguards. Each half of the round handguard is identical, simplifying logistics by not requiring a top/bottom or left/right pair. The Model 609 Commando has a forward assist, while the Model 610 Commando does not. A Model 610B with a four-position selector was available, but not used by the U.S. military. All versions are equipped with the 4.25-inch (108 mm) long moderator.

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