The Colt 9mm SMG, and its select fire variant, the Colt SMG M635, is a 9×19mm Parabellum high rate of fire submachine gun designed and manufactured by Colt and based off of the M16 design.
The Colt 9mm SMG started production in 1982, and still manufactures it today. The Colt 9mm SMG is based off the design of the Colt M16A2 assault rifle. However, the most common of the current Colt productions of the Colt 9mm SMG are that of the RO635, which features select fire options. The Colt 9mm SMG is intended for use by Civil and Police Forces, such as the DEA.
The Colt 9mm SMG is largely based off of the M16A2 assault rifle, however the operating systems are a bit different. However, the Colt 9mm SMG is a closed bolt, blowback operated submachine gun, rather than gas operated like the standard 5.56×45mm M16 rifles.
The Colt 9mm SMG currently has two major variants, the RO635, and the RO639, with a lesser known third being the RO633. The RO635 features a Safe/Semi/Full Auto selective fire trigger group, while the 639 features Safe/Semi/3-round Burst selective fire trigger group. They both have around a 10.5 inch (266 millimeter) barrel. The 633 was a modified compact version with a 7 inches (180 mm) barrel, hydraulic buffer and simplified front sight post used by the DEA.