It was something of an eventuality that Colt released an AR-15/M16-style weapon chambered for the ubiquitous 9x19mm Parabellum pistol cartridge. The cartridge had been in use for decades prior to the 1980s and saw service in both World Wars while becoming the cartridge-of-choice for many semi-automatic pistols and submachine guns. The Colt entry became the Model 635 (known to NATO as the "SMG 9mm NATO") which, as expected, chambered the 9mm round and fired from a blowback action (as opposed to direct impingement gas as seen in the M16) through a closed-bolt system.
The Model 635 - generically called the "Colt 9mm SMG" - retained the general design lines of the classic M16 U.S. military assault rifle (its own design based on the AR-15). It shared some qualities from the earlier Vietnam War-era Colt "Commando" assault carbine. A telescoping butt was installed for compactness which brought the overall length of the weapon down from 29 inches to a handier 25.5 inches as needed. M16-style fire controls were retained meaning that operators already familiar with the larger cousin could easily adapt to managing the smaller offering. One of the more unique design elements apparent to the Model 635 was the magazine which was slimmer and taken from the Israeli UZI SMG design. In order to accept these new magazines into the M16-style feed, a special internal modification was introduced. The Model 635 fed from either 20- or 32-round straight detachable box magazines and the standard barrel measured 10.5 inches long.
Accuracy and familiarity proved the Model 635's selling points but the system did not find many takers. Militarily, only the USMC, Malaysia, and the Argentine Army adopted the type and special police forces of Bangladesh and India were other operators. Locally, the United States Marshals Service, the U.S. Diplomatic Security Service (DSS), and the Drug Enforcement Administration (DEA) saw enough usefulness in the design to accept it into inventory.
The Model 639 became a related variant given a select-fire trigger group containing a three-shot burst functionality but lacked the full-automatic mode featured in the original Model 635. The Model 633 appeared with a shorter 7" barrel assembly for improved compactness along with a simplified forward sighting device - these went on to serve the DEA.
Manufacturing Colt's Manufacturing Company (CMC) - USA
Argentina; Bangladesh; India; Malaysia; Pakistan; United States
Colt 9mm SMG - Base Series Name
Model 635 - Standard model with semi-/full-automatic mode.
Model 639 - Three-round burst fire capability added; sans full-automatic mode.
Model 633 - 7" barrel assembly and revised front site for use by US DEA.
SMG 9mm NATO - NATO Designation for the Model 635
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