Colt/Knights Armament 9mm SMG Suppressed upper assembly. Built by Colt and Knights Armament in a joint project for the U.S. government. The suppressed upper receiver was to be used with the Colt 9mm RO633 or RO635 for covert operations.
The Colt AR-15 Resource
"A site dedicated to the history of the Colt AR-15 rifles, carbines and associated items"
The Colt AR-15 Resource 