The M1 SMG was introduced in April 1942 as a simplified war expedient version of the original Colt M1927 submachine gun. The various simplified/redesigned features include a side mounted bolt handle, a simple stamped "L" type fixed rear sight with side protectors, horizontal walnut forearm, fixed butt stock, and the short 10 1/2 inch barrel with no cooling fins on the barrel, and no compensator on the muzzle. The receiver is marked: "THOMPSON SUBMACHINE GUN/CALIBER 45 M1A1(with the A1 markings Xed out)/NO. 594049" and the right side is marked "AUTO-ORDNANCE CORPORATION/BRIDGEPORT CONNECTICUT U.S.A.". The Xed out markings appear to be arsenal done during the arsenal refurbishment/overhaul to convert it back to the earlier M1 version; originally equipped with the M1A1's simplified bolt (with a fixed firing pin), the weapon is equipped with a M1 bolt (with a floating firing pin). Additionally, a metal barrel band has been installed on the barrel and forearm ahead of the sling stud. The left front edge of the receiver is stamped with the Rochester Ordnance district inspector initials "F.J.A.." with a encircled "GES", and a single "P" proof on side of the barrel. The lower trigger housing is marked "FULL/AUTO" and "SINGLE" and "FIRE/SAFE" with no serial number present on the trigger guard. This SMG is complete with two 30-round magazines.