Authored By Dan Alex (Updated: 9/26/2016):
The M3A1 was a further development of the base M3 submachine gun. Entering service in December of 1944, the M3A1 looked to further simplify the original weapon's production process and practices in order to streamline the end-product and ship the weapon out in quantity. Additionally, this period of revision allowed for a second look into correcting some deficiencies inherent in the original M3 design. The M3A1 differed from its predecessor primarily by its redesigned bolt retracting mechanism. This also forced the prominent hinged cover to be enlarged, allowing the user to fit his finger into the recess and pull the bolt back. In another effort to make the weapon system more versatile and, in effect, "battlefield friendly", a reservoir of oil for in-the-field lubrication of parts was incorporated into the pistol grip and various parts of the system were re-engineered to double as tools when the weapon was stripped down to parts.
By all accounts, the M3A1 was not much of an improvement over the original M3 to which neither system ever achieved any level of acceptability or likeness with soldiers - they instead preferring their trusty M1 Carbines and M1 Thompsons. Nevertheless, the M3 series went on to see extensive combat actions through the end of World War 2. She was still in circulation and utilized in her given role in the upcoming Korean War as well. Beyond that, production also occurred outside of the United States by foreign forces eager to take on a cheap weapon system that was nonetheless robust and fairly easy to operate.
The M3 model was produced by the Guide Lamp Division of General Motors in Detroit, Michigan, as well as the Ithaca Gun Company of Ithaca, New York. Some M3 models incorporated unusual-looking additions like muzzle-mounted flash hiders. Argentina designated their M3s as PAM1 and PAM2. The PAM1 was noted for its chambering of the 9x19 Parabellum cartridge while the PAM2 featured a grip-mounted safety.