MANUFACTURER – General Motors, Guide Lamp Division, Anderson, Indiana. Ithaca Gun Company, Ithaca, New York.
STATUS – Obsolete
SERVICE – US Military and US allies
Field experience with the M3 submachine gun quickly pointed out some weaknesses in the design. Primarily, the retracting handle assembly gave trouble in use with the troops. It was found that the original metal used to make the assembly became brittle under heat treatment. That system was changed and a corrected assembly was issue to the troops with the intention that unit armorers could correct the M3 submachineguns that were already issued. Another problem was the troops were using the stock wire as a cleaning rod. The rod was too long for cleaning the weapon from the muzzle and could damage the front of the bolt. Also the magazine catch was too open and the operator could inadvertently drop the magazine while holding the weapon.
A modified design of the M3 was brought forward in April 1944 as the M3E1. During the development of this design it was found that the troublesome retracting handle was not necessary to the operation of the weapon. The retracting handle was eliminated and a simple finger hole was put into the front of the bolt. To cock the bolt, the operator opened the enlarged ejection port cover over the longer ejection port, stick his finger into the front hole and pulled the bolt back. The safety tab in the ejection port cover was made larger, but operated exactly the same as on the M3. The cover was also given a stronger spring to help hold it in position.
To make a tight barrel assembly easier to remove in the field, two flats were cut into the barrel collar. The flats allowed the stock assembly to be used as a wrench when removed from the weapon. The end of the rod of the stock assembly was drilled and tapped to hold a bore cleaning brush or cleaning patch holder. On the back of the stock assembly was welded a formed metal plate. The plate would prevent the rod from going in and damaging the bolt face when it was used as a cleaning rod. Additionally, the reversed “L” shaped tab on the plate could be used as a magazine filler. That eliminated the need to carry and additional piece of equipment.
The oiler on the left side of the Housing Assembly was removed and a larger oil can put inside of the pistol grip. The end cap of the oiled extended out the bottom of the grip slightly. A stamped metal guard was placed under the magazine catch, surrounding the catch button itself. The ejector, part of the Housing Assembly on the M3, was moved and attached to the receiver body. Additional minor changes resulted in the M3E1 being adopted as the M3A1 submachinegun in December 1944. In April 1945, approval was given for the replacement of all models of Thompson submachinegun with the M3 (limited standard) and the M3A1 (standard issue) submachineguns.
