The M3 Grease Gun was a submachine gun used by the United States Army During World War II From 1942 onwards. It chambers the .45 ACP also used in the Thompson Sub-Machine Gun and Colt M1911.Production of this weapon was in full swing in 1943 and was made to supplement the Thompson Sub-Machine Gun and eventually replace it due to the Thompson SMG Being to expensive to manufacture. The M3 was also inspired by another gun: the STEN submachine gun by the fact that both weapons had been made with sheet metal parts and (in later variants of the STEN) had a folding butt stock.