The M3 Sub-Machine Gun was produced as a cheaper alternative to the expensive Thompson which was Time Consuming to produce as it required a lot of well machined parts. The M3 was introduced in 1942 and was similar to the British Sten & German MP 40 in that it used simple Stamped Parts welded together to form the outside of the weapon. The internal parts then being fitted afterwards. The first models were plagued by reliability problems because the feed mechanism from the magazine had a tendency to jam easily if foreign matter got in to it. Short term solutions included plastic caps to keep dirt out of spare magazines. To rectify this problem a new version was produced, the M3A1 which ironed out many of these problems. This version was introduced in 1944. The Thompson was then relegated to a standby weapon as the "Grease Gun" was adopted as the standard American Sub-Machine Gun for the rest of the War. It went on to see service in Korea and Vietnam. The "Grease Gun"