The M3 was a superior alternative to the Thompson submachine gun. In brief, the M3 was cheaper to produce, fired more accurately, was lighter, and was also chambered in 45 ACP. The M3 was commonly referred to as the "Grease Gun" or simply "the Greaser", owing to its visual similarity to the mechanic's tool.
Intended as a replacement for the .45-caliber Thompson series of submachine guns, the M3 and its improved successor, the M3A1 began to replace the Thompson in first-line service in late 1944 and early 1945. Due to delays caused by production issues and approved specification changes, the M3/M3A1 saw relatively little combat use in World War II.