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Submachine Gun, Cal. .45, M3/M3A1 ( 1942) was nicknamed the "Grease Gun" because of its appearance. The M3 was a blow back submachine gun fielded in December 1942 by the United States Army during World War II. It could only be fired on fully-automatic. It used the caliber .45 ACP cartridge in 30-round magazines. Its rate of fire was 350-450 rounds per minute. It had a length of 745mm, or 570mm with the stock retracted. The M3A1 was used during World War II and the Korean War. 679,200 were produced.

• M3 ( 1942) was designed specifically as a low cost substitute for the Thompson submachine gun. Production was simplified by making use of stamped metal parts. A number of deficiencies were found during the initial two years of use. These deficiencies were corrected in the model M3A1.

• M3A1 ( 1944) had a larger ejection port and a stronger cover spring. It was also designed so it could fire 9mm Parabellum cartridges by changing the barrel and bolt and adding an adapter to the magazine. Following World War II, a curved barrel was made for use with the M3A1. A flash suppressor was developed for use with both the M3 and M3A1.

See also

• list of common WWII infantry weapons
• list of individual weapons of the US Armed Forces