M-3 Submachine Gun

The M-3 Submachine Gun, introduced in December 1942, was a blow back design that could only be fired on fully-automatic. The M-3A1 was used during both World War II and Korea.

Soldier with Gun, submachine, cal. .45, M-3A1
Soldier with Gun, submachine, cal. .45, M-3A1.

More photos and videos of the M3 and M3A1 Submachine Gun are available at the linked page.

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10 Nov 1944 Accidental detonation of 3800 tons of ammunition on USS Mount Hood [AE-11] while anchored on Manus Island [Papua New Guinea] destroys itself and 22 small boats, damages 36 nearby ships, and kills 432 men with 371 more injured.
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Gun, Submachine, Cal. .45, M-3

The M-3 submachine gun was developed early in World War II as a low cost alternative to the effective but expensive Thompson submachine gun. About 679,200 of the M-3 and M-3A1 submachine guns were produced. Following World War II, the role of submachine guns was greatly diminished with the introduction of assault rifles and light portable machine guns. M3 submachine guns were still used by Special Forces, air crews, armored vehicles, counter-terrorist units, and certain U.S. Navy personnel into the 1990s.

Gun, submachine, cal. .45, M-3

The M-3 was designed specifically to simplify production, compared to the Thompson SMG, by making use of stamped metal parts instead of the refined machining required for the Thompson. A number of deficiencies were found during the initial two years of use, corrected in the model M-3A1.

In addition to many small changes, the M-3A1, introduced in 1944, had a larger ejection port and a stronger cover spring. The external cocking lever and its internal parts were eliminated, replaced by a slot in the bolt so it could be cocked by inserting a finger.

Following World War II, a curved barrel was made for use with the M-3A1. A flash hider was developed for use with both the M-3 and M-3A1.

Often called the "grease gun" because of the resemblance, the M-3 and M-3A1 submachine guns used the .45 cal. ACP cartridge in 30-round magazines. The M3 and M3A1 were designed so they could fire 9mm Parabellum cartridges by changing the barrel and bolt and adding an adapter to the magazine. It's cyclic rate of fire was 350-450 spm.

Equipment for gun, submachine, cal. .45, M3 and M3A1
Equipment for gun, submachine, cal. .45, M3 and M3A1. Click photo for larger image.

Gun, submachine, cal. .45, M-3 w/hider, flash, M9
Gun, submachine, cal. .45, M-3 w/hider, flash, M9.

Gun, submachine, cal. .45, M-3A1
Gun, submachine, cal. .45, M-3A1.

Spare parts for gun, submachine, cal. .45, M3 and M3A1
Spare parts for gun, submachine, cal. .45, M3 and M3A1. Click photo for larger image.

The M-3 Submachine Gun was replaced in the U.S. military by the M-16 rifle, especially the form of the M-4 Carbine, a light and maneuverable weapon that fills the role well.

At the Olive-Drab.com YouTube Channel, the video Automatic Weapons: American vs. German (1943) compares the M3 Submachine Gun to the MP-40 Schmeisser and other weapons.

Military Manuals for the M-3 Submachine Gun

  • TM 9-1005-229-12 various dates including October 1969: OPERATOR'S AND ORGANIZATIONAL MAINTENANCE MANUAL (INCLUDING REPAIR PARTS AND SPECIAL TOOLS LIST): SUB-MACHINE GUN, CAL. .45, M3 W/E (FSN 1005-672-1767) AND M3A1 W/E (FSN 1005-672-1771) (REPRINTED W/BASIC INCL C1-2)
  • TM 9-1005-229-35 various dates including September 1969: DIRECT SUPPORT, GENERAL SUPPORT, AND DEPOT MAINTENANCE MANUAL (INCLUDING REPAIR PARTS AND SPECIAL TOOL LISTS) FOR SUBMACHINE GUN, CAL. .45, M3, W/E AND SUBMACHINE GUN, CAL. .45, M3A1, W/E (REPRINTED W/BASIC INCL C1)
  • FM 23-41 with various dates including October 1943: SUBMACHINE GUNS, CAL. .45, M3 and M3A1

The NSNs are: M3: NSN 1005-672-1767 and M3A1: NSN 1005-672-1771.

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