The M3 submachine gun (officially the United States Submachine Gun, Cal. .45, M3) was an American submachine gun that was designed by George Hyde, Frederick Sampson and René Studler in 1942 and produced by the General Motors Guide Lamp Division from 1943 to 1945. It was developed for the US Army during World War II as a cheaper alternative to the expensive Thompson submachine gun. The weapon was commonly termed the grease gun (or similar nicknames) due to its passing resemblance to the actual tool.[1]

History[edit | edit source]

During World War II, the United States Army Ordnance Board observed the effectiveness of various submachine guns used by the eastern front, such as the Sten and MP 40; after conducting these observations, the Ordnance Board decided that it would conduct a study in an attempt to develop a submachine gun that would be similar to a Sten and submitted requirements to the Ordnance Department for this new weapon.[1]

The requirements submitted required that the new weapon be a select-fire submachine gun of sheet metal construction and chambered for the .45 ACP round; it should also be inexpensive and easy to manufacture in large quantities. Various other accuracy requirements and other small specifics were also put forward. The benchmark for performance for the weapon would be the Thompson submachine gun.[2] The weapon that would come out of these specifications would be known as the T15.

An employee of General Motors' Guide Lamp Division (also known as Guide Lamp) named George Hyde was tasked to design this new weapon; he worked alongside Frederick Sampson[3] (chief engineer of GM's Inland Division[4]) and René Studler (R&D officer of the United States Army Ordnance Board)[4] to design the new weapon. Come October 1942, however, the specifications for the T15 were suddenly altered, resulting in the removal of any select-fire functionality and the addition of a caliber conversion kit allowing its user to convert the weapon to fire the 9×19mm Parabellum round if required. This version of the weapon would be designated the T20.[2]

When it came time for the trials, Guide Lamp produced five prototypes of the T20 and five conversion kits; during the trials, the T20 performed excellently in all categories. Although failures were reported, these were mostly due to either defective or faulty magazines. With the results of the trials showing, the T20 was officially adopted as the United States Submachine Gun, Cal. .45, M3. The M3 was used during World War II, with some 606,694 manufactured from 1943 to 1945.[2] Some 1,000 M3s chambered for 9mm were also manufactured by Guide Lamp and used by the Office of Strategic Services.[5]

Due to its construction, the M3 was supposed to be a minimal-cost small arm that was meant to be disposed of when deemed inoperable;[6] it was due to this that few replacement parts (if any) were made available, even to ordnance-level commands by the time the M3 was drafted into service. A shortage of M3s in service however eventually caused the United States Ordnance Workshops to manufacture additional parts to keep the existing weapons operational.[7]

After being drafted into service, complaints about the M3's unserviceability began to surface, mainly regarding the charging handle retraction mechanism on some M3s; similar reports came from American forces stationed in the United Kingdom during the war.[2] Investigations were launched on the M3's design; these revealed several issues with the design, mainly with the charging handle's retraction spring design and rear sights that could be easily bent. As the war progressed, however, even more issues began to surface and more changes to the design were made.[2]

All these changes were incorporated into a simplified variant of the M3 known as the M3A1, designed based on feedback by various branches of the military when it came to using the M3.[2] The M3A1 was adopted as the United States Submachine Gun, Cal. .45, M3A1.[8] While originally intended to be produced in such volumes that it could eventually replace the Thompson submachine gun in service, this never came to be due to the various production delays with the M3, causing production of the Thompson to stretch until February 1944.

Production of the M3 and M3A1 ended in 1945 with the end of the war, although various other countries such as Argentina[9] and China[10] produced clones of the weapon in various quantities. Use of the M3 and M3A1 lasted well until the late 1950s and early 1960s in front line combat, when they were largely withdrawn. However, use of the M3 continued until the 1990s as a secondary armament on vehicles. Outside of the United States, however, the M3 saw service well into the 1990s. Most notably, the M3 was the weapon of choice of the Delta Force, prizing it for its performance when a suppressor was equipped.[11]

A total of 606,694 M3s and 48,669 M3A1s were produced.

Design Details[edit | edit source]

The M3 is a blowback-operated submachine gun made of stamped sheet metal; the sheet steel used to construct the weapon was 1.5 mm (0.059 in) thick and was stamped into two halves which were then welded together to create the receiver. The M3 uses a fixed firing pin which is milled into the bolt face. The bolt is drilled lengthwise in order to support two guide rods on which dual recoil springs were mounted; this supposedly allows for larger machining tolerances while providing operating clearance if unwanted solids make their way into the action.[2]

The techniques of stamping, pressing, spot welding and seam welding are heavily used throughout the construction of the M3, with only important parts such as the barrel, bolt and action being machined; this is meant to reduce the amount of man-hours required to assemble one weapon. A knurled metal cap at the front of the receiver is used to keep the removable barrel in place. The barrel is cold-swaged and features four right-handed grooves to act as rifling. The barrel could also fit a proprietary conical flash hider of which few were produced.[2]

The weapon also features fixed rear sights, and the only real safety of the weapon was the hinged dust cover covering the ejection port. Additionally, the weapon features a single-piece wireframe stock made of formed steel which telescopes within two tubes located at the rear of the receiver; both ends of the stock are tapped and drilled to allow it to act as a makeshift cleaning rod. The stock may also be used as a disassembly tool or a wrench to remove the barrel.[10]

The M3 takes thirty-round magazines patterned after the Sten's magazines and are known to jam quite frequently, although this is mainly due to faulty followers as opposed to the actual gun's design; the magazines used by the M3 were the main source of many soldiers' complaints about the weapon throughout its service life.[12] These magazines were also noted as being very difficult to hand-load and is more susceptible to jamming by dirt and grit when compared to other magazine designs.[2] The weapon was also susceptible to unintentional discharge if dropped, with the cheap construction of the M3 also susceptible to bending and denting if dropped; damage from the drop can sometimes be enough to bind the bolt.[13]

One of the most notable things about the M3 was its charging handle, which was a pivoting crank located on the right of the receiver. When the crank was operated, a pawl engages a notch which pulls the bolt back. The bolt is then pulled back until it locks onto the sear. The handle consists of nine parts and adds a decent amount of weight to the weapon.[10]

The later M3A1 was a highly simplified version of the M3, with some notable design changes, such as a magazine loading tool welded to the stock, the spare lubricant clip removed and replaced by an oil reservoir inside the pistol grip and most notably, the ejection port lengthened and the charging mechanism altered entirely. Instead of using a crank, the M3A1 did not have an external charging handle; instead, there was a recess in the bolt which its user can insert a finger inside and pull the bolt back. The M3A1 was a good 0.2 pounds (0.091 kilograms) lighter than the M3 mainly due to this updated charging mechanism.[2]

Ammunition[edit | edit source]

The M3 normally took .45 ACP ammunition, though the specifications put forward required that the M3 could fire 9×19mm Parabellum ammunition through a conversion. 25,000 conversion kits were supposed to be produced originally, but changes in specifics resulted in only 500 actually being obtained.[2]

These kits included a new barrel, bolt, recoil springs, a magazine well adapter and a 32-round Sten magazine. The sights of the M3 were not altered for this conversion however and it was discovered that the M3 shot high when converted although this was later deemed of little importance to fix.[2]

These kits required the crank mechanism and trigger guard on the M3 removed before the barrel could be unscrewed and replaced. These kits were also made for the M3A1, although the barrel could simply be unscrewed and replaced, with no other parts needing to be removed.[2]

Variants[edit | edit source]


Highly simplified version of the M3. Produced from 1944 to 1945. Changes included:

  • Charging mechanism completely altered from crank to recess in bolt; ejection port lengthened to accommodate this change
  • Retracting pawl notch removed with altering of charging mechanism
  • Clearance slot for cover hinge rivets added
  • Safety lock moved further to the rear
  • Magazine loading tool welded to stock; could also act as a cleaning rod stop
  • Two flat cuts cut into barrel bushing; meant to assist in removing the barrel using the stock as a wrench
  • Barrel ratchet redesigned with longer locking lever, allows for easier removal from barrel collar
  • Spare lubricant clip removed
  • Oil reservoir and oiler added, located in pistol grip; stylus on oiler cap could also be used as a tool to remove the extractor pin

Various M3s were converted to M3A1 standard over time (by simply removing the crank that acted as a charging handle and not removing the rest of the action inside the weapon), although faults with the magazine and reports of unintentional discharge still occurred regardless.[14]

The 30-round magazines were retained and were a continued source of complaints. Caps were provided to shield loaded magazines' feed lips;[15] initially, these were made of hard Tenite plastic and designated the T2, although these were later replaced with rubber caps which could be removed with less noise than the Tenite caps. During the Vietnam War it was discovered that these rubber caps could cause rust to form on the covered portions of the magazine and lead to corroding ammunition.[2]


Variants of the M3A1 designed at Fábrica Militar de Armas Portátiles (or FMAP-DM) in Argentina designed in 1954. The PAM1 (Pistola Ametralladora Modelo 1, lit. "Machine pistol Model 1") was constructed of thinner steel than the M3A1, was of smaller size, chambered in 9mm Parabellum, was lighter in weight and had an increased cyclic rate; this was probably due to an incomplete transfer of details.[16]

Various problems with the PAM1, such as overheating while firing (due to the weapon's thinner sheet steel receiver), uncontrollability while firing fully automatically (due to the higher fire rate), led to an improved version known as the PAM2 designed in 1963. Production ended in 1972 with 47,688 produced.[16] Used by the Argentinian Army during the Falklands War with captured examples being studied by the British.[17]

Type 36

Very close copy of the M3A1 manufactured by the Mukden Arsenal in 1947. Resembles the M3A1 but lacks the oil reservoir in the pistol grip and the two cuts in the barrel to allow for easy removal using the stock. Approximately 10,000 produced before the Arsenal was overrun by Communists in 1949.[1]

Type 37

Very close copy of the M3A1 produced at the 60th Jin Ling Arsenal in 1948. Is chambered in 9mm Parabellum, has a slightly longer barrel and a slightly modified bolt. Was produced until 1949 before the Arsenal was overrun by Communists, after which production was moved to Formosa (now Taiwan) and renamed the Type 39 when the employees of the arsenal fled to Formosa.[18]

Trivia[edit | edit source]

  • One M3 cost about USD 15 to manufacture in 1943[19] (est. USD 272 in 2018 dollars).

References[edit | edit source]

  1. 1.0 1.1 1.2 Ingram, Mike, The MP40 Submachine Gun, 2001
  2. 2.00 2.01 2.02 2.03 2.04 2.05 2.06 2.07 2.08 2.09 2.10 2.11 2.12 2.13 Iannamico, Frank, The U.S. M3-3A1 Submachine Gun, 1999
  4. 4.0 4.1
  5. Cadiou, Yves, Richard, Alphonse, Modern Firearms, 1977
  7. Dunlap, Roy, Ordnance Went Up Front, 1948
  9. Guzmán, Julio S., Las Armas Modernas de Infantería, 1953 (in Spanish)
  10. 10.0 10.1 10.2 Thompson, Leroy, The M3 "Grease Gun", 2016
  11. Haney, Eric L., Inside Delta Force: The Story of America's Elite Anti-terrorist Unit, 2002
  12. Faris, Bob, The Browning Machine Gun: Reflections of an Ordnanceman, 2007
  14. Hackworth, David H., Sherman, Julie, About Face: The Odyssey of an American Warrior, 1989
  15. Hogg, Ian V., Weeks, John, Military Small Arms of the 20th Century, 6th ed., 1991
  16. 16.0 16.1
  19. Carter, Gregg Lee, Guns in American Society: An Encyclopedia of History, Politics, Culture, and the Law, 2002

External Links[edit | edit source]

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