M3 submachine gun

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M3 "Grease Gun"
M3A1 with stock extended from Modern Firearms
Type	Submachine gun
Place of origin	United States of America
Service history
In service	1942–1994
Used by	Argentina, China, Japan, Philippines, United States
Wars	WWII, Chinese Civil War, Korea, Vietnam, Falklands War, Desert Storm (limited)
Production history
Designed	1942
Produced	1942—
Number built	680,000 approx.
Variants	M3, M3A1
Specifications
Weight	3.7 kg (8.16 lb)
Length	570 mm (22.4 in), stock retracted; 745 mm (29.3 in), stock extended
Barrel length	203 mm (8 in)
Cartridge	.45 ACP, 9 x 19 mm
Caliber	.45 ACP (11 mm), 9 mm
Action	Blowback
Rate of fire	400–450 rounds/min
Muzzle velocity	280 m/s (920 ft/s)
Effective range	~50 m (54.7 yd)
Feed system	30-round detachable box magazine

The M3 "Grease Gun" (more formally United States Submachine Gun, Cal. .45, M3/M3A1) was a submachine gun developed by the United States during World War II as a cheap substitute for the Thompson. It was nicknamed the Grease Gun because of its resemblance to an automotive grease gun. (It also contains an oil reservoir in the grip.)

[edit] History and design

When World War II began, the Thompson submachine gun was the standard U.S. submachine gun. However, the Thompson was comparatively expensive in terms of machining and time to manufacture. Newer Thompson models cost less to manufacture (e.g. the M1928 vs. the M1A1), but a brand new design was required to be produced much more economically. The basic concept of a crude, cheaper, mass-produced firearm traces back to the Chauchat of World War I, the most produced machine gun of that war. After the prototype Marlin M2 design proved too expensive to produce, the .45 caliber M3 was adopted in 1942, designed specifically for simplified production using pressed and stamped metal parts. Similar reduced manufacturing costs for a submachine gun design were undertaken by the British (Lanchester to the Sten), Germany (MP34, MP38 to MP40), and others. The Soviet Union, France and Italy would also make inexpensive submachine gun designs in the 1940s.

M3 in use in Brittany, France, August 1944

The gun was made by welding two pressed-metal shells together to form the exterior of the weapon. The M3 used the blowback method of operation. It could be fired only in fully-automatic mode, but experienced soldiers could usually fire single shots with it due to its very low rate of fire (400–450 rounds per minute). The barrel was held on by a simple nut and the bolt traveled on two guide rods and springs inside the receiver. This provided clearance between the bolt and receiver, keeping foreign matter from jamming the firearm. A major weak point of the Grease Gun was its magazine. Unlike the Thompson's double-column, dual-feed magazine, the Grease Gun used a double-column design that narrowed to a single-cartridge width at the feed end of the magazine. This meant that cartridges in the double-column magazine had to overcome friction in order to reach feeding position, and required a loading device to fill the magazine to capacity.^[1] The magazine design was also sensitive to dirt and debris. The U.S. Army later issued plastic caps or covers to keep loaded spare magazines from picking up excess dirt and to protect the feed lips, but this proved to be an incomplete solution. Moreover, the Grease Gun's heavy bolt and relatively weak recoil springs (designed to provide a low rate of fire) sometimes failed to strip the cartridge from the magazine, jamming the weapon.^[2]

In its original version, the M3 fired the .45 ACP cartridge (the same one used by the Thompson and the Colt M1911 pistol) from a 30-round detachable box-type magazine. Before firing, the ejection port had to be opened manually by the operator; this also functioned as the weapon's safety. An oiler is contained in the weapon's pistol grip. The stock doubles as the wrench for the barrel nut, a screwdriver, the cleaning rod, and as a magazine loading tool.

Far easier to manufacture than the Thompson, the M3 incorporated several updated design features, including a barrel that detached without tools, and a bolt that rode on two wire guide springs. A low cyclic rate of fire and straight-line recoil thrust made it easier to control than many other submachine guns, especially during automatic fire, though the spindly wire-frame stock fit few users and was rather too short.^[3]

The M3 was designed to be a disposable firearm once damaged or disabled, and no spare parts were provided to Army ordnance commands. This decision proved to be a minor catastrophe after inevitable supply bottlenecks caused reserve stocks of the M3 to run out in certain commands, forcing ordnance technicians to make emergency repairs and fabricate pawl springs in order to provide frontline units with operating weapons.^[4]

In spite of the M3's much greater simplicity and clever bolt design, the firearm was less reliable than the .45 Thompson, with a cocking mechanism that tended to break frequently and a single-column feed magazine (copied after the British Sten and German MP40) that sometimes prevented reliable feeding.^[5] When the M3 was adopted as a standard firearm, the Thompson was categorized as a "Limited Standard" or "Substitute Standard" submachine gun. The later M3A1 model corrected some of the faults of the earlier M3. New features included a revised and simplified cocking mechanism, a larger ejection port, a stronger cover spring, a reinforced rear sight, and a cartridge-feeding device built into the stock.

The M3 and M3A1 served through the Korean War and the Vietnam War. They remained in limited use with U.S. military into the 1990s, to include service in the 1991 Gulf War (e.g. drivers in the 19th Engineer Battalion, which was attached to the U.S. 1st Armored Division, deployed with the M3A1 as an alternate arm) and as defensive weapon for the crews of M88A1 ARV, until replaced by the M4 Carbine.

[edit] Foreign Service

Both Nationalist China and Argentina produced locally-manufactured versions of the M3/M3A1 submachine gun for use by their own forces. Nationalist M3 guns captured by Communist forces after the fall of mainland China in 1949 were used by the latter in the Korean War. Argentine M3A1s were made under license by Fabrica Militar de Armas Portatilles "Domingo Matheu" (FMAP DM); the Chinese version was called the Type 36.

The Philippine Marine Corps currently uses the M3 as personal defense weapons for armor crews and has issued locally modified sound and flash suppressed versions to their special operations units after tests in 2004.

The Japanese Ground Self-Defense Forces had been formerly equipped with the M3 before they switched to the Minebea PM-9 submachine gun after Allied occupation of Japan came to an end. A small number are held in reserve with special forces units.

Formerly arming the South Korean military, the M3 was replaced with the Daewoo K1 rifle.

[edit] Variants

[edit] T20

• Experimental designation of what was type-classified as the M3. Development of the T15 project.

[edit] M3

M3

• Entered service December 1942;
• Designed specifically as a low-cost substitute for the Thompson submachine gun. Production at General Motors automobile parts plants was simplified by making use of stamped metal and only a little machining. A number of deficiencies were found during the initial two years of use. The M3 had not used the Thompson submachine gun's magazine, but a new design based on that of the British STEN and German MP40. Like those weapons, the M3's magazine narrowed to a single column at the feed end of the magazine, causing increased friction and occasional jams, especially when exposed to dust and dirt.^[6] Combat introduction was not until the Normandy campaign (June 1944), having been delayed until initial deficiencies were corrected.

[edit] M3A1

M3A1

• Entered service December 1944;
• The A1 model corrected some of the faults of the earlier version. New features included a larger ejection port, a stronger cover spring, and a change to the cocking method. The original M3 was cocked by a crank mechanism that proved unreliable in service. On the M3A1, the bolt had a machined recess which was exposed when the ejection port cover was opened. The user had to insert a finger in the recess to pull the bolt to the cocked position. Unfortunately, the M3A1 retained the M3's single-column feed magazine, which proved problematic throughout the firearm's service life.^[7]
• The M3A1 could also be adapted to fire the 9 mm Parabellum round by changing the barrel and bolt, and an adapter permitted the use of the magazine from the British Sten gun or the German MP40