207,372 Pages


An M3A1 Submachine Gun in service with Philippine Special Forces, with a Piccatinny rail and Suppressor attached

The M3 Submachine Gun series (also known as The Grease Gun), Is an American submachine gun, Chambered in .45 ACP which was developed by the United States during WWII, as a cheaper substitute to the Thompson Submachine Gun Series. Due to it's physical appearance, it earned the name 'Grease gun' among the Troops under whom it served. Despite being less accurate then the M1A1 Thompson Submachine gun, It was lighter and Cheaper than the former, as well as being much faster to produce,

History & DesignEdit

In 1941, the U.S. Armies own Ordnance Board noted the performance and Combat effectiveness of the various models of submachine gun employed on the western european front, particularly the German MP 40 and The British STEN Series; and subsequently began a study to develop a Submachine gun for the army that was based off of the same Principles as the Low-Cost British Sten gun, at the end of 1942. The Ordnance Department requested that the army submit Specifications for the design of the new Submachine Gun, received a separate set of requirements from the Infantry and Cavalry Branches for a select fire weapon with full- or semi-automatic fire capability chambered in either .45 ACP or .30 Carbine.

The two requirements from each branch were then evaluated and amended by officials at the Aberdeen Proving Ground testing facility. The amended specification requested a submachine gun of sheet metal construction chambered in .45 ACP. A New design, Primarily designed for fast and cheap Manufacture, with as little machining as possible to help high volume production , and featuring a Select fire control between Semi and Fully-Automatic firing moles with a heavy and durable bolt to maintain a fire rate of 500 rounds/min as well as the requirement to achieve 90 percent accuracy from a standing position in full-automatic mode on a 6x6 foot target at a distance of 50 yards. The benchmark weapon for analysis of the M3's performance would be the Phased-out M1928A1 Thompson Submachine Gun. This weapon would then go on to Replace the M1A1 Thompson in the U.S. Army, due to it's High production period and cost.

At the beginning of the war in 1939, the Thompson SMG cost $209 per unit to produce, this was later lowered to $70 in 1942, and then a lower $45 per unit in 1944. By the end of the war the U.S. Army was Fielding M3 Submachine Gun's to replace it's Thompson Submachine gun's in front line combat units. However, due to Production Issues and Specification changes, Delays in production occurred that Ultimately caused the M3 Submachine gun to see only Limited use in the war, and led to the production of the M3A1 Variant of the Submachine Gun in 1944, which featured Various Improvements over it's base model, and was subsequently used in the Korean War, and Later Conflicts. The M3A1 Variant was especially popular with the Navy SEAL's, who later used M3A1's with a Suppressor attached for Cover Operations in Vietnam. It has recently found use In modern times, among the Philippines armed forces, who have modernized the weapon by adding a Piccatinny rail mount to allow the use of optics, and a modern suppressor for the weapon system.

1000 M3 submachine guns Chambered in 9x19mm Parabellum were manufactured by Guide Lamp industries. These original 9x19mm M3 Grease Guns, Had a unique marking of "U.S. 9 mm S.M.G." on the left side of the magazine well, and lacked the M3 Model Designation. They were delivered to the OSS in 1944. Additionally, Rock Island Arsenal and Buffalo Arms Corporation manufactured parts for a limited number of 9mm conversion kits for the M3.  25,000 kits were requested for procurement, However this was later changed due to the Ordnance Comitee's recommendation in

December 1943, that only 500 9x19mm conversion kits should be procured. Manufacture was authorized in February 1944, However, only a limited number of kits were Manufactured. These conversion kits included a new 9mm bored barrel, a new replacement bolt and new recoil springs. Additionally a magazine well adapter for use with British Sten gun 32-round magazines, and a replacement 9mm Sten magazine of British manufacture were also included. As the M3's sights were not altered for the new cartridge, the 9mm M3 shot high at 100 yards, however the sighting error was deemed insignificant, and without consequence. The OSS also ordered approximately 1,000 .45-caliber M3 submachine guns with an integral Bell Laboratories sound suppressor. Specially drilled barrels and barrel nuts were manufactured by Guide Lamp, while the High Standard Firearms Company produced the internal components required and were responsible for final assembly0. The Bell Laboratories suppressor was estimated to be only 80% effective at noise reduction, than the British suppressed STEN Mk IIS Suppressor.
Id smg m3 700 06

American infantryman firing at North Korean troops during the Korean War

With its stamped, riveted, and welded construction, the M3 was originally designed as a minimum-cost small arm, to be used and discarded once it became inoperative. As such, replacement parts, weapon-specific tools, and sub-assemblies were not made available to unit-, depot-, or ordnance-level commands at the time of the M3's introduction to service. In 1944, a lack of M3 submachine guns created by the need for interim production changes forced the hand of U.S. Army Ordnance workshops to fabricate pawl springs and other parts to keep existing weapons functional.

The M3 and M3A1 were mostly phased out from active U.S. frontline service from 1959 and into the early 60s, however continued to be used until the mid-1990s as vehicle crew backup weapons. During the mid 1970s tank drivers of the 1st Battalion 67th Armored attached to the 2nd Armored Division were issued the M3A1, due of its size and portability. During the Gulf War, drivers of the 19th Engineer Battalion attached to the 1st Armored Division were equipped with the M3A1 as part of their vehicle TOE.

Design and Function Edit

The M3 was an automatic submachine gun, operated by an air-cooled blowback-operated system that fired from an open bolt. Manufactured from basic .060-in. thick sheet steel, the M3 receivers construction consisted of two stamped halves that were then welded together. The M3 was striker-fired, with a fixed firing pin contained inside the bolt. The bolt was drilled longitudinally in order to support two parallel guide rods, upon which were mounted twin return (recoil) springs. This configuration allowed for larger machining tolerances while providing operating clearance in the event of dust, sand, or mud ingress. The M3 featured a spring-loaded extractor which was housed inside the bolt head, while the ejector was located in the trigger group.Like the British Sten, time and expense was saved by cold-swaging the M3's barrel

Operating mechanism Edit

220px-Basic Function M3 SMG Illustration

The M3 operating sequence is as follows: the bolt is cocked to the rear using the cocking handle located on the right side of the ejector housing. When the trigger is pulled, the bolt is driven forward by the recoil springs, stripping a round from the feed lips of the magazine and guiding the round into the chamber. The bolt then continues forward and the firing pin strikes the cartridge primer, igniting the round, resulting in a high-pressure impulse, forcing the bolt back against the resistance of the recoil springs and the inertial mass of the bolt. By the time the bolt and empty casing have moved far enough to the rear to open the chamber, the bullet has left the barrel and pressure in the barrel has dropped to a safe level. The M3's comparatively low cyclic rate was a function of the relatively low pressure generated by the .45 ACP round, a heavy bolt, and recoil springs with a lighter-than-normal compression rate.

Features Edit

M3 receiver markings Edit

The gun used metal stamping and pressing, spot welding and seam welding extensively in its construction, reducing the number of man-hours required to assemble a unit. Only the barrel, bolt and firing mechanism were precision machined. The receiver consisted of two sheet metal halves welded together to form a cylinder. At the front end was a knurled metal cap which was used to retain the removable barrel. The cold-swaged, rifled barrel had 4 right-hand grooves. M3 and M3A1 submachine guns could be fitted with an optional, detachable flash hider, though none saw any service in World War II. A later production flash hider designated Hider, Flash M9 was produced in time to see service during the Korean War. It proved popular in combat, as frequent night engagements emphasized the need to reduce flash signatures on small arms. In Korea, U.S. soldiers equipped with automatic weapons were taught to look above the flash of their weapon during night firing, a tactic that sometimes prevented the detection of crawling enemy infiltrators and sappers.

Projecting to the rear was a one-piece wire stock made from a formed steel rod that telescoped into tubes on both sides of the receiver. Both ends of the stock were tapped and drilled so that it could be used as a cleaning rod. It could also be used as a disassembly tool or as a wrench used to unscrew the barrel cap.

The M3's cocking handle assembly was located on the right-hand side of the receiver on the ejector housing, just forward and above the trigger, and consisted of nine parts. As the handle is pulled to the rear, a pawl rises to engage a notch in the bottom of the bolt, pushing the bolt to the rear until it locked back on the sear.

The fixed sights consisted of a rear aperture sight preset for firing at 100 yards (approximately 91 m) and a front blade foresight. All M3 submachine guns were test-fired for accuracy at a distance of 100 feet (30 m). With the sights set at six-o'clock on a bullseye target, each gun was required to keep four out of five shots within or cut the edge of a three-inch (76 mm) bulls' eye to meet accuracy requirements.

The weapon's only safety was the hinged ejection port dust cover. This cover had a projection on the underside that engaged a notch on the bolt, locking it in either its forward or rearmost positions. The M3 had no mechanical means of disabling the trigger, and the insertion of a loaded magazine would load the gun. With receiver walls made of relatively thin-gauge sheet metal, the M3/M3A1 were subject to disabling damage if dropped on an open dust cover - the covers bent easily, negating the safety feature. Dropping the gun on a sharp or hard surface could dent the receiver enough to bind the bolt.

The M3/M3A1's 30-round magazine was the source of complaints throughout the service life of the weapon.Unlike the Thompson, the M3 fed from a double-column, single-feed detachable box magazine which held 30 rounds and was patterned after the British Sten magazine; the single-feed design proved difficult to load by hand, and was more easily jammed by mud, dust, and dirt than double-column, double-feed designs like the Thompson. Additionally, the feed lips of the single-feed design proved more susceptible to feed malfunctions when slightly bent or damaged. Plastic dust caps were later issued to cover the feed end of the magazine and keep out dust as well as protect the sensitive feed lips.

Variants Edit

M3A1 Edit

In December 1944, a modernized version of the M3 known as the M3A1 was introduced into service, with all parts except the bolt, housing assembly, and receiver interchangeable with those of the M3. The M3A1 had several improvements:

  • Most significantly eliminating the troublesome crank-type cocking lever assembly, replaced by a recessed cocking slot machined into the top front portion of the bolt, letting it be cocked by putting a finger into the cocking slot and pulling back the bolt.
  • The retracting pawl notch was removed, and a clearance slot for the cover hinge rivets was added.
  • The ejection port and its cover were lengthened to allow the bolt to be drawn back far enough to be engaged by the sear.
  • The safety lock was moved further to the rear on the cover.
  • To make loading the single-feed magazine easier, a magazine loading tool was welded to the wire stock; it also served as a cleaning rod stop.
  • The barrel bushing received two flat cuts that helped in barrel removal by using the stock as a wrench.
  • The barrel ratchet was redesigned to provide a longer depressing level for easier disengagement from the barrel collar.
  • The spare lubricant clip (on the left side of the cocking lever assembly) was removed, replaced with an oil reservoir and an oiler in the pistol grip of the receiver assembly. The stylus on the oiler cap could also double as a drift to remove the extractor pin.

At 7.95 pounds empty, the M3A1 was slightly lighter than the M3, at 8.15 pounds empty, primarily due to the simplified cocking mechanism. The M3A1 was formally approved for production on 21 December 1944

The M3A1 modifications resulted in a more reliable, lighter weight, easier to maintain, and easier to field strip submachine gun; the original M3 needed both the trigger guard removed and the cocking crank assembly detached from the receiver housing before unscrewing the barrel, but the M3A1 only required the user unscrew the barrel. To date, only one 9mm conversion kit for the M3A1 has been discovered.

Because it had already been issued in large numbers, the existing M3 magazine design was retained, despite demonstrated deficiencies exposed during the weapon's firing trials and its early combat service. In an effort to improve reliability, a hard plastic Tenite cap designated T2 was adopted in November 1944 to fit over the feed lips of loaded magazines. These caps protected the feed lips while keeping out dirt, sand, and debris. Sometime during the 1960s the hard T2 plastic cap was replaced in service with one of pliant neoprene rubber, which could be removed with less noise.Unfortunately, during service in the humid climate of Vietnam it was discovered that the rubber cap caused rust to form on the covered portion of the magazine, while causing loaded ammunition to corrode.

Initially, M3 submachine guns returned for repair were not upgraded to the M3A1 standard, but merely inspected to ensure they had the improved M3 housing assembly and magazine release shield.During the Korean War, existing M3 guns in service were converted to the improved M3A1 configuration using additional new production parts. During the conversion, armorers frequently removed the M3 cocking handle, leaving the rest of the now-redundant cocking mechanism inside the subframe. Overall, the M3A1 was seen by most soldiers and Ordnance technicians as an improvement over the M3. However, complaints of accidental discharge continued to occur even as late as the Korean War. These incidents were sometimes caused by dropping the weapon on a hard surface with an impact sufficient to knock open the ejection port cover and propel the bolt backwards (but not enough to catch the sear). The return springs would then propel the bolt forward to pick up a cartridge from the magazine and carry it into the chamber, where the bolt's fixed firing pin struck the primer upon contact.

In 1945, the Guide Lamp factory manufactured 15,469 M3A1 submachine guns before production contracts were canceled with the end of the war. During the Korean War, Ithaca Gun Co built another 33,000 complete guns as well as manufacturing thousands of parts for the repair and rebuilding of existing M3 and M3A1 weapons.

See alsoEdit

This page uses Creative Commons Licensed content from Wikipedia (view authors).

Ad blocker interference detected!

Wikia is a free-to-use site that makes money from advertising. We have a modified experience for viewers using ad blockers

Wikia is not accessible if you’ve made further modifications. Remove the custom ad blocker rule(s) and the page will load as expected.