M3 submachine gun

The M3 was an American .45-caliber submachine gun adopted for U.S. Army service on 12 December 1942, as the United States Submachine Gun, Cal. .45, M3. Compared to the Thompson submachine gun, the M3 was cheaper to produce, lighter, more accurate, and was also chambered in .45 ACP. The M3 was commonly referred to as the "Grease Gun" or simply "the Greaser," owing to its visual similarity to the mechanic's tool.

Intended as a replacement for the .45-caliber Thompson series of submachine guns, the M3 and its improved successor, the M3A1 began to replace the Thompson in first-line service in late 1944 and early 1945. Due to delays caused by production issues and approved specification changes, the M3/M3A1 saw relatively little combat use in World War II.

History


In 1941 the U.S. Army Ordnance Board observed the effectiveness of submachine guns employed in Western Europe, particularly the German 9mm MP 40 and British Sten guns, and initiated a study to develop its own Sten-type submachine gun in October 1942. The Ordnance Department requested the army to submit a list of requirements for the new weapon, and ordnance in turn received a separate list of requirements from both the infantry and cavalry branches for a shoulder-fired weapon with full- or semi-automatic fire capability in caliber .45 ACP or .30 Carbine. The two lists of requirements received by ordnance were then reviewed and amended by officials at Aberdeen Proving Ground. The amended requirement called for an all-metal weapon of sheet metal construction in .45 ACP caliber, designed for fast and inexpensive production with a minimum of machining, and featuring a dual auto and semi-automatic fire capability, a heavy bolt to keep the cylic rate under 500rpm, and the ability to place 90 percent of all shots fired from a standing position in full-automatic mode on a 6x6 foot target at a range of 50 yards. The benchmark for testing the M3's performance would be the M1928A1 Thompson.

George Hyde of General Motors's Inland Division was given the task of designing the new weapon, while Frederick Sampson, Inland Division's chief engineer, was responsible for preparing and organizing tooling for production. The original T15 specifications of 8 October 1942 were altered to remove a semi-automatic fire function, as well as to permit installation of a kit to convert the weapon's original .45 caliber to that of 9mm Parabellum. The new designation for the 9mm/.45 full-automatic-only weapon was the T20. Five prototype models of the .45 T20 and five 9mm conversion kits were built by General Motors for testing. At the initial military trials, the T20 successfully completed its accuracy trials with a score of 97 out of 100. In the endurance test, the test weapon fired more than 5,000 rounds of brass-case ammunition, with only two failures to feed. Four army test boards composed of multiple army service branches independently tested and reviewed the T-20 prototype weapons including the Airborne Command, the Amphibious Warfare Board, the Infantry Board, and the Armored Forces Board. All four branches reported malfunctions caused by the M3 magazine, mostly attributed to defective or jammed magazine followers.

The T-20 was formally approved by U.S. Army Ordnance for production at GM's Guide Lamp Division in Anderson, Indiana in December 1942 as the U.S. Submachine Gun, Caliber .45, M3. Guide Lamp produced 606,694 of the M3 variant submachine gun between 1943 and 1945. Although reports of malfunctions caused by the single-feed magazine design appeared during the initial firing trials, no changes were made to the M3 magazine.

Around 1000 M3 submachine guns in caliber 9mm Parabellum were built by Guide Lamp. These original 9mm guns, identified by the markings "U.S. 9 mm S.M.G." on the left side of the magazine well (without any model designation, such as M3), 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. Though 25,000 kits were originally requested for procurement, this was changed to a recommendation by the Ordnance Committee in December 1943 that only 500 9mm conversion kits be obtained. Procurement was authorized in February 1944, but it is believed that only a limited number of kits were actually produced. These conversion kits included a new 9mm barrel, replacement bolt and recoil springs, a magazine well adapter for use with Sten magazines, and a replacement 9mm STEN magazine of British manufacture. As the M3's sights were not altered for the new cartridge, the 9mm M3 shot low at 100 yards, but the sighting error was deemed inconsequential. The OSS also requested approximately 1,000 .45-caliber M3 submachine guns with an integral sound suppressor (designed by Bell Laboratories). Specially drilled barrels and barrel nuts were manufactured by Guide Lamp, while the High Standard Firearms Company produced the internal components and assembled the weapon. The Bell Laboratories suppressor was estimated to be only 80% as efficient as the British suppressed STEN Mk IIS.

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 shortage of M3 submachine guns created by the need for interim production changes forced U.S. Army Ordnance workshops to fabricate pawl springs and other parts to keep existing weapons operational.

After its introduction to service, reports of unserviceability of the M3 commenced in February 1944 with stateside units in training, who reported early failure of the cocking handle/bolt retraction mechanism on some weapons. Similar reports later came from U.S. forces in Britain who were issued the M3. An investigation revealed several deficiencies in the construction of the M3's bolt retraction mechanism, together with issues concerning barrel removal and retention as well as easily bent rear sights. As a result several product improvements were incorporated into all new M3 production, including a new design retracting pawl with improved heat treatment, a new spring stop fitted to the right-hand brace of the retracting lever, a modified ejector featuring a cocking lever trip, a larger ratchet pad with improved heat treatment to more securely retain the barrel assembly, and strengthening gussets fitted to the sides of the fixed 'L' rear sight. After new complaints were raised about accidental magazine releases and failure of the wire buttstock to remain in place in the collapsed position, two additional changes were made to M3 production and approved by Ordnance on 31 August 1944. This included a small sheetmetal guard around the magazine release button, and the inclusion of a stop between the two rods forming the wire stock at the butt end. In December 1944, in response to field requests for further improvements to the basic M3 design, an improved, simplified variant of the M3 was introduced, the  M3A1. 15,469 M3A1 submachine guns were produced before the end of World War II.

It was originally hoped that the M3 could be produced in numbers sufficient to cancel future orders for the Thompson submachine gun, and to allow the army to gradually withdraw the Thompson from front-line service. However, due to unforeseen production delays and requests for modifications, the M3 never replaced the Thompson during World War II, and purchases of the Thompson continued until February 1944. A total of 622,163 M3/M3A1 submachine guns of all types were assembled by the end of World War II, by which time the Thompson, at over 1.5 million guns produced, outnumbered the M3 and M3A1 in service by a factor of nearly three to one.

Design details
The M3 was an automatic, air-cooled blowback-operated weapon that fired from an open bolt. Constructed of plain .060-in. thick sheet steel, the M3 receiver was stamped in two 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 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


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


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 ft. 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 complaint 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.

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

The M3A1 modifications resulted in a submachine gun weighting less and more reliable, easier to maintain, and easier to field strip (the original M3 need the trigger guard to be removed and the cocking crank assembly to be detached from the receiver housing before unscrewing the barrel, but the M3A1 needed the user to merely 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 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.

The M3 and M3A1 were largely withdrawn from U.S. frontline service in 1957, but continued to be used until the mid-1990s by armored vehicle crews and truck drivers. During the 1991 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.

Foreign variants
In 1954, a variant of the U.S. M3A1 submachinegun was designed at the Argentine FMAP (Fábrica Militar de Armas Portátiles) factory in the city of Rosario and put into production the following year as the P.A.M. 1 (Pistola Ametrelladora Modelo 1). Constructed of somewhat thinner-gauge steel than the U.S. M3A1, the P.A.M. 1 was in essence a 7/8 scale replica of the U.S. weapon in 9mm Parabellum caliber, but was lighter and had a higher rate of fire. In service, the P.A.M. 1's thinner sheet steel receiver tended to overheat with extended firing, while the gun itself proved somewhat more difficult to control in automatic fire despite the smaller caliber. Additionally, triggering the weapon to fire individual shots proved difficult owing to the increased rate of fire. Problems with accidental discharges and accuracy with the P.A.M. 1 led to an improved selective-fire version with a grip safety on the magazine housing known as the P.A.M. 2, first introduced in 1963. Colloquially referred to as La Engrasadora (the Greaser), 47,688 P.A.M. 1 and P.A.M. 2 submachine guns were produced between 1955 and 1972. A number of P.A.M. 1 and P.A.M. 2 submachine guns were used by the Argentine Army during the Falkland Islands War with The United Kingdom in 1982, and captured examples were tested by British military forces.

Users



 * 🇦🇷 Argentina
 * 🇧🇴 Bolivia
 * People's Republic of China: Copies made as the Type 36 and used in the Korean War by Chinese soldiers.
 * 🇨🇴 Colombia: Used by the National Army of Colombia and the National Police of Colombia from the 1950s up to the 1970s, when it was replaced by the UZI submachinegun.
 * 🇩🇴 Dominican Republic
 * 🇪🇨 Ecuador
 * 🇬🇷 Greece Used by the Greek armed forces during World War II and the post-War World II period.
 * 🇬🇹 Guatemala
 * 🇯🇵 Japan: Used by the JSDF for a short period of time before the adoption of the Minebea PM-9. Known to be used by JGSDF tank crews as a personal defense weapon.
 * Republic of Korea: Mainly used by Republic of Korea Army Special Warfare Command.
 * 🇲🇰 Macedonia: 707 surplus M3 submachine guns were transferred to Macedonia in 1999.
 * 🇲🇦 Morocco: 1,472 surplus M3A1 submachine guns were transferred to Morocco in the 90s.
 * 🇵🇭 Philippines: Had their M3 submachine guns released from reserve stockpiles by the Philippine Navy for the Philippine Marine Corps's special forces due to budget constraints. Modifications done on the refurbished weapons include an integral suppressor and a Picatinny rail. The weapon had been tested with a prototype on May 2004.
 * Soviet Union Received military aid from the US via Lend-Lease.
 * 🇺🇸 United States
 * 🇺🇸 United States