The M3 and M3A1 Grease Gun

By Frank Iannamico

Just a short while later the Germans simplified their original design of the MP38, by utilizing sheetmetal stampings, welded and pressed together. The result was a weapon that could be produced very inexpensively, but more importantly during a major war, manufactured in a short period of time. The new sheet-metal machinegun was called the MP40 maschinenpistole. Despite the fact that the weapon was made of inexpensive materials and methods it was just as reliable as the weapons that were produced from more traditional techniques. While fighting the Germans in North Africa in 1942, the American Army captured a number of MP40 weapons. These were promptly shipped to the Aberdeen Proving Ground in Maryland for evaluation and testing. The Ordnance personnel at Aberdeen were quite impressed with the methods and materials used to make the rugged German submachine gun.

The standard United States submachine gun issued during most of World War Two was the Thompson. The first model of the famous “Tommy Gun” that was procured by the U.S. Army was the 1928 model. The 1928 Thompson was of a design conceived over twenty years earlier. Although extremely reliable and rugged, the Thompson was very labor intensive to produce, heavy and expensive. The M1 and M1A1 Thompson was introduced in 1942, although simplified for ease of manufacture, they were still far too time consuming to produce in the numbers needed to supply the United States and her allies. The U.S. Marines were forced to adopt and procure 80,000 .45 caliber Reising submachine guns in 1942, due to the shortage of Thompsons.

The U.S. Ordnance department had started to test both domestic and foreign submachine guns as early as 1939, even as their first orders for the Thompson were being placed. The testing failed to find a suitable replacement for the Thompson. The Ordnance Department decided to develop their own weapon, the T-20.

The United States Army Ordnance Department recruited the General Motors Corporation to assist with the design and development of the T-20. The GM Inland Division’s Chief engineer Fredrick Sampson was assigned to head up the project. After the successful and thorough testing of the T20 prototypes, the T20 was officially adopted as the U.S. Submachine Gun, Caliber .45, M3. The M3 -T20 prototype had an overall score of 95 out of a possible 100 in the standard Aberdeen small arms test, higher than any previous weapon tested.

On 29 January 1943 the Guide Lamp Division of the General Motors Corporation, and the U.S. Ordnance Department completed negotiations of a contract to manufacture the M3 submachine guns. The initial cost was $17.93 per unit, minus the bolt assembly. This cost would be amended several times during the life of the GM Guide Lamp contract. The contract to manufacture the bolts for the M3 was awarded to the Buffalo Arms Company of New York at a cost of $2.58 per piece. Ordnance contracts W-294-ORD-2107 and W-33-ORD-825 for the initial 300,000 units were awarded to Guide from the Cincinnati Ordnance District. The Guide Lamp factory was located in Anderson, Indiana. Guide Lamp was also manufacturing the .45 caliber sheet metal Liberator pistols, and Browning machine gun barrels. At the peak of production Guide was turning out a new M3 submachine gun every 2.4 minutes. A total of 605,694 M3 models would be accepted by the Ordnance Department from 1943 until early in 1944. The simplified M3A1 model was only produced in 1945, 82,281 were built before production ceased at the end of July.

The US .45 caliber M3 submachine gun, was an air-cooled, automatic only, weapon that fired from an open bolt. The weapon’s rate of fire was a somewhat slow 350- 400 rounds per minute. Semi automatic fire could be quite easily achieved by careful manipulation of the trigger. The U.S. troops that were issued the M3 were not immediately impressed by the new weapon, mostly because of its slow cyclic rate. They perceived that the effectiveness of any given weapon was directly related to the amount of rounds it could expend in a short period of time.

Although the cyclic rate was slow and the appearance unorthodox, the M3 was quite a reliable and effective weapon within its design limits. Its toy-like appearance generated several nicknames for the weapon, some not very flattering. The one that stuck was the grease gun, for its similarity in appearance to an auto mechanics tool. The M3 was easily manufactured from two die-stamped halves of sheet metal that were welded together. At first problems were encountered from the heat of the welding process warping the sheet metal receiver, but the problem was soon solved. The barrels were rifled by using the time saving cold swaging method. The bolt assembly was basically the only part requiring any extensive machining. The double feed, single stack magazine capacity was 30 rounds of .45 ACP ball ammunition. A magazine loader was issued to aid in loading the magazines.

After the M3 was in service for a period of time, the Ordnance Department felt that most of the problems with the weapon’s design had surfaced, and they set requirements for improving the initial design. One of the biggest problem areas with the M3 was with the cocking handle and its related parts. This troublesome assembly would be completely eliminated in the improved M3A1 design. A new bolt was designed that was cocked by the finger of the operator. An enlarged ejection port was also needed to incorporate the new style bolt. The design also allowed for much easier field stripping by eliminating the need to remove the ejector housing in order to remove the bolt assembly from the receiver. The new model was standardized as the M3A1 December 1944. The M3 was then classified as Substitute Standard. The M3 and M3A1 were destined to completely replace the Thompson as the standard U.S. submachine gun, but by the time World War Two ended in 1945, not enough had been produced. Production was abruptly terminated in July of 1945 as the war was in its final days.

During the Korean Conflict of 1950 to 1953 the Thompsons and the M3 and M3A1 submachine guns were pulled from storage and sent to fight another war. By the time hostilities in Korea had ended, the U.S. was facing a shortage of submachine guns according to the peacetime requirements. The United States had provided an enormous amount of WWII weapons to South Korea as military aid during the war. In 1955 the Ithaca Gun Company of Ithaca, New York was awarded contract number DA-19-058-ORD-7854 by the Rochester Ordnance District to manufacture 70,000 M3A1 submachine guns. Production was halted after only 33,227 were produced. In the interim the United States had been searching for a new modern service rifle to replace the M1 Garand rifle. As a result of years of testing and evaluation the Ordnance Department adopted the M14 as the standard U.S. Service Rifle of the U.S. Army. The new M14 was to replace the M1 Rifle, M1 Carbine and the .45 caliber submachine gun. Due to a number of problems the first M14 rifles were not issued until 1959.

When the United States sent advisory personnel into Vietnam in the early 1960s, the troops were armed with many weapons from WWII. As the war endured, U.S. personnel were eventually issued M14, M16 and M16A1 rifles. On 11 December 1961, the United States began to supply an enormous amount of military aid to the South Vietnamese Government. Included in the aid were many World War Two small arms including 1919A4 - 1919A6 machine guns, BARs, M1 rifles, M1 - M2 carbines, and M3 - M3A1 submachine guns.

In order to keep the M3 and M3A1 weapons in serviceable condition during the Vietnam War, the production of spare parts was resumed. The Vietnam era parts will be stamped with only the Ordnance drawing number of the part. The letter codes GL indicating Guide Lamp, and the ITG code representing the Ithaca Company are absent. There was one insignificant change introduced during the Vietnam era, and that was the introduction of the chromium-lined barrel. The corrosion resistant chromium bore was implemented because of periods of extreme humidity and rainfall in the country. These barrels are easily recognized by the dull silver appearance of their bores and chambers.

Suppressed or “silencer” equipped versions of the M3 and M3A1 weapons were used by U.S. sniper teams in Vietnam to quietly dispatch any enemy personnel that might compromise their positions. These weapons were fitted with suppressors manufactured by the SIONICS corporation. A few suppressor-equipped grease guns were also used by the enemy in Vietnam. The enemy weapons used a suppressor that was very similar in construction to those made by Bell Laboratories for the Office of Strategic Services (OSS) during WWII. Since the OSS grease gun suppressors had no identifying markings on them, it wasn’t known for certain if the enemy suppressors were refurbished U.S. issue or Chinese copies. There was one internal difference noted. The enemy suppressors used oil soaked felt, original U.S. produced versions ones did not.

(Dan’s Note: There were a number of Special Operations personnel and others who have described taking an M3A1 Greasegun, and replacing the recoil springs with cut down M2HB springs- this increased the cyclic rate to around 800rpm, but was destructive to the rear end of the receiver).

A number of U.S. M3-M3A1 submachine guns were also captured and used against the United States forces and their South Vietnamese allies. The Viet Cong Guerrillas especially favored the compact and easily concealed “grease gun”. Communist China had supplied the Viet Cong and NVA troops with a substantial number of their own indigenously produced version of the M3A1. The Chinese copies of the M3A1 submachine gun were designated as the M36 when chambered for the .45 caliber cartridge and the M37 chambered for 9mm rounds. These two weapons were direct copies of “grease guns” that the United States had supplied to a desperate China during WWII. The weapons were very similar to the U.S. manufactured M3A1model except for the Chinese markings on the magazine housings.

The M3 and M3A1 grease guns are the only U.S. weapons adopted during WWII that continue to serve even today. Some weapons like the famous Thompson Submachine Gun endear, while others like the utilitarian M3-M3A1 grease guns simply endure.

This article was excerpted from the book The M3 and M3A1 Grease Gun. The book is available from Moose Lake Publishing 207-683-2959


This article first appeared in Small Arms Review V6N1 (October 2002)
and was posted online on December 27, 2013


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