Surplus Review: August 1999

By Frank Iannamico

The M3 Submachine Gun

The U.S .45 Caliber Submachine Gun, M3 and M3A1 “grease guns” were certainly one of the less refined weapons ever adopted by the United States, but the M3 enjoyed a longer service life than many other more respected weapons. The venerable grease gun served from the first models accepted in 1943, to still being a limited issue item to Army Reserve and National Guard armored units today. It was noted in a U.S. Army document that a few M3 and M3A1 submachine guns were still in service in 1998.

The United States Army first encountered German troops armed with the MP40 in North Africa in 1942. Several examples were captured and returned to Aberdeen Proving Ground for a complete evaluation. The Army personnel at Aberdeen were quite impressed with the MP40, mostly from its inexpensive sheetmetal construction.

Even before US troops encountered the MP40 the Army was searching for a new cheap, easy to manufacture submachine gun. On 6 February 1941 a requirement was set by the Small Arms Development Branch, Technical Division of the Ordnance Corps for the replacement of the Thompson Submachine Gun. The U.S. Army tested over twenty foreign and domestic submachine gun designs in search of a suitable replacement for the Thompson. After an exhaustive testing program the Army accepted a design by Hyde/Inland.

The Hyde-Inland gun was adopted as US Submachine Gun, .45 Caliber, M2, in April 1942. Marlin was awarded a contract to produce the new U.S. M2 submachine gun at a cost of $38.58 each. Many production problems were encountered, and a second testing of a production line sample revealed even more functioning problems. Ordnance engineers from the Springfield Armory made numerous small changes in the design to alleviative some of the problems. Another testing program revealed many problems still existed. Few M2 submachine guns were actually built and they were declared obsolete in June 1943.

While the M2 was being evaluated, another submachine gun design was being developed. This design was another George Hyde idea. The prototype was known as the select fire T15. The design used no critical metals and required a minimum of time consuming machining. Almost the entire weapon was made from simple sheet metal stampings. The bolt assembly rode on two steel rods that fit into two holes stamped into the rear of the receiver. The rod/bolt assembly was held in place by the barrel that simply was screwed into the front of the receiver. The bolt would slide on the two steel rods never touching the inside of the receiver. This kept the moving parts impervious to dirt, making it an extremely reliable design.

As the project progressed, there were a few changes. One was a low cyclic rate, and a full automatic only operation. An additional requirement was set for an easy conversion to the 9mm cartridge that was common in Europe. The new prototype weapon was designated the T-20.

US Army Ordnance R&D officer Réne Studler recruited General Motors to assist with the T-20 development. Fredrick Sampson, Chief engineer of GM’s Inland Division was assigned to the project. After the successful, 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 Aberdeen test, higher than any previous weapon tested. A contract was awarded for the initial 300,000 units to the Guide Lamp Division of General Motor Corporation in January 1943. The Cincinnati Ordnance District awarded the contracts W-294-ORD-2107 and W-33-ORD-825 to Guide.

The new submachine gun was adopted by the United States Army on Christmas Eve 1942. New M3’s were being delivered to the army from Guide Lamp by the summer of 1943. The first M3 submachine guns were issued to Rangers, paratroopers, and armored crews. The US Marine Corps would also issue the M3 by the war’s end.

On 29 January 1943 the Guide Lamp Division was given an order to manufacture 300,000 M3 submachine guns at an initial cost of $17.93 per unit, minus the bolt assembly. This cost would be amended several times during the life of the Guide Lamp contract. The contract for the M3 bolts was awarded to Buffalo Arms at a cost of $2.58 per piece. 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 army from 1943 to the end of 1944. The simplified M3A1 model was only produced in 1945, 15,469 were built before production ceased.

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 US .45 caliber M3 submachine gun, is an air cooled, fully automatic only, open bolt design. The cyclic rate was a slow, and unpopular with the troops, 350- 400 rounds per minute. Semi automatic fire could be achieved by manipulation of the trigger. The troops that were issued the M3 didn’t like the slow cyclic rate. They equated the effectiveness of a weapon with the amount of lead it could spit out in a short period of time. Magazine capacity was 30 rounds of .45 ACP ball ammunition. Although the cyclic rate was slow and the appearance unorthodox the M3 was a very reliable 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 a tool used to lubricate automobiles.

Much of the weapon was constructed from .060 inch sheetmetal. The stock was made from two hardened steel rods and could be retracted along the receiver by pushing a release button located above the left side grip. This was a convenient feature as it reduced the weapons overall length considerably for storage or carrying in vehicles. The ejector is riveted onto a sheet metal housing that is secured to the receiver by a tab in the front, and a spring steel trigger guard. The trigger is also a sheet metal stamping and is attached to the sear by a sheet metal bar. The sear is made from mild steel, and pivots on a pin that is installed through the receiver. This entire assembly is secured by a u shaped pin that in turn is held in place by the ejector housing.

Both sights are fixed and calibrated for a 100 yard range. The rear sight is a aperture type welded to the receiver. The front sight is a metal protrusion located at the front end of the receiver. The weapon could be easily field stripped and repaired without tools. The standard M1 carbine sling was issued for use with the M3. The retracting stock was made of such a length that it gave the shooter a similar feel of the service rifle. A straight-line bolt/stock axis kept barrel climb to a minimum.

The barrel is chambered in .45 ACP caliber. It is pressed and pinned into a large threaded barrel nut that simply screws into the forward end of the receiver. The safety is the worst feature of the M3. The safety consists of a tab on the ejection port cover. This tab fits into a hole drilled into the bolt. allowing the bolt to be secured in the forward position, or in the rearward position (off of the sear). The safety is applied by simply closing the ejection port cover. Opening the cover disables it.

The M3 has a overall length of 29.8” with the stock extended, and 22.8” with the stock retracted. The weight was 8.15 pounds empty. 10.25 pounds loaded (M3 model) with 30 rounds of 234 grain ball service ammunition. Barrel length is 8”. Velocity of the .45 ACP round from the M3 is approximately 900 feet per second. The finish applied to the M3’s was a distinct green type II phosphate or the type III black oxide.

There were very few changes in the basic M3 design, although a few problems did develop in the field. One of the problems was with the cocking handle retracting pawls breaking. An investigation revealed that the steel pawls were being made too hard and therefore were brittle, and easily broken. This problem was fixed by changing the manufacturing procedures of the steel used in the parts. Another problem was the retracting handle springs were being damaged when troops attempted to remove them for maintenance. There were also numerous complaints from troops about the placement of the cocking handle.

Early manufacture M3s are recognized by their simple L type rear sight. The rear sight was sometimes damaged under rough use and models manufactured after March 1944 have gussets attached to the sides of the sight to make it much less prone to damage. Later M3 models also incorporate a cocking handle trip lever on the ejector. It is a 5/8” long tab attached to the side of the ejector projection. The M3 ‘s ejector housing also had a curved metal shroud for storage of a oiler. The oil container is the same as those used for the M1 and M2 carbines. A sheet metal shield to protect the magazine release button from being accidentally pushed was also incorporated in later M3 production. A newly designed spring was used to keep the shield in place.

The M3 30 round double stack, single feed box magazine caused problems in dusty or dirty environments. This problem was also discovered in early T15 tests of the design, but it was never addressed. The magazine and follower were formed from sheet metal. WWII M3 magazines were manufactured by the Keeler Brass Company, Sparks-Withington Company and the Bethlehem Steel Company.

After the M3 was in service for a period of time the Ordnance Department felt that most of the problems with the weapon 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 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.

Other improvements and changes incorporated in the M3A1 were:

A larger oil container that was contained inside the pistol grip.

A new stock design that served as a cleaning rod and a magazine loading tool. The stock could also be used as a wrench to remove a tight barrel.

A new barrel nut that had “flats” machined on it so a wrench (or the stock) could be used to easily remove it.

A stronger spring on the ejection port cover/safety.

A different design for the rear guide rod retainer, so it could clear the ejector and allowing the bolt assembly to be removed from the receiver without removing the ejector housing.

An additional 33,227 M3A1 models were manufactured by Ithaca in 1955-1956 under the Rochester Ordnance District contract DA19-058-ORD-7894. The Ithaca M3A1 is identical to the Guide Lamp models except for the pattern of the “checkering” on the pistol grip. Ithaca parts are all marked ITG. The Ithaca serial numbers ranged from 721330 to 754556 Ithaca’s entire production equated to about one month’s production of the M3 by Guide in 1944. Ithaca also manufactured replacement bolts for the M3 model from 1953 to1954.

It is interesting to note the extremely brief time period between the conception and production of the M3 submachine gun. The project was authorized in October 1942. Five working prototypes were available for testing by November 1942. The M3 was formally adopted in December 1942, and production began in May of 1943, a total of seven months! Comparatively, the M1 Garand development began in 1919 and the first production models came off the assembly line in 1936!

The M3A1 remained the standard U.S. submachine gun until 1957. With the adoption of the M14 Rifle in 1957, the M3A1 was relegated to substitute standard.

Although the M3 would not see a lot of action in World War II it would be more widely used in Korea and Vietnam. The M3 in its silenced form was used as special operations weapon until the 1990’s. Although the M3 submachine gun would never achieve the reputation or status of its famous predecessor the Thompson, the M3 was an effective reliable weapon that would have a service life with U.S. forces second only to the famous 1911 service pistol. Some weapons endear, while others like the utilitarian grease gun, simply endure.

(Editors Note: Watch for Frank’s Newest book “The M3 Grease Gun” to be available soon!)

This article first appeared in Small Arms Review V2N11 (August 1999)
and was posted online on March 11, 2016


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