By Frank Iannamico

The M3 submachine gun design had begun as the T-15 prototype, which was developed by the Ordnance Department and the Inland Division of General Motors. The three key individuals who shared much of the responsibility of the project were: Frederick Sampson, Chief Engineer of the Inland Division of General Motors; George Hyde, who had a number of original submachine gun and light-rifle designs to his credit; and U.S. Army Ordnance R&D officer Colonel René Studler. No submachine gun requiring extensive machining operations would be considered for adoption. The requirements called for an all metal weapon fabricated from sheet metal stampings to permit fast and inexpensive production with a minimum of machining operations, and no critical metals, such as aluminum, were to be used.

The original T-15 specifications of October 8, 1942, OCM 19007 were altered to include a kit to enable the weapon to be converted from its original .45 caliber to 9mm which was the standard pistol and submachine gun cartridge of the British and the Germans. Another amendment to the original T-15 design was the elimination of the semiautomatic function. This was done to simplify the design. The cyclic rate was such that semiautomatic fire could be accomplished by trigger manipulation. The new designation for the new 9mm/.45 full-automatic-only weapon was the T-20. Five prototype models of the T-20 and five 9mm conversion kits were built by General Motors for testing. The cyclic rate was relatively slow at 400 rounds per minute. There was very little muzzle climb. In the standard test of firing at a 6ft x 6ft target at 50 yards, the T-20 scored 97 hits out of a possible 100. This was a higher percentage than achieved by any other weapon tested in the trials except the Hyde-Inland M2.

U.S. Submachine Gun, Caliber .45, M3

The M3 submachine guns were all metal, fabricated mainly of stamped steel parts to take advantage of speed and economy of manufacture and assembly. Its weight distribution, along with its slow 350-400 rounds per minute cyclic rate, allow for excellent accuracy for a weapon of this type, regardless if the weapon is fired as a pistol with the stock retracted or as a carbine with the stock extended. Control of the weapon when firing bursts is enhanced by the stock being in direct axis with the bore of the barrel assembly. The internal parts were fully enclosed to protect them against any dirt, water or mud. The rear sight, barrel bushing, sear pin bushings, hinge assembly and sling loops were all welded in place. Dual guide rods and springs were employed to provide support and control for the heavy bolt without touching the inside walls of the receiver. The bolt/rod/spring assembly was easily removed from the receiver as a complete unit.

Soldiers’ initial reaction to the M3 was generally negative, mainly because of the weapon’s appearance. The slow cyclic rate also was disliked by troops, who equated effectiveness of a weapon by its cyclic rate. Many epithets were immediately bestowed on the M3; the name that stuck was the “grease gun” because it resembled a tool for lubricating automobiles. After being in service for a few months, the M3 began to gain some respect, but it would never achieve the status of the Thompson submachine gun.

The Guide Lamp Division of General Motors Corporation

General Motors’ Guide Lamp Division was a peacetime manufacturer of automobile lamps, headlight buckets, hubcaps and bumper guards. The Guide Lamp production plant was located in Anderson, Indiana. Guide Lamp had a lot of expertise and experience in sheet metal stampings and was an excellent choice for the manufacturing of the M3 submachine gun.

By June 1944, 1,000 M3s were being manufactured every 24 hours. The initial Guide Lamp contract price for the M3 was $17.92 per unit less the bolt assembly. The initial price was later amended to $18.36 per unit to cover the cost of minor production changes and the packing and shipping of the completed units. The M3 bolt assembly manufacture was subcontracted to the Buffalo Arms Company at a cost of $2.58 per piece. The bolts were then shipped to Guide Lamp for assembly. The total cost of the M3 was nearly one-half the price of the least expensive M1A1 model Thompson. More importantly, the time for producing each weapon was cut in half thus allowing production to keep pace with the growing war-time demand. The M3 was made almost entirely from simple .060 inch-thick sheet metal stampings. The only major parts requiring any machining were the barrel and bolt. The receiver was made from two die-stamped sheet metal halves. The two pieces were then welded together to form the receiver.

The M3 barrel was manufactured by cold swaging, a process that saved a lot of production hours. A steel 40-inch tube for the barrel would first be reamed to the correct inside diameter. The rifling would then be pressed into the barrel by inserting a mandrel and compressing the tube as it is forced through the die. The long piece of tubing would then be cut in sections to produce five M3 barrels. By May 1943 the first M3 submachine guns were rolling off the assembly lines at Guide Lamp. A patent for the M3 firearm construction was filed on May 1, 1944. The inventors listed were Frederick W. Sampson and George J. Hyde. Patent number 2,403,306 was granted.

The first serviceability problems with the M3 were reported by troops undergoing training in the United States during February 1944. The complaint was that the bolt cocking handle assemblies were failing. A closer look at the problem revealed that the retracting pawl on the cocking handle was cracking adjacent to the rivet hole where the pawl was riveted to the brace. An investigation revealed that the metal that was being used in the manufacture of the parts was not well-suited to the heat-treating process. Immediately the correct metal was substituted for the parts involved, and the width of the metal at the rivet hole was increased. Armorers in the field upgraded all M3s in service with the new parts.

The U.S. M3A1 Submachine Gun

The M3 was thought to be as simple and reliable as possible; however, the Ordnance Department felt that the weapon could be simplified even further. A study was conducted to determine if it were possible to eliminate the cocking handle assembly that was the source of most problems and complaints. A way to simplify field stripping and maintenance was also under study.

During the development stages of the M3(E1) submachine gun, the following Ordnance Department rejections, changes and additions were made:

• Eliminate the complete cocking assembly handle and associated parts by the redesign of the bolt.
• The modification requires enlargement of the ejection port.
• A new hinge and a stronger cover spring riveted to the receiver and a redesigned cover plate with improved safety locks.
• Incorporate an ejector slot cut in the full length of the bolt as well as a redesigned guide rod retaining plate to permit removal of the bolt assembly without removing the ejector housing.
• Design the stock to permit its use as a magazine loading tool, eliminating the need for a separate item for that purpose.
• Drill and tap the forward ends of the stock to accommodate a bore cleaning brush.
• Incorporate a larger oiler in the pistol grip.
• Modify the barrel nut to allow its removal using the wire stock as a tool.

Six pilot models incorporating the above modifications were designated as the M3E1 submachine gun. On December 21, 1944, the M3E1 Submachine Gun was approved and officially adopted as: Submachine Gun, Caliber .45 M3A1, thus reclassifying the M3 as Limited Standard.

The total submachine guns manufactured from 1943 to 1945 by Guide Lamp: 606,694 M3s and 82,281 M3A1 models, for a total of 688,975 weapons. The entire World War II production of the M3 and the M3A1 would total only a little more than one-third of the Thompsons produced during the war.

The M3A1 remained the Standard submachine gun of the U.S. Army until the adoption of the M14 in 1957. The M3A1 submachine gun then was relegated to Substitute Standard. The M14 rifle was, in theory, replacing the M1 rifle, the carbine and the submachine gun.

More Firepower!

During World War II, the primary U.S. weapons were the .30 caliber M1 rifle, the .30 caliber M1 carbine and the .45 caliber submachine gun. The M1 rifle was semiautomatic and had a magazine capacity of 8 rounds; it was an accurate weapon designed for long-range targets. The semiautomatic M1 carbine used a less powerful .30 caliber cartridge than the rifle and was a short-range weapon primarily intended to replace hand guns. The submachine gun had a full-automatic function and a magazine capacity of 30 rounds, but its range was limited.

What was needed was a weapon in between the long-range battle rifle and the short-range submachine gun. This was demonstrated by the Germans when information was received to the effect they were fielding a select-fire weapon, the MP43, using a 7.92mm Kurz (short) mid-range cartridge.

As the pace of the war accelerated, U.S. troops encountered new types of terrain and new enemy tactics; the need for more firepower was anticipated.

The T29 Submachine Gun

Inspired by the German MP43, during fall 1944, it appeared advisable to investigate the possibility of modifying the M3 submachine gun to permit the firing of the carbine cartridge caliber .30 M1. This investigation was entered into in view of the many reports received from the field requesting the development of the submachine gun which would fire the caliber .30 carbine round. Considerable study was given by personnel of the design section of the Guide Lamp Division of the General Motors Corporation that was manufacturing the M3 submachine gun.

To reconfigure the M3 submachine gun to accomplish the above, it was necessary to use a spring-loaded ejector to soften up ejection. To facilitate retracting the bolt, and still maintain the proper spring load to prevent the bolt from striking the rear receiver in recoil, it was necessary to employ both a shorter, stronger spring and a longer, low-rate spring; the short spring being required primarily to stop the bolt in recoil and the long spring to feed and fire the cartridge. A 30-round magazine was made by attaching two 15-round M1 carbine magazines together; the magazine well was enlarged to accept carbine magazines. A 14-inch long barrel was used to maximize velocity and reduce muzzle flash. The bolt was redesigned for the .30 carbine round.

The .30 caliber T29 weapons were tested during the fall of 1944. The modified submachine guns incorporated the basic design characteristics of the M3A1 submachine gun were completed, and function fired 1500 rounds per weapon. There were many functioning problems encountered due to the more powerful cartridge. Despite the longer barrel, the report and flash were quite excessive. Further study of the T29 submachine gun showed the Type A spring-loaded ejector and the feed ramp would require further development. However, in that the select-fire caliber .30 M2 carbine was standardized in September 1944, it was not deemed advisable to continue further development work on the T29 submachine gun concept, and the T29 project was terminated on November 16, 1944.

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Excerpted in part from the book The M3-M3A1 Submachine Gun, available from Chipotle Publishing LLC.

Special thanks to Curator Alex MacKenzie and the entire staff at the Springfield Armory National Historic Site.
Springfield Armory National Historic Site
Springfield, MA
413-271-3976
www.nps.gov/spar

During the Second World War, Germany fielded a number of new weapons produced from simple sheet metal stampings. The German 9mm MP40 machine pistol was the first successful sheet metal weapon to be made in large numbers followed by the German MG42 machine gun, and the Sturmgewehr. The MP40 weapon started a world revolution in small arms design. The methods and materials used allowed weapons to be manufactured cheaply and very quickly in large numbers – very advantageous during a large scale war. Weapons manufactured by these methods proved as durable as their labor-intensive counterparts made primarily of milled steel. One of the first designs fielded by the Allies was the 9mm British Sten Mark I in 1941. This was soon followed by the even more utilitarian Mark II and III Sten models.

Seeing the benefits of such a design, the United States Ordnance Department began to develop a similar submachine gun that was to be fabricated from mild steel sheet metal. After an in-depth study of the German MP40 and the British Sten by the Ordnance Department engineers, the requirements for a similar U.S. weapon were established on 6 February 1941. Development began by the Small Arms Development Branch of the Ordnance Department with assistance from the Inland Division of the General Motors Corporation. One of the first new submachine gun models to be designed was the T15 submachine gun. The T15 was a .45 caliber weapon that featured a straight open-bolt blow back operation commonly used in most submachine gun designs. The T15 quickly evolved into the simplified T20 model after several requirements were revised. One of the design changes was the elimination of semiautomatic function, and a requirement for the weapon to be easily converted to fire 9mm Parabellum ammunition. Because of the slow cyclic rate of the weapon it was decided that there was no need for a semiautomatic feature thus allowing the design to be further simplified.

The T20 had one very unique design feature that separated it from all other submachine guns of the day. On virtually all previous submachine gun designs, the bearing surfaces of the bolt would move forward and rearward supported by the inside surfaces of the receiver. On the T20 weapon, the bolt was designed with two horizontal holes that ran through the entire length of the bolt. The bolt then rode on two steel rods that were inserted into the holes, and were held in place by a steel plate oriented by two holes located in the rear of the receiver. Each guide rod had its own separate recoil spring. The steel guide rods were supported at the front by a steel guide plate that was indexed in the receiver by two integral tabs on the plate. A spring steel circular clip kept the bolt, guide rods and recoil spring assembly together until the barrel could be screwed onto the receiver. The front guide plate was secured to the receiver by the tightening of the barrel nut assembly. The primary advantage to the design was that the bolt never contacted the inside surfaces of the receiver. The unique arrangement made the T20 submachine gun nearly impervious to stoppages from dust, mud water or even sand. The T20 was one of the few weapons that was able to successfully pass the Ordnance Department’s rigorous mud and dust tests.

The receiver design of the U.S. T20 prototypes also differed radically from other submachine guns that used a simple circular tube for the basic receiver. When a tube receiver was used, a separate housing for containing the trigger and sear assembly needed to be designed and attached to the main tube. This would complicate manufacture somewhat as the two pieces would need to be accurately oriented to each other. In the design of the T20, the receiver was constructed by joining two separate stamped sheet metal pieces by welding. The receiver, the housing for the trigger and sear assembly, and pistol grip were all an integral part of the single assembly. The only other separate parts required were a dust cover/ejector housing for the trigger mechanism and a simple spring steel trigger guard that also held the cover in place. Other parts like the barrel bushing, sights and ejection port cover were attached to the receiver assembly by rivets or welding, no threaded fasteners were used.

The method of manufacturing barrels was borrowed from the British, who produced their Sten machine carbine barrels by the cold swaging method. The M3 barrel was also manufactured by cold swaging, a process that saved a significant amount of production hours. The steel tubing for the barrel would first be reamed to the correct inside diameter. The rifling would then be pressed into the barrel by inserting a mandrel and compressing the tube as it was forced through the die. The 40-inch piece of tubing would then be cut in sections to produce five M3 barrels. This barrel making process was much faster and less expensive than broaching or other methods. Accuracy of fire remained well within the requirements established by the U.S. Ordnance Department for submachine guns.

The T20 was recommended for adoption as the Caliber .45 Submachine Gun, M3 on December 24, 1942. The contract for manufacture of the M3 was awarded to the Guide Lamp Division of General Motors who were experts in sheet steel fabrication for the automobile industry. However, there were several problems encountered during initial manufacture of the M3. One of the problems was being able to accurately join the two receiver halves together by welding. A second problem was the thin sheet metal receiver halves were warping from the heat generated by the welding process. While Company and Ordnance engineers were engaged in resolving these problems, the Ordnance Department ordered the resumption of M1A1 Thompson Submachine Gun production.

The original M3 submachine gun production schedule had planned for 20,000 units to be produced by July 1943, but only 900 acceptable units had been completed. Before long the welding problems of the receiver were solved and the M3 was in full production. At the height of production in 1944 one-thousand M3 submachine guns were being produced every twenty-four hours.

The Guide Lamp initial contract price for the manufacture of the U.S. M3 was $18.36 per unit after being adjusted to cover the cost of minor production changes, and the packing of the completed units. There were a large number of subcontractors involved that supplied various small parts to Guide Lamp. The only major part that was subcontracted out was the bolt assembly, which was manufactured by the Buffalo Arms Company of New York. The manufacture of the M3 submachine gun was further simplified with the introduction of the M3A1 model in 1945.

While the unique design of the M3-M3A1 receiver made the weapons extraordinarily reliable, the design of the magazine proved problematic. It remains a mystery as to why the U.S. M3-M3A1 submachine gun was not configured to use the existing and excellent double stack-double feed magazine from the Thompson. The Thompson magazine was a proven design and already in production. Instead, the 30-cartridge M3-M3A1 magazine was a double stack, single feed design that contributed to stoppages when exposed to dust and mud. The single feed configuration had previously proved troublesome when used in both the British Sten and the German MP40 weapons. While the M3 was undergoing Ordnance testing, virtually all jams and stoppages were attributed to the weapon’s magazine. During testing of the M3 by the Infantry Board, they had suggested a few ways to improve the magazine’s reliability, but the problems were never addressed. The only fix was a rubber and eventually a plastic cap to keep dirt and debris out of the magazine. The cap was to be kept on the magazine until it was ready to be placed into the weapon.

Although many martial arms collectors of today are put off by the U.S. M3 and M3A1 submachine gun’s appearance and slow cyclic rate, the weapons were very cleverly designed. The M3-M3A1 has often unjustly received criticism based solely on its utilitarian toy-like appearance. The M3 and M3A1 submachine gun remained in U.S. service many years after most foreign and domestic World War II era weapons were declared obsolete.