M3 Submachine Gun “Grease Gun”

By the beginning of 1941, although the US was not directly involved in World War II, the US Army recognized the need for a submachine gun and the weapon’s role on the battlefield. Already on hand were a number of the popular (and feared) Thompson submachine gun and more were on the way, but the appearance of the German MP38 and the BritishSten” indicated that different production methods could be employed in future mass produced designs.

Using an imported Sten, the US Army Ordinance Board started a design study to produce an American Sten-type submachine gun. The project was handed over to a think tank of specialists, including the designer of the Hyde M2 and two executives from General Motors, to whom the production details were entrusted. In a relatively short time they had designed a weapon and built early prototypes for trials.

The first of the early models was handed over for trials just before the infamous Pearl Harbor attack that drew the United States into World War II. The project was given a new priority and not long after, the new submachine gun was designated the M3.

The M3 was just as unpleasant in appearance as the Sten. The M3 was of all metal construction with most parts simple steel stampings welded into place. The man gun body was tubular, the barrel assembly screwed on to the front. This combined with the unusual stock gave the M3 the nick name “Grease Gun” since it resembled the tubular construction of one. Below the main body hung a 30 round box magazine. An awkwardly placed and flimsy looking cocking handle was placed just forward of the trigger on the right hand side of the weapon. The cartridge ejection port was under a hinged cover that would flip up to the top of the weapon.

The design was simple to the point of no safety system and the fire was in fully automatic only. Only the barrel, breech block, and trigger mechanism required any machining. A telescoping wire butt was fitted to the weapon.

The M3 was rushed into production and once it was issued to the troops ran into acceptance problems. It was with the general infantryman the M3 became known as the “Grease Gun” and was regarded with equal affection. However, once in action the M3 proved itself effective. Unfortunately, the assembly lines upon which the weapon was assembled had previously produced vehicle parts. The inexperience of the workers with firearm manufacturing led to all sorts of in-service problems. The cocking handles broke off, the wire stocks were bent, some critical parts broke because the steel was too soft to handle the stress, and so on. The M3 received more than its share of in service development and modification, but what is most important is that the M3 rolled off the lines in massive numbers to be rushed to the front.

The M3 never did overcome the first impression it made on the troops. Whenever possible the men opted for the Thompson submachine gun or captured German MP38s and MP40s. However, in the Pacific Theatre there was often no alternative to the M3 due to the lack of Thompsons and the poor quality of captured Japanese Type 100 submachine guns. In this situation the design gained grudging acceptance.

For some branches of the service the M3 became almost blanket issue. Transport drivers and tankcrewmen found it easy to stow and handle in close quarters.

From the outset the M3 was designed with the ability to rapidly be changed to accept a 9 mm round by simply changing the barrel, magazine and breech block. This was frequently used when airdropping the M3 to resistance fighters. A silenced M3 was also produced in limited numbers.

As simple as the M3 was to produce, in 1944 it was decided to make it even simpler. The production know-how and combat experience resulted in the M3A1, which followed the same general lines of the M3 but with some substantial changes. For the general infantryman the best change was the enlargement of the shell ejection port to expose the entire breech block travel. This allowed the user to place his finger inside the weapon and slide the breech block to the rear for cocking, thus eliminating the need for the flimsy cocking handle. A flash hinder was added to the muzzle and some other miner changes were incorporated.

The M3 and M3A1 were still in production when the war ended. It was decided to phase out the Thompson in favor of the two new designs.

Apart from the appearance, the M3 guns were not perfect weapons. They were rather prone to breakage, the ammunition feed was far from perfect and the lack of a safety caused alarm. But the weapon worked and was available in large numbers. In war these two factors were more important than dreaming and wishing for something better.


  • Caliber: .45 in
  • Length, butt extended: 29.33 in (745 mm)
  • Length, butt retracted: 22.44 in (570 mm)
  • Weight: loaded: 10.25 lb. (4.65 kg)
  • Magazine: 30-round box
  • Rate of fire: 350-450 rpm
  • Muzzle velocity: 920 ft. (280 m) per second

Source: specifications and other bits I didn’t remember I looked up in The Encyclopedia of Weapons of World War II, much of this is from memory and too much History Channel

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