M3 grease gun

The **M3 Grease Gun** (officially the **United States Submachine Gun, Cal. .45, M3**) was an American submachine gun that was designed by George Hyde, Frederick Sampson and René Studler in 1942 and produced by the General Motors Guide Lamp Division from 1943 to 1945. It was developed for the United States Army during World War II as a cheaper alternative to the expensive Thompson submachine gun. The weapon was commonly termed the ***grease gun*** (or similar nicknames) due to its passing resemblance to the actual tool.

During World War II, the United States Army Ordnance Board observed the effectiveness of various submachine guns used by the eastern front, such as the Sten and MP 40; after conducting these observations, the Ordnance Board decided that it would conduct a study in an attempt to develop a submachine gun that would be similar to a Sten and submitted requirements to the Ordnance Department for this new weapon.

The requirements submitted required that the new weapon be a select-fire submachine gun of sheet metal construction and chambered for the .45 ACP round; it should also be inexpensive and easy to manufacture in large quantities. Various other accuracy requirements and other small specifics were also put forward. The benchmark for performance for the weapon would be the Thompson submachine gun. The weapon that would come out of these specifications would be known as the **T15**.

An employee of General Motors' Guide Lamp Division (also known as Guide Lamp) named George Hyde was tasked to design this new weapon; he worked alongside Frederick Sampson (chief engineer of GM's Inland Division) and René Studler (R&D officer of the United States Army Ordnance Board) to design the new weapon. Come October 1942, however, the specifications for the T15 were suddenly altered, resulting in the removal of any select-fire functionality and the addition of a caliber conversion kit allowing its user to convert the weapon to fire the 9×19mm Parabellum round if required. This version of the weapon would be designated the **T20**.

When it came time for the trials, Guide Lamp produced five prototypes of the T20 and five conversion kits; during the trials, the T20 performed excellently in all categories. Although failures were reported, these were mostly due to either defective or faulty magazines. With the results of the trials showing, the T20 was officially adopted as the **United States Submachine Gun, Cal. .45, M3**. The M3 was used during World War II, with some 606,694 manufactured from 1943 to 1945. Some 1,000 M3s chambered for 9mm were also manufactured by Guide Lamp and used by the Office of Strategic Services.

Due to its construction, the M3 was supposed to be a minimal-cost small arm that was meant to be disposed of when deemed inoperable; it was due to this that few replacement parts (if any) were made available, even to ordnance-level commands by the time the M3 was drafted into service. A shortage of M3s in service however eventually caused the United States Ordnance Workshops to manufacture additional parts to keep the existing weapons operational.

After being drafted into service, complaints about the M3's unserviceability began to surface, mainly regarding the charging handle retraction mechanism on some M3s; similar reports came from American forces stationed in the United Kingdom during the war. Investigations were launched on the M3's design; these revealed several issues with the design, mainly with the charging handle's retraction spring design and rear sights that could be easily bent. As the war progressed, however, even more issues began to surface and more changes to the design were made.

All these changes were incorporated into a simplified variant of the M3 known as the **M3A1**, designed based on feedback by various branches of the military when it came to using the M3. The M3A1 was adopted as the **United States Submachine Gun, Cal. .45, M3A1**. While originally intended to be produced in such volumes that it could eventually replace the Thompson submachine gun in service, this never came to be due to the various production delays with the M3, causing production of the Thompson to stretch until February 1944.

Production of the M3 and M3A1 ended in 1945 with the end of the war, although various other countries such as Argentina and China produced clones of the weapon in various quantities. Use of the M3 and M3A1 lasted well until the late 1950s and early 1960s in front line combat, when they were largely withdrawn. However, use of the M3 continued until the 1990s as a secondary armament on vehicles. Outside of the United States, however, the M3 saw service well into the 1990s. Most notably, the M3 was the weapon of choice of the Delta Force, prizing it for its performance when a suppressor was equipped.

A total of 606,694 M3s and 48,669 M3A1s were produced.