The M3, known as the Grease Gun, was a sub-machine gun designed by the US Army Ordnance Board and produced by General Motors. It was used by the US Infantry during World War II and the Korean War. The M3 was just as unpleasant-looking as the British Sten. Construction was all-metal with most parts simple steel stampings welded into place. Only the barrel, breech block and parts of the trigger mechanism required any machining. A telescopic wire butt was fitted and the design was simple to the point that there was no safety system fitted and the gun could fire fully-automatic only. The main gun body was tubular and below it hung a long 30-round box magazine. From the outset the M3 had been designed to have the capability of being rapidly converted to 9-mm caliber by simply changing the barrel, magazine and breech block. This facility was sometimes employed in Europe when the M3 was dropped to resistance forces.
Once the M3 was issued to the troops it soon ran into acceptance troubles. The very appearance of the weapon soon provided it with the nickname of "Grease Gun" and it was regarded with about as much affection. But once in action it soon showed itself to be effective, but the rush into production on lines that were more used to producing motor car and truck components led to all manner of in-service problems. The cocking handles broke off, the wire stocks bent in use, some important parts of the mechanism broke because they were made of too soft a metal, and so on. Consequently the M3 received more than its fair share of in-service development and modification, but what was more important at the time, it rolled off the production lines in huge numbers for issue to the troops at the front.
Simple as the M3 was to produce it was decided in 1944 to make it even simpler. The result of combat experience allied with production know-how resulted in the M3A1, which followed the same general lines as the M3 but with some quite substantial changes. For the soldier the most important item was that the ejection cover was enlarged to the point where the full breech block travel was exposed. This enabled the firer to place his finger into a recess in the block to pull the block to the rear for cocking, thus doing away with the awkward and flimsy cocking handle. A flash hider was added to the muzzle and some other minor changes were incorporated. The M3A1 was still in production when the war ended, by which time it had been decided to phase out the Thompson guns in favor of the M3 and M3A1.
Type: sub-machine gun
Country of origin: USA
Manufacturer: General Motors
Caliber: .45 (11.43mm)
Length, butt extended: 745 mm (29,33 in)
Length, butt retracted: 570 mm (22.44 in)
Weight loaded: 4.65 kg ( 10,25 lb)
Magazine: 30-round box
Rate of fire: 350-450 rpm
Muzzle velocity: 280 m (920 ft) per second