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Arsenal - M-3A1 Grease Gun

By Carl O. Schuster 
Originally published on HistoryNet.com. Published Online: July 26, 2010 
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Illustration: Gregory Proch

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Commonly known as the "Grease Gun" because of its similarity in appearance to the mechanic's tool of the same name, the M-3 submachine gun was the simplest firearm issued to U.S. combat troops in the 20th century. In Vietnam, the Grease Gun was a favorite because it provided instant close-range firepower, was tolerant of the field environment and was easy to maintain.

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Entering U.S. Army service in 1943 as a low-cost replacement for the 1928 Thompson or M-1 submachine gun, the M-3 and its improved M-3A1 variant saw extensive service in World War II and Korea. The initial production model, with its prominent cocking handle, had been replaced completely by the M-3A1 before any U.S. troops deployed to Vietnam. Lighter and more reliable than the earlier version, the M-3A1 was issued to South Vietnamese army, air force and regional forces as part of America's military assistance program. American forces also carried the M-3A1, particularly in the early years before the M-16 was issued in large numbers. Even then, virtually every American and South Vietnamese tank crew carried at least one M-3A1 aboard. It could also be found on U.S. Navy ships, river gunboats, among SEAL teams and in military police units.

The Grease Gun was a blowback-operated submachine gun that fired a .45-caliber pistol round from a 30-round magazine loaded from underneath the receiver. It could be easily converted to fire 9mm ammunition. The M-3A1 fired over an open bolt and only in fully automatic mode. It had no mechanical means of disengaging the trigger. Inserting the magazine loaded the weapon, and opening the ejector port made it ready to fire. Closing the ejector port prevented it from firing. Some guns had a flash hider, but that was not a standard feature.

All parts of the M-3A1 were stamped except for the barrel, bolt and firing mechanism, which were precision machined. That not only reduced manufacturing costs, but it also facilitated field maintenance. One could cannibalize a damaged weapon to repair a salvageable one. The Grease Gun was a robust, comparatively light automatic weapon that was easy to clean and maintain.

The only consistent complaints about the M-3A1 were its tendency to rust in salt-air environments, and loaded Grease Guns could fire when dropped on a hard surface with sufficient force to open the ejector port and shock the trigger. However, its simplicity and reliability made it a popular weapon in Vietnam among helicopter and tank crews, Provincial Reconnaissance Units, Mobile Strike (Mike) Force and Civilian Irregular Defense Groups. It was also found in most Army of the Republic of Vietnam infantry squads before 1970, and the Viet Cong used captured Grease Guns, alongside some former Nationalist Chinese weapons provided by the People's Republic in the late 1950s. More than 670,000 were produced before the last production line was closed in 1952, and served with the U.S. Army until 1992.

M-3A1 Grease Gun
Length with stock        22.8 in.
Barrel length                    6 in.
Ammunition                   .45 cal. / 9mm
Weight loaded                9.7 lbs.
Weight empty                 7.6 lbs.
Max. rate of fire             360-450 rounds/min.
Nom. rate of fire             60-80 rounds/min.
Max. effective range     100-150 meters


3 Responses to “Arsenal - M-3A1 Grease Gun”


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    • 1.1
      James Creeden says:

      Say what?? The grease gun was surely a potent weapon for close quarters battle,as house to house and all urban environs go. The complaint about rust in tropical climes is valid,but any good combat fighter will keep his weapon maintained to prevent that.An oily shoelace and metal rod works just fine as far as in-country cleaning methods go! Never carried one,but people who did tell me good things about this stamped part" tough old bastard":to quote a friend… JIMMY C.

  2. 2
    Peabody US Army Retired says:

    We had one M3A1 in our Recon Platoon in 70-71 as well as a CAR-15 and two M79's elephant guns The latter fired a variet of rounds but the shot gun round was the most favored for work in thick vegetation. No telling where they came from they were not on the property books. Most of us carried the M16 with the home made sling and 30 round magazines when we could get them. I think they were all donated to a Ranger Company. I heard later when the unit rotated a lot of extra stuff went that route as we didn't want the REMF's and staff pukes to get them. I know the rear echelon was hot for souvenirs and would confiscate just about anything so they could go home and pretend they had been to war. Those particular weapons (CAR15 and M3A1) were used by the point with an over the shoulder sling which left one hand free for easing through the foliage. Number two or three carried the thumper (M79) loaded depending on terrain and vegetation. On occasion we had a sniper with the scoped M14 or a two man M60 team when we were in our 'other mode.' Damn good unit with a lot extra skills (ranger and SF guys as their unit was downsized then pulled out) until they started sending us shitcanned leftovers from the Metrical Division. and the shake'n'bake whip'n'chills.
    I thought at that point time to leave. As a preference I preferred the M16 and ours still had the three finger flash suppressors except one time we tried the sound suppressor.. Didn't work of course the bullet breaks the sound barrier and it didn't come with the slower velocity ammo. That one ended up staying behind. If you knew where to look though you could find just about anthing. But everything had a purpose and foremost was lighter, quieter load. Helmets, flak vests, and other such never made it to the field. Enough memory lane. The recon plt was part of E Co, 3/187th (Rakkasans Recons) 101st Airmobile. Little joke many of us were jumpers so we referred to the division in that way. Good unit. Sgt. Peabody



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