The origins of the M3 begins during the early years of the Second World War. Though the United States fielded the venerable Thompson submachine gun—easily one of the more high-powered submachine guns of that war—it was a rather expensive firearm to produce. Several attempts were made to replace the Thompson with a cheaper but still combat effective alternative, such as the odd-looking T2. Experimental models like the T2 were a failure, but the M3 succeeded mostly because it was cheap.
And the M3 was very cheap. The M3’s receiver was essentially two pieces of stamped steel, mirror images of each other that were welded together. Liberal use of spot welding, stamping, and riveting made the M3 much cheaper than the Thompson, which relied on precision milled steel parts.
Surprisingly, the M3 was originally envisioned as a sort of temporary-use weapon, to be used until failure. Soldiers were not given much maintenance or repair equipment, and were told to ditch their broken M3 in favor of a new one rather than trying to repair the submachine gun.
Thanks in part to the M3’s heavy bolt, it fired at a slow 350-400 rounds per minute, making it quite controllable and therefore aiding accuracy despite its wire stock and and non-precision parts. Thanks to the M3’s distinct profile, it was nicknamed the “Grease Gun” due to its resemblance to a mechanic’s lubrication tool.
When first introduced into service, the M3 suffered from reliability problems, mostly due to its single-feed magazine, and not due to the weapon itself. The M3A1 would be introduced in 1944 that further simplified the design and became the final M3 iteration. Despite the M3’s design as a replaceable weapon, it enjoyed relatively wide use, both during the Second World War, and afterward.
Office of Strategic Services
A silenced version of the M3 was also built as a response to a suppressed version of the STEN submachine gun, favored by the British Special Operations Executive. The American Office of Strategic Services equipped some of their operatives with M3s that used a very interesting and novel suppressor system.
Unlike most suppressors which use a series of baffles that allow propellant gas to expand, the M3’s OSS suppressor was essentially two stacked suppressors. Each suppressor section was filled with differing wire mesh screens that allowed for gas expansion. A fascinating video of the OSS M3 can be seen here and is well worth the watch.
Despite the M3 and M3A1’s simplicity and decidedly unsophisticated design, the weapon served with SEALs teams in Vietnam, and even in a niche capacity until the early 1990s. During Operation Desert Storm, some engineering battalions were equipped with the M3s due to its compact size.
The Grease Gun’s exceptional longevity—nearly half a century—would no doubt have come as a surprise to the M3’s original designers.
Caleb Larson is a Defense Writer with The National Interest. He holds a Master of Public Policy and covers U.S. and Russian security, European defense issues, and German politics and culture.