The U.S. Army’s M3 submachine gun from World War II drew inspiration from the British STEN. Likewise, the suppressed M3 followed the suppressed versions of the STEN — the Mk. II and Mk. VI.
The U.S. Office of Strategic Services formed in June 1943, modelling itself on the British Special Operations Executive. Like the SOE, the OSS quickly recognized the need for specialized silent weapons. Imported STENs initially met the need. Then in late 1942, the Americans developed a suppressed version of their own M3.
The OSS contracted the High Standard Company — best known for its .22LR silenced pistols — to assemble 1,000 silencer-equipped M3s. General Motors’ Guide Lamp Division drilled ports in the M3s’ barrels and Bell Laboratories provided the 14.5-inch-long suppressors.
The system didn’t use baffles, as many contemporaries did. Instead, the M3’s barrel had 48 six-millimeter ports along the length of its barrel, which allowed gases to vent into an expansion chamber filled with wire mesh. The front section of the suppressor was an extension of the expansion chamber and came filled with tightly-stacked mesh washers.
While the suppressed M3 had the advantage of using the subsonic .45 ACP round, it proved to be only 80 percent as effective as the STEN Mk. II(S)’s suppressor. The suppressed STENs were more popular with OSS field agents, who favored their lighter weight, greater accuracy and quieter report. An unsuppressed M3 weighed nearly eight pounds unloaded.
The suppressed M3 saw some service with the OSS in occupied Europe and may have also seen combat in Korea. It was certainly deployed by SEAL teams, helicopter pilots and long-range recon patrols during the Vietnam War.
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