Editing Thompson submachine gun (section)

====Magazine developments====
[[File:Thompson Magazine.JPG|thumb|Drum and box magazines]]
Military users of the M1928A1 units had complaints of the "L" 50-round drum magazine. The [[British Army during the Second World War|British Army]] criticized "the [magazine's] excessive weight, [and] the rattling sound they made" and shipped thousands back to the U.S. in exchange for 20-round box magazines. The Thompson had to be cocked, bolt retracted, ready to fire, in order to attach the drum magazine. The drum magazine also attached and detached by sliding sideways, which made magazine changes slow and cumbersome. They also created difficulty when clearing a cartridge malfunction ("jam"). Reloading an empty drum with cartridges was a difficult and involved process in which the 50 rounds would be inserted and then the magazine wound up until a minimum of 9 to 11 loud "clicks" were heard before seating the magazine into the weapon.

In contrast, the "XX" twenty-round box magazine was light and compact. It tended not to rattle, and could be inserted with the bolt safely closed. The box magazine was quickly attached and detached, and was removed downward, making clearing jams easier. The box magazine tripped the bolt open lock when empty, facilitating magazine changes. An empty box was easy to reload with loose rounds. However, users complained that it was limited in capacity. In the field, some soldiers would tape two "XX" magazines together, in what would be known as [[Jungle style (firearm magazines)|"jungle style"]], to quicken magazine changes.<ref name="Thompson">{{cite magazine|url=http://www.americanrifleman.org/articles/2011/2/15/thompson-submachine-gun-the-tommy-gun-goes-to-war/|title=Thompson Submachine Gun: The Tommy Gun Goes to War|access-date=2016-02-04|magazine=American Rifleman|first=Bruce|last=Canfield|publisher=National Rifle Association}}</ref>

Two alternatives to the "L" 50-round drum and "XX" 20-round box magazines were tested 6 December 1941, at [[Fort Knox|Fort Knox, Kentucky]]. An extended thirty-round box magazine and a forty-round magazine, which were made by welding two 20-round magazines face to face, jungle style, were tested. The testers considered both superior to either the "XX" box or "L" drum. The 30-round box was approved as the new standard in December 1941 to replace the "XX" and "L" magazines.{{sfn|Iannamico|2000|pp=161, 173, 175}} (The concept of welding two box magazines face-to-face was also carried over to the [[United Defense M42|M42]] submachine gun.)