At an Auto-Ordnance board meeting in 1919 to discuss the marketing of the "Annihilator," with the war now over, the weapon was officially renamed the "Thompson Submachine Gun." While other weapons had been developed shortly prior with similar objectives in mind, the Thompson was the first weapon to be labeled and marketed as a "submachine gun."
From Gangland to the Battlefield - 15 Amazing Facts About the Thompson Submachine Gun - http://www.warhistoryonline.com/war-articles/gangland-battlefield-15-amazing-facts-thompson-submachine-gun-%e2%9e%94.html
The United States Thompson submachine gun (Tommy Gun) was one of the most used guns by the US during World War II, used by many nations like Britain and Canada much like most American guns. In this picture you have two different mags, the most common on the left and the barrel one on the right which contains more ammo.