Wow! I didn't know that the Tommy gun went back so far!

Despite the image the Thompson picked up in the gangster movies, they were a very scarce weapon. Only 15,000 of the first model produced. First 500 went to Ireland (Irish Republican Army smugglers). Others to Marine Corps, police departments. Every small town needed one as a prestige item. When WWII began, Auto-Ordnance still had over half the original run in its warehouse. At $200 each, few people could afford one. Actual gangster use was rare. The Kansas City Union Station massacre of 1933 was committed with the three Thompsons owned by the KCMo police department, then under mob control. They were left in an open police car to be "stolen", then returned to the department after the shooting. From what I hear, KCMo still has the guns but will not allow anyone to see them. A few months later, the mob boss of Kansas City, Johnny Lazzia, was gunned down with one of these same Thompsons as he came out of his apartment.

Technically, the Italians invented the sub machinegun in WW1 with the Villar-Perosa gun for aircraft. But the contemporary configuration for ground usage comes from the WW2 Bergmann MP-18 that was issued to Sturntruppen for anti-trench warfare. [pstwar this became the Bergmann MP-28 and then on to the Erma MP-38/40. Postwar W Germany went to the Walther MP-K and MP-L then got the HK MP-5. Reuinfied they went to the HK MP-7 PDW which is the highest standard with 4.6mm armor penetrator round.