Popular Mechanics:

Bootlegging gangsters of the 1920s and 30s firing a barrage of bullets at the G-men in pursuit—that’s the mental picture you might have of the Tommy gun. But while the Thompson submachine gun was designed for the trenches of World War I and gained notoriety as a gangster’s weapon, it was the battlefields of World War II that saw it win its place in history alongside the other best-known firearms of all time, with as many as two million made.

I loved old gangster movies as a kid (and even still) and you always saw the bad guys with a Tommy Gun. I had no idea of the history behind it.