The North Side Gang attempted a drive by assassination of Al Capone, with the would be killers armed with Thompson submachine guns.
Capone was inside a nearby restaurant at the time, conducting business, and only his bodyguard was wounded. The event did cause him to order Thompsons himself, which were not restricted from purchase in any fashion at the time.
These would have been the M1921 Thompson, not the M1928 Thompson that is more familiar to most people, although telling the difference between the two at a glance is difficult. They were extremely expensive.
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