The NFA (National Firearms Act) was enacted in 1934 and controls the ownership, transfer, and even interstate travel of certain firearms and destructive devices through registration and taxation.
NFA items include rifles and shotguns with barrels shorter than 18" in length, machine guns, select other weapons, and firearm silencers or suppressors.
The main goal was to curtail, if not prohibit, transactions with these firearms which were said to pose a significant crime problem.