Which of the following is NOT a common method for smuggling drugs into the U.S.?

Submarines represent a less common method for smuggling drugs into the U.S. compared to the other options. While semi-submersible vessels have been used by drug traffickers, they are less frequently employed due to the complexity and cost involved in their construction and operation. In contrast, methods such as drones, hidden compartments in vehicles, and body packing are much more prevalent and accessible for smugglers. Drones are increasingly being used for smaller payloads, hidden compartments in vehicles take advantage of the large volume of vehicle traffic, and body packing is a method where individuals ingest or conceal drugs internally, a tactic that has been historically common due to its simplicity and concealment potential. These options illustrate more common and varied tactics that smugglers utilize to bypass law enforcement efforts.