The use of submersibles by traffickers is on the rise and presents a transnational security threat. From 2001 through 2010, approximately 175 documented drug transits from South America to global destinations occurred on self-propelled semi-submersible (SPSS)-type platforms. While transporting illicit cargo in the maritime domain is not new, the stealthy SPSS — a long-range vessel that is extremely difficult to identify and track — raised significant national security concerns. This Article examines the economic and environmental incentives that led to the development of semi- and fully-submersibles, the U.S. criminal law enacted to combat this threat, the Drug Trafficking Vessel Interdiction Act, the issues raised in the appellate cases that affirmed the Act’s constitutionality, and unresolved legal and operational issues to address the submersible threat.