CIMSEC – Russia and North Korea are both fielding a novel type of naval weapon – nuclear-armed torpedo drones. These new weapons introduce a variety of strategic and operational challenges that further complicate a worsening threat environment. They also pose critical legal questions about whether their intended concepts of operation are lawful. These weapons have a fearsome potential to weaponize the maritime environment, and precise questions of their legality should be resolved in order to dissuade their proliferation.