In this article for the Atlantic Council, National Preparedness Commissioner Elizabeth Braw sheds light on the growing threat of the Russian Dark fleet, which has been rapidly expanding. The Dark Fleet comprises legacy shipping vessels without proper maintenance and insurance. The article explores (i) the risk this presents to other maritime vessels in proximity, (ii) the risk to insurance and maritime regulations from associated risky behaviours and accidental harms, and (iii) the additional role that Dark Fleet vessels perform in heightening Greyzone aggression.