Recent attention among governments, civil society organizations and the media has focused on technical, military, legal and ethical issues of the weaponization of increasingly autonomous technologies. Experts have suggested that fully autonomous weapons are likely to first appear in the relatively “uncluttered” maritime environment. Yet, policy-makers have directed relatively little attention to the specific issues and challenges in this environment that might be different or more acute than on land or in the air. This paper aims to shed light on these issues in order to inform the broader debate on the weaponization of increasingly autonomous technologies. It is the fourth in a series of UNIDIR papers on this theme.