This article evaluates unmanned military systems deployed in naval warfare. Even more than unmanned aerial systems, unmanned naval systems (UNS) pose a challenge to the law applicable in armed conflict. Thus, the status of such systems as well as the legal consequences that arise out of that classification will be analysed. However, as of today no agreed classification exists. Therefore it is argued that states should classify UNSs as warships. Thus, they would be entitled to sovereign immunity and passage rights under international law of the sea. Additionally, under international humanitarian law they would be entitled to exercise belligerent rights, most importantly to engage in attack. As a downside, they may be lawfully targeted anytime during an armed conflict.