Two categories of ethical questions surrounding military autonomous systems are discussed in this article. The first category concerns ethical issues regarding the use of military autonomous systems in the air and in the water. These issues are systematized with the Laws of Armed Conflict (LOAC) as a backdrop. The second category concerns whether autonomous systems may affect the ethical interpretation of LOAC. It is argued that some terms in LOAC are vague and can be interpreted differently depending on which ethical normative theory is used, which may increase with autonomous systems. The impact of Unmanned Aerial Vehicles (UAVs) on the laws of war will be discussed and compared to Maritime Autonomous Systems (MAS). The conclusion is that there is need for revisions of LOAC regarding autonomous systems, and that the greatest ethically relevant difference between UAVs and MAS has to do with issues connected to jus ad bellum – particularly lowering the threshold for starting war – but also the sense of unfairness, violation of integrity, and the potential for secret wars.