Autonomous systems, including unmanned aerial vehicles (UAVs), anti-munitions systems, armed robots, cyber attack and cyber defense systems, are projected to become the centerpiece of 21st century military and counter-terrorism operations. This trend has challenged legal experts, policymakers and military ethicists to make sense of these developments within existing normative frameworks of international law and just war theory. This paper highlights a different yet equally profound ethical challenge: understanding how this trend may lead to a moral deskilling of the military profession, potentially destabilizing traditional norms of military virtue and their power to motivate ethical restraint in the conduct of war. Employing the normative framework of virtue ethics, I argue that professional ideals of military virtue such as courage, integrity, honor and compassion help to distinguish legitimate uses of military force from amoral, criminal or mercenary violence, while also preserving the conception of moral community needed to secure a meaningful peace in war’s aftermath. The cultivation of these virtues in a human being, however, presupposes repeated practice and development of skills of moral analysis, deliberation and action, especially in the ethical use of force. As in the historical deskilling of other professions, human practices critical to cultivating these skills can be made redundant by autonomous or semi-autonomous machines, with a resulting devaluation and/or loss of these skills and the virtues they facilitate. This paper explores the circumstances under which automated methods of warfare, including automated weapons and cyber systems, could lead to a dangerous ‘moral deskilling’ of the military profession. I point out that this deskilling remains a significant risk even with a commitment to ‘human on the loop’ protocols. I conclude by summarizing the potentially deleterious consequences of such an outcome, and reflecting on possible strategies for its prevention.