This article contributes to the debate among just war theorists about the ethics of using armed drones in the war on terror. If violence of this kind is to be effectively restrained, it is necessary first to establish an understanding of its nature. Because it is difficult to conceptualize drone-based violence as war, there is concern that such violence is thus not captured by the traditional jus ad bellum (just resort to war) framework. Drone strikes probably do not constitute a law enforcement practice, so the peacetime ethics of criminal justice do not apply either. One possible solution is to develop and apply a legitimization framework of jus ad vim (just resort to force) in which vim is “force short of war,” although this depends upon a vim–bellum distinction being a sustainable one. Moving beyond discussion of these three alternative concepts of drone-based violence, the article suggests a fourth—vis perpetua (perpetual force)—and explores the ethical implications thereof. As a form of violence that presents no physical risk to individual users of force, a program of drone strikes poses a moral problem if it is intended to continue indefinitely, leading to the systematic endangerment of innocents without the eventual promise of peace.