This essay investigates the change in the Catholic attitude toward nuclear weapons as articulated by Pope Francis. Francis has generally followed the position of his immediate predecessors with regard to the Catholic teaching on just war. While the resort to armed force remains a morally justifiable option if the principles of just war have been met, the pope forcefully emphasises the tools of nonviolent peacebuilding. Recently, however, Francis made an original just war argument when he broke with the Church’s established (...) position on nuclear weapons. The pope declared both the use and possession of nuclear weapons “immoral” and, thus, abandoned the Church’s reluctant acceptance of nuclear deterrence that had survived the end of the Cold War. In this essay, I analyse the rationale behind Francis’s decision to break with nuclear deterrence, which is mainly grounded in the disillusionment about the failed promise of nuclear disarmament. Furthermore, I assess the impact of the new position with regard to Catholic soldiers serving in nuclear armed militaries. (shrink)