In the light of the conviction of Sergeant A. Blackman (2013) and the investigation of an SAS non-commissioned officer Colin Maclachlan (October 2016) for an alleged ‘mercy killing’ in Iraq, this study day explores the morally-ambiguous battlefield. The law is clear that ‘mercy killing’ is not a recognised concept, although ‘diminished responsibility’ is well-established. The armed forces of the United Kingdom and other Western countries are also clear that the Law of Armed Conflict and the Geneva Conventions apply to all situations of combat. Yet the moral ambiguity of the battlefield, an extreme arena, reappears through time. Can this contradiction between the law and the soldier’s experience be resolved?