The saying that ‘the first casualty of war is truth’ is most commonly attributed to the ancient Greek playwright Aeschylus. Perhaps he should have said that war’s first casualty is rationality. Nothing stirs the emotions of men like the sight of the latest hardware of war: F-35 fighter planes, hypersonic missiles, MOAB bombs and the like, or one’s enemies finally getting it in the neck. It is at times like this that the classic just war theory, formulated by St Augustine, St Thomas Aquinas and the Spanish School of Salamanca, among others, proves itself to be a treasure for the Church, allowing us to think straight about war.