This position paper examines the February 28, 2026, joint kinetic operation conducted by Israel and the United States. It sets out the legal case for treating the operation as a lawful exercise of preemptive self-defense under Article 51 of the UN Charter in response to an imminent threat posed by Iran. Grounded in the Caroline test, ICJ jurisprudence, and relevant principles of international law, the paper argues that the operation was a measure of last resort, not an act of aggression