Since the February 2022 Russian invasion of Ukraine, the prospect of an Article 5 North Atlantic Treaty Organisation collective defence operation in Europe has increased significantly. Were this type of operation to occur, it would present different challenges to the Defence Medical Services (DMS) than those of the era of the International Security Assistance Force in Afghanistan, where air superiority was assured, and combat casualty numbers did not approach the tens of thousands experienced by Russia and Ukraine in the first months following the invasion. This essay examines how the DMS could prepare for such an operation using four key themes: preparing for prolonged field care, training medical personnel for combat, recruiting and retaining medical personnel and planning for post-traumatic stress disorder.