War has influenced the citizen, health services, and the state in the United Kingdom across the 20th Century. The creation of the Ministry of Health (MoH) after World War 1 and the organisation of the Emergency Medical Services to treat casualties from air attacks during World War 2 shaped the new NHS in 1947. The Ministry of Defence (MOD) and the MoH created contingency plans as part of Civil Defence during the Cold War. The closure of military hospitals in the 1990s deepened mutual dependencies. The wars in Iraq and Afghanistan reinforced this synergy, firstly in the treatment of military casualties in the NHS, secondly in the mutual employment of health professionals in the Regular and Reserve forces, and thirdly in the application of the Armed Forces Covenant in the care of family members of Service personnel and Veterans. Finally, the recent COVID crisis demonstrated the value of medical personnel in the Armed Forces as a national strategic reserve to support the NHS during health emergencies.