The Emergency Medical Service (EMS), also known as the Emergency Hospital Service (EHS), was a state-run network of free hospital services organised by the Ministry of Health in Britain during the Second World War (1939-1945).

In June 1938, anticipating mass civilian casualties and noting the dysfunction of existing hospital arrangements, the British government charged the Ministry of Health with reorganising healthcare provision across the country. The Ministry responded by commandeering hospital sites and building up large numbers of directly-employed medical staff. By October 1939, the EMS had secured access to nearly 1,000 operating theatres, stockpiled millions of bandages and dressings for future casualties, and set up a national blood transfusion service.

By demonstrating the administrative benefits of a comprehensive, state-run system of healthcare, the EMS is often credited as the key forerunner to the National Health Service (NHS), which was established in 1948.