Ambulances carrying wounded to Field Hospital No. 1, Neuilly, June 7, 1918 U.S. Signal Corps photo. A field hospital is a large mobile medical unit, or mini hospital, that temporarily takes care of casualties on-site before they can be safely transported to more permanent hospital facilities. A field hospital is larger than a temporary aid station but smaller than a permanent military hospital. The United States Army Ambulance Service was a unit of the United States Army during World War I. It was established by General Order No. 75 of the War Department in May 1917. It primarily provided medical services to the French and Italian Armies during the War. It incorporated the volunteer sections of the American Field Service, which had been formed before the American entry into the war.
