Ambulances carrying World War I wounded to Field Hospital No. 1 in Neuilly, France. In the US army during the First World War, each division had four field hospitals and four ambulance companies. Two of the field hospitals were positioned just out of range of enemy artillery and the other two were waiting further back, ready to leapfrog ahead if there was an advance. The ambulance companies ferried soldiers to these hospitals from dressing stations at the front in what became known as the 'Sanitary Train'.