The United States Army Ambulance Service (USAAS) 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.
This is partial text from the full article (usually with photos) at https://armorama.com/news/casemate-illustrated-special-u-s--army-ambulances-medical-vehicles-in-world-war-ii