This picture shows some of the field hospitals. As you see can they are small tents. Here are some regulations for a field hospital, At least one surgeon and one assistant surgeon to manege supplies. 3 medical officers to conduct all surgical operations, operating surgeons based on their skill. One of the assisting medical officers to perform all anesthesia.
Background
When the war began the Surgeons and assistant surgeons were completely unprepared for what the war brought them. They had no experience with the numbers or types of casualties the war had. At the beginning of the war there were 30 surgeons and 83 assistant surgeons. The first field hospitals were small tents with a few beds or tables. The food and water often became contaminated. During this time no antibiotics were available. Chloroform or Ether was used as a Surgical Anesthesia.