Nancy Andreasen, author of The Broken Brain, traces the social history of this mental illness in a 2004 American Journal of Psychiatry article. The features of what we call PTSD have long been noted in the annuls of warfare. More recently, in World War I it was called shell shock, and those who had it were shot for cowardice in the face of the enemy. In World War II it was recognized as a mental illness and called battle fatigue. Afflicted soldiers were removed from the front and given counseling designed to return them to battle within the week -- though there is one infamous story about General Troglodyte Patton who, while touring a hospital, cursed and slapped one such soldier for his "cowardice."
The DSM I, from the post-WWII era, recognized battle fatigue as Gross Stress Disorder. It was removed from the DSM II in the early 1960s , when U.S. society was not regularly confronted with this cost of war.