The Aircraft Warning Service (AWS) was a civilian service of the United States Army Ground Observer Corps instated during World War II to keep watch for enemy planes entering American airspace. 
 
These civilian observers received extensive training to become quite skilled in the recognition of aircraft. This training was so productive that it became quite popular with even non-AWS citizens. Aircraft recognition became a popular hobby providing the country hours of entertainment and resulted in many books and publications, including aircraft recognition flash cards, on the subject. 
 
This is a very nice, unissued, and original WWII US Army Air Corps AWS Observer Armband. It is unsewn,  ~17"L x 4"W, and has NO mothing. A great piece of US homefront militaria from WWII.