This is an example of a 21st Airship Group distinctive uniform collar insignia. The 21st Airship Group was formed at Scott Field, Illinois, on June 26, 1922 from the units of the I Corps Balloon Corps. Between the Wars, the group was the only active lighter-than-air headquarters in the Air Servce and then the Army Air Corps. With no need for lighter than air units, the Air Corps disbanded the unit on May 27, 1939.
This object is on display in Boeing Aviation Hangar at the Steven F. Udvar-Hazy Center in Chantilly, VA.