U.S. Special Delivery 16c Bi-color Great Seal Airmail Special Delivery 1938 Siou
16c Bi-color Great Seal Airmail Special Delivery 1938 Sioux City, Iowa Airmail Special Delivery to New York, N.Y. Illustrated Envelope honoring National Air Mail Week, May 15-21, 1938, by Sioux City, Ia. Home Market of the Great Northwest.