APA (7th ed.) Citation

United States. Air Mail Service. (1921). U.S. air mail. [publisher not identified].

Chicago Style (17th ed.) Citation

United States. Air Mail Service. U.S. Air Mail. [Place of publication not identified]: [publisher not identified], 1921.

MLA (9th ed.) Citation

United States. Air Mail Service. U.S. Air Mail. [publisher not identified], 1921.