APA (7th ed.) Citation

United States. Post Office Department. (1929). Air mail service. GPO.

Chicago Style (17th ed.) Citation

United States. Post Office Department. Air Mail Service. [Washington]: GPO, 1929.

MLA (9th ed.) Citation

United States. Post Office Department. Air Mail Service. GPO, 1929.

Warning: These citations may not always be 100% accurate.