APA (7th ed.) Citation

United States. Postmaster General. (1929). Air mail service. U.S. GPO.

Chicago Style (17th ed.) Citation

United States. Postmaster General. Air Mail Service. Washington: U.S. GPO, 1929.

MLA (9th ed.) Citation

United States. Postmaster General. Air Mail Service. U.S. GPO, 1929.

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