1923 Landing facilities and proposed airway system in the United States, by the United States Army Air Service, from the Digital Commonwealth - commonwealth jh343z06d. (<a rel="nofollow" class="external free" href="https://www.digitalcommonwealth.org/search/commonwealth:jh343z06d">https://www.digitalcommonwealth.org/search/commonwealth:jh343z06d</a>)
United States Army Air Service
Digital Commonwealth