MLA

of Strategic Services. Research, United States. Office, and Analysis Branch. Bulgaria, Railroads and Railroad Facilities [Cartographic Material] / Compiled and Drawn in the Branch of Research and Analysis, OSS. The Office, 1943. https://collections.library.yale.edu/catalog/15498828.

APA, 6th edition

of Strategic Services. Research, U. S. O., & Branch, A. (1943). Bulgaria, railroads and railroad facilities [cartographic material] / compiled and drawn in the Branch of Research and Analysis, OSS. [Maps]. The Office, https://collections.library.yale.edu/catalog/15498828.