MLA

Koch, Frederick R. (Frederick Robinson). Other correspondents and unidentified. Box 48, folder 981. [1942], [1954]. https://collections.library.yale.edu/catalog/16601852.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 48, folder 981"])([1942], [1954])[Other correspondents and unidentified]. https://collections.library.yale.edu/catalog/16601852.