MLA

Koch, Frederick R. (Frederick Robinson). Music/The Battle of Britain: excerpts titled "14.M.3" and "Introduction to March for Record". Box 336, folder 1949. [1969]. https://collections.library.yale.edu/catalog/2055250.

APA, 6th edition

Koch, Frederick R. (Frederick Robinson). (["Box 336, folder 1949"])([1969])[Music/The Battle of Britain: excerpts titled "14.M.3" and "Introduction to March for Record"]. https://collections.library.yale.edu/catalog/2055250.