MLA

Lees-Milne, James, 1908-1997. Churchill, John Spencer. Box 27, folder 1009. [ca. 1930s]. https://collections.library.yale.edu/catalog/2007168.

APA, 6th edition

Lees-Milne, James, 1908-1997. (["Box 27, folder 1009"])([ca. 1930s])[Churchill, John Spencer]. https://collections.library.yale.edu/catalog/2007168.