MLA
Andrew [last name unknown]. Letter from Andrew (Camp Huger, Suffolk, Virginia), to "Dear Sarah,". Andrew was probably from Beaufort, South Carolina. October 23, 1861. Civil War Collection. Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/982x3ffcjv-cor.
APA, 6th edition
Andrew [last name unknown]. (October 23, 1861)[Letter from Andrew (Camp Huger, Suffolk, Virginia), to "Dear Sarah,". Andrew was probably from Beaufort, South Carolina]. Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/982x3ffcjv-cor.
Chicago
Andrew [last name unknown], Letter from Andrew (Camp Huger, Suffolk, Virginia), to "Dear Sarah,". Andrew was probably from Beaufort, South Carolina, October 23, 1861, Civil War Collection, Stuart A. Rose Manuscript, Archives, and Rare Book Library. https://digital.library.emory.edu/purl/982x3ffcjv-cor.