Who is the only naval POW known to have kept a diary at Andersonville? "A carpenter and ship joiner originally from South Scituate, Massachusetts, Frederic Augustus James left a wife and two young daughters home in East Boston when he enlisted in the Union Navy in August 1862." James was taken prisoner during a failed attack on Fort Sumter in September, 1863, and eventually sent to Andersonville. He died there on September 12, 1864. His diary was preserved and given to his wife by a fellow prisoner who was exchanged.
Edit - As far as I am able to determine, Nathan Hopkins was a naval POW held at Andersonville for a time, but there is no record that he kept a diary while he was there. Charles Hopkins of the 1st New Jersey Infantry did keep a diary at Andersonville, but he was not a naval POW.
I believe this may be Frederic Augustus James (“Andersonville Raiders” and my kindle edition shows a location 1437 & location 1602). He was a sailor, wrote a diary (Civil War diary; Sumter to Andersonville) and find a grave has him dying at Andersonville in 1864. BTW - I never knew the complete story of the Andersonville Raiders until I read your book. It was an excellent read on a difficult subject.
Frederic Augustus James, a sailor on the Housatonic who died as a POW at Andersonville, is believed to be the only sailor at Andersonville to have kept a diary. Source
Frederic Augustus James (1832-1864), Carpenter's Mate, USS Housatonic.
James was captured September 8, 1863, while participating in a failed attack on Fort Sumter in Charleston Harbor. He was imprisoned at Columbia, S.C.; Richmond, Va.; Salisbury, N.C.; and finally, Andersonville, Ga. where he died of dysentery September 15, 1864. He is buried there in grave number 8858. it is believed that one of his shipmates brought the diary to his widow at the end of the War.
Source: Frederic Augustus James, "Frederic Augustus James Papers", Massachusetts Historical Society Collections Online.
Source: "Frederick Augustus James", Find A Grave. https://www.findagrave.com/memorial/8107913/frederick-augustus-james