Fitz John Porter
After being released as part of a prisoner exchange in October the same year, Prentiss was promoted to major general and served on the court-martial board that convicted Fitz John Porter. His dissenting voice in the final vote damaged his political clout. Prentiss was sent to Arkansas and won the Battle of Helena on July 4, 1863. In 1863, he resigned to tend to his family. Historian Ezra J. Warner speculated that Prentiss felt that he was being shelved after having proved his abilities at Shiloh and Helena.