On November 15, 1861 he was assigned as chief of staff to under Major General Don Carlos Buell. General Buell successively commanded the Department of the Ohio and the Army of the Ohio. In this assignment, Fry participated in the Battle of Shiloh and the Siege of Corinth in April and May 1862. Fry was promoted to the rank of major on April 22, 1862 and to lieutenant colonel on December 31 of the same year. On October 8, 1862 Fry participated in the Battle of Perryville, Kentucky. Fry then served as assistant in charge of the appointment branch of the Adjutant-General's Office, at Washington, D. C. from November 12, 1862 until he was appointed provost marshal general of the United States Army. In this capacity he was responsible for tracking deserters, enforcing military laws and overseeing the Invalid Corps. He was appointed to the position, with the rank of colonel, on March 17, 1863 and was promoted to brigadier general on April 21, 1864. Fry served as provost marshal general until the office was abolished on August 27, 1866. Effective on March 15, 1865, but probably awarded later, Fry was brevetted to the rank of major general in the Regular Army in recognition of his service at the First Battle of Bull Run, the Battle of Shiloh and for "faithful, meritorious and distinguished service as Provost Marshal General during the war." Later career With the abolishment of the position of Provost Marshal General, Fry reverted to his permanent rank of lieutenant colonel and served as the adjutant general of the Division of the Pacific from December 3, 1866 to May 17, 1869 and of the Division of the South from June 19, 1869 to July 14, 1871. He also served as adjutant general of the Division of the Missouri from July 24, 1871 to November 26, 1873 and of the Division of the Atlantic from Nov. 28, 1873 to July 1, 1881. On March 3, 1875 Fry was promoted to the rank of colonel. He served as adjutant general of the Department of the East from January 1, 1878 until his retirement from the Army on July 1, 1881. After retiring, Fry devoted his time to writing military histories. In 1885 he wrote Killed by a Brother Soldier, detailing the murder of Major General William "Bull" Nelson by Brigadier General Jefferson C. Davis (not to be confused with the