During the memorable campaign of Gen. Thomas from Chattanooga to Atlanta, Colonel Duffield was acting Provost Marshal General of the Army of the Cumberland, participating in all the hard fought battles of this gallant Union commander, among them being Resaca, Missionary Ridge, Peach Tree Creek and Jonesboro. This campaign terminated at Atlanta, where, on October 14, 1864, he was mustered out by reason of expiration of service.