In early 1864, Stoneman was impatient with garrison duty in Washington and requested another field command from his old friend Maj. Gen. John Schofield, who was in command of the Department of the Ohio. Although originally slated for an infantry corps, Stoneman assumed command of the Cavalry Corps of what would be known as the Army of the Ohio. As the army fought in the Atlanta Campaign under Maj. Gen. William T. Sherman, Stoneman commanded an unsuccessful raid of the infamous Andersonville Prison. In the course of the raid he and his aide, Myles Keogh were captured by Confederates outside of Macon, Georgia. However, the 5th Indiana Cavalry Regiment under Col. Thomas Butler made a valiant stand, allowing the rest of his forces to retreat. They were surrendered as well, despite protest by Col. Butler. Stoneman became the highest-ranking Union prisoner of war, and he remained prisoner for three months.