Enlisted in Company C, Indiana 13th Infantry Regiment on 20 Dec 1863.
Promoted to Full 2nd Lieutenant on 19 Dec 1864.
Promoted to Full Captain on 01 May 1865.
Mustered out on 05 Sep 1865 at Goldsboro, NC.

TO HIS REWARD CAPT. A.O. MITCHELL WAS CALLED THIS MORNING.
A Long and Useful Life Ended by the Summons of His Master.
It was with universal sympathy and sadness that the news announcing the death of Capt. A.O. Mitchell was heralded this morning.
Shortly after 8 o'clock his frail body, that has been fighting death for the past few days, succumbed to the inevitable and another faithful servant was called to his reward as his spirit ascended to a better world. Several days ago Capt. Mithell was siexed with an attack of pneumonia and was in a dangerous condition for sveral days, but rallied from its effects and was thought to be on a fair way to recovery, when he suffered a relapse from the effects of which he failed to recover.
Capt. A.O. Mitchell was born in Dearborn county, Ind., on September 5, 1840. His earlier education received careful attention and as he grew to manhood developed strong mental as well as physical attainments. He was captain of Company K, 13th Indiana Infantry Volunteers, and a member of the "Old Guard." He enlisted at the first call for volunteers and served through the entire war with honor to himself and country.
Captain Mitchell moved to this city from Richmond over six years ago, since which time he has occupied a conspicuous place in the advancement of public weelfare of the city. A great portion of his busy life in this city has been spent in the newspaper work. He held the position of city editor and advertizsing manager of the Daily Record at different times and no employees of the office was ever held in higher esteem or greater favor by either by the management or employees than was he.
The deceased was a member of the Whitewater lodge No. 41 I.O.O.F. at Richmond, a member of the G.A.R. of this city and a member of the Continental Union of Richmond. He was an enthusiastic worker for the Continental Fraternal Union and was universally known as assistant deputy organizer for this organization. He was a devout Christian, having taken membership in the M.E. church over fourteen years ago and his life has been an open book, the pages of which have led many a wearly traveler to a better life.
Aat the time of his death he was one of the class leaders of the M.E. church and regarded as one of the pillars of the church.
The funeral services will be held this evening at 7 o'clock at the late residence of the deceased on North E street, conduted by Rev. Krider. The remains will be shipped to Richmond tomorrow on the early Panhandle train, where the principal service will be held tomorrow afternoon at 2 o'clock, conducted by Rev. Krieder at the First M.E. church a that place. The remains will be laid to rest in the family lot in Earlham cemetery.
The deceased leaves a wife ad adopted daughter, Minnie, who is now in Californin, and a host of friends to mourn his demise. (Elwood Daily Record, January 3, 1898.)