Before the Antietam Campaign:
"Before the Civil War, Nimrod Burke was employed by Melvin Clarke, a prominent attorney in Marietta, Ohio. On April 12, 1861 when the Civil War erupted, Clarke was commissioned as a Major with the 36th Ohio Infantry in the Union Army. Major Clarke hired Nimrod Burke as a civilian teamster and scout for the 36th Ohio Infantry. Clarke's unit was sent to fight Confederate forces in eastern Virginia. Clarke was promoted to full Colonel on the day he was killed in the Battle of Antietam, near Sharpsburg, Maryland on September 17, 1862".1

In the Antietam Campaign:
Clark assumed command of the Regiment in Maryland after Colonel Crook was given command of the Brigade (probably on 14 September).

The remainder of the War:
His only son Joseph D. Clark had enlisted in the 148th Ohio Infantry and was killed at City Point, Virginia on 9 August 1864