At the outbreak of the Civil War, Camp returned to Ohio and enlisted in the 142nd Regiment of the Ohio Volunteer Infantry. Camp saw action at the Battle of Island Number Ten and the Battle of Petersburg. In June 1864, Camp's regiment successfully guided supplies through the hostile Virginia wilderness to reinforce General Ulysses S. Grant at the Battle of Cold Harbor. In February 1865, shortly before he was mustered out with the rank of major, Camp accompanied General Joseph Alexander Cooper to Knoxville. Impressed with the virtually untouched mineral resources of the surrounding region, Camp decided to make the city his permanent home.