William served two tours of duty during the Civil War. First "joined up" in 1861 for one year, serving with the 15th Reg., got out and then "joined up" again with brother, Thomas Campbell in 1862 in 3rd Reg. and remained in Forrest's Cavalry until close of the war in 1865.

CONFEDERATE TENNESSEE TROOPS

 3rd Regiment, Tennessee Cavalry (Forrest's) 

  3rd (Forrest's Old) Cavalry Regiment was organized at Memphis, Tennessee, in
 October, 1861, as an eight-company battalion. In January, 1862, it was increased to  regimental size. The history of this unit is very complex because over twenty
 companies from Tennessee, Kentucky, Texas, Mississippi, and Louisiana were
 attached to it at one time or another. After the Battle of Shiloh, four companies were
 transferred to the 4th (Russell's) Alabama Cavalry Regiment and thereafter it was
 called 18th or 26th Battalion, Balch's Battalion, and McDonald's Battalion. It fought
 at Fort Donelson and Shiloh, and during April, 1862, contained 463 effectives. The unit
 was attached to Forres's, F.C. Armstrong's, and E.W. Rucker's Brigade, and served in
 the Army of Tennessee and the Department of Alabama, Mississippi, and East
 Louisiana. It confronted the Federals in Tennessee, Mississippi, Kentucky, and
 Alabama, and surrendered in May, 1865. The field officers were Colonels Nathan B.
 Forrest and David C. Kelley; Lieutenant Colonels P.T. Allin, Robert M. Balch, and
 Edward E. Porter; and Majors James C. Blanton, William E. Forrest, Charles McDonald, and Edwin A. Spotswood.