Following the outbreak of the Civil War and the firing on the Union garrison at
Fort Sumter in
Charleston Harbor, Candy was appointed on September 21, 1861, as a
captain and assistant
adjutant general of volunteers. He served on the staff of
Charles Pomeroy Stone at the time of the
Battle of Ball's Bluff. Candy resigned his staff position on December 3, 1861. He was commissioned
colonel of the
66th Ohio Infantry on December 17 of that year. Candy led his regiment under
Nathaniel Banks in what became
II Corps of
John Pope's
Army of Virginia, serving in
John W. Geary's brigade of
Christopher C. Augur's
division. When Geary was wounded in the
Battle of Cedar Mountain, Candy succeeded to brigade command. Banks's corps missed the
Second Battle of Bull Run, and Candy was absent when the corps—newly dubbed
XII Corps,
Army of the Potomac—fought in the
Battle of Antietam. XII Corps was in reserve during the
Battle of Fredericksburg, but it participated in Maj. Gen.
Ambrose Burnside's
Mud March. When XII Corps was transferred west under the command of Major General
Joseph Hooker later in 1863 to relieve the
Army of the Cumberland besieged at Chattanooga, Candy was transferred with his brigade. It fought at the
Battle of Wauhatchie. Candy was injured early in the
Battle of Lookout Mountain, and he also missed the
Battle of Ringgold Gap. When XII Corps and
XI Corps were combined into Hooker's
XX Corps of the Army of the Cumberland, Candy became commander of a brigade in Geary's second division. He led it in Major General
William T. Sherman's
Atlanta campaign until August 4, 1864. Candy was mustered out of the volunteer service on January 14, 1865, and he received a
brevet appointment as a
brigadier general on March 13, 1865. ==Postbellum career==