[1] Upon the outbreak of the American Civil War, he was part of the forces that occupied Alexandria, Virginia and subsequently participated in the battles of Blackburn's Ford and 1st Bull Run.

[1] Despite being discharged on January 13, 1864, Carroll re-enlisted in Light Battery G of the 3rd Artillery Regiment at Washington, D.C., on February 3, 1864.

He was stationed at Little Rock, Arkansas, and made active patrols on the area to counter any potential Confederate cavalry movements.

He also served in negotiations with the Comanche and the Kiowa tribes in September 1869 and enforced reconstruction policies at Marion County, Texas from January to February 1870.

While he was recovering, Carroll was suggested for a brevet promotion to lieutenant colonel but after becoming sick, Carroll was recovering until March 1881 when he began scouting for the Ute Mountain Ute Tribe in Colorado and Utah for the rest of the year as he was primarily stationed in Fort Lewis.

[1] On May 23, 1896, Carroll was promoted to lieutenant colonel of the 6th Cavalry Regiment and by the time the Spanish–American War broke out, he was given command of the 1st Brigade of the V Corps.