[1][2] In 1856, he was appointed second lieutenant in the 1st U.S. Cavalry Regiment, serving in a variety of frontier outposts and occasionally battling hostile Indians.

[2] On December 31, 1862, Long was wounded in the left shoulder at the Battle of Stones River while commanding Company K of the regiment.

[3] On February 23, 1863, Long was appointed colonel of the 4th Ohio Cavalry, a regiment which recently had surrendered to the Confederate raider, Brigadier General John Hunt Morgan.

[2] On August 18, 1864, President Abraham Lincoln appointed Long a brigadier general in the volunteer army to rank from the same date.

[5] Long was mustered out of the volunteer service on January 15, 1866[4] On April 10, 1866, President Andrew Johnson nominated Long for appointment to the brevet grade of brigadier general in the Regular Army of the United States, to rank from March 13, 1865, for gallantry at the Battle of Selma, and the U.S. Senate confirmed the appointment on May 4, 1866.

[7] After recovering from the wound suffered at the Battle of Selma, Long was assigned to command the Military District of New Jersey.