[1] Armstrong was born on the Choctaw Agency in the Indian Territory, where his army officer father had been stationed.

[2] His gallantry in a battle against Indians near Eagle Spring gained him a commission as a lieutenant of the 2nd Dragoon Regiment in 1855, following his graduation from the College of the Holy Cross in Worcester, Massachusetts.

[1] In 1863 Armstrong was elected as colonel of the 3rd Louisiana Infantry Regiment, and was soon given command of the cavalry of Major General Sterling Price.

[4] Two months later, he was promoted to brigadier general[4] and commanded a cavalry division under Nathan Bedford Forrest at the Battle of Chickamauga.

[3] Armstrong and his men accompanied Lt. Gen. Leonidas Polk's corps to Georgia and served in the Atlanta Campaign, before participating in Lt. Gen. John B.

[3] He saw action during the campaign against Murfreesboro, and led much of Forrest's rear guard after the Hood's defeat at the Battle of Nashville.