When the American Civil War broke out in 1861 Littlefield organized a company of infantry, which became Company F of the 14th Illinois Infantry, and was elected as its Captain. After serving in the west at Shiloh and Corinth, Littlefield was made Lieutenant Colonel of the new 14th Illinois Cavalry. In 1863 he was sent to the South, briefly commanded the 54th Massachusetts Infantry, a colored unit, and was ordered to recruit black troops. Littlefield raised the 4th South Carolina Infantry(African Descent); whose Colonel he became. When the United States Colored Troops were organized his regiment became the 21st USCT Infantry. On November 26, 1864 Littlefield was given a brevet promotion to Brigadier General of Volunteers. He served as brigade and district commander and was mustered out on April 25, 1866. He died on March 7, 1899.