 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.