At the beginning of the Civil War, neither Union nor Confederate armies allowed blacks to enlist (due to racism and political reasons in the North, and racism and cultural/economic reasons in the south). As the war continued, however, the reality of casualty numbers and fewer white enlistments forced a policy change. The U.S. Congress officially authorized the mustering of black troops in July 1862.
In general, white soldiers and officers believed that black men lacked the courage to fight and fight well. Their units were relegated, at first, to ditch digging details, fortification building, and guard duty. Black units were commanded by white officers. By 1863, attitudes began to change when black soldiers saw action and succeeded with bravery and skill. Eventually, black troops engaged in 39 battles and over 400 “small clashes,” with 68,178 reported casualties.
Approximately 180,000 African Americans comprising 139 regiments and 10 artillery batteries served in the Union Army during the Civil War. By the end of the war black soldiers totaled nearly 10% of the Union Army. On the Confederate side, where resistance to black troops was much higher, a bill was finally passed by the “Confederate Congress” in March 1865 allowing slaves to take up arms for the South. This approval, however, was “too little, too late.”
Source: Jones, Terry L. Historical Dictionary of the Civil War, Vol. 1, 2002, pp 190-191
William Townsend makes note of “Negro Regiments” in his diary:
August 6, 1863 “. . . received an order to report all of those wishing to be examined for commission in Negro Regiments I think of sending my name in”
August 8, 1863 “. . .sent in my name & Sergt Clark to be examined for commissions in negro Regts . . .”