I was in Frederick, MD today at the National Museum of Civil War Medicine and saw this about the Colored Troops. The 65th U.S. Colored Troops (U.S.C.T.) suffered more deaths from disease than any other Union regiments - 755 troops died. 465 members of the 49th U.S.C.T. died of disease as compared to the 62 who died in combat. White troops didn't feel the blacks would be able to fight their former owners and torturers so they were assigned to high fatigue labor, garrison or other non combat duty that kept them in one location. This led to a high rate of disease and death. Later when it was determined the blacks would withstand the battles the black troops were sent to fight at Port Hudson and Milliken's Bend in Mississippi and at Fort Wagner in South Carolina. If you're interested in Civil War history and haven't seen the movie 'Glory' you may find it worthwhile to watch. It's the history of the 54th Massachusetts Regiment (colored) and their involvement in the battle at Fort Wagner. Fort Wagner was a fortress that was pretty much invincible and the mission was suicidal but the 54th attacked anyway.
Approximately 179,000 African Americans enlisted in the Union Army and 10,000 black sailors served in the Union Navy.