To amplify what u/Adamrises said, the Union Army used freed slaves... as slave combat engineers. Literally marched them in front of the Confederates at bayonet point and forced them to dig trenches and build fortifications. I remember having one of the Union officer's letters home read in a college class, and the proto-wokeists was more upset at him openly calling them niggers than by admitting that he had whipped women and children to get them to dig faster.