 After roughly a month 's furlough back in Massachusetts during February and March 1864 , the 21st returned to the Army of the Potomac as part of a newly reorganized IX Corps , rejoining the army a day before the Battle of the Wilderness on May 4 , 1864 . Lt. Gen. Ulysses Grant had become general @-@ in @-@ chief of the Union army and intended to follow the Army of the Potomac in the field , relentlessly pushing Lee 's Confederate army over the course of the summer of 1864 . Walcott of the 21st wrote , " There was to be little of the romance or strategy of war in that horribly bloody work of that summer 's campaign in Virginia . " 
