McGraw family in U.S. military

My grandfather served in World War I, my dad in World War II, my uncle in the Marines just after Korea, myself in Germany during the Vietnam era, my brother in Vietnam, and one other brother in the Navy during the "Nam" era. I also have a nephew who is a "lifer" and a major in the U.S. Army right now. I have always heard that I had a couple of relatives who fought for the Union in the Civil War, but I have no idea who they were.