Four years ago last month, Commandant Gen. James Conway announced that he had selected Sgt. Maj. Carlton Kent to serve as his sergeant major of the Marine Corps. It’s a demanding position that requires those who hold it to be equally comfortable while offering blunt advice to a four-star general, inspiring junior Marines and articulating the Marine Corps’ needs on Capitol Hill. Following Conway’s retirement in October, the time is coming for Kent to move on, too. The sergeant major is expected to retire this spring after completing a four-year term as the Corps’ top enlisted Marine. He has held the position…