President Barack Obama shakes hands with Army Gen. Martin E. Dempsey, incoming chairman of the Joint Chiefs of Staff, at the change-of-responsibility ceremony on Joint Base Myer-Henderson Hall, Va., Sept. 30, 2011. Navy Adm. Mike Mullen, outgoing chairman, retired after 43 years of service. DoD photo by U.S. Navy Petty Officer 1st Class Chad J. McNeeley