President Barack Obama, Defense Secretary Ash Carter and Marine Gen. Joseph F. Dunford Jr, the 19th chairman of the Joint Chiefs of Staff, at the change of responsibility ceremony with the 18th chairman of the Joint Chiefs of Staff Army Gen. Martin E. Dempsey, on Summerall Field, Joint Base Myer-Henderson Hall, Arlington, Va. Sept. 25, 2015 DOD photo by D. Myles Cullen (released)