Gen. Martin E. Dempsey, Chairman of Joint Chiefs of Staff, in November of 2013. Paul J. Richards /AFP/Getty Images hide caption

itoggle caption Paul J. Richards /AFP/Getty Images

Robert Gates in June 2011, his last month as secretary of defense. Alex Brandon/AP hide caption

itoggle caption Alex Brandon/AP

Robert Gates waves and President Obama claps at the then-defense secretary's farewell ceremony in June 2011. Jason Reed/Reuters /Landov hide caption

itoggle caption Jason Reed/Reuters /Landov