The 18th Chairman of the Joint Chiefs of Staff Gen. Martin E. Dempsey and senior U.S. military leaders welcome United Kingdom's Chief of the Defence Staff Gen. Nick Houghton and senior U.K. military leaders to the National Defense University on Fort Lesley J. McNair, Washington, D.C., May 5, 2015. The coalition partners joined for a Combined Chiefs of Staff meeting to discuss common strategic policy, and current and future military challenges facing the two countries. (DoD photo by Army Staff Sgt. Sean K. Harp/Released)