U.S. Army Gen. Martin E. Dempsey, right, chairman of the Joint Chiefs of Staff, welcomes British Gen. Sir Nicholas Houghton, chief of defense staff, 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.