Two F-16A Fighting Falcons from the North Dakota Air National Guard's 178th Fighter Squadron lead an F-15C Eagle from the 27th Fighter Squadron at Langley Air Force Base, Va., during a combat air patrol mission in support of Operation Noble Eagle over Washington D.C. in an undated photo. National Airport and the Pentagon are seen at left, with downtown Washington seen on the other side of the Potomac River. Photo by Greg L. Davis/Usaf/Reuters