Gen. Mark A. Milley, the chief of staff of the Army, speaks to attendees Sept. 11, 2015 at the 137th NGAUS General Conference & Exhibition in Nashville, Tenn.

Gen. Mark A. Milley, the chief of staff of the Army, speaks to attendees Sept. 11, 2015 at the 137th NGAUS General Conference & Exhibition in Nashville, Tenn.