170402-N-PO203-146 NATIONAL HARBOR, Md. (April 2, 2017) A child tries out a human-powered submarine during the 2017 Naval Stem Exposition, co-sponsored by the Navy League of the United States and the Office of Naval Research. The event offers hands-on activities and provides middle and high school students an introduction to naval STEM careers and educational opportunities. (U.S. Navy photo by John F. Williams/Released)