<a href="https://en.wikipedia.org/wiki/Project_Blue_Book" id="mwASY" rel="mw:WikiLink" title="Project Blue Book">Project Blue Book</a>: The United States Air Force closes its study of <a href="https://en.wikipedia.org/wiki/Unidentified_flying_object" id="mwASc" rel="mw:WikiLink" title="Unidentified flying object">UFOs</a>.