Airman 1st Class Devin Oliver, 436th Civil Engineer Squadron fire protection apprentice, performs the ringing of the bell ceremony during the 19th Anniversary 9/11 memorial event Sept. 11, 2020, at Dover Air Force Base, Delaware. The ringing of the “four fives” is a firefighter tradition that signals and honors when a firefighter has perished in the line of duty. (U.S. Air Force photo by Mauricio Campino)