U.S. Air Force Airman 1st Class Angel Estrada, a 1st Special Operations Civil Engineer Squadron firefighter, performs the bell ringing during a 9/11 Memorial Ruck Ceremony at Hurlburt Field, Florida, Sept. 10, 2021. Ringing the bell is a tradition used to honor those who died during the 9/11 terrorist attacks. (U.S. Air Force photo by Senior Airman Miranda Mahoney)