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Flags at Joint Base Andrews, Md., fly at half-staff in remembrance of those who lost their lives in the 9/11 terrorist attacks on the United States. Sept. 11 is also known as Patriot Day, which is an annual observance on September 11 to remember those who were injured or died during the terrorist attacks in the United States on September 11, 2001. (U.S. Air Force photo/ Senior Airman Katie Spencer)