Only worn once against the New York Yankees on September 11, 2021 to commemorate the 20th anniversary of 9/11. The Septe...mber 11 attacks, commonly known as 9/11, were four coordinated Islamist suicide terrorist attacks carried out by al-Qaeda against the United States in 2001. That morning, 19 terrorists hijacked four commercial airliners scheduled to travel from the New England and Mid-Atlantic regions of the East Coast to California. The hijackers crashed the first two planes into the Twin Towers of the World Trade Center in New York City, two of the world's five tallest buildings at the time, and aimed the next two flights toward targets in or near Washington, D.C., in an attack on the nation's capital.