– President Bush, now aboard Air Force One, announces from Barksdale Air Force Base that U.S. military is on high alert worldwide.

– Hijacker Mohammed Atta (on AA 11) mistakenly transmits a message to air traffic control: “We have some planes. Just stay quiet, and you’ll be OK. We are returning to the airport.”

The 9/11 Timeline: A Minute-by-Minute Account of the Attacks That Changed the World

– For the first time in history, the FAA grounds all civilian aircraft over the continental U.S. All incoming international flights are diverted to Canada.

– UA 175 crashes into the South Tower (2 WTC) between floors 77 and 85. The impact is broadcast live to millions watching on television. It is now clear this is a deliberate attack.

On the morning of September 11, 2001, 19 terrorists hijacked four commercial airliners. They deliberately crashed two into the Twin Towers of the World Trade Center in New York City, one into the Pentagon in Virginia, and a fourth—whose passengers fought back—into a field in Pennsylvania. Nearly 3,000 people were killed in the deadliest terrorist attack on U.S. soil.