Donald Rumsfeld
The United States was attacked on September 11, 2001 by al Qaeda terrorists who hijacked commercial airliners and crashed them in coordinated strikes into both towers of the World Trade Center in Lower Manhattan, New York City and the Pentagon in Washington, D.C. The fourth plane crashed into a field in Shanksville, Pennsylvania, and its target was likely a prominent building in Washington, D.C., most probably either the Capitol Building or the White House. Within three hours of the start of the first hijacking and two hours after American Airlines Flight 11 struck the World Trade Center, Rumsfeld raised the defense condition signaling of the United States offensive readiness to DEFCON 3, the highest it had been since the Arab-Israeli war in 1973.
Aircraft hijacking
On September 11, 2001, 19 al-Qaeda Islamic extremists hijacked American Airlines Flight 11, United Airlines Flight 175, American Airlines Flight 77, and United Airlines Flight 93 and crashed them into the Twin Towers of the World Trade Center, the southwestern side of the Pentagon, and Stonycreek Township near Shanksville, Pennsylvania (after passengers acted to stop the hijackers; its intended target was either the White House or the U.S. Capitol) in a terrorist attack. All in all, 2,996 people perished and more than 6,000 others were injured in the attacks. This casualty toll makes the hijackings the most fatal in history.