The informed defense officials laid out a timeline of the events surrounding the series of terrorist attacks as follows: (Times are EDT and reflect actual, rather than scheduled departure times of flights.)

7:59 a.m.: American Airlines flight 11 takes off from Boston's Logan International Airport.
8:14 a.m.: United Airlines flight 175 takes off from Boston's Logan International Airport.
8:20 a.m.: American Airlines flight 11 stops transmitting IFF beacon signal while over the Hudson River.
8:20 a.m.: American Airlines flight 77 departs Dulles International Airport near Washington.
8:38 a.m.: Boston air traffic center notifies NORAD that American Airlines flight 11 has been hijacked.
8:43 a.m.: FAA notifies NORAD that United Airlines flight 175 has been hijacked.
8:44 a.m.: Otis Air National Guard Base in Mass. orders to fighters scrambled.
8:46 a.m.: American Airlines flight 11 strikes the World Trade Center's north tower.
8:47 a.m.: NORAD informed of the plane striking the World Trade Center.
8:50 a.m.: United Airlines flight 175 deviates from its assigned flight path.
8:52 a.m.: Two F-15 Eagles take off from Otis ANG Base in effort to intercept hijacked plane(s) after first plane has struck the World Trade Center.
9:02 a.m.: United Airlines flight 175 strikes the World Trade Center's south tower (F-15 fighter jets from Otis ANG Base are still 70 miles away.)
9:25 a.m.: FAA notifies NORAD that United flight 77 may have been hijacked.
9:27 a.m.: (approximate time) NORAD orders jets scrambled from Langley Air Force Base in Virginia to head to intercept United Airlines flight 77.
9:35 a.m.: Three F-16 Fighting Falcons take off from Langley AFB headed toward Washington area.
9:37 a.m.: American Airlines flight 77 is lost from radar screens.
9:38 a.m.: American Airlines flight 77 strikes the Pentagon.
9:49 a.m.: F-16 fighter jets arrive over Washington, D.C. to perform Combat Air Patrol (CAP) over city. (The fighters broke the sound barrier and traveled supersonic at 720 knots to Washington, making the approximately 130 miles in 14 minutes.)
The following timeline is for United Airlines flight 93, scheduled to fly from Newark International Airport to San Francisco. The flight crashed in Pennsylvania.
8:42 a.m.: United Airlines flight 93 takes off from Newark International Airport.
9:16 a.m.: FAA informs NORAD that United Airlines flight 93 may have been hijacked.
9:40 a.m.: Transponder signal from United flight 93 ceases and radar contact is lost.
10:02 a.m.: After a review of radar tapes, a radar signal is detected near Shanksville, Pennsylvania.
Courtesy of CNN

8:45 a.m.: Jet airliner crashes into the north tower of the World Trade Center in New York.
9:03 a.m.: A second airliner crashes into its twin south tower, causing a devastating explosion.
9:10 a.m.: President Bush, in Sarasota, Florida, is reading to children in a classroom when his chief of staff, Andrew Card, whispers news of the attacks into his ear.
9:20 a.m.: American Airlines says one of the planes that crashed into the Trade Center was American Airlines Flight 11, hijacked after takeoff from Boston en route to Los Angeles. The FBI investigates reports of planes being hijacked before the World Trade Center crashes.
9:29 a.m.: First reports of casualties indicate that at least six people were killed, with at least 1,000 injured.
9:30 a.m.: President Bush declares: "We have had a national tragedy. Two airplanes have crashed into the World Trade Center in an apparent terrorist attack on our country."
9:43 a.m.: Abu Dhabi television reports it received a call from the Democratic Front for the Liberation of Palestine, claiming responsibility for crashing two planes into the WTC. However, leading officials later deny the claim. Senior law enforcement officials say car bomb explodes outside of State Department in Washington, D.C. Federal protective services later denies car bomb attack occurred.
9:43 a.m.: Another plane crashes into the Pentagon in Washington. The nerve center of the U.S. military bursts into flames and a portion of one side of the five-sided structure collapses.
9:48 a.m.: Government buildings in Washington, including the White House and the Capitol are evacuated with officials citing a credible threat of a terrorist attack. Authorities across the country go on alert, tightening security at strategic facilities and evacuating high-profile buildings. US monuments and museums in Washington D.C. are closed.
9:49 a.m.: The Federal Aviation Administration shuts down all airports across the U.S. Financial markets suspend trading in the wake of the attacks.
10:00 a.m.: Officials at Somerset County Airport say United Airlines Flight 93, en route from Newark, N.J., to San Francisco, crashes in western Pennsylvania, about 80 miles southeast of Pittsburgh. The crash site is 85 miles northwest of Camp David.
10:05 a.m.: The south tower of the World Trade Center collapses.
10:29 a.m.: The north tower of the World Trade Center collapses.
12:33 p.m.: United Airlines confirms a second of its planes has crashed at an unknown location.
12:39 p.m.: Flown to Barksdale Air Force Base near Shreveport, Louisiana, President Bush makes a second statement, vowing to hunt down and punish those responsible.
2:48 p.m.: New York Mayor Rudy Giuliani says the eventual death toll from Tuesday's attack may be "more than any of us can bear."
2:51 p.m.: The Navy dispatches missile destroyers and other equipment to New York and Washington.
4:25 p.m.: Securities and Exchange Commission says all financial markets are closed for the day. The American Stock Exchange, the Nasdaq and the New York Stock Exchange say they will remain closed on Wednesday.
4:30 p.m.: President Bush leaves Offutt Air Force Base in Nebraska aboard Air Force One to return to Washington, where he will make a nationally televised address.
5:25 p.m.: World Trade Center 7 collapses.
8:30 p.m.: President Bush addresses the nation. "These acts of mass murder were intended to frighten our nation into chaos and retreat," he said. "But they have failed; our country is strong."
8:35 p.m.: President Bush attends national security meeting.
Courtesy of Time.com and FOX News. 

American Airlines Flight 11, from Boston, Massachusetts, to Los Angeles, California, crashed into the north tower of the World Trade Center with 92 people on board. 

American Airlines Flight 77, from Washington to Los Angeles, crashed into the Pentagon with 64 people aboard. 

United Airlines Flight 175, from Boston, Massachusetts, to Los Angeles, California, was the second hijacked plane to strike the World Trade Center, plowing into the south tower. Two pilots, seven flight attendants and 56 passengers were on board. 

United Airlines Flight 93, from Newark, New Jersey, to San Francisco, California, crashed in rural southwest Pennsylvania, with 45 people on board.

WASHINGTON (CNN) -- The Department of Defense has said a total of 126 Pentagon personnel are missing. The Navy released Thursday a list of 42 names of people connected with that branch of service. 

On Friday, officials announced the names of 84 more people who have been identified as unaccounted for following Tuesday's attack on the Pentagon. The list includes 74 Army personnel -- 52 of them Department of the Army civilians or Army contractors -- and another 10 civilians working in the Pentagon for Defense Department agencies.