"It ran on the crawler on the TV that a car bomb had exploded outside the State Department," Deputy Secretary of State Richard Armitage said. "I went out and looked with diplomatic security and didn't see anything, called my colleagues around town and, on the video conference screen, told them there was nothing to it."

Meanwhile, Secretary of State Colin Powell was in the air on his way back from a trip to Lima, Peru.

"It was frustrating," he said. "We flew seven hours and the worst part of it was that because of the communications problems that existed during that day, I couldn't talk to anybody in Washington.

"There were rumors that a fourth plane might have been heading either to the White House or the State Department," he added. "We didn't know. Who could have imagined?"

‘Worry About the Continuity of the U.S. Government’

National Security Adviser Condoleezza Rice was in a bunker beneath the White House at the time.

"At that moment, you have to worry about the continuity of the United States government," she recalled. "It was very clear that Washington was under attack."

Vice President Dick Cheney, also in the White House bunker, said officials arranged for the evacuation of the congressional leadership, especially House Speaker Dennis Hastert, R-Ill., third in line of presidential succession.

The congressional leaders flew aboard military helicopters to a top-secret bunker — the "Mount Weather" Emergency Operations Facility in Bluemont, Va. — where they stayed until returning to Washington in the afternoon. The bunker is part of a nuclear survival plan and equipped with food and phones.

"There was a granite-like stone on the sides," said Senate Minority Leader Trent Lott, R-Miss. "I mean, literally there it was, like a cave."

A secret State Department report says there are 19 emergency operating facilities for federal officials that are located within a 300-mile radius of Washington.

‘Fear Ran So Deep’

The president, too, was safe, in a protective cocoon aboard Air Force One at 45,000 feet.

"I urged the president not to return until we could find out what was going on," Cheney said. "It was important that we not bunch up in Washington."

"The fear ran so deep," White House press secretary Ari Fleischer recalled. "The fear was that this was an attack whose intent was to decapitate the government — in other words, to take out the congressional leaders, to take out the president, to take out the vice president so the government could not function. Decapitation."

"It was very clear that they were going for symbols of power and for the seats of power," Rice said. "To bring the president back and to put him in the same building with the vice president would have been foolhardy, frankly, because decapitation then of the U.S. government is quite easy."

But aboard Air Force One, nobody in the back knew where the plane was going, including ABCNEWS' Ann Compton.

"At one point," Compton said, "Ari Fleischer, the press secretary, came back and said, 'This is off the record. The president is being evacuated. … The president is being evacuated for his safety and the safety of the country.'"

About 50 minutes after the second plane hit the World Trade Center, television monitors aboard the plane showed flickering images of the destruction in New York and Washington.

"Some stations just fade in and fade out," said Eric Draper, a White House photographer. "So we weren't getting complete reports, just kind of pieces, bit by bit."

‘Worse Than Any Disaster Movie’

In New York, at 9:59 a.m. ET, there was the sound of an explosion and a huge dust cloud rose at the World Trade Center.

"The second building that was hit by the plane has just completely collapsed," ABCNEWS' Don Dahler told anchor Peter Jennings over the air as the clock ticked to 10 a.m. ET. "It folded down on itself and it's not there anymore."

"My God," Jennings said as he watched the collapse replayed.

In the White House bunker, "the mood was very somber at that point," Cheney said. "I've seen pictures of all of us as we sat there and watched on television, as you could see that first building collapse."

A half hour later, the other tower fell, too.

"It's worse than any disaster movie," Compton exclaimed aboard Air Force One.

‘Freedom Will Be Defended’

On the president's plane, officials made the decision to fly to the nearest secure facility, Barksdale Air Force Base in Louisiana, where Air Force One touched down to refuel just before noon ET.

Bush "got on the phone with the vice president and he said … 'I can't wait to find out who did it,'" Fleischer said. "'It's going to take a while and we're not going to have a little slap-on-the-wrist crap.'"

The president then recorded a statement to the nation.

"He was hot," Fleischer said. "It was reflected in his words. … I'll never forget it. His first reaction is, 'We are at war.'"

"Freedom itself was attacked this morning by a faceless coward, and freedom will be defended," Bush said in his speech. "The United States will hunt down and punish those responsible for these cowardly acts."

Air Force One lifted off again, but with a lighter load. Aboard were just a few key aides and Secret Service agents. The press pool was trimmed from 13 to five, including ABCNEWS' Compton, and Fleischer said he could not say where the plane was going.

"It was like being on the Twilight Zone plane, because there was nobody around anymore," said Ellen Eckert, a White House stenographer.

Soon, jet fighters appeared just off the plane's wing, "so close I could see the pilot's face," Eckert said.

The president began to insist that he be brought back to Washington, said Karl Rove, the White House counselor.

‘He Was Ice, Ice Cool’

But first, there was another stop, at Offutt Air Force Base outside Omaha, Neb. The president and his aides disappeared into a tiny brick building and descended down staircase after staircase into a blast-proof bunker at 3:30 p.m. ET, where the president led a video teleconference of his national security team.

"He was ice, ice cool, and I thought very appropriately so," Armitage said.

"The president was saying, 'We're going to find out who did this,'" Transportation Secretary Norman Mineta said. "'We're going to seek them out and we're going to destroy them.'"

Back in the air just before 5 p.m. ET, Bush walked back into the press area of the plane.

"There was an antsiness about him," Compton said. "He couldn't wait to get back to Washington. He couldn't wait to do something, say something."

‘That’s The 21st-Century War’

At about 6:42 p.m. ET, a somber-looking Bush gave a military salute and boarded the Marine One helicopter.

"Off the left side window, you could see the Pentagon," Fleischer said. "It was the president's first eye-to-eye connection with the attack on our country and he said aloud, to nobody in particular, 'The mightiest building in the world is on fire. That's the 21st-century war you just witnessed.'"

Arriving at the White House, Bush embraced his wife, and went down to the command bunker.

"For all of us, it was very somber," Cheney said. "It had been a very emotional day."

Night fell. The search for survivors continued in New York, and National Guard Humvees patrolled Washington's streets, as Bush prepared to address the nation.

"The word 'war' crept into the language, and then it went out again," Powell recalled. "We argued about whether it was the right word."

"He used the word during the course of the day, that we were at war," Cheney said. "But my recollection is he was concerned about that his speech that night needed in part to be reassuring to the American people."

As the president began his speech at 8:30 p.m. ET, telling Americans "our very freedom came under attack," members of the president's Cabinet, national security team and entourage watched from the bunker below.

"It was one of those moments where you could hear a pin drop," said David Bohrer, a White House photographer.

‘Get the Troops Ready’

After the speech, "he came and joined us and we, you know, congratulated him," Powell said. "It was the first time we were all together. … So it was a tense time, but, I recall also, it was a calm time."

By 9:30 p.m., Bush's team was planning their response over the coming days, "planning for what would become a war," Fleischer said.

"He made it clear that this was not to happen again," Attorney General John Ashcroft said. "I think he used words like, 'Don't ever let this happen again.'"

"The order was to get the troops ready," Federal Emergency Management Agency Director Joe Allbaugh said. "It was that simple. It was that direct. Get the troops ready."

ABCNEWS' Charles Gibson contributed to this report.