“All day I had been a good soldier: stolid, resolute, unemotional, rational, and dispassionate,” writes Matthew Klimow, recalling the wave of emotion that overwhelmed him as he arrived home from the Pentagon on 11 September 2001. There was sadness for the lives lost. But there was another emotion, too: humiliation.

“We, as a nation, had been humbled,” writes the retired army colonel, who remained at the Pentagon even after it was struck by a hijacked airliner, killing all 64 people onboard and 125 inside the building. “The fighting force of which I was part had been impotent, unable to protect our fellow citizens. The darkness I felt matched the darkness inside my house as I opened the door.”

Klimow recalls the longest day of his career in As the Pentagon Burned, a study in leadership and a first-person account of the chaos that unfolded at the headquarters of the US defence department in Arlington, Virginia, on the day that planes also hit New York and Shanksville, Pennsylvania. Donald Trump will mark the 25th anniversary of the United States’ worst terrorist attack in a ceremony at the Pentagon on Friday.

Klimow’s book recalls how leaders at all levels suppressed their emotional shock to respond with calm determination and grace under pressure. But it also tells how the attacks revealed a tension between military protocol and the need for improvisation, and how coordination was plagued by erroneous intelligence, overlapping chains of command and communication gaps – including a critical half-hour when Donald Rumsfeld, the US secretary of defense, was unreachable.

Born and raised in Johnson City, New York, Klimow’s career spans more than half a century of military and diplomatic service. He entered the military academy at West Point in 1970 and graduated in 1974, commencing a 29-year army career that took him from commanding paratroopers in the 18th Airborne Corps to earning the Silver Star for gallantry during the Gulf war.

On the morning of September 11, Klimow was executive assistant to Gen Richard Myers, vice-chair of the joint chiefs of staff. The chair, Gen Hugh Shelton, took off early for Hungary. The acting role fell to Myers, who would assume the position full-time on 1 October.

Klimow was in his office by 5.15am. Since Myers’ confirmation hearings before the US Senate were imminent, he left for Capitol Hill around 8.45am, taking along his young aide-de-camp, Capt Chris Donahue. Klimow remained at his desk, his eyes drifting to a television monitor kept on mute.

Suddenly, the screen filled with the horrific image of the World Trade Center’s north tower on fire. Speaking by phone from Monterey, Tennessee, Klimow, 74, says: “When I looked up, there was the newscast of the World Trade Center burning and I turned the volume up and I was just dumbfounded because it’s such a clear blue sky. I was in denial. I kept thinking it’s some freak accident, a small airplane maybe, and they were speculating the same thing on the newscast.”

The secure “red switch” telephone began to bleep. On the other end was Gen Ralph Eberhart, commander of North American Aerospace Defense Command (Norad). “That set off alarm bells with me as soon as I heard his voice, which I knew. He asked for General Myers. I said he’s on Capitol Hill. And he said, ‘Colonel, it’s urgent. Get hold of him. Get him to a phone. I need to talk to him now.’”

Klimow immediately called Donahue, and told him to barge into a senator’s office and retrieve Myers. The red switch rang again. This time Eberhart’s words were chilling: “We have several airplanes in the air on radar. An unknown number of them have been hijacked.”

As Klimow frantically took notes, his secretary waved wildly: Shelton was calling on an unsecure line. Klimow found himself with the secure red switch handset pressed to his left ear, and the unsecure telephone to Shelton in his right. He began a frantic double-relay, feeding the developments to the towering, impatient four-star general across the ocean.

Then, the ground shook. “All of a sudden, Mary Turner, our secretary, jumped up and said, ‘I think the building moved!’ Then there was absolute pandemonium outside our door. People were shouting, running down the corridor and I yelled, ‘Shut the door, Mary, I can’t hear!’”

Panic

In his deep focus, Klimow had not heard the thunderous impact of Flight 77 slamming into the western facade of the Pentagon. Finally, a National Military Command Center (NMCC) watch officer broke into the red switch conference: the Pentagon had been hit.

By chance the plane had smashed into a newly renovated wedge of the Pentagon, outfitted with state-of-the-art ballistic glass. This helped reduce the casualty count, but prevented the kinetic energy from escaping, channelling fireballs through the long corridors and hallways.

Klimow went to the river entrance to meet Myers, and the two men fought their way back up the stairs into the burning building. Two police officers tried to bar their entry. Myers and Klimow pushed past them and descended into the NMCC, a windowless cold war labyrinth.

Early reports via the red switch incorrectly stated that American Airlines Flight 11 – which had already struck the World Trade Center – was confirmed hijacked, and heading toward Washington.

A critical friction point existed between Norad and the air national guard. Norad scrambled jets from Langley air force base, but initially lacked the rules of engagement (ROE) to shoot down civilian aircraft. Meanwhile, the Secret Service prompted the launch of fighters from Andrews air force base, outside the normal military chain of command. Those aircraft were operating under a more permissive “weapons free” rule of engagement.

The Langley pilots initially flew east because an erroneous generic flight plan sent them that way, and they believed they were responding to the threat of a cruise missile attack from the sea. This lack of “situational awareness” delayed their arrival in Washington.

Klimow, meanwhile, experienced a sudden dread when he turned around and realised Myers was gone. As the executive assistant, Klimow’s sole purpose was to remain at the acting chair’s side.

“I panicked,” he confesses. “I tore out of there. I ran as fast as I could into the corridors of the Pentagon and I can’t tell you how eerie it was because there are 22,000 people who work in the Pentagon and the place was deserted, there was a film of smoke in the air and they didn’t turn off the fire alarm. There’s this blaring alarm with a recorded message to evacuate the building just echoing.

“I ran to our office. It was absolutely deserted and I stood in the centre of our office thinking, where did he go? It struck me, he’s with Secretary Rumsfeld, which is the office above us, so I ran up the staircase and darted into the outer office. Gen Myers was coming out of Rumsfeld’s inner office and he shook his head and said, he’s not here.”

Humiliation

When Flight 77 struck, Rumsfeld’s immediate instinct was to run toward the fire, helping carry stretchers and rescue survivors. Klimow regards it as an act of personal bravery that nevertheless created a serious operational problem.

“For 30 minutes, no one could get hold of the secretary of defense when our country is under attack,” Klimow says. “He eventually made his way into the NMCC and described the destruction outside and he was calm and cool, like everybody. But when he talked to Vice-President [Dick] Cheney, I knew something was amiss, and it took me weeks later to figure out what had happened.

“He was briefed by General Myers on Norad’s response and the rules of engagement, and the vice-president was talking to him about fighters coming out of Andrews air force base with different rules of engagement, but they were talking past each other. They didn’t realise they were talking about two different responses by the air force.”

Klimow’s wife, Edie, a retired army nurse and major whom he met in Germany, had spent the day racked with anxiety. Their son, Daniel, in middle school, had been told by teachers that the Pentagon was under attack. “He had this vision of terrorists running through the hallways with machine guns,” Klimow says.

It was after midnight when Klimow finally walked out of the smoking ruins of the Pentagon. Covered in grey soot and smelling of burning jet fuel, he drove home to Arlington, Virginia. The silence was broken by a sound he had never imagined hearing over the capital.

“It was the eeriest thing. It was the sound of American jet fighters overhead. When I realised that my own neighbourhood, my own capital city and my own country had to be protected by a combat air patrol, it was humiliating to think that we had been so surprised by such a devastating attack.

“The lights were off in the house and I thought Edie must be asleep, but I opened the door and she was there waiting for me. That’s when we had this big emotional embrace and knew that we would get up the next day and start working on a solution.”

Wisdom

The solution that Klimow and his colleagues began drafting on 12 September would eventually morph into the “war on terror”, a sprawling military campaign that would redefine the global order, not necessarily to the US’s advantage. Looking back from the vantage point of 2026, Klimow views those choices with sober realism.

“Everything looks different with hindsight but, that cliche aside, we had little choice but to enter Afghanistan militarily and to make sure that the launching pad for what al-Qaida used to do to us was eliminated from Afghanistan.

“Did we make wise decisions tactically or operationally? Sometimes yes, sometimes no, but strategically I don’t think in the days and weeks following 9/11 there was any doubt in most people’s mind that this required military action, not just diplomacy.”

Diplomacy became Klimow’s own second act during a five-year spell as the US ambassador to Turkmenistan. It gave him a close perspective on the end of the US’s longest war: the 2021 withdrawal from Afghanistan after 20 years and the return to power of the Taliban.

Amid the mayhem was a familiar face: Donahue, the captain whom he ordered to barge into a senator’s office on 9/11. Donahue rose to become a major general commanding the 82nd airborne division. On 30 August 2021, a night-vision photograph was beamed across the world, showing a solitary US soldier boarding the final C-17 transport plane out of Taliban-controlled Kabul airport. It was Donahue – the very last US soldier to leave Afghanistan.

“Talk about the irony of being there at the beginning and being there at the end,” Klimow muses.

The days and weeks after 9/11 were arguably the last time the United States was truly united. The Iraq war, financial crisis, social media, rise of Donald Trump and Covid-19 pandemic have divided and redivided the nation. But 25 years later, Klimow refuses to despair.

“There were seams that were ripping in our society in the 1960s, and I was witness to that. But we pulled things together,” he says. “It’s not the same situation, of course, but I have a firm belief that we go through cycles like this, and America’s principles, and our resilience, and our devotion to liberty and freedom are unshakable.

“I’m still a big believer in the American dream and what we can do together, and the belief that we will continue to pull together, in ways that may be different from some of our historic past, but our resilience and the brilliance of our nation’s founding still make that possible.”