On the afternoon of September 11, 2001, as the building still belched smoke in the wake of a passenger plane’s impact, Dr. Paul Mlaker was already at work, cataloging damage to the building to understand exactly what had happened in the attack.
“Every time another body was found, everything sort of paused,” Mlaker said, his voice breaking with emotion. “Out of respect.”
Mlaker, who retired in 2015 after a 40-year career with the U.S. Army Engineer Research and Development Center, or ERDC, spoke in a new documentary released by the center this month about the little-known reinforcement work that had gone into the Pentagon ahead of the attacks – work that the center contests saved thousands of lives.
At 9:37 a.m., after both towers of the World Trade Center in New York had already been hit, American Airlines Flight 77 crashed into the Pentagon’s western side. In the building, 125 military and civilian workers were killed and dozens more sustained injuries. In the mazes and corridors of the massive office building, the search for remains would continue for three weeks, and end with about one-third of those lost still unaccounted for.
But, horrific as it was, the casualty toll was mitigated by reinforcement work that had already begun on the building, which was built in 1941 and had marked its 60th anniversary that year. In light of troubling world events like the first World Trade Center bombing in 1993 and the Oklahoma City bombing in 1995, officials believed it was time to retrofit the building in a five-phase renovation effort that prioritized safety and stability over aesthetics.
“The retrofit didn’t envision what happened,” Mlaker said. “It was more for something like a truck bomb going off.”
Nonetheless, the work included features like blast-resistant windows, ballistic materials and wall reinforcements. And the first phase of work, involving “Wedge 1” of the Pentagon building, divided up like a five-sided pie, had just been completed days before the plane hit the building.
The morning of September 11, Mlaker said, he’d had a conference call scheduled with the American Society of Civil Engineers to develop a standard for blast-resistant design. But of course, the test was coming sooner than anyone had anticipated.
On the west side of the building, according to ERDC officials, the impact of the plane destroyed the first and second floors, but the remaining three floors remained standing for another 35 minutes, allowing hundreds of people the chance to evacuate.
A side-by-side photo of two Pentagon window offices tells the story of the difference the retrofits made. One office just 17 meters north of impact that had received the new ERDC reinforcement technology looks untouched, its curtains still neatly framing its windows. Another non-reinforced office, 90 meters north of impact, is totally destroyed, its windows blown out and walls and ceiling burned and shredded.
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Michael Sullivan, the acting director of the Pentagon’s renovation program, said at the time that the blast-resistant features “proved to be worth every penny” and had saved thousands of lives.
After 9/11, officials with ERDC said work began in earnest to prepare the building for a dangerous new world.
“Our researchers realized that we were entering a different time for warfare, weapons being used differently than they were designed for, strike tactics that would be different than we imagined, complex types of attacks, and as much as possible, catching us by surprise, sometimes in urban settings or in austere environments,” Bart Durst, who retired from ERDC in 2024, said in a podcast interview released by the center.
“So, the program leaders for each of these areas began to quickly respond as we got through the initial days by adapting the approaches in the existing programs to address what we felt would be the likelihood of what’s going to come, especially as America began to prepare for its response, we knew that our forces were going to be put in motion, and the operational scenarios were not totally clear to us at the time, but we knew that we had to develop techniques that could be used … So it was very challenging times. We immediately, passionately, were driven to go in and respond with [sic] adapting our programs.”
Since 9/11, officials said, ERDC has secured 21 patents focused on better protecting the force.
Feature Image: Aerial view of the Pentagon Building showing emergency crews responding to the destruction caused when a hijacked commercial jetliner crashed into the southwest corner of the building, during the 9/11 terrorists attacks. (Tech. Sgt Cedric H. Rudisill/U.S. Air Force)
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