Andrew Usas, 32, of Manhattan was in high school when the World Trade Center was attacked by terrorists. Now, 15 years later, Usas is building bikes for the children of military families who are fighting the war on terror.

More than 500 employees from companies that worked next to the World Trade Center volunteered to build 500 bicycles personalized with the names of the children who will receive them: Three hundred of them will go kids whose parents serve in the 2nd Battalion, 75th Ranger Regiment in Washington state and the 200 remaining bikes will be given to FDNY and NYPD families.

“It makes it personal and a lot more real,” said Usas, who along with co-workers at the Bank of New York Mellon and several NYPD officers with the community affairs unit assembled four bikes in 45 minutes Wednesday at the 69th Regiment Armory on Lexington Avenue.

Usas, who was in his social studies class in upstate Saratoga Springs on the morning of Sept. 11, 2001, said he remembers his family “lost family friends” that day. But it was not until he relocated to Manhattan after college in 2008 that he heard the personal stories.

“When I moved to New York, the stories were still fresh in people’s minds,” said Usas, whose office is at the former World Financial Center adjacent to where the towers once stood.

Steve Corry, 62, also an employee with BNY Mellon, said, “I always walk through the memorial [National September 11th Memorial Museum] during lunch and this just gives me an opportunity to do so something for somebody.”

Lee Ielpi of Great Neck, co-founder of the 9/11 Tribute Center, which organizes the event to recognize the National 9/11 Day of Service and Remembrance, said it is the mothers who get tearful when the children receive their new bicycle.

“The kids are laughing and happy. They can’t wait to see their bikes,” Ielpi said. When they run to their bikes, their moms are crying.”

The 9/11 Tribute Center was the first to offer tours of Ground Zero two years after the attacks. Tour guides are survivors, first responders, residents and people who worked in the neighborhood. “Thousands of people were coming to the site and there was no one here to tell them anything expect for the guys making up stories and selling books, which was quite distasteful,” said Ielpi, 72.

A retired firefighter, Ielpi lost his son, firefighter Jonathan Lee Ielpi of FDNY Squad 288, in the collapse. It’s in his memory that the mission of the Tribute Center is to keep the 9/11 story alive for future generations and create a spirit of giving and “how we can make the world better,” Ielpi said.