On the morning of Sept. 11, 2001, millions of Americans awoke to scenes of horror as terrorists launched the worst terrorist attack in our country’s history.

From apartment windows and office buildings in New York and beyond, they heard the planes and saw smoke clouding the morning sky. The fear they felt quickly spread to Washington and Shanksville, Pa. Across the country and around the world, an estimated two billion people watched the shocking events of that day unfold, witnessing a series of assaults that would reshape our nation.

Amidst the grief and uncertainty that took hold in the aftermath of the attacks, hundreds of thousands of Americans stepped forward to serve. For them, 9/11 was not only a national tragedy. It was a call to rise in support of their country and their communities at the moment when that service and patriotism was most needed.

In the 12 months after 9/11, more Americans enlisted in the Armed Forces than in any year since. During the first full recruitment year after the attacks, more than a quarter of a million people signed up. As the country mourned the 2,977 victims killed on 9/11 and struggled to imagine what might lay ahead, these brave volunteers accepted the risks of military service to protect the United States and its ideals.

Many were deployed into combat zones, leaving behind families and setting aside future plans. Some returned home with lasting wounds, seen and unseen, while thousands did not return, having made the ultimate sacrifice. Their sacrifice impacted not only their brothers and sisters in uniform, but also their families and communities here at home, which were forever changed by their loss.

As the president and CEO of the 9/11 Memorial & Museum, I’ve seen firsthand the impact that the Global War on Terror has had on our community. Having served seven years in the U.S. Air Force, I also know that for many, the impacts of military service are profound and lasting, shaping the wellbeing of veterans and that of those closest to them long after their service ends. Thirty years after I left the Air Force as a captain, I’m still inspired by the high standards of integrity and performance set by the officers and enlisted service members who taught me how to lead.

The legacy of the veterans who have returned home, the service members we’ve lost in the years since, and the loved ones who continue to grieve remind us that 9/11 was never an isolated moment in time. The ripple effects of the attacks are still felt today, touching thousands of veterans and military families who visit the 9/11 Memorial & Museum each year, and millions more in our communities.

Twenty-five years later, our gratitude to those who served in the aftermath of one of our nation’s darkest days remains as important as ever. That is why we proudly welcome active duty service members and veterans to the 9/11 Memorial Museum for free year-round and are privileged to host military enlistment and re-enlistment ceremonies on this sacred site. This Veterans Day and every day, we must honor the heroism our troops demonstrated immediately after the attacks while recognizing the lasting impacts of that service.

As we commemorate the legacy of 9/11 on the military community, we also know that the importance of remembrance becomes more urgent. 100 million Americans have come of age with no personal memory of the attacks. Our promise to “never forget” means not only preserving the memory of those who perished on 9/11, but also that of the military veterans and others whose selflessness helped our nation find strength and hope after tragedy and loss. That is why we’re expanding our reach and deepening our commitment to education about the history of 9/11 and its aftermath.

Hillman is the president & CEO of the 9/11 Memorial & Museum.