But for some of the soldiers here, 9/11 is half a lifetime ago.
Pvt. Parker Wattson still has a baby face at 20 years old, but he is a battle-hardened combat medic. He was getting ready for his sixth grade class in Vancouver, Wash., as the towers collapsed 3,000 miles away in New York City.
"I wasn't sure what was going to happen," he told me. "It was a little frightening at first. I was reassured by my parents that we'd be alright."
An even younger boy, Lee Williams, then only 10 years old, was a fifth grader running for his life in New York City on that day.
"The booms," he recalled, "me and my mom running down West Side Highway, running across Brooklyn Bridge."
Now, Pvt. Williams is 19 years old and proud to serve like so many others his age.
Pvt. Andrew Richards, also 19, remembers watching the towers fall.
"I was homeschooled, so I saw it on TV," he said.
Did he think he would be fighting in Afghanistan someday?
"Ever since then, I kind of wanted to," he said.
Capt. Alex Haig, grandson of the former U.S. Gen. Alexander Haig, was a college student in Washington on 9/11. He remembers watching the smoke rise from the Pentagon after American Airlines Flight 77 crashed into one side.
"When we come home sometimes, it's difficult because I don't think we're a country at war at all times, but all my friends are serving, so it's something I think about every day," he said. "It's very much a part of my reality and my friends' reality."
And there is another reality for older soldiers inspired to serve after 9/11. They have been in two wars now -- Iraq and Afghanistan -- and they have suffered so much loss it is difficult to comprehend.
"I personally know 10 that have been killed," said Sgt. 1st Class Marcus Jermaine Miller.
How can he live with it?
"I personally am numb to it," he said. "There are hundreds of soldiers I've tried to save. Some I could. Some I couldn't."
Losing Soldiers, Friends in Afghanistan: 'You Can't Dwell On It'
Asked how many soldiers he's known personally that have been lost that throughout his four deployments, Sgt. 1st Class John Howerton, 31, said, "Twelve on this deployment so far.
"You can't dwell on it, I guess," he said. "You got too much other stuff to think about."
Indeed, they do. 9/11 will always be a powerful memory, but on the battlefield, these soldiers have so much more to think about.
ABC News' Richard Coolidge contributed to this report.