Javier Altamirano remembers exactly where he was the morning of the 9/11 attacks.

The then 13-year old boy was home in New York City when he saw the smoke billowing from the World Trade Center towers. "It was surreal, I didn't believe that it was happening," Altamirano told NBC News.

Altamirano, now 28 and a U.S. Army Specialist, will soon deploy to Afghanistan —15 years after the 9/11 attacks and subsequent "War on Terror" began. America's longest ever war, one that will soon outlast a second sitting U.S. president, is arguably the most glaring legacy of the worst terrorist attack to ever strike American soil.

Andrew Card holds a unique place in the nation's post-9/11 history. At the time, Card served as President George W. Bush's chief of staff and was tasked with delivering the news of the attacks to the president as he sat before elementary school students in a Florida classroom.

With just 11 words, Card's message to the president was brief but consequential. The infamous photo of Card whispering the news of a second attack on the World Trade Center into President Bush's ear is one that would be forever etched into the memory of a healing nation.

"I thought about the words I would use," Card told NBC News. "And I leaned over and whispered in his ear: "A second plane hit the second tower. America is under attack."

Card accompanied the president and his team on a flight to Washington, with a first stop at Barksdale Air Force Base in Nebraska. When the cabinet finally arrived at the White House that evening, Card says the "fog of war was still real" as officials feared more attacks were coming.

"There was a high degree of concern," Card said.

The aftermath of the attacks was immediate. Bush, under pressure to reassure a grieving nation on edge, tapped Pennsylvania Gov. Tom Ridge to fundamentally re-imagine the nation's security. The result would be a re-alignment of the Coast Guard and the creation of two new government agencies: the Transportation Security Administration (TSA) and the Department of Homeland Security. Ridge would serve as the department's first director.

"I think 9/11 elevated the role and the responsibility of literally hundreds of thousands of Americans that go to work every single day in the federal government," Ridge told NBC News. "Their job prior to 9/11 was to keep you safe, but there was a new level of alert and a new level of commitment in a post-9/11 world."  

That new post-9/11 world would bring the ubiquitous long airport security lines, pat-downs to enter any large public place and a general sense of anxiety among a public constantly worried about the next potential attack. Americans were instructed to "say something" if they saw anything abnormal anywhere. The color-coded terror alert system was constantly in flux and became a feature of daily life.

Today, 15 years later, the nation is at a far different place. Osama bin Laden, the mastermind of the 9/11 attacks, is dead and al-Qaeda is a shell of its former self. There are raging privacy debates in the Congress and across the nation over how far the government should be allowed to curtail civil liberties in the name of national security. The deeply unpopular war in Afghanistan drags on with no end in sight before a public that polls show to be increasingly war-weary.

Still, the legacy of the September 11 attacks may not be fully known for decades. For millions of Americans, that fateful Autumn day changed everything.

"That day changed all of us," Card told NBC News. "It changed America. And it changed the world."