On a bright, terrorists turned commercial airliners into weapons of mass destruction. Thousands of lives were lost in an instant.
As people ran from the danger at the World Trade Center, first responders ran into it. Roughly half of New York City's fire units rushed to lower Manhattan to help, and 343 firefighters were killed.
Fifteen men from Engine 54, stationed about four miles north of the World Trade Center, were among those who died. Leonard Ragaglia was one of those 15 men from Engine 54. Now, his sons, Leonard Jr. and Anthony, are two of more than a dozen recent FDNY academy graduates who are children of fallen 9/11 heroes. They are weeks away from completing their probationary period.
Leonard now works in Engine 54, where the roll call from September 11, 2001 is still on the wall.
"Everybody passed away that day," Leonard told "CBS This Morning" co-host Tony Dokoupil.
Asked why the roll call is still on display at the firehouse, Leonard said, "like they always say, you know, you never forget. You always — you have that memory of how great those guys were."
Recalling that morning, Leonard said he remembers his grandmother picking him up from school. He was 10 years old at the time.
"We went home. And, they eventually had said, 'Your dad is missing. We're looking for him,'" he said. "Everyone's just sitting around, watching the TV, ... waiting by the phone, hoping for the best."
Leonard Ragaglia, Sr. was just 36 years old. Asked how their dad would have felt seeing his sons in FDNY uniforms, Leonard said, "I think he would have felt very proud of it."
"Extremely proud," Anthony said.
Their dad died "doing what he loved to do: help people," Leonard said.
"And that's the reason why I chose this job. And I have the honor and privilege of working in the same firehouse that he worked in, the same company. So it really means a lot to me."
Anthony said he always admired his dad and what he did.
"And then I think, as I matured and as the time went on, year after year, it became more and more of something I wanted to do," he said about becoming a firefighter.
Leonard remembers visiting his dad at the firehouse and said it still "looks the same."
"I even have the honor of working with a few guys that worked with my dad. They still work in this firehouse today," he said.
They share funny stories about his dad with him.
"They said, you know, he was the biggest guy in the house. So that when he would go work out in the gym, the next guy's workout would be taking all his weights off," Leonard said. "So, you know, even if we're cooking a meal in the kitchen, they'd be like, 'Oh, your father would have put two sticks of butter, not just one.'"
Anthony, who was 7 years old on 9/11, is now part of Engine 217 in Brooklyn.
"Even though I'm in a different borough, different house and stuff like that, just knowing that I do what he did, it really brings me a long way and helps me every day to do what I love to do," he said.
At the firehouse, calls can be heard coming in.
"Do you ever think that the next call could be a call like the one your father went to?" Dokoupil asked Leonard.
"You always have the chance of that happening, but just as he did, I'd be ready to go. And I'd feel honored doing it, knowing that that was what he was doing that day. So I'd feel honored," Leonard said.
Asked how he hopes America remembers 9/11, Leonard said, "I just hope that any of the memorials or stuff that they do every year never goes away."
"It's something that can't be pushed to the side," he said. "Everybody needs to know what happened that day. The tragedy and the guys that gave their lives need to be remembered."
"They always say, 'We will never forget,'" Anthony said. "And it should be something that is instilled years and years later, no matter how much time passes, because I think the event itself shows you the danger of … what they really go through every day and what can happen on any day."