AMNA NAWAZ: Twenty years ago this month, U.S. Marines began fighting the largest urban battle since the Vietnam War.

More than 12,000 American, British, and Iraqi troops fought for Fallujah just west of Baghdad, which had become an insurgent stronghold.

Now, in collaboration with the news organization the War Horse, Nick Schifrin spent time with the Marines who still remember and feel that battle like it was yesterday.

NICK SCHIFRIN: Section 60 of Arlington National Cemetery is filled with men and women who never returned from Afghanistan and Iraq.

It is filled with sacrifice.

It is filled with memories.

Twenty years ago, Corporal Mike Ergo and the men of Alpha Company, 1st Battalion, 8th Marine Regiment, assaulted Fallujah.

Their mission, take the mayor's compound in the city center.

The fight was through narrow streets.

MAN: That was incoming.

Incoming!

NICK SCHIFRIN: It was deadly, and as seen in this BBC footage, dangerous.

MAN: I'm fine, man.

SGT.

MIKE ERGO (RET.

), U.S. Marines: I ran off first, and took a couple of steps and then immediately tripped and fell on my face.

And I looked to see what I'd fallen on, and it was a body of an insurgent.

NICK SCHIFRIN: Then-21-year-old Ergo and the team's mission was to clear the city of al-Qaida backed insurgents without overwhelming airpower.

So they went house to house.

SGT.

MIKE ERGO (RET.

): Originally, before we deployed, we were still concerned about winning the hearts and minds of the Iraqi people.

And so we obviously didn't want to destroy it to save it.

And as we walk through the city and were clearing it house to house, I had already developed the sense that I was expendable, just like my teammates were.

NICK SCHIFRIN: We spoke in the National Museum of the Marine Corps in Quantico, Virginia.

A new exhibit dedicated to the battle for Fallujah mimics its streets, down to the trash.

War can be imitated, but it cannot be recreated.

SGT.

MIKE ERGO (RET.

): I felt the whoosh of air going by me, of bullets creeping between my point man and I.

And I just assumed that was it.

The door opens and they toss a grenade out.

And we clear the area.

And I make sure everyone gets out, especially the guys on the stairs.

And as I turn around, the explosion happens, and I get a little shrapnel in my body, and most of its stopped by my armor, but a little piece of it gets into my neck.

LT. COL. AARON CUNNINGHAM (RET.

), U.S. Marines: At any given time, there may have been a half-dozen 360-degree firefights going on in our narrow sector.

NICK SCHIFRIN: Then-31-year-old Aaron Cunningham was Alpha Company's commander.

Fallujah was the largest battle that he or any of Alpha Company had ever fought.

LT. COL. AARON CUNNINGHAM (RET.

): Brutal, absolutely brutal.

It was a close fight.

Imagine turning a corner, and see how close you and I are?

That's how close.

And the toughest guy wins that fight.

NICK SCHIFRIN: And not everyone came home.

In six weeks of combat, the battalion lost at least 20 Marines.

Alpha Company lost three, including Lieutenant Dan Malcom, the company fire support team leader, shot in the back while briefing Cunningham.

LT. COL. AARON CUNNINGHAM (RET.

): Just a good -- a good man.

He was killed in the execution of this job, and he was doing it admirably.

That's one of the many pieces of my soul that got left in that city.

You can't leave an environment like that without some trauma.

I mean, it exists.

NICK SCHIFRIN: Fifteen days later, Lance Corporal David Houck from the 1st Battalion, 8th Marines died in Fallujah.

He was Ergo's friend.

For years, Ergo was too overwhelmed to visit his gravestone.

On this visit, he released 20 years of grief.

SGT.

MIKE ERGO (RET.

): You know, I asked my friend Robbie (ph), "Hey, where's Dave?"

because I just wanted to see him.

And he was like: "Didn't make it, man.

He got shot."

And I think it's just that surprise, just thinking I was out of it, thinking he was out of it, made it safe.

He didn't.

NICK SCHIFRIN: And you never got to say goodbye.

SGT.

MIKE ERGO (RET.

): Never got to say goodbye.

Never got to go to a funeral, I mean, never really got to tell him how much he meant to me as friend.

So, I did today.

NICK SCHIFRIN: And behind every Marine lost, there is a family, often themselves lost.

KATHLEEN FAIRCLOTH, Mother of Fallen U.S.

Soldier: Bradley was a rebel with a cause.

After 9/11, he was determined to go into the service.

And I was determined he was not.

And he won.

But he was part of something bigger than him, and I think that's what he really wanted.

NICK SCHIFRIN: Kathleen Faircloth is the mother of Alpha Company's Lance Corporal Bradley Faircloth, killed in Fallujah on Thanksgiving day.

His death sent his mother into despair.

KATHLEEN FAIRCLOTH: Bradley was my reason.

He was all the stuff that made me get up and function on a daily basis.

And so, once he was gone, it just completely deflated and waking up pissed me off.

And I tried repeatedly over and over to not wake up.

I'm like, God come on, give me a break.

There's lots of people dying.

I bet they like live living.

You can take me.

If you got a quota to fill, I'm raising my hand.

Get me out of here.

And the days just kept going, like, ugh.

You feel like such a failure that you cannot end your own life.

NICK SCHIFRIN: Since 9/11, American service members and veterans have been four times as likely to die by suicide than in combat.

War shadows its survivors long after guns go silent.

Ergo returned from Iraq in 2005.

SGT.

MIKE ERGO (RET.

): I would ride my motorcycle, blacked out, come in and out of consciousness as I was riding around and hoping someone would hit me, hoping I'd drive off the corner or drive -- took a turn too hard and be done with it.

NICK SCHIFRIN: And yet battle breeds brotherhood.

And two decades after Fallujah, Alpha Company held a reunion.

They are linked by loss, but also love that can help heal.

They call Kathleen Faircloth Squad Mama.

She calls them the family that saved her.

KATHLEEN FAIRCLOTH: I would die for them, willingly die for them, in a heartbeat, if it would help them.

I would lay down my life for them, because they will never know what they have done for me.

They will never know that they can't - - they sent me flowers the first Mother's Day.

Sometimes knowing that there's somebody on the other side of the America that might come and go, hey, mama, what are you doing, you know what I mean?

And I can't pay them back.

But I would die for them if it helped, willingly, in a heartbeat.

NICK SCHIFRIN: Mike Ergo healed at home.

SGT.

MIKE ERGO (RET.

): One day, my wife told me that she couldn't go down the path with me anymore in terms of how much I was drinking and using drugs.

She said I'd have to make a choice and either keep using or choose her.

And I stopped drinking and using drugs on July 11 of 2012.

NICK SCHIFRIN: Your wife saved you?

SGT.

MIKE ERGO (RET.

): My wife saved my life.

If she hadn't had the courage to tell me, demand that I stop, I would not be alive.

There's not a doubt in my mind.

I would be dead.

I'd be a statistic.

NICK SCHIFRIN: And now Ergo has transformed his pain into purpose.

Today, he directs a VA vet center to help veterans who suffered like him.

SGT.

MIKE ERGO (RET.

): I talk to men and women and help them understand that there is good stuff right below that hurt, and that if they have the courage to feel some more discomfort, it's almost like washing out an infected wound.

It's going to sting a little at first, but we're going to make the result even better and help them connect to their values, the things they love, the people they love and care about, the person that they want to be.

And so that became my new mission, my new why, is to help other people feel that hope again.

NICK SCHIFRIN: And that, he says, is the best way to honor those who never came home.

For the "PBS News Hour," I'm Nick Schifrin in Arlington, Virginia.