The following is a script of "A Forgotten Corner of Hell" which aired on Nov. 23, 2014. Anderson Cooper is the correspondent. David Schneider and Joyce Gesundheit, producer.
More than 400,000 Americans died fighting in the Second World War. Adding to the heartache of that staggering loss, nearly one in five of those killed was declared missing in action. To this day, the families of some 73,000 unaccounted for servicemen have lived with the mystery of how they died and have been deprived of the comfort that comes from a burial. At the end of the war, the technology didn't exist to find and identify many of the missing, but today it does. This is the remarkable story of a group of volunteers who spend their own time and money quietly searching for these long lost servicemen -- remarkable because of what they've discovered in recent years. They are doing it, they say, for the fallen and their families. And focus on Palau, a Pacific island nation that saw some of the fiercest fighting of the war 70 years ago, a place some pilots called "a forgotten corner of hell."
Fly today over Palau's 586 small islands and miles of barrier reefs and you'll see no sign of the carnage that once occurred here. But beneath the jungle canopy you can still find the rusted ruins of Japanese anti-aircraft guns; and in the clear blue water, a graveyard of planes and the men who flew them. As the Second World War raged in the Pacific, the islands of Palau were teeming with Japanese soldiers and under attack by American planes. The skies overhead were filled with Hellcats, Corsairs, Avengers and B-24 Liberators. On September 1, 1944, this B-24, number 453, and its crew took off on a bombing mission.
[Announcer: A Liberator is hit!]
453, like the B-24 in this newsreel, was shot out of the sky and disappeared into the sea. It was one of more than 200 American planes lost over Palau during the war.
[Announcer: Our Pacific island warfare is not cheap.]
Dr. Pat Scannon: This was a tough place. This was no pushover. There was as much anti-aircraft fire available in this part of the Pacific as anything that was over Tokyo.
"It was one of those special moments in life where from one step to the next I knew I had to know what went on."
Today, Dr. Pat Scannon leads a group of volunteers that look for the wreckage of American warplanes and the missing airmen who flew them, including 453 and its crew of 11. They call themselves the BentProp Project. Many have military backgrounds. With permission from the Palaun government, they come every year, paying their own expenses, to search in the sea and on land.
[Dr. Pat Scannon: I think that's what took my breath away when I saw that star and bar.]
When Scannon's team finds the remains of Americans, they inform the U.S. military, whose job it is to recover and identify the missing airmen.
It all started when Scannon was vacationing in Palau 20 years ago and came across the wing of a B-24 with its propeller sticking out of the water at low tide. The bent prop gave the group its name.
Anderson Cooper: Did it surprise you that it was still there?
Dr. Pat Scannon: Oh absolutely.
Anderson Cooper: That moment you saw that, what did you think?
Dr. Pat Scannon: I think somebody died there.
The wing and engine of the B-24 Scannon found in 1993 are still here -- the propeller undisturbed in a few feet of water. Scannon says he hasn't been the same since he first found it.
Dr. Pat Scannon: It was one of those special moments in life where from one step to the next I knew I had to know what went on. It just was wrong to me that this wing is sitting here and nobody knows anything about it.
Finding the answers rarely comes easily or quickly. Scannon's team spent 10 years looking for 453 -- acting on hunches and old battlefield reports. But it wasn't until 2004 and a tip from a local fisherman that they finally found the wreckage.
Anderson Cooper: That's the tail section of the plane. It was about a mile away from where they'd been searching all those years.
Dr. Pat Scannon: A mile away underwater is -- you might as well be on the moon. We spent years doing grid searches in the area that we thought it was.
Anderson Cooper: Just methodically square by square underwater?
Dr. Pat Scannon: Square by square underwater. Because we knew it had to be here. A B-24 is a big thing. And you know, at least on the map, these waters don't look that big. So how hard could it be? At least that's what we thought. Well, it turns out it's hard.
We went to 453 to dive with Pat Scannon and his team, the site is now protected by the Palaun government.
Anderson Cooper: When you first enter the water, it's only a few seconds before you see the first signs of the plane. The plane impacted and as it hit the water and that's why it's now laying in sections. At first you might mistake it for coral, in fact coral has been growing over it. And over here you can see the propeller.
"There's a whole generation of people in my family that just did not speak of this because of the unknown."
Dr. Pat Scannon: At the end of the game, it's not about finding aluminum. It's not about finding wreck sites. It's about finding the MIAs who are no longer MIA.
The remains of eight crew members were found at this site and later recovered and identified by the U.S. military. One of the men was Jimmy Doyle, a 25-year-old Texan, who was 453's nose gunner. You can still see the turret where he was sitting when the plane crashed and where his remains were found. That diver, pausing in the spot, is Jimmy Doyle's grandson, Casey Doyle, an active duty Marine who now volunteers with the BentProp Project.
Casey Doyle: Just to know where the last few moments of his life were, is a very special time, and to see that down there, there's probably still a little physically, a little bit of him and the rest of the crew still down there, so it's an incredibly powerful and special place for me.
Until BentProp found the wreckage, Jimmie Doyle's family didn't talk much about him. Some family members actually believed he survived the war and started a new life.
Anderson Cooper: What did people say about your grandfather?
Casey Doyle: There's a whole generation of people in my family that just did not speak of this because of the unknown.
Dr. Pat Scannon: You can tell a family that their loved one is missing or that their loved ones were captured and were POWs. But I swear to goodness, I have talked to families who really believe that grandpa somehow made it out, was saved by the natives and had amnesia and was living on an island being taken care of by young native girls.
Anderson Cooper: And families really believe that?
Dr. Pat Scannon: I have heard it.
Anderson Cooper: Why would people think that?
Dr. Pat Scannon: I think it comes with the hope that someone missing may show up.
Jimmy Doyle finally returned home with seven of his crew members in 2010 -- 65 years after their plane was shot out of the sky. A memorial was held in Arlington National Cemetery, where some of the men were buried. Pat Scannon was invited to attend.
Anderson Cooper: What was that like to be at Arlington?
Dr. Pat Scannon: I was, I felt that my job on that plane was done. And I actually stepped back and watched the ceremony from a ways off. And it was extremely emotional.
Anderson Cooper: You're emotional just thinking about it?
Dr. Pat Scannon: Yeah. It's, I think about it a lot, actually.
Anderson Cooper: What's the emotion for you?
Dr. Pat Scannon: Happiness. That they know what happened.
"We could bring him home to family. And we can do a proper burial, we can honor them."
But not everyone from 453 has come home. Just after the plane was hit, three crew members parachuted out, including 22-year-old Art Schumacher. All three were quickly captured by the Japanese, and according to witnesses, taken to a camp in the jungle and executed.
The BentProp team is still looking for their remains, but searching on land is no easier than in the ocean. Pat Scannon has tried to pinpoint the location of the graves by traveling to Japan to interview former Japanese soldiers stationed in Palau. And he's tracked down Palauans who say they saw the men just before they were captured.
Dr. Pat Scannon: So you saw the parachutes?
Dr. Pat Scannon: Do you know how many?
Man: Well, I saw like three, I think.
One Palauan drew a map in the dirt showing where he believed the prisoners were executed. Using that information, the BentProp team has identified two spots in the jungle where they think as many as a dozen Americans were killed. We were with them when they started digging.
The red sticks are where buried pieces of metal were detected -- probably fragments of munitions, but perhaps a prisoner's button or zipper. The chance of finding Art Schumacher and the others on the first dig may be small, but Schumacher's niece Jo has flown here from Washington.
Anderson Cooper: What would it mean to find your uncle?
Jo: Well, gosh, we could bring him home. We could bring him home to family. And we can do a proper burial, we can honor them. And they gave their lives for the country.
Scannon's team has found debris from at least 30 American planes over the past 20 years. In addition to the eight airmen recovered from 453, BentProp's other discoveries could lead to the return of 16 more MIAs from Palau. But many planes crashed in far less accessible parts of the ocean and dense jungle and their crews never found.
Anderson Cooper: Do you know how many Americans are still missing here?
Dr. Pat Scannon: We think it's somewhere between 70, 80 American airmen crashed in this area. The real question is how many crashed inside the barrier reef. Inside the barrier reef means we can possibly find them.
Anderson Cooper: Why? Because outside...
Dr. Pat Scannon: It's 2,000 feet deep.
In 2005, Scannon's team found this wing of a TBM Avenger in the jungle. They believe the rest of the plane is in the water nearby and they've been searching for it the past nine years.
"It was very emotional. And when you put your finger on the plane, it's real."
Dr. Pat Scannon: We've never been able to find the fuselage, so somewhere out here there's a fuselage with, possibly, with two MIAs on it.
To find the Avenger, BentProp has now been joined by a team from the Scripps Institution of Oceanography and the University of Delaware. They bring high technology to the hunt. This research torpedo, called REMUS, can scan large areas of ocean with sonar. Eric Terrill leads the effort.
Eric Terrill: We ran the REMUS a few hours off of the mangroves here and found a couple of targets. Drop down. Get some visuals on the targets.
Dr. Pat Scannon: If there's a place it ought to be, it's right here.
Terrill leads the way with a handheld sonar device and is the first to come across debris, including part of the plane's tail. When the sonar shows signs of something ahead, he turns around to get Pat Scannon.
Dr. Pat Scannon: He comes swimming up to me, grabs my hand and practically yanks my arm off. And so I figured he probably knows something. And this gray hulk becomes an airplane. And there's a big propeller right there. You get misty, I got misty underwater. You know, "Maybe this isn't such a good thing to do underwater, you know?" But, you know, I couldn't help it. It was very emotional. And when you put your finger on the plane, it's real. And that's what we did.
Anderson Cooper: You touch it?
Dr. Pat Scannon: You touch it. And...
Anderson Cooper: Why?
Dr. Pat Scannon: I don't know. Science is about facts. I mean, my eyes saw it, you know? I mean, so fact was it was there. But touching it, you know, just gave it a sense of finality. We all knew what this was. And what it meant.
Anderson Cooper: There are Americans down there?
Dr. Pat Scannon: There are Americans down there. The families don't even know yet. And it's not that I'm wanting to keep a secret, but we also, until the remains are properly identified, we don't want to hold out false hope.
To get proper identification, BentProp notifies the U.S. military of the discovery, but the actual recovery and identification of remains by the military can take years.
Dr. Pat Scannon: This plane was shot down over this area the 4th of May, 1945.
Every time BentProp finds wreckage of a plane with missing airmen, they hold a small ceremony. They videotape it so that, one day, the families of the MIAs will know the respect shown to them by Scannon and his team, who spent their own time and money to find them.
Over the Avenger crash site this year, BentProp unfurls an American and a Palauan flag and speak of the men who were lost. They say their names, their ages, what they've learned of their lives. And at the end of every ceremony, Pat Scannon recites a poem written during World War I. It's called "For the Fallen."
Anderson Cooper: Would you read it to me?
Dr. Pat Scannon: Sure, I'll read it to you. I can't read it without standing up. Can I stand up?
Anderson Cooper: Of course.
Dr. Pat Scannon: So, "They shall not grow old, as we that are left grow old: / Age shall not weary them, nor the years condemn. / At the going down of the sun and in the morning / We will remember them."