NARRATOR: In Thailand... (lightning crackles) A flooded cave... 12 young boys and their soccer coach trapped somewhere inside.

With monsoon season just beginning, and water levels rising, time is running out.

(clock ticking) ♪ ♪ JOSHUA MORRIS: They were moving so much water out of there.

The problem was, it's like turning the faucet on and trying to siphon water out at the same time.

NARRATOR: As an international team of elite divers searches miles of submerged passages, the whole world watches in suspense and wonders... REPORTER: In Thailand, there is a very concerning situation.

NARRATOR: "Can the boys still be alive?"

We came back to some pretty horrifying news.

NARRATOR: But then... MAN: How many of you?

MAN 2: They're all alive.

MAN 1: 13, brilliant.

NARRATOR: Now an impossible decision looms.

How to bring 12 children out...

The only option we had was to go with the diving option.

NARRATOR: ...through some of the most dangerous diving conditions in the world?

KEN O'BRIEN: Even the professional cave divers said, "This is some of the sketchiest diving we've ever done."

ERIK BROWN: You couldn't see your finger in front of your face until you touched your mask.

NARRATOR: A desperate mission begins.

IVAN KARADZIC: Panic usually leads to instant death.

♪ ♪ NARRATOR: "Thai Cave Rescue," right now, on "NOVA."

♪ ♪ Major funding for "NOVA" is provided by the following: ♪ ♪ NARRATOR: It was a nightmare that gripped the world.

A stunning display of courage and technical prowess in the face of life-threatening danger.

The miraculous rescue of these 12 young boys and their soccer coach from one of the deadliest environments on Earth-- a flooded cave.

♪ ♪ The Tham Luang cave in northern Thailand.

MAN: Well, this is it, Tham Luang.

NARRATOR: It's a popular destination for day-trippers and adventurous locals.

(camera shutter clicks) In the dry season, explorers plumb its twisting depths.

The cave is located within the Doi Nang Non mountains.

It winds for an incredible six miles, a limestone labyrinth of tight passageways and expansive chambers.

Saturday, June 23, 2018.

12 young soccer players and their coach venture inside the cave, a trip to celebrate a boy's birthday.

(thunder rumbling) But soon after, the skies open up, and a powerful monsoon storm strikes.

(lightning crackling, thunder rumbling) ♪ ♪ In Mae Sai, where the boys live, a rainy night has descended.

Beginning to worry, parents start calling around and gradually learn the boys have gone to the cave.

When they travel there, they are met by an alarming scene.

Bicycles locked to a fence, along with abandoned soccer cleats.

Worse, water is rushing into the cave, with no sign of the boys.

Officials are on the scene, and, realizing the boys may be in mortal danger, some parents enter the cave.

Among those desperate to find them is Mr. Bandit Phanphalakorn, a close friend of one of the boy's fathers.

(speaking Thai) (translated): I went in a short distance, but didn't dare go any further.

But one of the boy's fathers continued with the rescue team.

He went on for about an hour and a half, but started to have breathing difficulties, so had to return.

NARRATOR: It's now 1:00 a.m., and the boys have been missing for half the night.

But where are they?

What's happened to them?

Fearing the worst, local governor Narongsak Osottanakorn makes a tough call.

(speaking Thai) (translated): From that Saturday night until Sunday, we realized we couldn't do anything much about the situation.

So we decided to stop the operation, to rest and collect new crew and equipment.

(thunder clapping, rain cascading) NARRATOR: If the boys are somehow still alive, deeper in the cave, they'll have to spend the rest of the night on their own.

But as heavy rain continues, can anyone really rest as water levels continue to rise, and not just at the entrance?

The intensified rainwater is pouring into a deep, underground stream north of the cave, causing water to flow furiously down the northern passage, trapping the boys somewhere within the subterranean maze.

To make matters worse, water is also entering from the south, while the groundwater below is thought to be rising, flooding the cave in many low-lying areas.

(translated): I was very worried.

I didn't eat, didn't sleep much, either.

I slept two to three hours, because I was thinking, because everyone was thinking as if your own son was missing.

♪ ♪ NARRATOR: The next morning, officials confront a daunting question: If the boys spent a terrifying night in a dry part of the cave, how can they be reached?

From the entrance, it's impossible to tell how badly flooded the rest of the cave is.

(talking in background) To aid the search, professional cavers arrive.

You see where, you see where it comes down like this.

NARRATOR: Among them is the first foreign rescuer, British caver Vern Unsworth.

If we can get up there... Mm-hmm.

we can virtually get to the GPS point and then do a search.

NARRATOR: Having spent years exploring the Tham Luang cave system, Vern's knowledge of its layout is vital to the search mission.

Up on the mountain, he leads a team hunting for alternative access points into the cave.

(people talking on radio) Another caver to arrive is Noppadon Uppakham.

This is one of the most challenging rescues he's attempted in a flooded cave.

(Noppadon speaking Thai) (translated): The rain was quite a major obstacle, because if the rainfall increased, we didn't know how much water would enter the cave, which could be dangerous for anyone searching inside.

♪ ♪ NARRATOR: Cavers quickly discover that in some places, water is up to their necks.

And farther along, it has risen all the way to the ceiling.

It's now obvious that if the boys are going to be found alive, qualified scuba divers with cave experience are required.

But how quickly can they be brought to the scene?

♪ ♪ The governor calls in Thailand's most formidable fighting force, the Thai Navy SEALs.

Like American Navy SEALs, they're an elite branch of the navy that takes on the most dangerous missions.

With them is Dr. Pak Loharachun, a highly trained diver and experienced doctor of the Royal Thai Army.

(speaking Thai) (translated): I had worries because we didn't know the conditions inside the cave, and crucially, we didn't know exactly where the kids were.

At that moment, the rescue was at a critical stage, as the water was torrential.

♪ ♪ NARRATOR: The rescuers need to make a guess about where the boys are.

(camera shutter clicking) Luckily, there are some maps of the cave, produced in the 1980s by French cavers.

No one knows how accurate they are, but from what can be pieced together, the interior looks like this.

The cave system is thought to be about six miles long.

A daunting distance, but such a long cave offers the hope that there are plenty of places dry enough for the boys to retreat to and flee the rising water.

One section, called Pattaya Beach, looks particularly promising, as its elevation suggests it may have stayed dry during the flooding.

But Pattaya Beach is about one-and-a-quarter miles from the flooded cave entrance.

That might mean swimming a vast distance underwater in tight spaces and pitch-black, murky conditions.

(translated): The SEALs team started work immediately when we were first told to look for the kids.

Each day, we tried to go as far as possible inside the cave.

♪ ♪ NARRATOR: As is normal protocol, the SEALs lay a guideline so they can find their way out again.

In zero visibility, a guideline is a lifeline.

The SEALS brace themselves in preparation for what they might find.

They push as far as they dare, but their air supply is too limited.

Thankfully, they find no bodies.

But that means the boys must be even deeper inside.

♪ ♪ Meanwhile, the water continues to rise.

♪ ♪ Rescuers try to stabilize levels by draining as much as possible using heavy-duty pumping equipment.

♪ ♪ But despite the rescue efforts, water levels inside the cave aren't decreasing.

And rescuers worry that Pattaya Beach may already be flooded.

♪ ♪ But they know the cave continues for a long way beyond that point.

So they can only hope the boys were able to move even farther into the cave.

But now, after more than 72 hours, the boys would be facing other serious problems.

Any food they had with them would likely have been eaten or ruined.

And despite the flooding, there may not be water that's safe to drink.

(speaking Thai) (translated): Humans can survive for three to four days without water, if they are not sweating.

But without water, the system inside the body breaks down, the kidneys stop working, and so on.

Eventually, we cannot survive.

NARRATOR: Day four.

(talking in background) The whole world is now following the story.

REPORTER: In Thailand, there is a very concerning situation.

Hundreds of searchers on the ground desperately look for 12 young Thai soccer players and their coach missing now since Saturday.

NARRATOR: The search has now become an international effort, as rescuers arrive from across the globe.

A makeshift rescue headquarters is set up outside the cave.

And up on the mountain, hundreds of volunteers continue the search for an alternative way into the cave-- still hoping they can reach the boys through another opening.

(radio squawking) (translated): The cave is limestone, full of cracks and holes, so we would walk the area in the hope of finding any possible sinkholes to be able to climb down inside the cave.

NARRATOR: But finding an alternative entrance, much less one that connects to the boys, is like trying to find a needle in a haystack-- with no guarantee it's even there to find.

For parents and the local community, the ordeal continues.

(translated): We were stressed, and couldn't sleep for worrying.

Everybody started to wear down, because we were sleeping so little and not getting enough rest.

We were just waiting to hear the news, waiting at the cave entrance to hear from whoever came out.

NARRATOR: Inside the cave, rescue teams face brutal conditions.

(water burbling) And as seasoned as they are as military divers, the Thai SEALs are not trained for cave diving.

They are learning as they go, making the search all the more dangerous and psychologically challenging.

It's time to call for specialists.

♪ ♪ Arriving on day five are Rick Stanton and John Volanthen-- members of the British Cave Rescue Council and two of the world's most experienced rescue divers.

John and Rick immediately don their scuba gear and plunge into the cave to assess the challenge.

(water burbling, breathing through air hose) Soon, Erik Brown and Ivan Karadzic join them.

Cave divers with this level of experience are a rare breed.

KARADZIC: How many cave divers there are globally?

There is probably, at this level, I think maybe less than a hundred.

NARRATOR: They bring specialized equipment and are provided with vast quantities of compressed air.

KARADZIC: As a cave diver, we always plan for the worst-case scenario, so we will come out of the cave with a minimum, with a minimum of a third of the gas supply still intact, in case something happens.

♪ ♪ NARRATOR: The search effort is proving enormously complicated.

So the Thai government reaches out to the U.S. military.

The Air Force's Pararescue troops respond-- elite airmen, trained to perform rescue operations in any environment imaginable.

Major Charles Hodges is their commander.

HODGES: When we landed in Chiang Rai, it was about 1:00 in the morning, on the 28th of June, early Thursday morning, and we went straight to the mouth of the cave.

And we realized, "This is a different environment than what we are used to.

We really need to be smart in how we, we handle this."

NARRATOR: Inside the cave, everyone fears the boys are now in danger of starving, even more so because they're young and slim, with few fat reserves.

And they must be burning energy just to stay warm.

(Pak speaking Thai) (translated): Normally, we can survive without food for seven to ten days.

I mean, if the body is active.

But if we lie still, we can normally survive without food for about two to three weeks, or even four.

♪ ♪ NARRATOR: Time is of the essence, and it becomes clear that pumping at the mouth of the cave alone isn't going to be enough to lower water levels.

♪ ♪ Groundwater engineer Thanet Natisri comes up with a new approach.

♪ ♪ He wants to divert water away from the myriad of sinkholes on top of the mountain to stop it running down into the cave and flooding it further.

NATISRI: They called me to see if I can come in and analyze the problem we have, and see if I can manage water inside the cave better.

I know right away that this project is not easy.

♪ ♪ NARRATOR: Josh Morris, a Thai-speaking American who has been translating and coordinating between the international dive teams and the Thai authorities, is also worried about conditions inside the cave.

MORRIS: They were moving so much water out of there.

But the problem was, it's like turning the faucet on and trying to siphon water out at the same time.

There's only so much you can do.

NARRATOR: Thanet and Josh join forces to battle the water.

♪ ♪ With a huge team of volunteers and military personnel, they head for the mountain.

Here we are.

MORRIS: Heading out to divert water out of the cave, to try and help these boys get the water level down.

(men speaking Thai) NARRATOR: Thanet instructs the team to find openings that could be channeling water into the cave.

♪ ♪ Using makeshift dams, plastic pipes, and bamboo, they begin to divert water away from sinkholes and down the mountain.

Over the next day, their efforts begin to pay off.

Amazingly, even though it's still heavily raining, water levels inside the cave finally stabilize... and start to drop.

It's the rescue mission's first real breakthrough.

Day seven: It's been a week since the boys went missing.

If by some miracle they are still alive, they are trapped somewhere dark and wet, with no food or clean water.

No one on the outside can fully comprehend what the boys must be feeling, and rescuers are concerned for their mental well-being.

So, too, is leading trauma expert Dr. Jennifer Wild of Oxford University.

She's monitoring the rescue intently, and is on hand to shed light on how the boys might be coping.

WILD: They would have been having thoughts about whether or not they would stay there, whether they would survive, whether they'd get out and see their family again, whether they would die.

And I think that would have been quite a frightening time for them.

NARRATOR: Dr. Wild thinks the boys' youth might be an advantage, protecting them from panic.

WILD: When we're younger, there is a tendency to be a bit more concrete in our style of thinking, which is actually protective.

So when we're faced with a problem, we focus very much on the here and now.

♪ ♪ NARRATOR: At the cave, another glimmer of good news.

By pumping water out and diverting it away from sinkholes, rescuers have now succeeded in partially draining the first half-mile of the cave, so the opening section is more or less walkable.

Rescue efforts intensify.

Hundreds of air tanks and supplies are brought almost a mile in, to a staging point they name chamber three.

Divers prepare for what might be their final push.

KARADZIC: They'd been in there for about nine days, and without food, potentially without water, so we didn't know their, their situation, so I was not sure in what condition we would find them in.

♪ ♪ NARRATOR: After ten days, and with thousands of people now involved in the search, we still don't know if the boys and their coach are alive.

Once more, divers deploy into the darkness.

KARADZIC: From the outside, it looked like an ants' nest.

There was people everywhere, movement everywhere, and it looked like it was chaotic.

There were soldiers, there were civilians, doctors, divers, engineers, hoses, lots of equipment, and lots of media out there.

But then, as we got introduced to the different teams, we started to see that this is not chaotic.

There is actually a master plan behind all that.

♪ ♪ NARRATOR: Soon after arrival, Ivan and Erik discover just how brutal conditions in the cave are.

BROWN: For me, this isn't the type of conditions that you would ever dive in.

If there wasn't an end goal, then in this situation, you'd definitely say, "I'm not going in there."

You couldn't see your finger in front of your face until you touched your mask.

You couldn't see a rock until you kind of smacked your head on it.

It had parts where you had to come semi-vertical on your side to squeeze through.

I mean, you would take a, take a breath in and squeeze your way through some of the, some of the tighter passages.

♪ ♪ NARRATOR: Leading the diving are the two British divers, Rick Stanton and John Volanthen.

After hours of swimming through the most perilous part of the cave, with zero visibility, they finally reach Pattaya Beach, the point where hopes were high that the boys would be found.

But when they surface, and shine their lights into the dank darkness, their hearts sink.

There's no one here, and now they only have enough air to go a little farther.

It seems hopeless, but they're so determined to find some sign of the boys, they run their tanks as dry as they dare.

Eventually, they find an air pocket and surface for the last time.

And when they shine their light into the darkness this time, they finally make the discovery everyone was hoping for.

MAN: How many of you?

MAN 2: They're all alive!

MAN 1: 13?

Yeah, 13.

Brilliant!

(kids chattering) NARRATOR: The divers are nearly 1,000 feet beyond Pattaya Beach.

It's here that the 12 tired, frightened boys and their coach have been seeking refuge.

The boys come down the slope to meet the two divers.

MAN 1: We are coming, it's okay.

MAN 2: It's okay.

MAN 1: Many people are coming.

NARRATOR: 13 people all found alive after a tense and desperate ten days of searching.

When the divers return with the happy news, the boys' families are elated.

(cheering) Their kids have been found alive.

(translated): The moment we heard the divers had found the boys and they were safe, right then, we felt very happy.

We hugged, we fell on each other hugging.

(speaking Thai) NARRATOR: The good news spreads around the globe.

Enormous relief in Thailand, as rescue teams found that youth soccer team-- look at that-- alive in a cave.

NARRATOR: Any thought that the divers would be facing a "recovery task" instead of a rescue are thankfully relieved.

But finding the boys was the easy part, compared to the challenge they now confront: mounting a rescue.

BROWN: The kids are found, so you had this surreal moment of happiness, and then, you know, that sort of calms down a little bit, and then, I think, the realization of what's going to have to happen next sinks in.

You're like, "All right, they found them, but now what are we going to do?"

(man speaking Thai) (translated): The mission of how to get them out is harder than how to find them.

Getting them out is not so easy.

♪ ♪ NARRATOR: As soon as the boys are found, Dr. Pak of the Royal Thai Army, a skilled diver, makes the dangerous journey to their location.

He urgently needs to assess them medically.

(Pak speaking Thai) (translated): First, I felt happy.

Then I thought, "What do I have to do next "to take care of their physical and mental health so they are ready for us to bring them out of the cave?"

I felt so relieved that all the kids could communicate well and could move and stand up.

I assessed them and concluded that there were no health complications, no infections, no symptoms that worried me, and that made me feel very good.

NARRATOR: Ten days into their ordeal, the boys and their coach are famished.

Dr. Pak provides them with some much-needed sustenance, tailored toward their calorie-deprived state.

He also notices the boys' feet and hands still bear signs of their rush to escape the rising waters.

(translated): When the kids tried to escape the flood, they had walked barefoot, and so there were some cuts on their feet.

All I had with me was an antiseptic.

The way we dressed the wounds wasn't medically correct, because we only had limited supplies, so we did what we could.

NARRATOR: As well as taking care of the boys' immediate needs, Dr. Pak reveals he will stay with them.

Before the boys were found, their coach, a former Buddhist monk, had come up with a resourceful way to help them overcome their fear.

He taught the boys to meditate.

WILD: Meditation is really useful, because it's all about detaching from thoughts, just recognizing that they're thoughts, and, um, slowing your breathing.

And from that perspective, it was really helpful.

NARRATOR: Shortly after learning the children are alive, the parents make a special gesture.

They choose to focus on the gratitude they feel toward the coach for caring for their children through such an unimaginable ordeal.

They write letters for the divers to deliver to Coach Ake, a touching and generous act of support.

WILD: I think here in the West it would have been absolutely normal for the parents to be furious, but the parents responded in such a gracious way, writing letters to the coach, would have helped him not blame himself.

♪ ♪ NARRATOR: Above ground, pressure mounts on the authorities to reveal their rescue plan.

Will they leave the boys in the cave for what could be several months, until the monsoon rains end and the water recedes?

Earlier in the mission, anticipating that the boys might not be able to wait it out in the cave, rescuers try to get them out sooner by flying a drill up onto the mountain, to open a shaft down to the boys from above.

It's a long shot, but if it pays off, it could shorten the boys' stay.

But there's a problem.

Creating an escape route would take the best part of a month at least.

So even if drilling succeeds, it's unlikely to be fast enough to save the boys from drowning, should the cave flood further, leaving just one option: a highly risky dive rescue.

For U.S. Airman Sergeant Ken O'Brien, the idea of swimming the boys to safety is riddled with danger.

O'BRIEN: Originally, we thought it could be a good idea, but then we realized none of them know how to scuba dive.

I mean, that, that was clear, they're children.

And this is the most dangerous diving in the world.

And even with the professional cave divers, they said this is some of the sketchiest diving they've ever done.

NARRATOR: And now there's a new problem.

Oxygen is the most important commodity for both the rescuers and the boys.

At sea level, oxygen concentration is 21% in the atmosphere.

But the prolonged presence of the boys, combined with the arrival of the rescuers, is using up the available oxygen in the cave faster than fresh air can seep in from outside.

MORRIS: Oxygen levels in caves can potentially shift if they get blocked off from the surface.

And the more oxygen you breathe in, the more CO2 you breathe out, so obviously you're contributing to the problem.

NARRATOR: Oxygen levels are edging into a danger zone.

KARADZIC: The oxygen levels was tested by the U.K. divers that went all the way into the kids there.

We have specialized equipment that allows us to check how much oxygen is in the air.

So the reading of 15% is, is okay, you can survive that, but we knew it's not going to stay at 15.

It's going to, every day, it's going to go down a little bit, and when you get to about 12%, ten percent, you can't survive that anymore.

♪ ♪ O'BRIEN: In our chamber, in chamber three, breathing rate was a little higher.

For the amount of work you're doing, you were a little more tired than usual.

NARRATOR: The fear is lower oxygen levels might cause the boys to feel sick.

And without a fresh supply of air, the problem will only get worse.

(shouting, equipment moving) Lack of oxygen is also a problem for the rescue divers.

The solution is to constantly ferry hundreds of oxygen tanks into the cave-- a time-consuming and exhausting job.

And it turns out... also a deadly one.

At 1:00 a.m. on Friday, day 14 of the rescue, volunteer rescue diver Petty Officer Saman Gunan is returning from an overnight mission delivering oxygen tanks.

(water burbling, breathing through hose) Saman is an experienced diver and former Thai Navy SEAL.

No one knows exactly what happened, but tragically, while swimming back to base camp, Saman becomes unconscious and stops breathing.

His dive partner swims his limp body out.

But by the time Saman is pulled from the water, it's too late.

He's died.

♪ ♪ The rescuers are shaken.

The flooded cave has claimed its first victim.

We came back to some pretty horrifying news on that day.

Morale definitely took a hit.

The last thing you want in any rescue situation is to... for something like this to happen.

KARADZIC: When you lose a team member in any situation, you get sad.

But on top of that Saman was not just any diver, he was a former Thai Navy SEAL, so he has a skill set that is very high, and that made you think a little bit that if a person like, like Saman can, can get into trouble and lose his life in there, maybe the same thing could happen again.

♪ ♪ (speaking Thai) (translated): Everyone was upset.

But it also made many people from the SEALs team more determined to gather together and help.

MICHAEL GALINDO: It was kind of shocking, like, "Hey, I was just talking to this guy, "you know, what a hero to come out of retirement "and to put himself in harm's way.

A lot of respect for him."

But it made it that much more real being inside that cave.

♪ ♪ NARRATOR: Saman's death is a stark reminder of the dangers still ahead.

Understandably, many rescuers are now even more worried about diving the boys out.

(speaking Thai) (translated): I thought of the kids' safety straight away, because every diver knows it's dangerous.

Honestly, I was worried whether the kids would be safe if we did it this way.

♪ ♪ NARRATOR: The boys' weakness, youth, and lack of experience suggest they might not make it out alive.

Officials are still considering a plan that would wait to bring the boys out until the monsoon rains have stopped.

But that could mean up to four months' additional delay, which could also prove deadly.

(man speaking Thai) (translated): At the same time, another storm was expected on Tuesday or Wednesday.

If we did nothing, and the water filled the cave again, they might have no dry place to stay.

Who would want to take the responsibility for that?

(thunder rumbling) NARRATOR: To help anticipate the likely rainfall, the Thai military and the governor are receiving high-resolution forecasting from Weather Decision Technologies in Norman, Oklahoma.

Meteorologists here are warning that the monsoon winds, bringing widespread rain to northern Thailand, are about to intensify.

The initial looks we did at the monthly forecast going forward showed that the threat for heavy rain was going to be increasing week after week after week as we move farther into the summer monsoon.

So the reality of it was more rain was on the way, and the threat was going to get substantially worse the longer they waited.

(air rushing through hose) NARRATOR: This dire warning of intensifying rain tips the scales and forces the authorities' hand.

They decide waiting will only increase the peril.

O'BRIEN: The odds of those children and the coach being alive even another week, let alone months, was very low.

NARRATOR: 15 days after the boys first went into the cave, the Interior Minister signs off on a risky rescue plan.

And the following morning Governor Osottanakorn makes an announcement to the press.

(Osottanakorn speaking Thai) (translated): There's no better day than today.

We are ready.

This is D-Day.

NARRATOR: The world, and the boys' parents, hold their breath.

The Thai authorities have decided that 13 people who have never worn scuba gear before must attempt a treacherous cave dive that has already defeated one highly experienced diver.

There was no other choice.

Not even something else-- I honestly believe there's...

When you sort of go through all the options that sort of got put on the table, you sort of kind of scratch them off.

There's really only one left.

We just knew the only option we had, even though it was not a great option, was to go with the diving option.

KARADZIC: The guys behind the plan, both the divers and the medics and the engineers-- they know what they're talking about.

It's not just something they came up with after five minutes' debate.

They'd been sitting for hours and hours and hours and used their experience to make sure that our mission and our planning was making it as safe as possible for the kids.

"We are going to get the kids out, but it's not going to be easy."

♪ ♪ NARRATOR: How can the divers protect these inexperienced boys from all of the dangers they will face?

Divers from the British Cave Rescue Council, who will be at the vanguard of the rescue operation, rehearse their mission in a nearby swimming pool with some local children.

Nothing quite like this has ever been attempted before.

So why has the job fallen to these men?

The British Cave Rescue Council, which had the divers and also had coordinators, without those guys, this never would have happened, and those guys are the best in the world.

NARRATOR: Eventually, they develop a straightforward plan: (water burbling) Swim each boy out of the cave accompanied by a dedicated diver.

(water burbling) One of the biggest challenges will be preventing each child from succumbing to deadly fear while traversing vast stretches of black water.

One of the things that the operation was afraid of was panic.

Inside any kind of overhead environment, such as a cave, panic usually leads to instant death.

♪ ♪ He's going to breathe his gas faster, he might take the equipment off that he shouldn't do.

And we cannot bring the panicky diver up to the surface.

NARRATOR: First, they have to reduce the fear of drowning and ensure a reliable air supply.

KARADZIC: It was decided that we had to find full face masks.

Having a full face mask allows the kids to breathe both with their mouth and with their nose.

The kids then were using a full face mask, and they were positioned in such a way that their head was facing down.

So that also allows the U.K. diver that was bringing the kid out to kind of protect the kid.

Whenever there was an obstruction, such as a rock or something, the diver would hit the rock instead of the kid hitting the rocks.

NARRATOR: But even that may not be enough to protect the boys and keep them calm.

So they decide to add one more precaution.

Each boy will be sedated for most of his perilous journey.

Inside the cave, Dr. Pak is joined by Dr. Richard Harris, an Australian anesthesiologist and cave diver.

His task will be to administer the precise dosage-- enough to relax the boy but not so much that breathing becomes compromised.

Finally, all is ready.

♪ ♪ Early morning, Sunday, July 8.

The first major rescue mission is primed to begin.

There are now five flooded areas of the cave, with shallow canals and relatively dry areas in between.

♪ ♪ Dozens of divers' air tanks have been positioned along the route.

U.S. airmen assist building rope rescue systems in key chambers.

And 13 ambulances, one for each child and their coach, wait outside.

Everybody, especially the boys' anxious parents, are desperately hoping there will be survivors in need of them.

You're not going to know how things are going to go, because this has never been done before.

You can have a pretty good plan but something this complex with these many moving parts, it's, it's never going to go exactly as planned.

NARRATOR: Now it's up to Dr. Pak to prepare the boys.

(speaking Thai) (translated): I explained every single detail so that they could understand, and also it was a good way to assess their mental state, whether they were ready to do this or not.

And everyone was okay with it, everyone was ready to leave the cave, whichever way.

NARRATOR: The Thai government has not commented, but the boys are believed to have been administered with a mild cocktail of the sedatives Valium and ketamine to calm them and create a state called "dissociative anesthesia," meaning the boys will be able to breathe by themselves but won't be conscious enough to panic or do anything dangerous.

♪ ♪ The rescue begins at the boys' ledge, dubbed chamber nine.

All along the route, different rescue teams are stationed, nervously poised for the big moment.

The divers from the British Cave Rescue Council take turns swimming the boys through the flooded areas.

They dive alone, about 30 minutes apart, for stretches as long as 15 minutes, or nearly 1,200 feet-- and through areas as narrow as two feet.

When the British divers reach a dry section, other divers take over and carry the boys out of the water to the next dive location.

In the flooded depths of the cave, the so-called Euro divers, Ivan and Erik, are sent to man chamber six.

The Euro team's role at that point was to go into the area called chamber six, which is roughly halfway into the cave.

When the rescue diver, the U.K. diver and the kid came to our position, we assisted them by... with changing their tanks and also making sure that the kid was still in good condition.

One of the things we had to do, the kids were using something called a full face mask, and we needed to make sure that this mask did not leak at all.

Obviously, if any kind of water was to come into the kid's mask, that could have meant drowning.

NARRATOR: But before Ivan can even reach his post, he runs into trouble.

KARADZIC: About one minute into the dive, maybe even less, my helmet somehow gets trapped in the ceiling above me, and too-short strap is strangling me.

And I know that letting go of this rope is not a good idea, because I will lose my orientation totally, but also know that not breathing is a really bad idea.

(breathing through hose) And I choose to let go of the rope, so I can use both my hands to undo the strap.

I get the helmet off, get it free from the entrapment in the ceiling, and then I go to the position where I think the rope is, and it's not there.

(water burbling) I find the rope again after 45 seconds, or a minute or something like that, it felt like a lot longer.

NARRATOR: Ivan makes a narrow escape.

Now he and Erik wait in their chamber for the first diver, and the first boy, to surface.

BROWN: You're sitting in the darkest place in the world.

And when you're in there for longer periods of time, your mind starts playing tricks on you.

There's a couple times me and Ivan sort of popped up, thinking that, you know, we saw light down there and give a yell, don't get anything back.

KARADZIC: Now I can see the light from the diver and can see the silhouette of the U.K. diver, and I can see that he's holding onto something, dragging something through the water.

When I get to about five, six, seven meters, I can see that from whatever it is he's carrying in the water, I can see bubbles coming up to the surface, which obviously indicates that the kid is still breathing and that was probably my best experience on, on this entire mission.

NARRATOR: When the divers and boys escape the flooded part of the cave, they are met in chamber three by U.S. Air Force rescuers.

The scariest part about this is I had no idea the condition of any of the boys or the coach.

There was a good chance that any one of them could have come up and been dead.

I would turn the child so that they were face up towards me, and I would listen to make sure that they weren't working too hard to breathe.

NARRATOR: It's still nearly half a mile from chamber three to the mouth of the cave, where the ambulances are waiting.

In one section, rescuers use a high-line to haul the boys' Skedco, a special stretcher, up a steep slope.

Once they hooked up the child to the Skedco, and we started bringing him across with the safety line, there's two spots where there was these rocks in the way, where we had one guy just help, assist him up and pull him over.

Very carefully, right, because it's super slippery, it's dark, you know, everyone just has their headlamps.

♪ ♪ I kind of felt like the entire thing was "Mission: Impossible."

The Sked stretcher was passed off to the Navy SEALs, who had an army of people in there to do a human chain to pass the sled all the way down.

♪ ♪ NARRATOR: The rescued boys are rushed one-by-one to the hospital, by ambulance or helicopter.

Their parents begin to get word but aren't told which children have been rescued or who's still in the cave.

(cheering) (man speaking Thai) BANDIT (translated): Every time the children were brought out, we hoped it would be our child.

All the time they were coming out, we were hoping.

NARRATOR: By the end of day 18, Tuesday, July 10, all 12 boys and their coach are free, and all are healthy.

Against all odds, the 18-day ordeal that had people around the world fearing the worst has ended in a miracle, thanks to an audacious rescue.

All 12 boys-- every child from that soccer team has been rescued.

NARRATOR: It's an unprecedented triumph.

(cheering) But as the world celebrates, inside the cave, there are still dozens of rescue workers.

And nearly a mile and a half into the mountain, Dr. Pak and three Navy SEALS still need to escape from the boys' location.

They begin their exodus, and not a moment too soon.

Crucial pumps diverting the water give out, and levels begin to rise.

(speaking Thai) (translated): I thought it would be easy to dive out, because they were pumping the water away.

But seven out of the nine pumps weren't working, so there was a lot of water flooding in.

NARRATOR: By deciding to leave equipment behind, the rescuers make it out in the nick of time.

O'BRIEN: You finally get out of the cave, and that's when you can finally be excited.

I mean, you're, you were completely exhausted, but it was exciting, there was rows of people cheering, high fives, flashes.

(cheering) BROWN: They bought a little bit of KFC in for us.

I think there was a little bottle of Jack Daniels that sort of got passed around and everyone had a little celebratory sip.

I mean, it was just lots of hugs.

NARRATOR: The thousands of volunteers from Thailand and around the world pulled off a miraculous rescue entirely against the odds... a marvel of bravery and human endeavor.

(cheering) HODGES: Just on a personal level, I've got four kids.

To see 12 of these kids and then the coach get rescued was incredibly satisfying.

♪ ♪ OSOTTANAKORN (translated): I felt so proud to be a part of it, one of 10,000 people who made this mission successful.

♪ ♪ (translated): It makes me happy to see that there are great moments like this in the world.

KARADZIC: Being part of changing the impossible to the possible, and that feels... that feels very good.

It feels great.

MORRIS: Knowing that you might see a dead child come up out of the cave was really challenging.

And, uh, yeah, seeing 13 boys come out, whoa, and the four SEALS, that was, that was pretty amazing.

NARRATOR: This incredible story of human endurance riveted the world's attention.

DIVER: We are coming.

Many people are coming.

NARRATOR: It was a testimony to the resolve of the people of Thailand, and showed us all what can be achieved by combining sacrifice, bravery, and teamwork with innovation and technology.

But much more than that, the amazing Thailand cave rescue gave 12 boys and their coach a future that many feared was lost.

♪ ♪ NARRATOR: A creature unlike any other.

MAN: You cannot outrun a peregrine falcon.

NARRATOR: Almost defying the forces of nature.

MAN: Top speed 242 miles an hour.

NARRATOR: Living on the edge of what is physically possible.

MAN: It tucks its wings in, aerodynamic like a bullet.

NARRATOR: What are the secrets behind these amazing abilities?

"World's Fastest Animal," next time, on "NOVA."

♪ ♪ Major funding for "NOVA" is provided by the following: To order this "NOVA" program on DVD, visit ShopPBS or call 1-800-PLAY-PBS.

This program is also available on Amazon Prime Video.

♪ ♪