Original subtitles

- Tonight, a historic catastrophe captured on film.

- [Broadcaster] It's burst into flames.

Oh, my!

Oh, the humanity!

- Of the 97 people on board the Hindenburg,

13 passengers, 22 crew, and one ground crew person

all perished in this event.

- The Hindenburg Disaster,

in many ways, it was the first viral video.

- For decades, experts believed

they knew what caused the disaster,

that leaking hydrogen ignited,

causing the airship to burst into flames.

But there may be more to this story.

- Eyewitness testimony says that

they saw orange and red flames,

but hydrogen, when it burns, it burns a light blue.

- Some people on the ground report having heard popping

inside the aircraft during that last turn,

like something inside of it went wrong.

- Now, we'll explore the top theories

behind this historic tragedy.

- Basically, the Hindenburg is flying with bandages on.

- He gets actual fabric from the Hindenburg,

and poof.

It goes up in flames.

- What really caused the Hindenburg Disaster?

(dramatic music)

- [Laurence] Frankfurt, Germany, May 3rd, 1937.

The world's largest aircraft, the Hindenburg,

prepares to depart for New Jersey.

The airship's tanks are full of hydrogen and nitrogen,

fueling its 11th transatlantic flight

to the United States.

- The Hindenburg is a derigable aircraft

that's filled with gas and that makes it lighter than air,

so it can basically float.

- Hindenburg provided something

that no other type of aircraft could provide.

Three day passage from Europe to the United States

in great luxury.

- [Laurence] At 7:16pm,

the Hindenberg takes off for Lake Hurst, New Jersey.

More than 10 stories tall, stretching 804 feet long,

the Hindenburg is roughly the same size as the Titanic.

Unlike a hot air balloon,

the Hindenburg is a rigid airship

constructed with a metal frame.

- It's filled with 16 cells of hydrogen gas,

which is a gas that's lighter than air,

which makes it buoyant.

It floats without needing to be lifted up

by any sort of wings.

- The ship has a triangular structure

through the very center that runs all the way.

That's actually what the crew would walk across.

And around that are these metal frameworks

like the ribs of a barrel,

and outside of that is an outer coverage,

seven acres of aeronautical cloth

that has been painted and carefully sealed

so that it is both waterproof

but also sturdy from the elements.

- Aluminum powder in the varnish

is what gave the Hindenburg its silver color,

but it also served the purpose of reflecting the sunlight

so that the hydrogen gas did not get heated,

inflate, and burst.

- [Laurence] Beyond its technical achievements,

the Hindenburg is a floating representative

of a sinister government.

- The swastikas emblazoned on the tail

were the national flag of Germany at the time.

So basically, the Hindenburg served as a flying billboard

for the Nazi government in Germany.

- [Soldiers] Sieg Heil! Sieg Heil!

- [Laurence] Thanks to recent upgrades,

the Hindenburg now carries 72 passengers

and almost as many crew.

A one-way ticket costs roughly $8,500 in today's money.

- The Hindenburg was set up for luxurious travel.

There were two decks

that included a dining room, washrooms,

a full electric kitchen, and even a smoking lounge.

They also had a grand piano

that had been constructed of aluminum

and covered in pigskin.

- For the most part,

the Hindenburg would travel about 650 feet

above land or sea.

Captains were very conscious of the passenger experience

and they would actually lower the altitude

to allow them to see amazing sights

that no one in humanity ever had,

like icebergs from above, floating by.

- [Laurence] After a four year long construction process,

work on the Hindenburg is completed in 1936,

and that spring, it begins its first international flights

to the United States and Brazil.

- It was spectacularly successful in 1936.

It went back and forth across the Atlantic,

both the North Atlantic and the South Atlantic,

and so they entered the 1937 season

with so much pressure on them to make this

first North American flight of 1937 a success.

- [Laurence] On May 6th, 1937,

after a nearly three day journey,

the Hindenburg reaches American soil.

- As the Hindenburg is heading for its destination,

Lakehurst, New Jersey,

there are storms ahead of it,

and so the Hindenburg can't land when it's supposed to.

It spends hours waiting for the storms to clear up,

and there are film crews and radio crews

waiting to see this amazing sight.

- What the ship is supposed to do

is approach a structure known as a mooring mast,

and once there, drop the landing ropes.

At that point, the ship drops its ballast

and then a crew of about 200 burly men

grab a hold of those ropes, attach them the winches,

and then start bringing it down to the ground.

- [Laurence] Then at 7:25pm, disaster strikes.

- As the ship is landing,

the tail is getting closer and closer to the ground

and they try to release hydrogen

in an effort to bring that ship back into level.

- Unfortunately, it's just not working.

The tail continues to fall below the bow.

And then suddenly, an explosion occurs.

- [Broadcaster] Oh, my!

It's burst into flames.

400, 500 feet into the sky.

(explosion booming)

This is terrible.

This is the worst of the worst catastrophes in the world.

The smoke and the flames now.

(dramatic music) (explosion booming)

Oh, the humanity!

- Of the 97 people onboard the Hindenburg,

13 passengers, 22 crew, and one ground crew person

all perished in this event.

- It's kind of insane to think that

people started jumping from the ship

in order to save themselves.

Some of them actually died because of the fall.

- Miraculously, about two thirds of the people on

actually lived through this disaster.

- [Laurence] Investigators immediately suspect

that sabotage is involved.

- Given that it is one of the most

visible spectacles on Earth and has a giant swastika on it,

naturally, that would seem to be the perfect target

to take down the Nazis.

So everyone immediately thought

there must have been a saboteur.

(tense music)

(clock ticking)

- Because the Hindenburg was used as a Nazi propaganda tool,

it's a natural target for anti-Nazi activists.

The Hindenburg senior captain Ernst Lehmann reports that

just before leaving Germany,

they received a warning that there was a threat

to bomb the Hindenburg when it was over American soil.

- Hugo Eckener was the head of the company

that built the aircraft, and he would ultimately indicate

that he received threats, directly, that the aircraft

should not proceed to Lakehurst, New Jersey

because something bad would happen there.

- Given this warning, the German security,

before taking off, was extremely stringent.

They went through the mail, they went through the luggage,

and nothing was found, but this was early days of security

and something may have slipped through.

- Charles Rosendahl, a commander of NAS Lakehurst,

suggested to the FBI

that they should investigate a passenger

who had a dog in the cargo compartment

right around cell six,

and he had been visiting the dog

unaccompanied by a member of the ship's crew.

- [Laurence] The man with the dog is soon identified

as passenger Joseph Späh.

- Joseph Späh is born in Germany

and then immigrates to the United States as a young boy.

He's an entertainer in the tradition of vaudeville.

He does monologues, standup,

he's also an acrobat and a contortionist.

And he's been on a tour in Germany

and now he's taken the Hindenburg back home.

During the latter part of his German tour,

he purchases an expensive German Shepherd puppy named Ulla

to use in his act,

and he takes Ulla back with him to America.

And so Ulla is in a kennel

and is kept in the cargo hold of the Hindenburg.

- [Laurence] Crew members report that during the flight,

Späh insists on feeding the dog himself.

- The passengers aren't allowed

to simply wander to the cargo bay on their own,

that's usually what the crew does,

so this behavior gets the crew's attention.

- Several of the stores report that

Späh was acting strangely.

In particular, when the Hindenburg

was delayed for several hours due to the thunderstorms,

he had this urgency to land.

- He was getting impatient when the Hindenburg

was not quite landing on time,

which if you had planted a bomb that, say, had a timer,

would be a reasonable thing to be doing.

- [Laurence] As investigators learn more

about Späh's background, suspicions deepen.

- In addition to having visited

the inside of the hull of the ship

without being accompanied,

Joseph Späh is a professional acrobat.

He easily could have climbed around the rigging of the ship.

- So because of his acrobat abilities,

he could have made his way outside

of where he was supposed to be,

worked his way to the tail of the aircraft,

climbed up a ladder all the way to the top,

and placed a time bomb somewhere on the airframe

between two hydrogen bags,

and that explosion could have brought the aircraft down.

- [Laurence] But even if Späh had the means to plant a bomb,

what was his motive?

- Although by this point, Späh is officially an American,

he is German by birth, and so maybe he thinks

that the rise of the Third Reich in Germany

is bad for his homeland.

In fact, some of the crew members on the ship

recall Späh making anti-Nazi jokes on board.

- He's investigated by the FBI, but they find

that there's absolutely no evidence suggesting

that he planted a bomb on the aircraft.

- The truth is, no one that looked at the wreckage

ever found any evidence of a bomb

or of any sabotage of the Hindenburg.

Some people who look at this feel that

the reason why Captain Pruss

and other bigwigs from the company

were pushing this idea of a saboteur

is because they wanted to free themselves

from any responsibility for this horrible tragedy.

- [Laurence] As investigators search

for the explosions caused, they turned to another clue.

Weather.

- There were storms all over the area

of Lakehurst, New Jersey that day.

And at the time of the Hindenburg landing,

winds were gusting at 30 miles per hour,

there was lightning, it was chaos.

- There's communication from the ground command

and the captain on the ship.

The commander on the ground, Commander Rosendahl,

he says the weather is too strong,

the thunderstorms are too much for the airship to come in.

And so the Hindenburg has to circle around a number of times

because it's three hours of storms.

(thunder cracking)

- Just because the storm has moved out,

we're seeing cells in the distance,

even upwards of 10 plus miles away

doesn't mean it's not gonna impact.

But people may have let their guard down,

thinking, okay, that activity has passed.

But that activity, it's still lingering.

- At the time, the New York Daily News

reports a number of theories

for what brought down the Hindenburg.

The leading theory, lightning.

(thunder cracking)

(tense music)

- [Laurence] A typical lightning bolt carries 300 million volts

and can reach temperatures of up to 50,000 degrees Fahrenheit.

- There's more than enough energy when it comes

to lightning to cause destruction.

We see that with forest fires

and even when it strikes tall buildings.

- [Laurence] And there's precedent

for lightning striking a Zeppelin.

- In 1917, a Zeppelin was brought down

and 23 people were killed

when it was struck by lightning over the Baltic Sea.

Another incident occurred in 1923

when an airship called Dixmude was struck by lightning.

It exploded in midair,

killing all 50 people on board.

- [Laurence] But while the weather conditions

improved enough in Lakehurst to begin landing,

some believe it's possible that the Hindenburg is struck

by a rare phenomenon called positive lightning,

which triggered the terrifying explosion.

(thunder cracking)

- During the storm, there's extreme electrical movement.

Negative charges build up on the bottom of the clouds,

positive charges build up on the top of the clouds.

- This so-called positive lightning

is a connection between the ground

and the upper reaches of the cloud

rather than the bottom reaches of the cloud.

So it has to travel a much greater distance,

and because of this, the lightning strikes

from positive lightning

can be up to 10 times stronger than negative lightning.

- These positive lightning strikes

can happen 20, 30 miles from a storm,

so you can be without a storm in your general area

and a bolt can come out of the blue.

- [Laurence] But those who know the Hindenburg

question whether it can be taken down by lightning.

- The captain of the Hindenburg, Max Pruss,

told investigators that he'd flown

through lightning storms in the Hindenburg

several times before and the ship had been hit.

But he said the lightning strikes

would basically just cause some burn marks

on the outside of the skin of the ship,

but there was no further damage,

so they were no problem as far as he was concerned.

- [Laurence] Witnesses on the ground

did not see lightning as a factor.

- There were many witnesses,

a thousand people on the ground looking up at the Hindenburg,

and nobody saw a bolt of lightning.

- [Laurence] But that doesn't mean the stormy weather

didn't play a role.

- The Germans knew a fair amount

about how to safely handle hydrogen,

and one of the biggest rules of all

was you do not land a hydrogen airship in a thunderstorm.

But they felt under pressure to land,

and so they basically ignored

one of the oldest rules in their own book.

- There was a bolt out of the blue,

a big flash that happened in a distance.

It came at the top of the cloud

and you might not necessarily see that.

So it's gonna strike about 20 to 30 miles away,

it's gonna be very quick.

So potentially, they may have just missed it

because it happened that fast.

- [Laurence] In the wake of the Hindenburg disaster,

both the American and German governments

conduct investigations

into the cause of the airship's explosion.

- So, the investigation interviews

witnesses on the ground,

it goes through all of the wreckage

that's in place there at Lakehurst,

and it takes into account every piece of possible evidence

that can be assembled

to put together a picture of what happened to this aircraft.

- [Laurence] In August 1937,

three months after the incident,

the US government releases its report.

The official German report is issued five months later.

Both come to similar conclusions.

- The Hindenburg is constantly venting hydrogen gas

to help with steering, to help slow it down,

and it is this hydrogen gas that the investigators find

that is responsible for the Hindenburg burning.

- [Laurence] As to what actually sparked that explosion,

neither report comes to a definitive conclusion,

but many scientists share the same theory.

- When you have a highly flammable mixture

of hydrogen and oxygen, all you need is a spark.

(flames roaring)

(tense music)

- [Laurence] On May 6th, 1937,

as the Hindenburg flies from New York City

south to New Jersey, the ship faces troubling weather.

- Around 6:00pm, there's heavy rain falling in Lakehurst

and lightning strikes were reported

throughout much of the day.

- Due to the storms, there's so much electrical activity

that local rubber factories are shutting down

because they have powdered rubber

and powdered rubber is combustible.

- Like hydrogen, rubber dust is incredibly flammable

and explosive.

So if it were to come into contact

with a spark from a lightning strike

or some other atmospheric electricity,

that would be a bad situation.

- By the time the Hindenburg is ready to land

in Lakehurst, New Jersey, it's already been pushing

through a high electric field for hours

- [Laurence] In the wrong conditions,

the Hindenburg's outer covering can act as a conductor.

- The German investigators determined that

the particular formula used for the dope for the fabric,

including the powdered aluminum,

creates a substance that has the ability

to hold a charge when it gets wet

and it was wet that day because of the rain.

- So what's happening to the Hindenburg

is very similar to what happens

when you rub your feet on the carpet while wearing socks.

It builds up an electric charge.

Then if you go and touch an electrical conductor

like a doorknob or a light switch,

that charge that you built up wants to go somewhere

and that's why you get this zap.

It's an electrical static charge.

- [Laurence] For the Hindenburg to go up in flames,

that spark needs to come into contact

with something flammable.

- Now, Hindenburg is traveling with 16 bladders

full of hydrogen,

which is extremely flammable.

We know that the aircraft probably

had a hydrogen leak in it

because as it's approaching the mooring mast,

it's tail heavy, nose high, tail down.

So they begin dumping ballast

from the after part of the aircraft

to potentially right the aircraft.

What the crew is doing is

treating a symptom, not the illness,

and the illness was there's a hydrogen leak

somewhere in the tail of the aircraft.

- [Laurence] At 7:21,

the Hindenburg arrives at its mooring mast

and prepares to land.

- The Hindenburg has just gone through a storm

and it's accumulated a lot of charge,

both on the skin and the metal frame.

So as the Hindenburg is coming into land,

it drops its landing lines

which are attached to the metal frame.

So the metal frame is grounded through those lines

and the excess charge on the metal frame

can move into the ground,

meaning there's not as much of a concentration of charge

on the metal frame.

So the skin, with a high concentration of charge,

will want to go to that lower concentration

and you get a spark.

- So if a spark is generated

and it comes in contact with free floating hydrogen,

(flames hissing)

there are gonna be flames and an explosion.

- [Laurence] Some critics challenge this theory.

- In particular, it's the timing.

The fire does not ignite at the moment

the mooring ropes are dropped.

If the idea is the ropes complete the circuit

and that's what generates the spark,

then we would expect to see the flames

at the moment the ropes are dropped.

Instead, the explosion happens four minutes later,

which could indicate a different trigger.

(explosions booming)

- In the months after the Hindenburg goes down,

US and German investigators agree on a key fact,

bad weather contributed to the airship's explosion.

But could something other than mother nature

have caused this tragic accident?

On May 3rd, 1937,

as the Hindenburg departs for Lakehurst, New Jersey,

the Zeppelin is already a worldwide phenomenon.

- The Hindenburg had had an amazing year in 1936.

It had done seven round trips to Rio de Janeiro

and 10 round trips to America.

- So the Hindenburg's maiden season

was really quite successful.

If you think about it, 200,000 miles, nearly 3,000 passengers,

with virtually no problem.

The record for the first year was very strong.

- The Hindenburg was looking to do a very rapid turnaround

and head back to Europe

for the coronation of King Georgia VI.

So because of that, there's intense pressure on a captain

to get this thing on the ground.

- [Laurence] Captain Max Pruss prides himself on punctuality,

but by the time the Hindenburg reaches Lakehurst, New Jersey

on the evening of May 6th,

the airship is already more than half a day behind schedule.

- There were strong headwinds over the Atlantic

and now, weather and storms in the northeast of America

is even pushing him further behind schedule.

It was horrible weather and so, anxious to land quickly,

Pruss decides to modify his final approach.

- He's no longer able to go in a straight line

because the wind has shifted,

and so in order to put the bow of the ship into the wind,

he needs to make a turn to starboard, or turn to right.

- The pilot is a little bit further

out of position than he wants to be,

and so the aircraft moves in

faster than it would typically approach,

and then it carries out this large swinging maneuver

to burn off air speed to reduce that momentum

as it approaches the mooring mast.

So it comes sort of hauling in as fast as it possibly can,

which is not a breakneck speed,

but for that aircraft, it is.

- Some people have expressed a thought

that this final turn may have overstressed the ship.

- Some people on the ground report having heard popping

inside the aircraft during that last turn,

like something inside of it went wrong.

- [Laurence] As the Hindenburg moves into its final position,

all hell breaks loose.

(tense music)

- It's believed that the popping

that some people on the ground heard during that last turn

may have been the sound of the wiring

that secured the rigid internal frame of the aircraft.

Maybe one of the wires snapped.

And that would've explained the popping noise

that was heard by some people on the ground

and that that last turn had caused

that high tension cabling to snap

and that it was somewhere in the tail section

of the aircraft.

- If a bracing wire snaps, you now have this jagged wire

that's flailing about on the interior of the ship

near some of the gas cells.

So a rusty, jagged wire could then flail about,

hit one of the gas cells, and cause a rip in it.

That rip then allows hydrogen

to leak out into the body of the ship and mix with air.

- [Laurence] With so much transatlantic travel,

the Hindenburg may have experienced wear and tear.

- You have to wonder,

the Hindenburg was constantly crossing the sea,

exposed to salty sea air,

which can add corrosion,

so that could have compromised its internal structure somehow.

- The bracing wires were made out of steel.

The aluminum framework was highly corrosive resistant,

but steel can corrode.

So over time, the Hindenburg is accumulating humidity

and that moisture can lead to corrosion,

which can also weaken the bracing wires.

- So if there was weakened metal

that was anywhere within the ship,

once the captain started to take those really sharp turns,

that could have added more stress

on the framework of the aircraft.

One of the broken wires could have actually punctured a hole,

then the hydrogen cells,

that would've released more of that hydrogen.

Hydrogen mixed with air

creates a very combustible and flammable environment.

- At this point, all you need is a spark.

Boom, the Hindenburg goes up in flames.

But the missing piece from this is

what caused a spark in the first place?

- [Laurence] Observers on the ground say

they saw signs of a different structural flaw.

- There were some witnesses on the ground

who said right before the explosion,

they could see parts of the outer covering

flapping in the wind on top of the ship.

- [Laurence] In 2020, some 80 years after the disaster,

author Michael McCarthy discloses new evidence

he uncovered in German archives that suggest

not only that this flaw contributed to the crash,

but that the Zeppelin company was well aware of the danger.

(tense music)

- The Hindenburg, it turns out, had a hidden structural flaw

that created a destructive rattling.

The problem was the outer cover, the aeronautical cloth,

which is supposed to protect the vehicle,

actually was rattling excessively.

And vibration bedevils all kinds of machinery.

Vibration is the thing

that makes things break down and fall apart,

and this is what was happening on the Hindenburg.

- They found that this flapping

was causing the metal ribbing to rub up against the cells

that held the hydrogen gas,

basically chafing and thinning.

- Germans learned about this several months

before the tragedy and they tried to fix it.

So what they decide to do is tie off with cord

all the metal crossovers

so that they reduce the amount of pressure

onto the gas bags,

and then they take strips of tape

that are one and a half inches wide

and they put 'em wherever

the gas bags had been abraded before

as a protective measure,

and they resow the thing back together, and off it goes.

So basically, the Hindenburg is flying in its second season

with bandages on.

- There's a belief that possibly some of that patching work

ultimately broke loose during

the bad weather that was encountering

over Ocean County, New Jersey that day,

and that maybe some of that flapping skin

was broken loose also by

whatever structure inside the aircraft may have broken loose

during the high turns

that immediately proceeded its final approach

to the mooring mast.

- [Laurence] Proving this theory is a challenge.

- The hydrogen fire that the Hindenburg encountered

was so severe, so strong,

that the physical evidence is virtually non-existent.

There are pieces, there are shards,

there are little things in museums and so forth,

but the physical evidence was virtually

completely destroyed.

- [Laurence] For decades, most scholars agree

the Hindenburg was brought down by an ignition of hydrogen.

Given how combustible that gas is,

it seems like a foregone conclusion.

Then in 1996,

a NASA scientist named Addison Bain

proposes a controversial new theory

that experts have targeted the wrong part of the ship.

- For years, the Hindenburg was frequently used

as the example for the dangers of using hydrogen as a fuel.

But while Bain was researching hydrogen

for his own rocket booster, he began to think that maybe

hydrogen was falsely accused.

- [Laurence] Bain says his first clue comes from the color

of the Hindenburg's flames.

- Eyewitness testimony says that

they saw orange and red flames.

But hydrogen, when it burns, it burns a light blue.

So maybe it wasn't the hydrogen that it was burning.

- [Laurence] Bain also says

that if there was a hydrogen leak,

it would've left a telltale sign.

- Shortly before the Hindenburg disaster,

there was a gas explosion in the United States

that destroyed a school and killed 300 people.

So the Germans were well aware of the dangers

of using hydrogen in these aircraft.

So to deal with that,

the Germans added an advanced early warning,

which had an odor component to it,

and it smelled like garlic.

- We know there was crew

stationed near the back of the aircraft,

but none of them reported smelling garlic or the gas

before the disaster occurred.

Another thing that Bain notices

is that once the tail of the aircraft

was engulfed in flames, it still remained level.

So to him, that meant that it was still buoyant

and hydrogen gas bags were still intact.

- So Bain comes up with a theory

that the plasticized lacquer on the skin of the Hindenburg

is much more dangerous than the hydrogen inside of it

because it contains elements that, when combined,

are highly combustible on their own.

(tense music)

- [Laurence] The skin of the Hindenburg is a cotton canvas

painted over with a substance known as aircraft dope.

- Aircraft dope is a type of lacquer

that is used on a cloth covered airship of some sort,

stiffens the fabric,

and it acts as a barrier against water, wind, and objects.

- [Laurence] The materials in the lacquer contain iron oxide

and powdered aluminum,

elements used today in rocket boosters.

Bain believes this ultimately dooms the Hindenburg.

- It was common practice

for lacquering airships at the time.

So imagine that.

Take the stuff from a solid rocket booster

and paint it all over your airship.

- [Laurence] Bain puts his theory to the test.

- He believes that the skin would burn up just as quickly

as rocket fuel would,

so he gets actual fabric from the Hindenburg

with that plasticized lacquer which he thinks is combustible,

and he puts a very high voltage, 30,000 volts

across that fabric, and poof.

It goes up in flames.

- Bain believes that this test proves his theory,

and that is that there was an electrical arc

that didn't set off hydrogen,

but instead set off the aluminum powder and the iron oxide

that make up the skin of the aircraft.

- When Bain reports his findings, he says to the press,

"The moral of the story is,

don't paint your aircraft with rocket fuel."

- [Laurence] But Bain's theory

leaves some questions unanswered.

- It's very difficult to conclude anything

from the color of the flames,

not only because the witness testimony is unclear,

but more importantly,

but Hindenburg was not a pure hydrogen flame.

It was a bunch of stuff.

You had a ship that had fabric covering,

it had metal, it had steel wires,

it had all sorts of combustible materials

burning all at the same time

that contributed to whatever color that flame was.

- What's interesting about the explosive paint theory

is that the photographs we see of the explosion

don't show the canvas going up in flames.

We see internal flames in the ship.

Also looking at how it burned,

there's lines that run along

the locations of those hydrogen cells,

which in the images,

it shows that the hydrogen was actually burning

and not the canvas itself.

- Anytime someone has a sensational theory,

it naturally invites challenges.

And one researcher actually looked at claims around paint,

and what he found was that there was no possible way

that a spark could physically ignite that dope material.

- They've done experiments using the chemical compounds

that were on the canvas

to estimate how long it would take for the canvas to burn,

and the estimate is about 40 hours,

not 34 seconds.

- [Laurence] In 2000,

an 81-year-old witness to the Hindenburg disaster

comes forward to tell his story publicly for the first time.

He was just 17 when the Zeppelin went up in flames.

- Bobby Rutan was a child of one of the Navy personnel

at the Lakehurst Navy Base

and he lived about 3,000 feet from the site of the disaster.

- He knew a lot about airships

because his father had died a few years earlier

in a disaster with another airship, the USS Akron.

- As a teenager, Bobby hung out in the hangers,

he sold souvenirs and answered questions

from tourists who came to view the zeppelins.

- [Laurence] On the evening of May 6th, 1937,

Bobby is on the base and goes out to watch the landing.

- As the Hindenburg is coming in,

Bobby thinks he smells some diesel fuel,

and then he hears what he thinks is an engine backfire,

which makes him think

that the fire and the disaster that he subsequently sees

is caused by the backfire of one of the engines.

(tense music)

Hydrogen isn't the only combustible fluid

that's on the Hindenburg.

It also burns around 300 pounds of diesel fuel

through the engines.

Diesel fuel is highly flammable,

so if it meets with something that's hot,

say an engine block,

then the diesel fuel itself can combust.

- [Laurence] There had been recent trouble

with one of the airship's engines.

- A fuel pump on one of the diesel engines

was replaced in flight,

but there's always the possibility that

the installation of the new pump

might have been completed incorrectly

and that there might still have been

a problem with that engine.

- So, some have suggested

that replacement caused the engine to backfire

and result in the ignition for an explosion.

- [Laurence] As the investigation gets underway,

Bobby immediately comes forward.

- Bobby told Charles Rosendahl,

who was the commander of the Lakehurst Air Base,

that he smelled this fuel

and that the backfire could've ignited it,

leading to the explosion.

- Commander Rosendahl is having none of it.

He doesn't want to muddle the story

because he believes that it's sabotage,

and he doesn't want Bobby saying to others

that there could be a cause that has to do

with say, the engine.

He even tells Bobby's stepfather that this

should not be information that's spread around.

- So why would Rosendahl do it?

He has two reasons.

One, he was the one who suggested

that the airship come in when it did

after circling for at least three hours,

and of course, it turned into a disaster.

So he has some personal responsibility there.

But it's more than that.

He is a real protector and an evangelist

for this form of flying.

Even when the technology starts to fade

in terms of people's enthusiasm for it

and the public's enthusiasm for it,

he still continues to be its main cheerleader.

So he doesn't want this information out.

- [Laurence] Bobby stays silent for decades.

He insists everything he says he saw that day is true.

- Years later, when asked if the fuel that he smelled

could have come from another source,

Bobby Rutan answers, "Absolutely not."

There is nothing on the base

that it could have given off that smell.

There's only blueberry fields on one side

and sand on the other.

- [Laurence] In 2007, the last surviving ground crew member

corroborates Bobby's account.

- Robert Buchanan had been on the job

in 1936 when the Hindenburg landed.

Buchanan recalls that as the airship is landing,

the pilot does a hard maneuver to slow the airship's descent.

- Robert Buchanan corroborates Bobby Rutan's account,

saying that he could see sparks

after the pilot completed that hard right-hand turn.

- He also heard the backfiring engine

and even saw sparks coming out of the engine.

- Buchanan feels intense heat, and he runs for the trees

It's so hot, he doesn't think he's gonna make it,

but once he makes the tree line,

he looks back and he sees flames erupting.

- [Laurence] It's a dramatic account,

but not everyone is convinced.

These decades-old memories add up.

- The Commerce Department interviewed hundreds of people,

not once did anyone suggest that there was a fire or a spark

that began on the engines, which were at the bottom.

And remember, fire was at the very top.

It was a sawtooth flame right along the tail,

nowhere near the engine,

so the distance is simply too far.

- The other problem with the idea

that the fire was started by one of Hindenburg's engines

is that it is not credible

that anyone who was located in the area

where the general public was allowed to watch the landing

could possibly have smelled anything

that was leaking or dripping

from an airship that was almost half a mile away.

In addition to that, the general public was in an area

that was right next to the aircraft hanger,

which was filled with aircraft

that were all powered by gasoline.

- [Laurence] The Hindenburg's fatal flight

remains a topic of enduring fascination.

- There was no footage of how it started.

The rubble was completely demolished.

We don't have the evidence to make a final conclusion

and so, we may never know what happened.

(flames roaring)

- Whatever triggered the explosion,

it didn't just spell doom for the Hindenburg,

but for the entire rigid airship industry.

Two years after the disaster,

transatlantic airplane passenger service begins.

A new age of international travel is born

and the Zeppelin fades into memory.

I'm Laurence Fishburne.

Thank you for watching "History's Greatest Mysteries."

(dramatic music)