All language subtitles for Unsinkable Japans Lost Battleship 1080p EN SUB

(dramatic music)
(plane engine roars)

The outcome of World War II is at stake.

Over 400 American and Japanese warships

do battle at Leyte Gulf.

It was the largest naval action in history.

(light music)

Japan is counting on a secret weapon

the Americans know almost nothing about,

except her name, Musashi.

You'll find, in the summer of 1944,

the naval intelligence experts groping

for an understanding of these huge ships.

At 72,000 tons,

she's the largest battleship ever built.

She's not just 10% bigger than some

of these other vessels, she's nearly double.

Bristling with anti-aircraft batteries

and massive 18-inch guns.

(guns banging)

You can't believe all the firepower

that comes up at one time.

Her builders boast, "She's unsinkable."

Yet, in her first major fight,

this super battleship is sent crashing to the ocean floor.

(water splashing)
(metal creaks)

But mysteries have always surrounded Musashi.

(dramatic music)

Now, Americans and Japanese researchers

are joining forces to unlock her most stubborn secrets.

(graphics whirring)

(Hirotada speaks in foreign language)

This front part

is where flooding is taking place.

Why did an unsinkable giant go down so fast?

Was it overwhelming American air power

or a fatal design flaw that sent

nearly 1,000 Japanese sailors to their death?

(Masahiro speaks in foreign language)

Hundreds of people are crying for help

in horrified voices as they were all sucked into the waves.

(plane engine roars)

To unravel the mysteries of Musashi,

the missing giant must first be found.

(water gurgling)

(waves splash)

(light music)

In February 2011, a research vessel

begins a three week expedition

in the Sibuyan Sea of the Central Philippines.

You know, if this was anywhere else,

all the coastline would have been changed

with buildings and high-rises and all sorts of things.

And that's not the case here, so we know we're looking at

basically what the pilots

saw 70 odd years ago.
(flash bulb popping)

The expedition is the brainchild

of the late Paul Allen, co-founder of Microsoft.

The son of a World War II veteran,

Allen committed significant resources

to searching for the war's most iconic missing shipwrecks.

Among them, the mysterious Musashi.

(ship crew chattering)

Rob Kraft is in charge of conducting all sub sea operations.

(guns bang)

Musashi was the pride of the Japanese fleet.

It was so important to the Japanese people

that they didn't even inform the population

that it has sunk.

Lots of people would like to find the Musashi.

It's one of the great battleships,

it's one of the truly remarkable ones

that haven't been found.

That is--
I think there's something--

David Mearns has made a career

out of hunting for lost shipwrecks.

(soft dramatic music)

After months spent combing

through military archives in the US and Japan--

And what it's showing you here.

He's identified the critical clues

he hopes will lead them to Musashi.

The key is that one.

One is visual,

(flash bulb pops)

aerial photographs taken by American pilots

during their final devastating attack.

(flash bulb pops)

There's the plane coming in lining up

right there to attack Musashi

and this is the next frame in the sequence.

You can no longer see the plane, but we see a torpedo hit.

(flash bulb pops)

Clearly recognizable in the background

of these photographs, is the outline

of Sibuyan Island a few miles to the south.

Outside this circle?

Outside the blue circle.

Outside the blue.

Yeah, yeah.

But there are other clues

that may narrow down the search even further.

And the most important one came

from one of the destroyers, the Japanese destroyer

that was ordered to stand by Musashi.

Kiyoshimo actually took a position for Musashi sinking.

Using the position reported

by the destroyer, Kiyoshimo,

Mearns and Kraft have determined

a high-probability search area.

The tool selected for the search

is called a multibeam echosounder.

It's a type of sonar that's mounted on a ship's hull.

An array of downward-looking beams emitting sound waves

sweeps across the seabed

to create an image of a mile-wide swath.

(soft dramatic music)
(water gurgling)

We're over here on the western side of our box.

We're running the first line to the east

and this happens to be line number 13.

And each line should take about four hours.

And because we're looking for,

in the terms of the depth of the water,

quite a small target.

We're mapping the seabed in very, very high detail.

So the byproduct of our search is a really detailed map

of this particular part of the Philippines.

Even though Musashi is as big

as a 75-story building, the battleship will only show up

as a small speck on this vast and unexplored seafloor.

There's no guarantee she can be found.

It all depends on her orientation on the bottom,

if she's in one piece, two piece, three pieces.

We should be able to detect that and see them

in what they call the backscatter imagery.

When you hit something hard,

it shows up as a very, very dark object.

(soft music)

It takes four days

to cover the high-probability area.

It yields an impressive picture of the seabed below,

including a newly discovered seamount.

But so far, there's no sign of Musashi.

So our highest probability to begin with

was all on the basis of this Japanese destroyer, Kiyoshimo,

which gave a precise sinking position.

It's now very clear that

that position wasn't as accurate as I had hoped.

And the cost of that, we're now having to expand the search.

(soft dramatic music)

Their focus shifts to the second,

albeit less precise clue--

That's the bow.

The aerial photographs taken

by the American planes attacking Musashi.

I mean, I think if we go down here,

we're gonna be able to, we're gonna be able

to get a better feel.

Yeah.

This cardboard box,

which has the same field of view

as the camera the airmen used,

allows Mearns to get a close approximation of what they saw.

Musashi would be about two kilometers closer

to the island from here when these photographs were taken.

(flash bulb pops)

And she sinks four hours later.

With the evidence gleaned from the photos,

they plot a new series of sonar runs.

That's what we've covered, that red line there.

Anywhere outside of that, she could be.

I would almost bias it further to the west,

because in that photograph,

(flash bulb pops)

she's clearly heading westerly

as opposed to north.
(flash bulb pops)

But the clock is ticking.

(flash bulb pops)

The expedition only has two weeks left

to find the mystery ship.

(soft dramatic music)

Musashi was first conceived in the 1930s,

(gun popping)

a time when Japan's efforts to expand it's territory

and influence in Asia and the Pacific

were increasingly blocked by it's former ally,

the United States.

Japanese national prestige had been dealt an insult

by the Washington Naval Treaty.

Just to put it in numbers,

the treaty created circumstances where

for every 100 United States warships that are built,

the Japanese are permitted 60.

It created a future in which the Japanese Imperial Navy

was going to be numerically inferior

to the United States Navy.

In response, a powerful faction

begins advocating for a different strategy.

(Toshiya speaks in foreign language)

Japan, at the time,

had neither the resources nor the budget

to build a large number of battleships

to fight against the US.

So they decided to counter quantity with quality.

That was the idea they came up with.

Quality meant constructing giant battleships

that could overcome the enemy's larger numbers.

The new battleship was called the Yamato-class

after it's prototype.

To win public support, this navy handbook likens it

to a powerful figure in a popular movie of the time.

(sinister music)

(crowd screaming)

The Hollywood film about a giant ape creating mayhem

in New York was a huge hit with Japanese audiences.

(woman screaming)

And so the comparison is not just a comparison

evocative of power and strength,

it's also kind of pointed squarely at New York City,

and, therefore, pointed directly at the Americans.

(soft music)
(film whirs)

In March 1938, construction of Musashi

began here at the Mitsubishi Shipyard in Nagasaki.

Incredibly, the giant gantry crane that built her

is still in use today.

The Japanese virtually had to reinvent

naval architecture and design of ships

to be able to build such colossal vessels.

Work proceeded under a literal veil of secrecy.

When they were being built, they were actually built

behind gigantic curtains

that were raised up in the shipyards.

And so even friendly people couldn't see

what was going on behind there.

So there was some attempt to keep it a secret.

A schoolgirl at the time,

Ms. Matsuura remember what it was like.

(Sachie speaks in foreign language)

I was told never to look

in the direction of the shipyard,

that soldiers are onboard keeping watch,

"You must not look or the soldiers will take you away."

Even as a child, I kind of sensed

that a big war was going to break out.

(dramatic music)

On December 7th, 1941, that war began.

In it's surprise attack on Pearl Harbor,

the Japanese Navy used carrier-based air power

to devastating effect against the American fleet.

Ironically, that success only reinforced it's faith

in it's own new super battleships.

A lot of the naval theory at the time

was based on this fleet-on-fleet engagement.

The Japanese, in particular, were still hoping

for that kind of thing.

This is how you arrest sea control from the other guy,

you defeat his fleet.

(guns bang)

In August 1942, Musashi began

secret sea trials.

Weapons and defenses carefully kept out of sight

from enemy spies were put to the test.

Mushashi's main armament came in the form

of three turrets mounting three Type 94 naval guns.

These were of 18-inch caliber,

and were therefore the largest naval guns in use

anywhere in the world.

(guns banging)

To defend herself, Musashi was shielded

by the heaviest armor ever used on a ships hull.

The high-grade steel came from low-phosphorous iron

secretly mined in Japanese occupied Manchuria.

For 19-year-old Masahiro Ohishi

and the hundreds of young sailors

assigned to serve aboard this giant,

Musashi was a technological wonder.

(Masahiro speaks in foreign language)

We never thought for a second

that Musashi would sink and people would die.

We believed that such a giant ship could not be taken down.

(soft music)

To them, she was the King Kong of the sea.

(dramatic music)

Day 14 of the Musashi search expedition.

Five, in this direction here.

At last, the team thinks

they're onto something.

It should be broken in four pieces sitting there.

One of their sonar runs

has revealed a promising target.

That is exactly what you wanna look for,

bow, superstructure, things falling off the superstructure,

blah, blah, blah, central area, engine room,

break here, explosion there, stern.

It's all gonna be right there.

And if it capsized, it's gonna be over.

But after making several more sonar runs,

they reluctantly reach the conclusion,

the object is too large.

You know, it's 100 meters bigger

than what we're looking for, so it's 30% bigger.

I think it's definitely something

other than geology, but I don't think it's Musashi.

(light music)

After three weeks,

the expedition is out of time.

The research vessel must return to port.

But they've covered a staggering 1,400 square miles,

an area as big as the state of Rhode Island.

What we now have is a very highly accurate map

of the entire area that we want to search.

We know where she's not, we've ruled out

large swaths of the Sibuyan Sea.

And their commitment to the task

has only intensified.

Everybody's kinda got a lot of blood, sweat and tears

in trying to find this wreck.

You know, you get this personal passion going

trying to find this thing.

(dramatic music)

But to succeed, they must first find

a better tool for searching the rugged sea floor below.

(water splashing)

(dramatic music)

By the time Musashi joined the Japanese war effort

in the Pacific in 1942, the momentum was about to shift.

The Japanese, actually, are prevailing at this point,

'cause they're better at surface warfare than we are

at this early stage in the game.

What then becomes clear

is that anytime aircraft carriers get involved,

the whole thing changes.

The US embraces naval airpower

in a way that it just hadn't before.

It revises the way that it trains, revises tactics

and it revises weapons to the extent

that it introduces a new fighter,

a new dive bomber, a new torpedo bomber,

and it even introduces a new torpedo.

The Mark 13 torpedo was more reliable

and could be dropped at higher altitude

than it's predecessor.

At the same time, American intelligence

secured a valuable lead.

On the island of Tulagi, Americans captured a document

that was a warship recognition manual

that was to be used by Imperial Navy sailors

to recognize their own ships.

And it had a drawing of a Yamato-class ship.

But after that, nothing.

It's as if Japan's most secret weapon had vanished.

You'll find in the summer of 1944,

the naval intelligence experts groping

for an understanding of these huge ships

and they came up with estimates that were just unbelievable.

But as they would later discover,

even those estimates were way too small.

(dramatic music)

By June 1944, American forces succeeded

in pushing the Japanese fleet,

totalling some 60 ships and 450 aircraft,

out of the Western Pacific.

The battle became known as the Great Marianas Turkey Shoot.

They call it that because they harvest

so many Japanese aircraft.

They shoot them down wholesale.

The Japanese lose half their carrier strength

and they lose almost all of their naval aviation.

American general Douglas MacArthur

was now poised to invade the gateway

to Japan itself, the Philippines.

On October 20th, MacArthur came ashore

on the eastern side of Leyte Island,

where American troops encountered little resistance.

The opinion, united, of American intelligence agencies

was that the Japanese Navy would not come out.

We based our ideas on the assumption

that the Japanese would need a considerable amount of time

to train new aircrew and pilots

for their aircraft carrier groups.

But American intelligence was ignoring

one critical fact: Japan's Navy remained committed

to fighting a decisive battle at sea.

It's surface fleet was still largely intact,

led by two giants Americans had yet to lay eyes on,

Musashi and Yamato.

American radio intelligence had knowledge

of the movements of these Japanese ships,

but still not of their characteristics.

On October 24th, 1944,

Admiral Kurita's Center Force, with 26 ships,

entered the Sibuyan Sea.

Two other slightly smaller Japanese fleets

approached from the south and north.

The Battle of Leyte Gulf was about to begin.

(soft dramatic music)

In the morning, when Kurita is crossing the Sibuyan Sea,

the reconnaissance flights picked this up,

and, of course, at that point, they're aware

they got two very large battleships down here.

American Pilots were the first

to catch a real glimpse of Musashi and Yamato.

We knew that they had two big battleships,

and that's about all we knew.

And it was, obviously, the biggest thing we'd ever seen.

Although caught by surprise,

the US Navy was prepared.

7th Fleet moved to guard the Leyte landing site itself,

while 3rd Fleet deployed in three groups to the north.

Unfortunately, the one element of the 3rd Fleet

that's closest to San Bernardino Strait

is a little bit weaker because it sent

one of it's carriers off to refuel.

It's sole remaining large carrier was only half the size

of the two giants bearing down on it

with 24 more warships in Japan's Center Force.

(soft dramatic music)

(man speaking faintly on radio)

In late February 2015,

Rob Kraft and David Mearns renew their search for Musashi.

Since they were last here,

they've found the perfect tool for the difficult task ahead.

It's now installed aboard the expedition yacht, Octopus,

equipped with state-of-the-art deep sea equipment.

Their key search tool is still so new,

it's rarely been used in the deep ocean.

(machine whirs)

AUV is an autonomous underwater vehicle.

Our AUV is capable of diving down to 1,500 meters.

It takes with it a side scan sonar system

that looks out on the sides and provides us an image

of things that may be lying on he seafloor.

It's survey route is selected based on

the bathymetric map that system engineer Wayne Szydtowski

compiled during the 2011 expedition.

This map is of the, basically, of the sub sea volcano

that we're seeing.

And so, using this map,

we then program the autonomous vehicle.

Traveling 2/3 of a mile down

and a few hundred feet above the ocean floor,

the AUV maps the terrain.

But distinguishing a man-made object

among the rugged volcanic outcrops is challenging.

Because a lava rock is as reflective

as the acoustic waves are that we use

to bounce off the metal of the Musashi.

After 18 hours, the AUV returns to the surface

and is brought onboard to download the data.

Everybody had a go at looking at this HYSCAN information.

Everybody, what do you see?

Oh, that's something shiny there.

That's a rock, no that's a rock.

No, that's something.

No, that's a rock.

The first AUV survey yields nothing,

as does the second.

And I'll tell you that, up to that point,

we were starting to second-guess ourselves.

We had searched a large portion of the primary search area.

And we weren't finding what we had hoped to find.

On the third run, they finally see something.

(water gurgling)

Generally, when you're finding a wreck,

it's either happening instantaneously,

but, in this one, it was a bit of a slow burner,

because there sonar image didn't sort of shout out,

"This is Musashi, this is where I sank."

it was more of there was an indication something was there.

David, buoy in the water.

That's a safe heading

Better wench that one up.

For a closer look, they launch

a remotely operated vehicle, or ROV.

It's smaller than a Volkswagen Bug,

but it's still quite substantial.

And it's on a cable as well, but in that cable

it has power conductors and fiber,

and through that, we get to watch

our HD camera that's on the end of a tether.

It will take the ROV an hour

to reach the ocean floor almost a mile below,

plenty of time to wonder if, at last,

they're going to set eyes on Musashi.

(dramatic music)

On the morning of October 24th, 1944,

the skies over the Sibuyan Sea were filled

with over 40 American warplanes.

US Naval aircraft that opposed the Japanese Center Force

in the Sibuyan Sea consists of the Hellcat fighter,

the Helldiver dive bomber, and the Avenger torpedo bomber.

The fighters led the way with strafing runs.

You're gonna go after the battleships

because they are the biggest target.

They can do the most damage to you,

and, therefore, you want to take them out.

But the Japanese gunners were ready,

(plane engines roars)

unleashing a hail of fire

from Mushashi's 100 anti-aircraft guns.

(guns banging)

(Akio speaks in foreign language)

Aerial attacks had become fierce

after war broke out.

So the decision was made

to strengthen anti-aircraft defenses,

and machine guns were also rapidly added.

But there was no industrial capacity

to manufacture bullet-proof armor at this point.

With little to protect them,

some of the gun crews suffered heavy casualties.

(Yoshiaki speaks in foreign language)

Everything was blown to bits.

There were pieces of machine gun everywhere

with human flesh stuck to them.

I could not believe that they were parts of human beings.

Bob Freligh was a 22-year-old pilot

flying an Avenger torpedo bomber that day.

The sky is so big up there, I don't see all the fighters.

I don't have time to look around to see anybody else

because everything happens like that.

What he did see was a giant battleships below.

The Musashi has 11 planes coming in on it.

You're coming down and you start leveling off.

And all this time, they're shooting at you

and you don't know whether this bullets gonna hit you or.

So you get about the distance that you think you should be,

at the altitude you should be, open your bomb bay doors,

and you're all set, boom.

(plane engine roars)

His rear gunner watched

as their 2,000 pound torpedo slammed

into Mushashi's port side.

(torpedo bangs)

The torpedo bomber is the most effective weapon

against a battleships because it can release something

that carries a great deal of punch.

The American Mark 13 torpedo carried a warhead

of 600 pounds of high explosive.

That was enough force to punch through an armor belt.

(dramatic music)

Musashi withstood the initial

American assault, but the attacks kept coming.

(torpedoes banging)

The fleets that are there at Leyte

consist of multiple aircraft carriers.

It's mind-boggling by today's standards

how many ships were there.

And so, as a result of that, they can continue

to attack and attack, and wave after wave coming in.

(torpedo bangs)

During the last wave, an American pilot

took his memorable series of photographs.

(flash bulb popping)

(plane engines roar)

The relentless onslaught began to take a toll.

When the Musashi loses speed and falls behind,

then it's obvious that she's damaged,

so now's the moment to close in for the kill.

(soft dramatic music)

Lionel Gilbow was the rear gunner

in a Helldiver bomber.

(plane whooshes)

I probably dived-bombed a battleship

with a 2,000 pound armor piercing bomb,

right down the stack.

(torpedo bangs)

These particular ships are very formidable ships,

but they also made very large targets

that were easily identified.

And I think that's one of the reasons

a lot of the aviators concentrated on Musashi,

and she paid the price as a result.

Yamato escaped the onslaught,

but at 7:39 p.m., four hours after the final attack,

Musashi, crippled, yet miraculously still in one piece,

rolled over and sank.

(propellers whirring)

(Masahiro speaks in foreign language)

Hundreds of people are crying for help

in horrified voices, as they were all sucked into the waves.

(water splashing)

(metal creaks)

(soft music)

In the pitch darkness of the deep sea,

the ROV pilot carefully maneuvers his vehicle.

We came across some very small pieces of debris

which looked the right age, looked the right material.

But we weren't quite certain.

Everybody was pretty much running on adrenalin

at that time.

It was very exciting.

The ROV moves slowly

through this unfamiliar landscape.

It took about, I guess, a half hour or 45 minutes

before we started getting into the heavier debris.

And then it became more and more obvious.

Look, you see them, right?

There's three characters over there, I think.

That's Japanese, it's a Japanese warship.

The minute we found the valve

that had the Kanji writing on it, it was like,

okay, this is Japanese, now all we have to do

is prove that it's Musashi.

To do that, they need to find the ship's bow.

There's the bollards, two bollards.

So we're not too far away.

It'll be above the degaussing cable.

Something's there.

It's there.

The gold paint is gone,

but the outline of the imperial Japanese flower emblem

is still there.

As soon as we found the chrysanthemum on the bow,

we knew what we were looking at.

That's, that's proof positive.

It wasn't the kind of jumping up and shouting for joy

that I've experienced in the past,

it was a sort of a quiet relief.

We had finally done it.

At long last, Musashi is found,

but a new, and still more intriguing mystery

is about to emerge.

(soft music)

Over the next week, the search team explores the wreck

of the super battleship.

There's some shells on the top

I think there's another one

of the mounts for a light, or a--

70 years after she disappeared,

they're compiling the first detailed picture

of a lost technological marvel.

Because there are no drawings for this ship

and there's only a handful of photographs,

so we're the first people really

to document what she looks like.

They also find signs of those who sailed her,

a shoe, a helmet,

and something unexpected on a warship.

That's film.

No, that's film.

That is a film strip.

It's not just a metal ship, these are crew

that served in it,

and some obviously died on the site as well,

so it's important to document that.

(soft dramatic music)

Musashi lies a good distance

from the sinking position reported

by the destroyer Kiyoshimo.

(flash bulb pops)

But that's not the only reason she was so hard to find.

The Musashi is literally on the side of a volcano.

And if you've hiked up a volcano before,

you'd know there's great big huge rocks and outcroppings

and boulders, and so it's hidden inside the geology.

The difficulty in finding the wreck

is also explained by her shocking condition.

Just the complete and utter destruction

of the ship itself, the stern and the bow sections

are really the only whole parts of the hull that remain.

The bridge is somewhat intact from what we can see,

but the rest, you know, the center section of the ship

was just completely destroyed.

So, essentially, it's broken it's back

in at least two different locations.

And for a ship that withstood so many attacks

from torpedoes and bombs and essentially sank intact,

that's more than I expected.

What then could have caused

such widespread destruction?

(graphics whirring)

It's a question which, so far, has no answer.

(dramatic music)

(guns bang)

One of the last pieces to be discovered

is Musashi's most potent weapon.

(guns banging)

Which is, obviously, what caught everybody's imagination,

these special 18-inch guns.

These guns are held into the body of the ship,

into the barbettes by gravity alone.

So when the ship capsizes, they're incredibly heavy objects

that just fall out under their own weight.

We found one of these guns after a week of searching.

By now, the expedition has assembled

an extensive record of Musashi,

over 100 hours of video footage alone.

We want to make sure that we have fully documented

the condition and the state of the wreck

so we can share that with everybody and, you know,

what we've done here and the data that we've gathered.

We'll provide the clues that people can use

to recreate or have an understanding

of what actually happened.

(light music)

The search team has opened a door.

Now, others must step in to unravel Musashi's final hours.

In March 2016, a group of Japanese experts assembles

in Tokyo to take up the challenge.

(soft dramatic music)

To help them, the Japanese broadcaster, NHK,

has created a valuable tool.

Like pieces of a gigantic puzzle, it's taken the hours

of digital images gathered by the search expedition,

painstakingly piecing them back together,

and creating a unique 3D model of the wreck.

(graphics whirring)

Only now is Musashi's enormous size apparent.

At 263 meters, some 900 feet,

she's longer than three jumbo jets.

(men speaking in foreign language)

To begin with, these experts want to find out

why a ship so many believed unsinkable

should fail it's first serious test.

(Masami speaks in foreign language)

(man speaks in foreign language)

What is that thing that looks like a hole?

Masami Tezuka has been studying the Musashi

for 30 years.

He believes he's identified one clue,

a damaged section protruding from the port bow,

most likely caused by a torpedo strike.

(Masami speaks in foreign language)

Musashi would lose speed as a result,

making it difficult to steer her.

From an attackers point of view,

a battleship that's dragging swuld have been easier to hit

with bombs or torpedoes.

The last photo of Musashi

shows her down at the bow, leading to the belief

that flooding here caused her to sink.

But a new scientific investigation

at the University of Kobe tells a different story.

Professor Hirotada Hashimoto, a specialist

in naval architecture, conducted the analysis.

When he simulates flooding inside the bow,

the ship does pitch forward.

But results show, water-tight compartments

in the rest of the ship would not have been affected.

(Hirotada speaks in foreign language)

Even if the bow,

including the part protected by armored plating,

is completely filled with water,

the ship will still be left with enough buoyancy.

So this flooding alone definitely could not have caused

the ship to sink or capsize.

To find answers to why Musashi sank,

these experts will have to look elsewhere,

starting in the place where Musashi was constructed.

(soft music)

At the Mitsubishi shipyard in Nagasaki,

the Japanese team makes an important discovery.

A file marked Musashi is uncovered in the company archives.

It contains more than 200 pages

of never-before released original blueprints.

By comparing images of the scattered pieces

of the wreck with the blueprint,

the team is able to identify them.

(men speaking in foreign language)

A pump, a boiler, all parts protected

by the heavy steel armor

intended to make Musashi unsinkable.

(Akio speaks in foreign language)

So the biggest question is

where did the armor go?

In the high-resolution sonar image

of the debris field, one structure attracts their attention.

Examining video footage from the area,

they discover a 90-foot piece of steel.

It looks like part of the missing armor.

(graphics whirring)

When they match it up to the 3D model,

they find it comes from the hull on the port side.

But how did it come loose?

Musashi's armor belt was so thick,

that everyone felt very confident onboard the ship,

that they could stand up to the punishment

of any weapon that could be thrown at it.

But, whereas ships making use of a thinner plate

that could be welded, Musashi's armor could not be welded.

It was simply too thick.

And so they turned back their the 19th century

and simply hot riveted the plates together.

A company that took part

in riveting the armor for Musashi

is still operating in Osaka.

Two workers recreate the technique used at the time

to join these two pieces of armored plate.

(dramatic music)

(machine banging)

A special hammer drives the rivet into place.

(soft music)

Japanese sailors assigned to Musashi

had great confidence in the ship.

They thought it was unsinkable, and that's because,

above deck, they saw nothing but guns and firepower.

But then below deck, they were aware

that the ship had the thickest armor

of any warship in the world.

But the Japanese investigation team

doesn't share the sailors' confidence.

(Hayao speaks in foreign language)

I think rivets were the problem.

No matter how thick the armor plates were,

they wouldn't last once the rivets came loose.

Musashi's armor was attached

at a slanting angle to deflect incoming shells.

(man speaks in foreign language)

She was built to withstand artillery duels

against other battleships.

But, instead, she was hit by torpedoes and aerial bombs,

which weren't weapons she expected to face

when she was designed.

(guns popping)

If a torpedo from an attacking aircraft

struck a a joint in the armor plate,

it could cause rivets to fail and seawater

to begin to seep in.

(plane engine roaring)

So how did this apparent vulnerability

to torpedo strikes go unnoticed?

(guns banging)

(light music)

(men speaking in foreign language)

The team discovers early concerns

about this possible design flaw.

A former officer on Musashi,

who earlier served on her sister ship, Yamato,

made this recording before he died.

(Haruo speaks in foreign language)

I heard from Yamato's crew

that during a torpedo attack,

although the armor remained intact,

the rivets were blown off,

and, gradually, water started to leak in around the joints.

It made me realize, if we were hit by a lot of torpedoes,

there would be more flooding,

and that could be her weakest point.

Shigeru Makino, a naval designer

who oversaw the construction of Musashi,

reported similar misgivings, but later wrote,

"The naval authorities decided

"to simply patch the armor joint

"rather than find a permanent solution to the problem."

In the minds of Musashi's 2,400 crewmen,

many still in their teens or early 20s,

the Imperial Japanese Navy instilled a beguiling illusion,

their super battleship was quite simply unsinkable.

(soft music)

One of them, Masahiro Ohishi, believed it to the very end.

(Masahiro speaks in foreign language)

Right up till the moment it sank,

I didn't think it could happen.

The Musashi wouldn't even budge an inch

with a torpedo or two striking her.

There would be no flooding, so we were told.

Musashi also proved vulnerable

to another unanticipated weapon,

armor-piercing bombs from the air,

as the search team discovered.

See that's an issue.

Yeah, once you get in there a little tighter--

Underwater footage revealed

one of several 3-foot holes rupturing the ships deck.

In a short section of the bow,

we saw the damage from the bombs.

So that's corroborating what the US pilots were telling us

about the hits they were getting on Musashi.

These weapons, although they are as crude and as simple

as they can be, sent through the air column,

penetrate decks and can explode below deck.

This, in the end, causes great destruction on Musashi.

(soft dramatic music)

Now, thanks to the 3D model of the wreck,

the full extent of that destruction can be seen,

especially up on the bridge, where the captain

and many of officers were stationed.

A gaping 20-foot hole gouged into the starboard side

marks where a bomb struck.

One crew member up here miraculously survived.

Kenji Otsuka remembers what happened.

(Kenji speaks in foreign language)

All the desks, chairs, everything,

flew to the port side.

Bodies of those who were killed were piled up there, too.

The blast wave knocked us over, killing some.

One man lost everything from his neck up,

sitting in a chair about 10-feet

from where I was, just dead.

Standing on an open observation deck,

Captain Inoguchi suffered a shrapnel wound in the shoulder.

Protected from the fire himself,

crewman Kotaki observed what happened.

(Tatsuo speaks in foreign language)

I saw him from behind.

He was covering his shoulder with his hand like this,

holding binoculars like this, and giving commands.

Any ordinary person would have collapsed from such injuries.

I thought, "That's a true commander."

Like her brave captain,

Musashi sustained multiple hits

from weapons she was never designed to face.

Incredibly, her unusual strength allowed her

to go down in one piece, leaving one final question,

what tore her to pieces as she sank?

(water splashing)

(dramatic music)

That's a 46-centimeter shell

underneath there, right?

When the search team

originally discovered Musashi--

The turret housing was blown away.

They couldn't believe the wreckage

was spread over such a wide area,

a square kilometer, more than half a square mile.

Most of the shipwrecks that I've done

are in deeper water than this,

and we're seeing debris fields of 300 meters, 400 meters.

So to see one twice or three times that size

is really telling me that not only

are we dealing with a large ship,

but a large ship that has been blown apart.

(man speaks in foreign language)

How does a ship that left the surface intact

now lie shattered over the ocean floor?

The Japanese team is determined to find an answer

to this final mystery of Musashi.

(man speaks in foreign language)

I'm not sure if it came from a boiler

or something else, but is it possible

this damage was caused by steam exploding?

One member doesn't think so.

Masatake Yoshida has been studying explosives

for over 30 years.

He believes something else tore Musashi apart.

(Masatake speak in foreign language)

I can't think of any explanation

besides a gunpowder explosion.

If an explosion like that occurred,

her internal parts would have shattered into many pieces.

(soft music)

But where did

this massive explosion take place?

One piece of debris in particular

has caught Yoshida's attention.

Although mangled almost beyond recognition,

it's part of the magazine, holding the shells

for one of Musashi's main guns.

(Masatake speaks in foreign language)

Thick steel like this

wouldn't have ended up being so badly twisted

if the ship had just sunk.

Since Musashi fired her main guns

only a handful of times during her final battle,

an estimated 160 shells and 100 tons of gunpowder

were still stored inside her.

(soft dramatic music)

Suspicion as to where the explosion occurred

falls on the second main gun.

So that was literally--

And firsthand reports

David Mearns uncovered seem to support it.

To see that level of damage on the seafloor

tells me only one thing, that the Japanese survivors

who heard explosions as it was capsizing,

those explosions were actually magazine explosions.

In the final moments,

as Musashi heeled over and sank,

a few eyewitnesses aboard a nearby destroyer

reported seeing the flash from a small explosion.

(Masatake speaks in foreign language)

Which means that some fires

were already burning inside her.

That makes me think that initial combustion

rapidly spread into an explosion.

Gunpowder contains some oxygen, so even underwater

where there's none, under the right conditions,

a combustive explosion can occur.

To test his hypothesis,

Dr. Yoshida ran a computer simulation.

It clearly shows a ship made of heavy steel

would have suffered catastrophic damage

from an explosion below her second main gun.

(dramatic music)

The ships core would have splintered

into hundreds of small pieces

with only the bow and stern remaining relatively intact.

The high-resolution sonar map confirms,

this is how the wreck rests on the seafloor.

David Mearns believes other factors also contributed

to the massive damage sustained by Musashi.

(soft dramatic music)

We see that a large section of the bow was imploded

and we can look at the drawings and know

that there's water-tight compartments in there,

and they've squeezed as the ship sank very quickly.

As Musashi plummets to the bottom,

a crushing pressure, equivalent to the weight of a car,

bears down on every square inch.

When it hits the sea bed, it's hitting the seabed,

actually, at very high speed, probably a minimum

of 15 knots, maybe as much as 25 knots.

And there's impact damage.

And all of this was evident in one section of the bow.

Somewhere in Musashi's twisted remains

lies her captain, Toshihira Inoguchi.

He went down with his ship

after handing over his final report.

In it, he wrote, "I am truly glad

"that the other battleship suffered almost no damage,

"and I feel some consolation in thinking

"that Musashi was able to assume the role of a victim."

(dramatic music)

(plane engines roaring)

(torpedoes banging)

Musashi bore the brunt

of the American air assault on October 24th, 1944,

(torpedoes banging)

leaving most of Japan's Center Force unscathed,

including the super battleship, Yamato.

Undetected, Admiral Kurita

and his 20 remaining ships steamed through the night

heading for the American landing site at Leyte

to catch the defending force from 7th fleet by surprise.

On October 25th, led by the super battleship, Yamato,

(guns banging)

the Japanese Navy launched the decisive surface attack

it had long sought.

But a bold strike by American destroyers

and destroyer escorts managed to confuse

the Japanese commander.

And so Admiral Kurita makes the fateful decision

to reverse course, and in so doing,

he walks away from what would have been

the most lopsided victory of the Japanese Imperial Navy

in the Second World War.

Japan's Navy had gambled

on winning the world's biggest sea battle

to bring America to the negotiating table.

But they made a fatal miscalculation.

Surface ships with big guns

were no longer the dominant force at sea.

The age of the battleships,

the building and the loss of the Musashi is the endpoint.

They weren't gonna be defeated by another battleship,

another great battleship, but by aircraft.

And that's when the era of aircraft carriers took off.

(soft dramatic music)

On October 24th, 2016, at Yasukuni Shrine in Tokyo,

surviving crew members from Musashi

gathered to remember their lost comrades.

The discovery of the wreck and the evidence it reveals

of Musashi's vulnerability is a cruel reminder,

this was not the unsinkable battleships

they were led to believe her to be.

But for crewman Tsukada,

the wreck still bears an important message.

(Yoshiaki speaks in foreign language)

I think the Musashi

would like the people to know

how bravely her crew members fought and died.

What an astonishing battleship she was,

how she fought and met her tragic end

in the emptiness of war, I think those are the messages

that the Musashi wants to send us.

(soft music)

For Bob Freligh, an American pilot who launched

one of the many torpedoes that sank her,

Musashi's discovery stirs thoughts of reconciliation.

I don't want any Japanese survivor

to think that I'm trying to laud these medals over them.

Our opportunity is, we have a common ground.

They are survivors of the same action

that I'm a survivor of,

and I'd just like to say, welcome, brother.

(bell dinging)

"At the going down with the sun,

and in the morning we will remember them."

We will remember them.

Above the wreck site

in the Sibuyan Sea,
(somber horn music)

the crew of the Octopus pay their own final respects.

It is a war grave.

You know, we as sailors and seafarers ourselves,

we have a lot of respect for what happened here.

(soft music)

Instead of warplanes,

they launch a flight of paper cranes,

symbol of the peace that has endured

for three-quarters of a century

between once bitter enemies of World War II.

(soft dramatic music)