The Somme: Secret Tunnel Wars

These are the rolling fields of Picardy in northern France.

It looks beautiful this evening,

but it was once the scene of some of the most appalling carnage

in military history.

This is the epicentre of the Somme battlefield.

EXPLOSIONS

The first day of the Battle of the Somme

was the greatest British military disaster of the First World War.

The village below us is La Boisselle,

and on 1st July 1916 in the valleys to either side of it

11,500 men became casualties - the highest concentration

on the entire battlefield that dreadful day.

We know a great deal about the killing fields of the Somme,

but in fact there was another battlefield here,

a private battlefield and it lies beneath my feet.

This is one the great mysteries of the Somme -

the hidden networks of tunnels that sleep beneath its villages and fields.

Here, British tunnellers fought a brutal underground war,

planting huge mines to destroy beneath the German front line.

Mines were the original weapons of shock and awe.

Their detonation at Le Boisselle on 1st July 1916

should have signalled the beginning of the end of the war.

To get under the German lines,

tunnellers had to play a terrifying game of blindfold cat and mouse.

To lose probably meant death.

You never knew where the enemy was.

He could be 40 metres away, he could be 40 centimetres away,

but the more noise you made, the less likely you were to survive.

But who were the men who fought in this subterranean battlefield?

And why, in the end, did British High Command fail to press home

the tactical advantage the tunnellers had given them?

Now we've been given the opportunity to explore these tunnels,

to find out what those men did.

Their story is the last great secret of the Battle of the Somme.

Whilst La Boisselle has now been rebuilt and the land returned

to agriculture, this crater field - the physical legacy of war -

is one of only a handful of untouched sites on the Somme today.

An invitation from the family that owns the land provided us with a unique opportunity

to investigate what happened to those who fought here, especially the tunnellers.

It all started with a hole in the ground.

It's quite tight here, but it's OK.

I can see a long way down it. It is clear.

'This is the strange world on which the novel Birdsong was based.

'Until now, it could only be imagined.'

-I'll just go a wee bit further.

-OK.

'We know 1,000 men once worked here.'

Keep your belly flat to the ground, it opens out pretty quickly.

'Our first venture underground proved remarkable.'

You can see to the end of the gallery.

'Above us, the evidence of the struggle has faded beneath the plough.'

There's candle burns here and there, but some of the wall has peeled off.

'Down here in the shadows we find a labyrinth, clearly intact -

'long hidden, still dangerous.'

Let's have a look. See if I can get down here.

A little bit tight, just here.

There's air pipe here.

Is the air pipe connected up?

No, it's just loose pieces.

'For the most part, history has overlooked the tunnellers' role

'and their primitive war has remained mysterious.'

Plenty of timber. 'But we soon found evidence of their character.'

Oh! There's writing here.

-Graffiti?

-Writing, yeah.

Look, you can see the pick mark here, of the man who's cut that out.

And on this face, which has been cleft, is this extraordinary poem.

I wish we could read the name of the author.

"If in this place you are detained, don't look around you all in vain,

"but cast your net and you will find that every cloud is silver lined.

"Still." Look at that, "still."

Those last five letters are really remarkable.

"Still", the word "still".

That speaks volumes because the man who wrote this,

he's right in the jaws of death.

"That every cloud is silver lined, still."

MUSIC: "Good-bye-ee" By RP Weston and Bert Lee

# I'll be tickled to death to go

# Don't cry-ee

# Don't sigh-ee

# There's a silver lining in the sky-ee

# Bonsoir, old thing, Cheerio, chin, chin

# Nah-poo, toodle-oo, goodbye-ee! #

The village of La Boisselle lies on the Roman road from Bapaume

to Albert, with the cities of western France beyond -

an ancient axis of invasion.

In the autumn of 1914, for the second time in 50 years,

an invading German army marched down this hill,

and it was here at La Boisselle that their progress was finally halted.

This is one of the earliest maps produced of La Boisselle.

It's a French one and it shows us exactly what the village was like

at the onset of positional warfare, at the onset of trench warfare.

The Germans were driving through on this axis,

pushing through the village,

trying to take Albert and Amiens and then curve around to Paris.

The French were coming in this direction,

pushing up the same axis and everything came to a stop

just here.

A contemporary German postcard depicts the fight for the village

as a glorious triumph, but one eyewitness described it as,

"Hell on Earth, which no living thing could survive",

such was the intensity of the fighting.

Another recorded that, "No sign of life appeared

"over the surface of the ground. Even the grass was withered

"by the fumes of high explosive - death, indeed, was emperor here."

La Boisselle was a cauldron.

The bitterest fighting was over the civilian cemetery.

And for a farm on the western edge of the village - it stood here -

this is all that's left of the courtyard.

The remains of the farm is where the story of tunnelling

at La Boisselle begins.

This is all that remains of that farm. This is the Granathof -

literally "exploded farm" - the name given to it by the Germans.

The French called it the Ilot.

And the fighting over this farm was so bitter,

between the French Breton troops and the Germans,

hundreds of people lost their lives fighting over a farmyard.

Which way is he lying?

There was a chest here, and probably one arm here.

-So his head is over here?

-Probably somewhere here.

So he's lying in this direction?

Yeah. In fact he's just like that, with the hands...

And probably there was the rifle here.

-This is his rifle?

-Yeah.

'Breton troops fought against heavy odds to hold back the enemy here.

'Their homeland and their pride was at stake.'

The French were not to withdraw behind the existing front line,

because they have bought that front line with

the lives of hundreds of their men.

And if that line was to be lost, if that line was to be given up,

it would be a betrayal of that sacrifice.

After only four and a half months of fighting,

by Christmas/New Year 1915, the war had descended into stalemate.

These flags here, the yellow flags, they represent the French front line

and the red ones, the German front line.

You can see how close together they are.

And what was about to take place was almost medieval -

trench against trench, static warfare, siege warfare.

The trenches were fortifications on both sides.

In between you had no-man's-land.

And that was the perfect environment for military mining.

It was on Christmas Day 1914 that French engineers

sank their first shaft at this very point.

And that was the beginning of a colossal struggle.

The huge crater made by the German mine that obliterated the Granathof

reveals the devastating nature of tunnel warfare - whether they

liked it or not, both sides were now locked in to subterranean conflict.

There was nowhere to hide from a mine -

it could destroy a trench and its occupants in an instant.

For the infantry, even the suspicion that they were

being undermined created a paranoia that quickly eroded morale.

Within 12 months, no-man's-land was a chain of craters and in fact

what happened was, as the explosive charges grew and grew in scale,

the two opposing sides blew each other further apart.

Tunnelling had long been a valuable tactic when enemy positions

proved impregnable, or in the case of a castle or fortress, immovable.

Military mining is as old as siege warfare itself.

It would be a mistake to think that military mining

and tunnelling was born in the First World War.

In fact, it has a 4,000-year history.

But there's only a handful of places on Earth where you can visit

an early mine, and this is one of them.

I'm on the east coast of Scotland at St Andrews Castle,

and beneath us here is not only an offensive mine but a counter mine -

the defence, coming down to meet the offence, and that is what

mining and tunnelling in the First World War was all about.

In 1546, a band of Protestant reformers and rebels

were besieged here.

When they detected noises suggesting the fort tower was being undermined,

they themselves started digging to intercept the incoming offensive tunnel.

You can see how the offensive tunnel just here

is dipping very steeply down - that's to get underneath the ditch.

The next target is that fort tower, and there

they would have dug a chamber out and packed it with gunpowder.

The reason why this place is so big is

because they were using pack animals to remove the spoil,

so donkeys or mules to carry it out up the steps.

The steps are original, but of course at La Boisselle,

those pack animals were the poor bloody infantry.

The key part of this system is just up ahead here.

This is the essence of military mining,

this is where the two tunnels met. The defence coming down here,

having heard these guys tunnelling towards them,

to stop them undermining the fort tower,

and the offence suddenly finding they are face-to-face with the enemy.

One of the strange thoughts that occurs to me crawling through this place...

..is that you could take any one of the tunnellers who worked here -

offence, defence, doesn't matter -

transport him 500 years into the future,

put him in a First World War uniform,

set him to work at La Boisselle

and within five minutes, he would know exactly what to do.

And that's because the methods for military mining

did not change one jot in 500 years, because they simply didn't have to.

Quick march!

Throughout 1915, the French were losing men hand over fist.

And the British were forced to take over,

to relieve them of more and more sectors down the Western Front -

Vimy, Arras and eventually on the Somme.

And it was at the end of July 1915

that the Black Watch arrived here, at La Boisselle.

And, on this plan, we can see

when the Black Watch arrived,

these shafts are actually untenable.

They're not deep enough, they're being blown apart by German mines,

so they've had to step back to give themselves space

to get underneath the Germans,

to undermine the Germans.

In trench warfare, if you're looking down upon your enemy,

you have all the advantage.

In tunnel warfare, you're better off underneath him.

Scone Street trench, originally dug by the French,

but they were all renamed by the Scots when they arrived in July 1915.

And this was a main thoroughfare,

this is the very first entrance ever dug by those men.

The tunnels and trenches around Scone Street

occupied by the Black Watch

are where we begin our deeper excavation.

Good morning, all.

-Good morning.

-Good morning!

Welcome to our new arrivals.

It's frankly been unbelievable,

what we've found, what we've learnt.

Every single minute we've been here has thrown up new information

which has been very, very surprising.

We're working on the surface

and we're working underground at the same time.

We don't have any objectives cos we don't know what we're going to find,

so we cannot place any objectives.

When you believe you know so much,

you find something, you realise just how little you know.

Really astonishing, what we're finding.

It's hard to know what to say, isn't it?

Imagine how easy it is to miss that.

By the summer of 1915,

the scale of operations at La Boisselle had dramatically increased.

At Scone Street, we uncover a prime ingredient of mine warfare.

Boxes of guncotton explosive.

And evidence of other materials

vital to maintain huge armies on a static battlefield.

-I think, yeah.

-What is that for?

Petrol tin, probably a petrol tin, used for carrying water.

When the armies came in here,

the natural population just shot up from a few thousand

to hundreds and hundreds of thousands of men.

There wasn't enough water for these men

and all the horses and everything.

So, when the tunnelling started,

they sank wells down through the water table

in other to draw water from 110 feet down

to serve the men in the trenches.

So the tunnels served three purposes -

one, to defend your own trenches,

two, to kill the enemy, three, to supply water.

Without water, you can't fight a war.

So no water, no war.

It didn't take the British long

to bequeath fresh names at La Boisselle.

The French "Ilot" was rechristened the Glory Hole,

a title that came to hold fearsome undertones

for the soldiers who served there.

This is what the sector looked like soon after the British arrived.

The French tunnels they inherited were unconnected,

low, narrow, airless,

hazardous and too shallow to be effective.

Improving the situation required skills that the Army did not have.

Until the arrival of a new kind of Royal Engineer unit.

Made up of professional tunnellers and miners,

specially drafted in for their underground expertise.

The Tunnelling Companies were the brainchild of one extraordinary man.

One, two, three.

This manhole, here in Manchester,

introduces one of the great characters of the tunnelling story.

John Norton-Griffiths, he was a millionaire, entrepreneur, engineer

and it was his men

who were digging the sewers in 1913 beneath Manchester.

When war was declared,

Norton-Griffiths' company was building an extension

to Manchester's main drainage system.

He relied on a unique breed of workers

to dig through the clay geology of the area.

They were known as clay-kickers.

Norton-Griffiths called them his "moles".

It so happened that Lord Kitchener, Secretary of State for War,

was a family friend.

Norton-Griffiths wrote to him

proposing that clay-kickers might be very useful to the Army.

Norton-Griffiths, of course, wasn't suggesting to Kitchener

that his moles should be digging huge sewer-like structures,

as we saw beneath the streets of Manchester.

No, what he was saying was that his men, his moles,

could dig small, narrow, constricted tunnels

which will get underneath the German lines swiftly,

but, most important of all, silently.

None of the British military establishment believed

that the war was going to extend beyond Christmas at that time,

so the letter was simply filed under "M" for moles.

In December, the Germans blew the first mines

beneath British positions.

More and more followed.

By mid January, panic rippled through the trenches

and the War Office.

Norton-Griffiths is called in by Kitchener

and he demanded 10,000 clay-kickers.

There weren't that many in the country,

but it put Norton-Griffiths in charge.

There was no time for military niceties.

On Thursday, 18 February 1915,

the first party of 20 kickers were told to leave this very sewers.

Later that same day, they arrived here,

at John Norton-Griffiths' London offices,

where they were attested and given a medical.

The 18 that passed were immediately dispatched to Victoria Station

for the next leg of their journey to an unknown destination.

The next stop was here -

Brompton Barracks, in Chatham, Kent,

home of the Royal Engineers.

So our 18 sewer drivers have arrived with no military training whatsoever

to be inducted into one of the most illustrious corps

in the British Army.

And these men couldn't salute, they couldn't march,

they didn't know the difference between a tin of bully beef and a brigadier.

And that sent vibrations of nervousness

through the corridors of power.

The old and the bold didn't know how to treat these men,

they were Royal Engineers now.

24 hours ago, they'd been sewer drivers.

Some of them could be trade unionists.

Even worse than that, some of them could be Scottish trade unionists.

But military training was of minimal importance.

The were there to dig,

to counter the escalating German underground threat.

That very same evening,

they travelled to France and within 36 hours,

Norton-Griffiths had them tunnelling towards the enemy.

His moles were now the most valuable commodity on the Western front.

This is the clay-kicking team.

You've got the kicker here with his kicking iron.

The bagger, who's passing the lumps of clay back to the trammer,

who will pass it to somebody else and they will take it out of the system.

Everything is being done in silence.

The kicking is done in silence.

It's not really a kick, it's a push.

And that's absolutely deliberate.

Once they've taken out nine inches,

they put another set of timber in,

so what you're doing is you're moving towards the enemy

nine inches at a time, nine inches at a time, nine inches at a time,

all the way to Berlin almost.

The men are working in silence,

they're working in very bad air.

The rule was if a candle would burn,

the air was good enough to work in,

if it went out, you left the tunnel, because there wasn't enough oxygen.

And they're also searching for the enemy.

The prime duty of the tunnellers was not offensive, but defensive -

to protect the infantry in the trenches from being undermined.

To do so, they had to intercept the Germans

and turn their galleries into graves

by blowing them in underground.

So what you had was listeners at the end of a tunnel like this.

And the first thing they would use were civilian listening kits.

This is...

You stick your ear to it, it's for finding water, leaks.

So that's the only tool they had at the beginning of the war.

If they didn't have that, they used this idea.

Biscuit tin, fill it with water...

and on the water surface,

the vibrations of German tunnellers nearby would make that water ripple.

Now, in November 1915,

Norton-Griffiths arrived at La Boisselle

with one of these - the geophone.

And with it, you could pick up a German tunnelling 100 feet away.

And you could track them in.

In chalk, you could pick them out

260 feet away,

an extraordinary distance.

And what that allowed you to do was to track their progress towards you.

And if they didn't hear you first,

you could choose the moment that you murdered them.

In clay, once the decision to blow the enemy had been taken,

a hole was silently drilled towards the source of the sound.

Their weapon was a steel tube packed with explosive,

a terrestrial torpedo known as a camouflet.

The gallery behind it was then tamped,

tightly backfilled with sandbags to maximise the explosive force.

What this conflict has, which no other part of the war has,

is the ultimate form of barbarism -

you wait before you blow until you know the maximum number of enemy

are at the end of that gallery.

You blow them in, it doesn't matter whether they live or die,

it doesn't matter to you.

But then, if you're very clever,

you've got another charge ready and the one thing you do know

is that miners will make the maximum effort to save their comrades.

So you wait for the rescue team to come down,

wait till they are digging and then, blow them as well.

In this deadly game, the challenge was to hear and kill the enemy

before he heard and killed you.

A race to the death.

It's funny, cos when you're digging at home,

you're digging for totally different reasons

than what you're digging for out here.

This seems to mean so much more, the rewards are far greater.

It means something that the men that are out here all the time,

you know, they'll never go home.

Norton-Griffiths knew that in sectors like La Boisselle,

where tunnels were driven through chalk,

the harder geology demanded different skills.

So he began to recruit coalminers.

Norton-Griffiths toured collieries

asking for men to come forward

and the men who by and large enlist

are those who've tried to join the infantry and have been rejected,

so men who are too old, men in their late 30s, into their 40s,

and many of them lie about their age.

The age limit is relaxed, so they'll take men up to 45,

but there are many even over 45 who were coming forward.

But the point is that these men are the elite miners,

they have decades of experience,

some have been underground since the age of 14

or even younger for the oldest men.

And they're highly skilled, they are the aristocracy of the coal mines.

Tunnelling at La Boisselle now entered a period of intense expansion.

It was complex and technical

and required the guidance of an experienced civilian mining engineer.

Norton-Griffiths insisted he knew the man for the job.

Norton-Griffiths wrote in his report to the engineering chief

that 179 Company needed a good strong man.

And that man that he had in mind was a mining engineer named Henry Hance.

Now, Hance was described as a first-class rascal.

But Hance was utterly focused and, it has to be said,

utterly ruthless in achieving the objectives.

The tunnellers had a traditional way of letting off steam,

they were often very fond of drink

and, in fact, drunkenness was a continual problem

that affected the efficiency of the tunnelling companies.

Something that really illustrates the ruthlessness of Henry Hance

was that where the tunnellers were living,

there was a boarded-up cellar which was full of wine and brandy.

And one day, Hance discovered

that the tunnellers who were living in a cellar

on the other side of the road to the wine cellar

had started a tunnel to try to get to it.

And he went in there with his sergeant major and another officer

and between them, they smashed every barrel and every bottle in that cellar.

Hance was a hard man,

but our excavations show he directed some great feats of engineering.

Four days of digging exposes a gallery

marked on military maps as "W Adit".

It descends to a depth of ten metres

and contains the remains of a tramway

employed to shift the vast tonnage of spoil being lifted day and night

from the deeps below.

This is W Adit cleaned by our archaeologists.

Look at the job they've done.

This is the original floor.

The gallery is in brilliant condition,

but when you look at the walls too,

the candle marks are all still there.

This was lit by candlelight, of course.

But what they've revealed on the floor

is absolutely astonishing, and this is miners' work.

Here, we've got the original sleepers for the railway,

we've got the original runners for the railway.

On top of those would have been too little steel rails

to run a little wagon from the shaft behind me up to the surface.

But most remarkable of all,

is because this thing was not mechanised, it was pushed by hand,

the tunnellers needed a little bit of help with that and here it is.

Those holes have been cut by those tunnellers

to put their feet in

in order to help them push this heavily-loaded wagon

up this slope to the surface.

So I'm walking in the very footsteps of those men,

even the angle is correct,

so they can push like a sprinter taking off from the blocks.

There is nowhere on the Western Front where you can do this,

except in these tunnels.

I'm in the footsteps of those men.

At the end of W Adit is W-Shaft,

the gateway to a deeper system,

the fighting levels beneath no-man's-land.

At first glance, prospects looked good for a descent.

What I'm doing here is using a mini high-definition digital camera.

I'm lowering it down.

There were tunnels going off in that direction,

and in this direction from this shaft.

There were tunnellers at the end of listening posts, listening for the Germans,

and men were working below, infantry were working below helping the tunnellers.

It's very peculiar sitting here

knowing what the history of this wall and hole in the ground is.

By November 1915, Hance's men had dug to 25 metres

and now began driving their first deep galleries

out towards the Germans.

From the right-hand gallery,

Hance's listeners had detected German picking 15 yards away.

Hance himself came in and he listened there for six hours

and he decided they had to blow, so he ordered a chamber to be dug

to hold 6,000 pounds of ammonal to destroy the German system.

That was completed at midnight on November 21, 1915.

And at half past one the following night, the Germans themselves blew

and it took his charge with their own explosion - and massive blast.

It was so powerful that the shock came right at the shaft,

out of the galleries and collapsed one of the entrances.

The rescue party came down, they brought canaries with them in cages,

They lowered the canary down to the bottom of the shaft

and brought it back up two minutes later dead.

They tried that again and exactly the same thing happened,

so a man went down in breathing gear

and he found at the bottom of this very shaft

which we're looking down now,

two men dead, gassed. Carbon monoxide gas.

Using the remains of the winch, which is over there in the corner,

they lifted their bodies up the shaft and carried them out.

But two men remained trapped -

John Lane, 45,

and Ezekiel Parkes, 37.

Both coalminers from Tipton, in the Black Country.

Parkes and Lane are just two of over 120 British and French tunnellers

who died at the Glory Hole.

They were simply recorded as "killed in action".

Perhaps mercifully, families had no inkling

of the character of their war or the nature of their death.

Yet, such event could not be a deterrent, work went on.

We believe the shaft can give us access

to three kilometres of tunnels

and a further, even deeper, level.

We've now cleared the shaft chamber, this is the original shaft chamber.

And what we're actually doing

is replacing what the tunnellers put in in 1915 in timber.

You can still see their original timbers.

We're replacing that with steel

and what we're going to do is build a steel cage here

to protect us from anything that might fall from the roof.

We'll also use the cage in order to brace this roof,

cos there's some very severe fractures

you can see in the rock here.

And so, the most hazardous part of our exploration begins.

Over 100 mines shook this chamber from below,

countless thousands of shells burst above it.

For a safe descent,

we need not only a team with many a specialist skill,

but a structure that will support the technical equipment -

winches, pumps, cables and ropes.

As the Somme summer turns to winter,

we secure the shaft and make it safe to descend.

All being well, we plan to be the first people for almost a century

to explore the lower levels of the Glory Hole.

This really is almost a journey into the Valley of the Kings for us, isn't it?

Right. OK.

'For us, as for the tunnellers at the time,

'the danger from gas is real.

'Carbon monoxide produced by underground explosions

'killed as many men as the blasts themselves.

'Colourless, odourless and lethal,

'pockets of it may still exist.'

Put it in front.

'We may also have other gases to deal with and low oxygen levels.

'For these are tunnels that haven't been open to the air for many decades.'

-..The bottle.

-All right.

Keep the bottle at the back, cos you're going to be...

'As a precaution, our team have gone through training

'with equipment made by the same company

'that manufactured the apparatus supplied

'to the tunnellers of the Great War.'

That's it.

There's a very strong breeze coming through the hole.

It's clean, clean air.

We are through, we are through.

Well done, well done.

'The air is clear, the shaft stable.

'Debris still blocks access to the lower levels,

'but we are able to clear a small hole for a first, brief glimpse.'

-Yes, you can see the gallery goes away to the left.

-Yeah.

In fact, I think I can see the remains of a wooden railway line.

The gas detector just slid away into another department.

-All right?

-Yeah.

Just caught on a knot on your back.

That's it, just move it... That's better.

Nice and steady, Pete.

-OK.

-Nice and steady.

-It's very tight.

-How do you feel?

-Very tight.

Very tight indeed.

-That's enough.

-Through there, that's it.

Does it open up, Pete?

It's absolutely clear.

There's railway lines...

Oh, God!

It's tiny and it just feels...primeval...

..primitive, which is precisely what this war was.

I'll take a photograph.

Here, finally, are La Boisselle's 25-metre fighting tunnels.

They give us entry to 11 more shafts

that descend to the deepest level near the water table.

'Just a few metres from the foot of W-Shaft,

'is the end of the gallery

'in which John Lane and Ezekiel Parkes were working

'on the night of 22 November 1915.'

And just up ahead here...

..is a place I've been rather nervous of seeing.

Here is the blocked gallery

where Ezekiel Parkes and John Lane still lie.

It's a grave.

But we need to pay our respects.

We're the first people down here in 95, 97 years.

They need to know we're here.

And they need to know that we know they are still here.

In early 1916, plans were laid for a major summer offensive on the Somme.

It was to present Hance's tunnellers

with their greatest challenge of the war.

Instead of simply offering protection,

they were now to play a key role in spearheading the attempt

to break two years of stalemate.

The French had thrown themselves at the German bull.

They'd lost hundreds of thousands of men and gained nothing at all.

And come 1916, with the Battle of Verdun going on,

which was designed to bleed France white.

That was the German goal - to bleed France white,

and force a political solution.

Then, came the turn of the British

in Picardy, on the Somme,

with French help, they were going to break this barrier

and force open warfare.

Smash the Western Front

and that is where La Boisselle came in.

Because this was in the epicentre of that planned battlefield

the Albert-Bapaume road

was THE main axis of Allied attack,

for this great battle of the Somme.

The village was German property.

It was impossible to attack it frontally

because of the crater field

and because it was bristling with weapons.

So the plan was to obliterate the German front lines

either side of it with artillery.

The tunnellers' job was to plant two huge mines on either flank.

On this side, Y-Sap,

and on the far side, Lochnagar.

That would blow a hole in the German defences,

which they could not defend.

And through those two holes would swarm the infantry.

Both mines were 179 Tunnelling Company's responsibility.

The 320-metre Y-Sap tunnel

was driven from the deep level near the cemetery.

Its purpose - to eliminate a multiple machine-gun position

on the north flank of the village.

'Mining efforts at the Glory Hole were redoubled

'in the months leading up to the attack.

'As the tunnellers inched their way towards the objectives,

'anticipation was mixed with fear

'were they about to deliver a knockout blow

'or would the Germans hear them and blow them up first?'

Timber been cut into the sidewall here.

Just to give them a little bit of extra protection.

Try to imagine, which we can't, of course,

a German blow taking place near here.

This wall would simply crush you against that wall

with the force of it.

You can see the ground has been shattered. That is from...

That's from German and British mine blows.

Shattered ground.

But it's still holding up.

What would you do in a place like this if there was an emergency?

If the Germans blew a mine and all those men...

There were 900 people working underground here.

How on Earth would you reach the shaft?

What a scramble that would be.

Oh, the horror of it.

I found the other shaft chamber, here, just on my left-hand side.

You might be able to hear the echo?

HE CHUCKLES

It's perfectly cut, as you would expect.

And that goes further on.

It goes on and on and on, I can't see the end of the gallery.

And off it are the listening posts and the mine chambers.

Off in the direction of the enemy.

In that easterly direction.

'Laying a mine isn't just about digging tunnels.

'It involves the excavation of underground caverns, mine chambers,

'to house the explosive charge.

'Once filled, the gallery behind was packed with sandbags of chalk

'to force the blast vertically.'

This is the entrance to a mine chamber.

There's a tunnel going out under no-man's-land,

cos we are under no-man's-land here.

And it goes forward and zigzags and there's a chamber at the end of it.

This bit has been blocked up, probably just backfill.

But I can see beyond.

But I've just seen something very,

very thought-provoking indeed,

because down here...

..are the cables for the mine.

They've been cut, fortunately.

But what we don't know, of course,

is whether there's still a mine in there.

What a very strange thought.

By early summer, excellent progress had been made.

But now, the galleries had to pass

beneath a belt of suspected German listening posts.

A new approach was required.

There were times when you were mining,

when there was no choice, but to work with noise.

However, when it came to the big mines,

which were being prepared for the beginning of the battle, Lochnagar and Y-Sap,

everything had to change when they reached a certain point.

The pick was put down in favour of the bayonet.

It was a little bit like a clay-kicking team, in fact.

One man with the point of his bayonet

just easing out a lump of chalk,

the second man catching it,

but the third man was an officer

and his job was to make sure

that those first two worked in the maximum amount of silence.

High Command finally selected 29th of June as the day of the attack,

to be preceded by the greatest artillery onslaught in history.

But completing Lochnagar by bayonet alone proved impossible,

the tunnel was stopped short

and two huge chambers dug to hold 60,000 pounds of explosive.

By far, the biggest British charge of the war to date.

The preliminary bombardment began on the 24th of June.

Over the next week, a torrent of 1.7 million shells

descended upon the Germans.

The countdown to the tunnellers' moment of glory was under way.

Hance had charged his men to plant 20 tonnes of explosives

beneath the Y-Sap.

30 tonnes beneath Lochnagar.

And two enormous charges under the Glory Hole itself,

to destroy the German tunnel system.

The bombardment was falling. Time was running out.

There was no more tension than at this moment.

Through these fields were lines and lines of infantrymen

carrying tins of ammonal explosives up to the mines, up to the chambers,

to charge them, ready for the first of July.

Nerves were at breaking point.

Even 100 years later,

these front-line German trenches are still two metres or more deep.

This is what the British had to contend with.

Henry Hance had an idea for this.

He wanted to blow Y-Sap early, several days early,

so it would wipe out the German machine-gun positions

and also shorten the distance

that the British troops would have to attack across no-man's-land.

The resulting crater, he said, could then be occupied

and employed to dig an advanced jumping-off trench

for the British infantry,

a trench that would effectively reduce the distance

across no-man's-land by over 150 metres.

What Henry Hance was trying to achieve by blowing up Y-Sap early

was to cut out the German chance of enfilade.

And that means firing the machine guns up no-man's-land,

along no-man's-land, at about knee height.

If you just trained your machine gun and fired it,

it meant that the British troops crossing this way

would have to walk through a stream of bullets

and they would be cut off at the legs, and when we talk about men being cut down like a scythe,

that's what happened with machine guns.

They were just cut down here and fall to the ground.

Hance's core commander agreed

that neutralising enemy fire from the flanks would save lives around La Boisselle,

but the explosion would warn the enemy an infantry attack was imminent.

So the answer was no.

'As the big day drew close, the attack was delayed.

'British commanders were most anxious that the actual moment of assault,

'now set for 7.30am on the first of July, should not be compromised.

'But it was compromised, and it happened here, at La Boisselle.'

Mine chamber. An uncharged mine chamber.

But also a listening post.

What the British were not aware of until after the battle

is something rather serious.

In fact, possibly the most serious but little-thought-of fact,

and that was that in one of the German tunnels, there was a chamber,

within which was a machine called a Moritz system.

And it was specially designed to pick up electrical impulses

passing through the earth itself.

Telephone impulses.

And somebody on the British side on the night of the 30th of June

sent a telephone message, unscrambled,

to one of the brigades holding the line here.

And it said, "Good luck tomorrow morning."

The only thing the Germans did not know after eight days of bombardment

was the moment of the British attack

and the British had just told them.

The first of July was a clear, warm day

but the air trembled with the thunder of artillery.

The infantry were poised to go into action,

all mines charged and exploders connected.

After months of toil,

the tunnellers were prepared and ready for their moment.

These trenches filled with infantry.

They knew nothing at all of what was going on beneath their feet.

They were not allowed to know that.

Because if they'd been captured with that information,

it could have led to the loss of those mines.

The tunnellers were ready to push the plunger down.

That was their moment of no return.

For the infantry, however, it was this, it was this sound.

That's when they knew they were going over the top.

7.28 two minutes to zero.

The scale of the eruptions was most dramatically seen from the sky.

Aerial observer Cecil Lewis had a unique view.

"There was an ear-splitting roar, drowning all the guns,

"flinging the machine sideways in the repercussing air.

"The earthly column rose, higher and higher to almost 4,000 feet.

"There it hung or seemed to hang for a moment in the air.

"Like the silhouette of some great Cyprus tree."

This is the extraordinary result of 30 tonnes,

60,000 pounds of explosive.

Everything in the path of this crater

would have been simply obliterated.

And finally, the shock wave from this massive explosion

passed through the German dugout, through the soldiers themselves,

haemorrhaging their brains.

Two minutes later, troops from the Tyneside Scottish and Tyneside Irish

rose to assault enemy trenches

that lay smoking and pulverised before them.

But something wasn't right,

in Mash Valley, next to the huge Y-Sap crater,

the leading waves were seen to wither and fall

before they had gone 100 metres.

The Germans had heard British tunnelling, evacuated Y-Sap,

installed their machine guns elsewhere

and throughout no-man's-land produced a lethal hail

of enfilade cross-fire.

Hance's worst nightmare had come true.

The Germans were not neutralised

and that's because the Germans were in dugouts,

deep shelters underneath the trenches.

They'd taken their weapons down there,

the moment the bombardment stopped or moved on,

up they came out of the dugout,

placed their machine guns on the parapets

and cut down the British soldiers, like corn.

They were scythed down like corn.

5,100 men lay in this valley before noon on the first of July.

On the other side of the village,

in Sausage Valley, where Lochnagar was blown,

over 6,000 men were dead, wounded and missing.

The killing fields astride the Glory Hole

saw the highest concentration of casualties

on the entire Somme battleground that day -

the most disastrous in British military history.

La Boisselle was meant to have fallen within 20 minutes.

That night, it was still in German hands.

Their two-year occupation had allowed them to create a bastion

with hundreds of deep shelters that withstood the pummelling of even the heaviest British guns.

And so, the tunnellers had achieved everything...and nothing.

The fact that it did not help the infantry was not their fault.

British High Command had put their faith in the guns,

that was the major weapon in their armoury.

But the Germans knew that, they had prepared.

And they put themselves underground out of harm's way.

So, at La Boisselle, the tunnellers did everything in their power

to assist the infantry to succeed,

but it was never going to be enough.

What happened on the first of July

exposed the limitations of mine warfare.

It can deliver destruction, shock and awe on a grand scale,

but only momentarily.

When La Boisselle finally fell to the British on the fourth of July,

the Glory Hole became immediately redundant,

abandoned as the front line crept forward.

No tunneller can keep up with a moving army.

Along the old Roman road, the battle continued until mid November,

claiming a further million casualties

for six miles of bludgeoned terrain.

Today, agriculture shares the fields and pastures of the Somme

with monuments to the fallen.

Little survives of the surface war,

but beneath lies the kingdom of the tunnellers.

The world they made at such great cost

and where so many remain entombed is all still there.

This is their monument.

Subtitles by Red Bee Media Ltd