-Firepower, fortifications, troops, and tanks often dominate stories of the Second World War.

What can sometimes go unnoticed is the role of deception in military strategy.

Camouflage, decoys, and disinformation all became tools for the Axis and Allies alike.

-Deception played a major role in the Second World War.

It was practiced on the largest scale it's ever been practiced in the history of warfare.

-Strategies ranged from a simple feint performed in the midst of battle to complex, long-planned campaigns designed to completely alter the enemy's perspective.

-The whole point in military deception and intelligence operations is to try and get the enemy to do what you want them to do, because that means you have a better chance of things going your way.

-There's no doubt that deception helped to save lives and bring a swifter end to World War II.

-The stories behind some of the most extraordinary feats of espionage and strategic subterfuge the world has ever seen.

-It changes the character of war, and it changes the way that war is waged.

And that's not going to change back.

♪♪ ♪♪ -The Second World War opened with an act of subterfuge that would serve as a justification for the German invasion of Poland.

From the outset, deceivers sought to hide the truth and display the lies across all theaters and campaigns.

♪♪ ♪♪ [ Crowd cheering ] By August 1939, Adolf Hitler had been German chancellor for six years.

Under the Fuhrer's iron hand, the empire had expanded its territory in Europe... with Poland the next target.

-Hitler had a social Darwinist view of the world and of humanity -- believed that humanity was split into so-called inferior and superior races, the most superior being -- in his eyes, of course -- the Germans, the most inferior being the Jews.

But, nevertheless, only slightly above them were the Eastern Slavs, including the Poles.

It deeply affronted Hitler that Poles were allowed to, as he saw it, multiply on Germany's borders.

And so he resolved to conquer Poland, not just conquer it, but to enslave and decimate its so-called subhuman population.

-German newspapers were filled with stories of Polish atrocities against ethnic Germans living in Poland.

They blamed the British government for inflaming violence when they pledged to defend Poland if the Germans invaded.

The Nazis plotted to fool the German people and neutral countries into believing war was an unavoidable and moral response to Polish hostility.

-In order to justify the invasion of Poland to the German people, Hitler ordered a series of false-flag operations to take place.

These false-flag operations took place along the Polish-German border.

They were organized by the Abwehr, the German military intelligence service under Admiral Wilhelm Canaris, and also by the Reich Security Service under Reinhard Heydrich.

Purpose of these false-flag operations was to show to the German people or to depict to the German people the idea that it was Poles attacking Germans and that Germany was only attacking Poland because it had been provoked to do so.

-The plan, Operation Himmler, involved numerous false-flag attacks designed to simulate Polish strikes against German targets.

-The Gleiwitz Incident was another of these false-flag operations.

It did not lead to as great a loss of life, but it's perhaps emblematic of the rather farcical, amateurish nature of these false-flag operations, but, nevertheless, the tragic consequences that they went on to have.

-On August 31, 1939, German SS officers garbed in Polish uniforms approached a transmission tower in Gleiwitz, a German town near the border with Poland.

The Gleiwitz radio station was critical to circulating pro-German sentiment.

According to testimony made by their leader, SS Sturmbannfuehrer Alfred Naujocks at the Nuremberg trials, the small group had just received a coded message via radio -- "Grossmutter gestorben," meaning, "Grandmother dead."

Naujocks bolted up the steps and into the station office, pushing past German staff.

Another officer seized a microphone and delivered a short anti-German message in Polish.

-[ Speaking Polish ] -The precise wording of this statement is unknown, but it was made to seem like the work of Polish saboteurs.

-To add a touch of authenticity to the proceedings, it was arranged for a Polish-speaking German citizen, who was also a pro-Polish agitator, to be taken to the police headquarters in Gleiwitz, drugged, shot, and then his body dumped at the back of the building as purported evidence that this was the work of the Poles.

-According to testimony by another German official, Erwin von Lahousen, prisoners from Dachau concentration camp were left at the site as false accomplices.

Referred to as "konserve" or "canned goods" by the Germans, their faces were disfigured to make identification impossible.

Within hours, German radio reported the incident as an anti-German attack by Polish soldiers.

Foreign correspondents were brought to the scene and the events were mentioned in international press, but any scrutiny of the attack was quickly eclipsed by the German advance the following morning.

At 4:45 a.m. on September 1, 1939, the invasion of Poland began.

♪♪ In a speech made at the Reichstag, Hitler announced the news of an offense as a justified retaliation to Polish attacks on German territory, including the attack on the Gleiwitz station.

-[ Speaking German ] [ Crowd chanting "Sieg heil" ] [ Cheering ] -Although Hitler did not refer to war in his speech, the meaning was clear.

The British and French governments had promised to assist in the case of an attack.

Both countries declared war on Germany two days later, on September 3, 1939.

The Gleiwitz incident is often considered the first act of the Second World War.

♪♪ ♪♪ Over the following six years of war, lies and disinformation would pervade Hitler's entire war effort.

♪♪ [ Clock tower chiming ] Even before the Invasion of Poland in 1939, Britain was devising sophisticated deception techniques to gather intel on the Axis... ranging from battle plans to technological developments.

[ Machinery whirring ] [ Telegraph beeping ] The person they chose to lead one of these key operations was an experienced spymaster, fluent in German, with a strong grasp of human psychology.

This appointment would prove to be essential to plans that were taking shape.

-Thomas Kendrick lived for around 40 years in the shadows of secrecy.

He was a very senior spymaster who worked for the Secret Intelligence Service, what we know today as MI6, and he had already 30 years in espionage and running spy networks across Europe in the 1920s and '30s.

And then, during the Second World War, he goes on to head a little-known intelligence operation that actually is now recognized as turning the tide of the war.

-This intelligence operation would require a different type of deception, mixing new technology with a keen understanding of how humans behaved.

It would become known as the M Room operation.

It spied on German prisoners of war.

-M Room operations was this vast bugging operation that started at the outbreak of war in 1939 and ran until just beyond the end of the Second World War.

It relied on an understanding of human intelligence, so the HUMINT, as one would call it, in the spy world.

-The plan was to take prisoners of war and place them in specially curated locations where concealed microphones would record all prisoner conversations -- not only with their captors, but also with each other.

Thomas Kendrick and his team of secret listeners would transcribe every word spoken to gain vital intelligence for the Allied war effort.

An unconventional aspect of this deception was rather than treat the prisoners with hostility, they would be treated with great respect to their rank and held in stately homes.

-And if you do that, they will throw caution to the wind.

They're not looking in the direction of "Why are we here?"

They're not asking, "Why have we got this stately home?"

So that, for me, is at the heart of this deception.

It's so clever.

-After starting operations out of the Tower of London, early successes led to the establishment of locations in the lavish surrounds of Trent Park, Latimer House, and Wilton Park.

High-ranking Axis generals were not confined to rudimentary cells surrounded by barbed wire.

At Trent Park, they were taken to accommodation more akin to a private gentlemen's club.

♪♪ Beyond the higher standards of bedroom, prisoners were allocated to a room for enjoying their favorite pastimes, such as painting, drawing, or playing billiards.

The luxury of the interiors was matched by the gardens and parklands of the manor.

The generals were free to explore the old woods, ancient oak trees, and Lime Tree Avenue.

Everything was carefully planned to make the prisoners complacent, and everything was bugged both inside and out.

-They didn't have to worry about interrogating the generals.

You just put them in this beautiful house, stately home, completely relaxed, and they give up the most incredible intelligence to those hidden microphones that they would never have given in interrogation.

-The tiny microphones used in the operation were concealed in places such as fireplaces, light fittings, even trees in the gardens, all of which were wired back to the M Rooms' listening stations.

-They were very sensitive.

They had to be able to pick up the conversations, and we weren't to miss a single piece of intelligence.

This operation began the moment the prisoners woke up in the morning until they went to bed, until the lights were out and they'd stopped talking, because they could just give up a valuable piece of intelligence just before midnight.

So this operated 24 hours a day, every single day of the war.

And it was one of, if not the longest deception mounted against Nazi Germany.

-On the 26th of May, 1943, secret listeners at Trent Park heard a discussion between a captured German general and a senior German officer discussing the development of the new wonder weapons -- the V-1 flying bomb and the V-2 rocket, at Peenemuende... including details such as its propulsion methods and travel distances.

-They are picking up intelligence on new technology that the Germans are developing even before it's being used.

And that's right across the German Army, Navy, and Air Force.

-As a result of the recorded conversations, secret reconnaissance missions to photograph Peenemuende were carried out.

These formed vital intelligence used in a wider plan to neutralize the development of the V-weapons -- Operation Crossbow.

-With the V-weapons, you can see a direct line between Hitler's generals spilling the beans to those hidden microphones... and the British bombing of Peenemuende in the middle of August 1943.

Imagine -- those V-weapons were virtually operational that summer of 1943.

If we hadn't knocked out Peenemuende, we couldn't have mounted the D-Day landings.

Those V-weapons could have been turned on our troops coming up through Italy.

I believe, at that point, we could have lost the war.

♪♪ -Spies in the Second World War were often regarded as solitary men that hid in the shadows, gathering secrets.

But figures from all walks of life engaged in espionage, and sometimes, they hid in the spotlight.

♪♪ The American-born French entertainer Josephine Baker was one of the most famous people in France, celebrated for her singing and dancing and loved for her stage persona.

-She became the toast of Paris very quickly.

Hemingway started writing about her.

Picasso started painting her.

She also became the poster child for a hair product known as Bakerfix, and if you see the pictures of her from the '20s and '30s, you see her hair affixed to her head in a very artistic way.

So she was probably the most famous black woman in the world at that time and certainly the richest.

-In 1937, Baker renounced her American citizenship and became a citizen of France.

[ Cheering ] ♪♪ From the outbreak of war, Baker was committed to serving her adopted country, believing that it was her duty to support the war effort and fight hatred and discrimination.

After France declared war on Germany in September 1939, Josephine Baker was recommended to Jacques Abtey, the head of counterintelligence in Paris.

-Jacques Abtey was very hesitant to consider her for undercover work, because he looked at her, she was a big star, she was glamorous.

she was beautiful.

-Abtey was skeptical at first, but a practice run to gather information at an Italian embassy party revealed the performer's natural ability to charm people and build their trust.

Abtey taught Baker the tricks of the spy trade -- hiding documents, writing in invisible ink, and improvising a story.

-Josephine attended embassy parties in Paris, the Italian Embassy, and the Japanese Embassy, and she would just flit around from person to person, just being Josephine Baker, and all the while, she would be keeping her ears open, picking up information as she could.

-By May 1940, France was a tinderbox ready to ignite.

With the full-blown invasion of the capital, many fled the city each day.

-After the Nazis invaded, Josephine swore that she would never perform in France as long as the Nazis were there.

Goebbels had already denounced her as a decadent artist.

He had also forbidden Jewish people or black people from performing.

So she left Paris for her chateau in Southern France, Les Milandes, and there, she hid weapons, she hid ammunition, and she also hid resistors.

Anything that the resistance needed, she opened her home for them to do.

-Meanwhile, Abtey was directed to convey critical information gathered by spies to the London-based resistance movement.

Only a performer like Baker could travel across Europe without drawing suspicion.

Adopting a disguise, Abtey would pose as her secretary and assistant.

For their first assignment, in November 1940, Baker and Abtey set off for Lisbon, ostensibly on a scouting trip for a planned tour of the Iberian Peninsula.

Wrapped in her favorite fur, Baker drove with Abtey to Toulouse, where they boarded a train destined to reach Spain through the Pyrenees Mountains.

Amongst her massive luggage, Baker's musical scores carried the intelligence given to Abtey, written in an invisible ink.

They hid details of the location and strength of the German divisions across Western France.

Convinced that no one would attempt to search her, Baker pinned photographs to her undergarments.

According to Abtey's account, the images carried in Baker's clothing revealed the German landing craft proposed for the future invasion of Britain.

[ Train whistle blows ] At each stop on the journey to Lisbon, Baker was swamped by a mass of fans.

No one gave a second glance to her silent assistant.

[ Crowd cheering ] Once in Portugal, Abtey delivered the crucial material to the British ambassador, who passed it on to London headquarters.

The scheme was a success and the first of many journeys across Europe and North Africa to transfer intelligence for the Allied cause.

-For her work in the war, she was honored with the Croix de Guerre, that is, the Cross of War.

She also was made a Chevalier of the Legion of Honor.

She received the Rosette of the Resistance.

She was made an honorary member of the Free French Forces by Charles de Gaulle, and when she died in Paris in 1975, she received full military honors at her funeral.

[ Bell tolling ] ♪♪ ♪♪ -At the outbreak of war, the British sought innovative means to combat German bombers and defend British cities and citizens.

Alongside new aircraft and detection technology, visual deception would play a key role in their strategy.

A special unit was set up to create decoys to lure German bombers away from their intended targets.

♪♪ -If you imagine, the British film industry at the time didn't have much work going on, and these were people who were really, really skilled at fooling people, through the lens of a camera, into thinking they were looking at something else.

-Working out of Sound City film studios in Surrey, the secret department created fake equipment and structures and developed special techniques to deceive the enemy.

The first decoy sites were known as "K" sites, decoy airfields designed to attract German bombers flying overhead during daylight raids.

"K" sites appeared as real airfields when seen from the air.

But through 1940, the German strategy shifted to favor night raids, where bombers could fly under the cover of darkness.

Nighttime decoy sites were needed to deceive the enemy, so "Q" sites were introduced, often at the same sites as the daytime decoy airfields.

-"Q" sites are essentially flat areas of land, sometimes agricultural fields, that are taken to be doctored to look like an airfield, and that means fake aircraft sometimes made of cardboard or wood, vehicles that are either the correct-looking vehicles or they're modified in some way.

Camouflage netting is used.

Gun pits, bomb dumps, operations rooms, telephone wires.

If it was on a real airfield, they had a mock version of it.

-Becoming operational in June 1940, "Q" sites featured distinct lighting patterns that would lure enemy aircraft at nighttime.

Flare paths lit by electricity were controlled from an operation room to imitate real airfields.

When enemy aircraft approached, a "Q"-site operator might exit the concrete shelter to manipulate a powerful lamp.

This would simulate an aircraft taking off, landing, and taxiing across rough terrain.

-According to a 1946 statistic, "Q" sites took 443 hits during the Second World War.

So that's 443 bombs or raids that did not land on real airfields.

There undoubtedly is some success in there.

♪♪ -After the devastating night bombing of the city of Coventry in November 1940, the department was tasked with the design of decoy sites that stood in for British cities and towns.

An evolution of the "Q" sites' decoy airfield, Starfish sites used lighting and fires to masquerade as urban areas.

-If you think from the point of view of a German pilot, you're flying along at night looking for some sign of there being a city below.

The sorts of things you might see were people peering from behind curtains quickly, little flashes of lights, and stuff like that.

-Starfish sites were treated with dazzling light shows to mimic factories and shipyards and simulate bombs exploding and buildings on fire.

As most of England was under blackout, these sites truly stood out.

-So, again, from a German pilot's point of view, you would be thinking, "Oh, the fire brigade are there trying to put the fires out.

I must be over the town.

This is where I'm going to drop my bombs."

-One of the most successful Starfish operations of the war involved a series of decoy sites located around Langstone Harbour and on Hayling Island.

These sites were set up to resemble the geography of the neighboring city of Portsmouth and its harbor.

Fire baskets and boilers were put in position.

Made of wood and wire netting and filled with fuel-soaked brushwood and reeds, fire baskets were ignited by flare cans placed inside.

When detonated, the blazing flare can and burning basket would mimic flames and smoke emerging from the windows and doors of a building.

The baskets were distributed across the site so they appeared as buildings from above.

Boilers released oil from a storage tank into a heated trough.

When triggered, the oil began burning.

A flush of water from another storage tank caused a brief explosion of white-hot flame rising over 30 feet in the air.

On the night of April 17, 1941, the Starfish sites around Langstone Harbour and on Hayling Island drew more than 140 enemy aircraft that rained down bombs originally intended for the city.

The decoy sites were hit by more than 200 munitions.

Only eight bombs hit the real target of Portsmouth.

Approximately 600 decoy sites were established across the United Kingdom throughout the war.

-While "Q" sites and dummy airfields and all these things couldn't actually stop the Germans from flying over and dropping bombs on the country, they could reduce the effect of them.

-More broadly, "Q" sites were integral to boosting civil morale during the devastating Battle of Britain in 1940.

Any bomb failure was a victory.

♪♪ ♪♪ British Prime Minister Winston Churchill once said to his Soviet ally Joseph Stalin, "Truth is so precious that it should always be attended by a bodyguard of lies."

-Many of the traditional military men were not in support of unconventional tactics, like deception, in the very beginning of the war, so the fact that Winston Churchill threw his support behind it allowed for deception to succeed.

-Churchill's backing was vital to the innovative work of British Colonel Dudley Clarke and his deception unit.

This unit created whole regiments and tank formations from canvas and metal.

What began as small-scale successes, made with trial and error, evolved into grand illusions that turned the tides of battle.

♪♪ ♪♪ Six months on from Italy's declaration of war on the Allied nations, British forces under the command of General Archibald Wavell were vastly outnumbered by Italian troops in the Western Desert Campaign in 1940.

-The Italians declared war on the British in June of 1940, and Wavell found himself in the most unenviable position possible.

-With no means of reinforcement, Wavell planned Operation Compass, aiming to exaggerate their numbers through visual deception and disinformation tactics.

♪♪ Operation Compass was a major victory for Wavell.

What could be achieved if the deception was performed on a much larger scale?

-So Wavell had no doubt that deception would play a pivotal role in operation in North Africa, and as Commander in Chief Middle East, he had to put into place that unit that would do that.

Now, he may not have had a role, necessarily, in executing and planning those missions, but he had to select a person who he thought would do that.

-Lieutenant Colonel Dudley Clarke already had a long and varied career in the British Army.

Wavell first recognized Clarke's unorthodox-but-innovative approach while they served in Palestine during the 1936 Arab uprising.

In December 1940, Wavell summoned Clarke to lead strategic deception in North Africa.

-And he knew his unorthodox views.

He knew that he was someone who thought outside the box.

He was a little bit curious, he was a little bit -- a little bit different, and he was willing to do these different things that could potentially make or break operations in deception.

-Clarke learned to shape deception strategies around enemy actions rather than thoughts.

"What do you want the enemy to do?"

should be the guiding question in the art of deception.

As Clarke's deception schemes progressed, he adopted the intentionally vague and theatrical title "'A' Force."

Later, his department was formalized as Advanced Headquarters "A" Force.

-"A" Force operated like a private army.

Dudley Clarke served as its commander, but it had multiple headquarters.

It had multiple subsections.

At its height, it had a total of about 600 officers and personnel.

-Clarke brought on specialists such as engineer Victor Jones, an expert in visual and tactical deception, and the diplomat Mark Ogilvie-Grant, who managed the spread of disinformation.

He even recruited Jasper Maskelyne, a third-generation stage magician.

-Jasper Maskelyne claimed after the war that he'd taken part in these incredible deception stories, that he'd made armies vanish in the desert, he'd made cities disappear.

Now, the likelihood is, is he hadn't done any of those things.

There were genuine deception organizations.

And so all of this was going on, but, of course, it was secret.

So it was almost as if the authorities allowed Jasper Maskelyne, after the war, to go out and do this incredible book of self-promotion because it hid the real story.

-One of the most notable examples of Clarke's deceptive plans was performed in the lead-up to the Second Battle of El Alamein.

In August 1942, the newly appointed commander of the Eighth Army, General Montgomery, charged Clarke with engineering a plan to deceive German commander Erwin Rommel about the timing and location of the Allied attack in Northern Egypt.

-This was the closest that the Axis forces came to Cairo and really put the British in a position of desperation, so as Montgomery began planning an attack at El Alamein, he not only implemented very significant training and resupply reinforcement of his forces, but also tasked "A" Force with carrying out a deception organization to cover the impending offensive.

♪♪ -Operation Bertram was designed to trick the Germans into believing the attack would launch in the South in early November, when it would, in fact, strike in the North two weeks earlier than expected and on a much larger scale.

The tactical illusion was far greater than anything ever seen in the war so far.

-They created roads.

They created pipelines, created supply depots, ordnance depots.

They carried out training exercises.

They placed real equipment, dummy equipment, everything.

And they did so in a way where the Germans would be able to observe it, but it looked like they tried to hide it.

-But how to hide the mass movement of tanks through the desert to the real site of attack?

They called in experts in visual trickery and disguise -- Geoffrey Barkas, a film-set designer, and Tony Ayrton, an artist, to design props for the operation.

As the 10th Armored Corps withdrew north, the tanks were disguised by the Sun Shield system.

They were fitted with side and top covers that made the tanks look like a 10-ton vehicle.

A quick-release device would allow the panels to be discarded quickly when the attack began.

The real tanks were quickly swapped out with dummies made from trucks enclosed in a metal-and-canvas frame.

Guns and their limbers were made to resemble 3-ton vehicles in a technique known as cannibal, where the gun and limber were disguised in a canopy of pole, wire, and netting.

A week before the attack, a double bluff was enacted.

The dummy field regiment was left to deteriorate.

As the days passed, it would become clear to the enemy these were dummies, but immediately before the battle, the dummies were replaced by real guns.

-The result was, when the offensive commenced, the Germans ran their panzers directly into those three and a half regiments of genuine guns.

♪♪ ♪♪ -The British were victorious at El Alamein.

Operation Bertram was a total success.

-It succeeded in all points.

It made the Germans think that not only were there more British forces there, but that the attack was coming from the south by putting the tanks behind the lines and making the enemy think that they weren't ready to go, they weren't ready to attack.

They thought they had weeks to go.

-We know that the British achieved the element of surprise because Rommel wasn't even in North Africa when the campaign began.

Had he any inclination that the British were about to go on the offensive, he would have been in North Africa.

-Operation Bertram marked the largest visual-deception campaign in the early years.

The techniques established here became critical to success in future campaigns.

♪♪ Throughout the Second World War, secret messages crisscrossed Europe, carrying information that would be used to make strategic decisions.

Many of these messages were secured using encryption, often by cipher devices.

♪♪ Strategists went to extraordinary lengths to crack the enemy's codes and unlock the details hidden in these messages.

But even with success, the major hurdle in code-breaking was in keeping the breakthrough a secret so that it could continue to be exploited.

Invented by a German engineer at the end of the First World War, the Enigma machine was a cipher device widely adopted by the German military and government in the mid-1920s.

The Germans believed the Enigma encryptions to be virtually unbreakable, but Polish and British mathematicians quickly set out to crack the codes.

As the war loomed, the British Government Code and Cipher School set to work.

-The code breakers were based in a country house called Bletchley Park in Buckinghamshire, about 45 minutes' drive from Central London, and this was an ideal location because it was away from the public eye.

This operation was so top secret, it had to be protected at all costs, and where better than to place it in the heart of the countryside?

-The German military relied on the Enigma to encrypt and decode secret information shared across the radio waves.

In British hands, the code could be used to unravel almost all German radio communications and uncover what the enemy planned to do next.

-And Enigma is used in different versions by the German Army, Navy, and Air Force.

The Navy version is proving really difficult to crack, and Alan Turing and the code breakers at Bletchley are really trying to break it, but they need codebooks, they need signal books, they need an Enigma machine, anything they can get to help them.

-The British Navy went to great lengths to capture codebooks and machines.

-In May 1941, the Battle of the Atlantic is pretty critical.

There is a dark time for the Allies at this point.

They are being savaged in the Atlantic by German U-boats.

-Help would come unexpectedly in early May 1941.

A German submarine, U-110, was patrolling east of Greenland's southern tip, Cape Farewell, when it was detected by British corvette HMS Aubrietia on sonar.

Aubrietia and the destroyer Broadway dropped depth charges, causing serious damage and forcing the U-boat to surface.

On May 9th, Broadway altered position in preparation to ram U-110, but at the last moment, the destroyer fired two depth charges below the U-boat, seeking to force the crew to abandon ship.

The German commander, Fritz-Julius Lemp, made the order for crew to depart before realizing that the U-boat was not sinking.

-The crew, the German crew -- they know how important it is to get secret material destroyed before the Allies can get hold of it.

The captain does attempt to swim back to the U-boat to destroy the secret material, but he's never seen again.

-The U-110 was bordered by a party from the destroyer HMS Bulldog, led by Sub-lieutenant David Balme.

The group captured a codebook, encryption settings, and an Enigma machine without realizing the importance of their find.

Designated "Operation Primrose," the events were to be treated with utmost secrecy.

Commander Baker-Cresswell ordered the damaged ship to be towed to Iceland, but it sank in bad weather the following day.

No references were made in official documents or war diaries.

Sailors from HMS Bulldog were sworn to silence.

Even the U.S. president, Roosevelt, was not told of the capture until January 1942, eight months after the event.

-It's the mother lode of a find, and that stuff is taken back to Bletchley Park, where it is used to break into German Naval Enigma, and this really gives the Allies a fighting chance in the Atlantic.

-Alongside materials from other intercepted Axis ships, the capture of the U-110 allowed code breakers to crack the Naval Enigma.

The intelligence unlocked by code breakers working at Bletchley Park was designated "Ultra" in June 1941.

The British went to extraordinary lengths to deceive the Germans and protect this secret.

Deciphered transmissions revealed details on the numbers and locations of Axis wolfpacks and ship convoys.

To safeguard Ultra intelligence, spotter submarines and aircraft were sent on sham reconnaissance missions.

At the same time, the Allies were able to place their submarines in the right spots to disrupt Axis shipping.

The Germans didn't realize their messages were being read and overestimated the size of this Allied fleet that seemed to be everywhere.

Their successes led Axis forces to believe some 400 Allied submarines were deployed in the Mediterranean.

In reality, there were only 25.

But the Germans never suspected that their communications had been intercepted.

-Why was it a deception operation?

Because the Germans believed their codes to be unbreakable, and we couldn't let on that we'd ever cracked these codes.

Because if you do that, you can no longer listen in and gain that intelligence.

You've no longer got that advantage over the enemy.

So we had to hold this deception, whatever it cost.

-Alongside masses of valuable intelligence, the capture of cipher documents and equipment and the work of code breakers also allowed strategists to follow the Nazis' reactions to Allied activities.

-And what this meant was that when the Allies mounted a deception operation, they could actually monitor its success through intercepted German messages.

-Ultra remained hidden from the Nazi leadership and the public throughout the war and for decades beyond.

♪♪ ♪♪ -Covert observation and reconnaissance were crucial to predicting the enemy's next move.

When a significant British territory was under threat of invasion, a plan was devised to maintain a secret observation post even if it fell into German hands.

♪♪ Operation Tracer was a modern-day Trojan horse.

A British Overseas Territory on the southern tip of the Iberian Peninsula, Gibraltar had long held strategic significance for British naval operations.

Dominated by a great limestone monolith, the territory provided an ideal position and vantage from which to control maritime movement between the Mediterranean and the Atlantic Ocean.

Under the Rock of Gibraltar lies a series of underground tunnels, first excavated in the 18th century and expanded during the Second World War.

The strategic value of the rock made it a likely target for German capture.

But the threat grew during 1940 with the decisive Axis victory in the Battle of France and emerging intelligence reports of a planned operation to seize Gibraltar.

-It's obvious that they'll try to take it because it's so strategically important.

The Director of Naval Intelligence, Admiral Godfrey, comes up with this plan.

If Gibraltar is taken by the Germans, they will leave a six-man surveillance team behind, which the Germans will not know about.

-Operation Tracer would allow the British to continue to monitor the movements of enemy vessels that threatened the British supply chain in the region.

The operation planned to seal soldiers inside the tunnel system and report observations back to the Admiralty using wireless communication.

-...calling 6-1.

-Plans were made to provision six men for seven years.

They would require access to enough food, water, and sanitation for this length of time.

In late December 1941, construction began.

Two observation posts would allow the team to monitor the Mediterranean -- east -- and the Bay of Gibraltar -- west.

A small radio room would connect the officers to their superiors.

A bicycle would be used to charge a generator that powered the radio.

-They don't know how long they'll be in there.

They leave dirt in the hallways so that if anyone dies, they can be buried.

And two of the men left in the area are doctors.

Because if medical attention is needed, there's no other way of getting it.

-Construction finished in August 1942, and each team member worked in Gibraltar in other roles to protect their secret mission.

-Luckily, it's not needed, because Gibraltar is not taken by the Germans.

But it was a serious idea, a serious plan to keep intelligence flowing from that area.

-After a final wireless-communications exercise, the chambers was sealed.

The planned operation was so carefully concealed that the existence of the stay-behind caves was not discovered until long after the war.

Operation Tracer was an ingenious plan that was devised, tested, and prepared, but never brought into action.

British deceivers put immense effort into every operation, preparing for all possible outcomes, even when they might never come to fruition.

♪♪ Those who engaged in deception often used skills developed in everyday life.

From the entrancing star to the set designers versed in creating illusions, deception was embedded in all aspects of the Second World War.

Unlike many other elements of warfare, deception did not always require superior technology or strength.

Rather, creativity and innovation were key to manipulating the enemy's perception of truth.

Techniques in subterfuge evolved over the course of the war.

As other nations entered the conflict, distinct deceptive strategies emerged, aimed at exploiting the enemy's weaknesses.

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