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00:01Just a few weeks before the Second World War,
00:05Germany's huge Graf Zeppelin crossed the North Sea on a daring spy mission.
00:12On board, a team of military and wireless experts
00:15spent the next 24 hours probing the mysterious towers that had appeared around the British coastline.
00:23This spy mission had been ordered by the head of German Signals, General Wolfgang Martini.
00:31He knew the war was just weeks away, and he desperately needed to find out more about the towers.
00:39Were the Zeppelin spies about to unravel Britain's greatest secret?
00:44In the summer of 1940, Britain fought for its very survival in the skies over southern England.
01:01But the full story has never been told.
01:09Churchill's few had gained a huge tactical advantage from the work of a brilliant team of scientists.
01:15In just four frantic years, Robert Watson Watt led the team that designed and constructed Chain Home,
01:26the world's first radar defence system.
01:29There was no plan B.
01:32The entire defence of Britain was gambled on Watson Watt and his boffins.
01:36The Battle of Britain was in fact won some years before by decision to build Chain Home
01:46and to develop the very effective communication system between it and fighting a man.
01:53That's something which one can't underestimate.
01:59It was the use of the information that was so important.
02:03It's exceedingly unlikely that we would have won the Battle of Britain in 1940
02:12without the ability to preserve our Hurricane, the Spitfires and our pilots on the ground
02:18until a real attack was developing.
02:21Beacon Hill, intercept raid 4-5.
02:28Radar gave the Royal Air Force a crucial 20 minutes early warning.
02:35This enabled Fighter Command to scramble and direct its fighters to exactly where they needed to be.
02:42This was the first attack on airfields.
02:43As the world's largest air force began its assault on Britain,
02:57Luftwaffe Commander Hermann Göring boasted he would seize control of British skies in a matter of days.
03:03Destroying the RAF was the prelude to Operation Sea Lion, the invasion of Britain.
03:09If air supremacy had passed to the Germans, they would have attempted Sea Lion and had it done so, it would probably have been successful.
03:18The RAF fought the Battle of Britain under the assumption that the Germans knew all the secrets of British radar.
03:27There could be no other reason behind the Zeppelin spy flight in those last weeks of peace.
03:36The collusion we reached was that they had located all the stations and therefore the most probable thing would be an attack on them in the early stage of the war.
03:46So why had the Germans not destroyed British radar before the battle?
03:53The mystery of the Zeppelin spy mission was not solved until long after the war.
03:59When the guns finally fell silent in 1918, the world had been traumatised by the horrors of modern warfare.
04:16Further conflict in Europe seemed inconceivable.
04:20After the immediate end of the First World War, there was a widespread feeling among the public that they didn't want any more war, that would be the end of war.
04:32And so, defences were run down immediately.
04:35The RAF, which had been created in 1918, became a fraction of itself.
04:39Partly because there was no sense that there was really any enemy out there who was now going to attack Great Britain.
04:44But things were about to change.
04:51The defeated Germany was soon ravaged by hyperinflation, unemployment and civil unrest.
05:00From this chaos, a sinister new force emerged.
05:05Hitler's rise to power was born of the resentment of the harsh reparations imposed at the end of the First World War.
05:12He promised a new and stronger Germany.
05:16By the time Hitler came to power in 1933, they were close to the point where they could now begin to build once again a military air force.
05:31And a military air force with advanced technology.
05:33He made his sidekick Herman Goering minister for air.
05:40Forbidden to rearm, the German aircraft industry had turned to civil aviation.
05:47This became part of Goering's plan to construct a secret air force.
05:52By the mid-1930s, German aviation was leading the world.
05:59But these new high-speed airliners and mail planes were barely disguised bombers.
06:07This was something I think the British had always anticipated.
06:14But they soon became terrified that all the rumours coming back of the aircraft that had been seen, camouflaged about developments of secret air bases and so on, suggested to them that Germany was going to be the real threat.
06:27For centuries, the sea had been Britain's natural defence.
06:36But a new and terrifying scenario now loomed.
06:41A new generation of German bombers could strike targets across the country before the RAF had time to intercept.
06:49Britain was no longer an island. It desperately needed an early warning system.
07:00Hostile aircraft coming in no face. First target south.
07:05During the First World War, sound locators were a successful method of being able to track aircraft close into the British coast.
07:13And during the 1930s, the British government decided to build even larger sound locators in the hope of detecting aircraft many miles away from the coast.
07:28If proven effective, these concrete sound locators could be developed into a national warning system.
07:34With the massive 200-foot sound mirror just completed, everything now depended on a crucial test.
07:44And there's a classic story of the air staff all assembled for a demonstration, listening to the incoming bomber formation.
07:54It sounded very much as if one of the planes had a faulty engine.
07:58And all they saw was the local dairy farmer with his milk cart and his milk shards rattling together.
08:11And that was the state of our air defence in 1934.
08:18Amongst those who witnessed the fiasco was the head of air ministry research, Hugh Dowding, and one of his scientists, A.P. Rowe.
08:26Rowe realized that the day of the sound locator was over.
08:33He wrote to his boss and said that unless urgent action was taken, Britain would lose the next war.
08:41It had taken a milk float to rattle the government into action.
08:47The RAF had neither the men nor aircraft to maintain a constant patrol over the entire eastern seaboard.
09:02German bombers could attack across the North Sea anywhere from the Orkneys down to the Isle of Wight.
09:09A vast area of 70,000 square miles.
09:13If an early warning system could be developed with a range of 100 miles, then RAF fighters could remain on the ground until the enemy was detected.
09:26In 1935 the idea of a warning system that would cover 70,000 square miles was the most utter science fiction.
09:37In the cinemas, popular serials were full of fantastic and futuristic ideas.
09:43Evil empires, robots, poison gas, and ray guns.
09:50Britain's defense establishment also got caught up in this science fiction fever.
09:57Rumors began to circulate that the Germans were developing a death ray.
10:10A high energy beam that would boil the blood of a pilot.
10:14This was taken seriously by Air Ministry and they offered a prize of an award of a thousand pounds for anyone who could kill a sheep at 200 yards.
10:28The death ray challenge found its way to the obscure radio research station near Slough.
10:47Its chief scientist was a lively Scot called Robert Watson Watt.
10:59Air Minister, all his name.
11:00Watson Watt.
11:02Watson Watt was a marvelous little chap. He bubbled away the whole time talking.
11:08He could certainly charm a monkey out of a tree, certainly without the slightest effort.
11:12Watson Watt asked his able assistant, Skip Wilkins, to get to grips with the death ray conundrum.
11:20He soon found the energy required would be out of this world.
11:26Hello, can you put me through to the Air Ministry, please?
11:29But Watson Watt sensed an opportunity with the Air Ministry.
11:32I'd like to speak to Dr. Wimpers, please.
11:34Watson Watt was a marvelous salesman.
11:37He could sell refrigerators to Eskimos without the slightest effort.
11:40Watson Watt replied to saying, absolutely impossible, but I believe I can use radio energy to detect an enemy bomber.
11:52Okay, bye-bye.
11:58But this extravagant claim was based on little more than a hunch.
12:02Watson Watt had been tracking thunderstorms by radio direction finding, when he became puzzled by some mysterious reflections.
12:10So when the Air Ministry demanded he prove his claim, he turned again to his young assistant.
12:24Wilkins estimated how much radio energy could be reflected from an aircraft.
12:31The answer surprised everyone. It was very favorable.
12:37Air Marshal Dowding, the head of Air Ministry Research and Development, saw the calculations but said, these scientific fellows can prove anything with figures. I want a demonstration.
12:50Within a few days, Wilkins devised a pioneering experiment.
12:56Permission to come aboard, Mr. Wilkins? Welcome, come on in.
13:01The mobile laboratory was an old ambulance packed with hastily improvised equipment.
13:06A Hayford bomber would fly a course between the BBC transmitter at Daventry and the van.
13:14Any radio reflections from the aircraft would disturb the display.
13:20AP Rowe from the Air Ministry joined them, as they anxiously awaited the bomber.
13:26As the engine drone grew louder, the spot refused to move.
13:41That could be atmospheric, Skip.
13:45The Hayford turned and made a second approach.
13:48It could be a tractor.
13:49No, no, no, no. That's a propeller.
13:51Of some sort.
13:55That is our man.
13:56We had contact.
13:57Contact.
13:58There he goes.
14:00Wilkins had made Britain's first radar contact.
14:04And Watson Watt was quick to realize the significance.
14:09Well, Skip, Mr. Rowe, Britain is an island again.
14:18With deep irony, Wilkins' success came on the very same day that Hitler revealed the Luftwaffe to the world.
14:31It was the first exhibition of military might by the self-appointed Führer.
14:38In just two years, the Nazis had constructed the world's largest air force in total secrecy.
14:45Hitler's old henchman, Hermann Göring, was given supreme command.
14:54The threat to Britain was now all too clear.
15:08Following that first radar experiment, Air Marshal Dowding took decisive action.
15:13Ten thousand pounds of funding allowed Watson Watt to gather a small team of scientists at a remote aerodrome in Suffolk.
15:22The conditions in the actual laboratories where we worked on radar were completely primitive.
15:28They were just wooden huts.
15:31All our test gear had to come over on the boat.
15:34Everything came over on the boat.
15:36And there simply wasn't much test gear anyhow.
15:39As the team explored the design of a national early warning system, some of the more fanciful ideas began to raise alarm.
15:49Watson Watt, in addition to being a good theoretical scientist, was also a practical chap.
15:54And he was not carried away by what they could eventually do as being the most wonderful thing.
16:00He would give people what was available at the time.
16:02He knew that the RF needed something quickly and he provided them with something.
16:06And if he gave them the third best, that was good enough.
16:09Watson Watt knew the frantic race to defend Britain could only be won by developing existing technology.
16:20But keeping it simple came with drawbacks.
16:24The problem was that to transmit enough radio power with existing technology required the aerials to be over 300 feet high.
16:33A national network would require dozens of these huge towers to be linked together to form a coastal chain.
16:44The echoes of any aircraft within that transmission area were picked up by a receiving system which could tell the direction from which the echo was coming.
16:53Watson Watt's third best system became known as Chain Home.
16:58Many still considered Watson Watt's ideas total fantasy.
17:10But he was gaining rapid progress.
17:17By July of 1935 Watson Watt and his team were successfully detecting aeroplanes out to 50, 60 miles.
17:26The radar team had cracked the basic mechanics of radar.
17:31It now had to evolve into an air defence system.
17:38It was not developed as a scientific device.
17:41It was developed as a war weapon for the use of fighter command.
17:45And the requirements of fighter command were of overriding priority.
17:48The expanding research team had outgrown the primitive huts at Orford Ness.
17:58Just down the coast, the imposing Bordsey Manor became the perfect home for Watson Watt's new wave of recruits.
18:07The drive was on to collect the best brains from Britain's universities.
18:18The impact of Bordsey Manor and all the equipment on me as a young man in my mid-twenties was colossal.
18:25As Bordsey's scientific elite grew, they gained a name that would stick with them.
18:33The boffins.
18:36We all felt the war was coming.
18:38That we only had a little time in which to be ready to defend this country.
18:43And that was the atmosphere.
18:58That year, things to come gave cinema audiences a terrifying spectre of modern war.
19:04One of the key features, really, I think, of British society in the 1930s was fear of bombing.
19:22They were told all the time, they were told by Stanley Baldwin, the Prime Minister,
19:25that the bomb would always get through.
19:28That contributed to this strong apocalyptic fear
19:31that somehow the bomb represented the end of civilisation.
19:42A year later, that fear became real.
19:49The public saw the Germans in Spain and the bombing of Guernica, which became high profile.
19:55The weekly newsreels left the public recoiling in horror.
20:01It played a very important part in building a strong resistance idea of waiting another war again.
20:12The Spanish Civil War proved the perfect testing ground for the destructive power of the Luftwaffe's men and machines.
20:19But it was not just in military aviation that Germany led the world.
20:34The Hindenburg was the latest of Count von Zeppelin's great airships.
20:38The 800-foot Leviathan was a potent propaganda tool, a symbol of a renewed Germany.
20:48That all changed on the evening of the 6th of May, 1937.
20:52The disaster at Lakehurst spelt the end of passenger carrying airships.
21:10But still under construction was the LZ-130, the new Graf Zeppelin.
21:16Once complete, it languished in its hangar, an enormous white elephant.
21:28As the first of the giant 350-foot towers went up at Bordsey, Watson Watts' confidence grew.
21:35He summoned the top mandarins of Whitehall for a full-scale demonstration.
21:42Well, the great day dawned.
21:45And this great fleet of aircraft left the dock at Felixstown.
21:50And then they were going to make an attack on Bordsey.
21:55Watson Watts told them how marvelous radar was and what a great replacement it would be for sound location.
22:01And the time came, of course, for these aircraft to appear.
22:06And nothing much was seen by the three observers.
22:10I was one of the observers.
22:12It became increasingly embarrassing.
22:13And then, finally, Watson Watts gave up talking, because nothing was appearing on the tube at all.
22:20And, of course, he could see no explanation for that, nor could he think of any explanation for it.
22:25And in the quiet, after he stopped talking, we began to hear the distant hum of aircraft engines.
22:33And at the same time as we heard them, or possibly one second before, we saw some faint echoes on the cathed ray tubes.
22:48As a demonstration of the efficacy of radar, it was about as bad as you could possibly get.
22:55The top brass stormed back to London convinced that Watson Watts was little more than a charlatan.
23:04Radar was all but finished.
23:14The disaster left only one senior figure still with confidence in the boffins.
23:19Air Marshal Hugh Dowding understood the huge technical challenges they faced.
23:27I'm quite sure Dowding could see no other solution to the effective defense of this country.
23:34Use of standing patrols and other means of detecting and directing fighter aircraft against incoming bomber streams
23:41was clearly well beyond the capability of the resources of the country.
23:45Radar had to be successful, and Dowding kept on supporting it right up to the hilt.
23:53Dowding was never afraid to push the boffins to their limits.
23:58And I recall a meeting at Fighter Command, which I was at,
24:03when he was having a great deal of trouble with the stability of the CH system.
24:08At this meeting, he was trumping the table, demanding why he couldn't have a stable system.
24:15And the senior scientist there, Harold Lander, said,
24:19well, sir, the scientists say it's not possible.
24:23And I remember beating the table and saying,
24:25if the scientists say it's not possible, get me another set of scientists.
24:28Dowding was an absolutely dedicated individual who drove forward the idea of making Radar the backbone of Britain's fighter defense.
24:42Radar gave Fighter Command a method of locating the attacking bomber.
24:51But that was only half the problem. The other half was to direct the fighter effectively to intercept.
24:56Dowding's new system would keep fighters on the ground until the enemy was detected by Radar.
25:04All fighter squadrons take off.
25:09B-1-1, Wing Commander speaking.
25:12Take off at once and patrol your area.
25:14Right. There's a Radar on the way.
25:17Now report by radio as soon as you're on patrol. That's all.
25:21Good luck.
25:22Once in the air, a constant stream of instructions by two-way radio would guide them to intercept.
25:33Orbit. Angels 15. And transmit for fix. Over.
25:38OK. Listening out.
25:40Scramble, bandits and angels became the new language of Fighter Command.
25:46Vector 350. Over.
25:49Vector 350.
25:505-0.
25:51Hello, Hazel 2-2. Forrest answering. Damn good show.
25:55As the development of Radar progressed, Watson Watt knew that his first priority was the defense of London.
26:06London was less than 90 minutes flying time from major Luftwaffe bomber bases.
26:12At the start of 1938, five radar stations began construction around the Thames estuary.
26:21The new radar network was going to need hundreds of trained personnel.
26:29Foreseeing a lack of manpower in wartime, the RAF began to recruit women operators.
26:35Nobody could be told what they were doing. It was absolutely Britain's top secret.
26:44We marched up and down. We saluted people. And so it went on for two weeks.
26:52And then we were all called into a hut and told where we were going to be sent.
26:57And I was told I was going to be a clerk, special duty. And everybody wanted to know what it was.
27:04I couldn't tell them. I had no idea.
27:06And we had our first lecture when they told us the secret of radar.
27:16When you were operating on a set, you had what was called a trace, which is a line of light across the screen, full of little things wiggling up and down like that.
27:27And these were either noise, interference, or the real thing, what you were looking for, the echoes coming off aircraft.
27:37By spring of 1938, the five Thames radar stations gave London a 20-minute warning.
27:45Yes, there is a major raid developing to the southeast.
27:48But air exercises were revealing a daunting problem.
27:5820 minutes was proving too little time for the RAF's biplanes to climb to height.
28:08The Air Defense of London would require a new generation of high-speed monoplane interceptors.
28:13But the complex Spitfire airframe was proving difficult to put into mass production.
28:20And the Hawker factory could not yet give full priority to the construction of the Hurricane.
28:26By March 1938, just 16 had reached the front line.
28:36A few weeks later, the Reichstag rose to the news that Austria was to unite with Germany.
28:43The new Graf Zeppelin made a triumphant flight over Vienna.
28:54It was no longer a white elephant, but a potent symbol of Nazi power.
29:02The flight was cover for a top-secret spy mission.
29:07The Graf headed east to shadow the Czechoslovakian border.
29:13On board, a team of military and wireless experts gathered intelligence on the Sudetenland.
29:20It was Hitler's latest territorial claim, and it brought Europe to the brink of war.
29:27As the Czech crisis deepened, Prime Minister Neville Chamberlain flew to Munich to confront Hitler head-on.
29:39The problem for Chamberlain when he arrives in Munich is that they were close to the clearing war in defence of the Czechs.
29:48But he knew perfectly well that Rihanna was still in an immature state.
29:52It had been going on now for three or four years in Britain, but the plan was really to have it completed by 1939-40, the very earliest.
29:59Chamberlain had just been briefed on Britain's readiness for war.
30:07I don't know how strong Chamberlain's poker face actually was, but at the time of Munich, Britain's air defences can best be described as dire.
30:17Munich became a deadly game of bluff.
30:20Chamberlain was aware that we had just 406 fighter aircraft. Of those, only 70 were Hurricanes and just 14 were Spitfires, not even operational.
30:34All the rest were obsolete biplanes.
30:40Air raids on London, Chamberlain had been told, would result in hundreds of thousands dead.
30:48Provoking Hitler risked creating that enormous catastrophe.
30:55And as Chamberlain flew back from Munich, his plane was plotted by the five coastal CH stations, passed to the filter room and passed up to the Operations Wheel of Fighter Command.
31:09Mollifying Hitler had bought a fragile peace.
31:16But Chamberlain's peace for our time hit a secret race to complete Britain's defences.
31:22A new Hawker factory was now producing Hurricanes in significant numbers.
31:29And the problems that had dogged the mass production of the Spitfire were finally solved.
31:36By the summer of 1939, five frontline squadrons had the RAF's fastest fighter.
31:43With the frantic construction of 14 new stations, radar coverage was extended from Newcastle to the Isle of Wight.
31:58The year after Munich was critical. During that year, the Chain Home system came into full operation.
32:08It had taken just four years from that first experiment to put Chain Home at the cornerstone of Britain's defence.
32:16This led us to ask ourselves the question, the Germans must know what we're doing.
32:26We're building these stations and all this activity going on.
32:30360-foot steel towers, 240-foot receiving towers. They can't have missed it.
32:35One German had been watching the towers.
32:44General Wolfgang Martini was the head of German radar.
32:52The latest reconnaissance alarmed him.
32:57Could the mysterious towers be British radar?
33:00Martini knew that war was only weeks away.
33:07He desperately needed to know more about the towers.
33:11And on the 3rd of August 1939, the radar station just north of the Thames at Canudon,
33:20spotted an echo moving in towards the Thames estuary.
33:23A massive echo, bigger than anything one had ever seen before, moving at some 60, 70 knots.
33:33Fighter command went into high alert.
33:36Could it be an invasion fleet?
33:40Or a huge formation of circling bombers?
33:42It turned out to be the German airship LZ-130, the Graf Zeppelin.
33:55And over some hours they plotted the movement of the echo from somewhere off the coast of Essex up to the north of Scotland.
34:01On board were the Luftwaffe's top wireless team, just returned from a spy mission on the Polish border.
34:14Martini's experts spent the next 24 hours combing the wavelengths for any evidence of British radar.
34:20Fighter command was in complete shock. The appearance of the Zeppelin could only mean one thing.
34:35The collusion we reached was that they had not only located all the stations,
34:41they would have measured their frequency and other important characteristics.
34:43And therefore, the most probable thing would be an attack on them in the early stage of the war.
34:50And indeed, we thought that Bordziata would be the prime target.
35:01As the German war machine rolled into Poland on the 1st of September 1939,
35:07Watson Watt decided the risk of attack was too great.
35:11Bordziata must be evacuated.
35:17A.P. Rowe was now the superintendent of radar research.
35:21He ordered the entire Bordzi scientific team to the safety of Scotland by any means possible.
35:29Rowe not only feared air attack on the radar stations, but the electronic jamming of the entire chain home system.
35:41On September 2nd, Rowe summoned me and told me everybody will be going to Dundee, but not you.
35:49You will stay and modify the whole chain.
35:55Jimmy Atkinson had developed a new type of display tube that filtered out enemy jamming.
36:00Every radar station in the country would need urgent modification.
36:07I said, well, what about transport?
36:10And Rowe said, well, just do the best you can. Use your initiative.
36:16Jimmy's ancient Austin became the latest secret weapon in the defense of the realm.
36:22He recruited his wife, Mona, to help with the driving.
36:30Now, I was paid subsistence, but of course, she didn't exist, even though she had to do most of the driving.
36:37And I slept during the day, ready to work at the next station at night.
36:40Each station was taken off the air while Jimmy fitted the top secret device.
36:50In September, we covered a total of 2,648 miles.
36:56The adventure was only complete when the intrepid couple had toured all 18 radar stations.
37:02In Dundee, the Boffins found a home in the austere teacher training college.
37:14The magic of Bordsey Manor had gone forever.
37:23Attention, everybody. It's just been announced by the Prime Minister.
37:27We are at war with Germany. From now on, anything may happen.
37:31As war was declared, Fighter Command braced itself for a German onslaught on the radar chain.
37:40But it didn't happen. And we couldn't understand why.
37:50The nation dug in and prepared for the worst.
37:55But the feared air raids on British cities never came.
37:58In April 1940, the phony war came to a dramatic end.
38:15The German Blitzkrieg rampaged through Holland and Belgium.
38:20A large British expeditionary force was supporting the defence of France.
38:30But the fast-moving panzers encircled and trapped them on the beaches of Dunkirk.
38:37Over 300,000 troops were snatched to safety by the Royal Navy and a flotilla of small boats.
38:44It was a miraculous escape.
38:45Amongst the vast amounts of materiel abandoned in the Maelstrom was some secret radar equipment.
39:00The British radar sets which had been captured were very crude mobile models.
39:07And the Germans concluded that whatever British radar was, it certainly wasn't up to much.
39:12The Boffins had little idea of the German intelligence picture of British radar.
39:22But with the Zeppelin mission and the capture of the equipment at Dunkirk, they feared the worst.
39:29The fall of France had taken just six weeks.
39:39Hitler now turned to Operation Sea Lion, the invasion of Britain.
39:45One of the factors that played a role in persuading Hitler that Operation Sea Lion was the possibility of this.
39:54Was that Hermann Göring really wanted to prove that his force could do it.
39:58That his force could win air supremacy over Britain.
40:00And I think, you know, people say that Göring is a fantasist.
40:03He's a boaster.
40:04But actually, they annihilated the Polish Air Force in a matter of days.
40:07They defeated all the aircraft thrown at them in the Battle of France with relative ease.
40:11The idea that you couldn't use the same tactics and destroy the RAF in four days, Göring thought,
40:17is not as implausible as it now looks.
40:23With the towers of Dover radar station clearly visible across the channel,
40:27the Luftwaffe began an attack on British ports and shipping.
40:36At first, the Canal Kampf seemed to go the Germans' way.
40:40Then the RAF began to appear.
40:46Dowding carefully positioned his fighters for the best advantage.
40:51The Germans began to think to themselves,
40:54well, why are we always meeting the RAF?
40:56We don't think it's very big, and yet here they always are.
41:00It began to ring rather quiet alarm bells in the German Air Force
41:05about whether the British actually had got some kind of system to detect incoming aircraft.
41:12Martini took his fears directly to Luftwaffe High Command.
41:17But Göring was an old-school thinker.
41:19Herman Göring was a successful First World War fighter pilot.
41:25For him, the offensive spirit of the Luftwaffe would be the deciding factor.
41:31Nothing at all to do with gadgetry.
41:33If Göring could draw the RAF into a decisive battle with his Messerschmitt aces,
41:41then the Spitfire and Hurricane could be wiped from the sky.
41:44But the events of the 11th of August were to shatter this confidence.
41:52The Luftwaffe mounted three widely separated raids across southern England.
42:00But Dowding had seen the build-up and had swarms of RAF fighters ready to intercept.
42:06In just a few hours, the Luftwaffe lost over 45 aircraft damaged or destroyed.
42:23But Martini had been monitoring RAF radio communications.
42:28His suspicions were beginning to grow.
42:32From intercepts, they were able to identify that fighters were being directed by radio towards the German bombers.
42:42Therefore, radar must be the basis of the British air defence system.
42:52Martini was also puzzled by the powerful signals they could detect from the towers.
42:56They were crude, but somehow they must play a part in guiding British fighters.
43:04Göring finally conceded.
43:07The towers must be destroyed.
43:16Early on the 12th of August, a crack ground attack squadron crossed the channel.
43:20The frontline radar stations of Dover, Rye, Pevensey and Dunkirk came under direct attack.
43:34At Ventnor on the Isle of Wight, a direct hit caused major damage.
43:38In the following days, Stukas joined the onslaught.
43:4719-year-old Avis Parsons was on duty at Poling near Chichester.
43:53And as a Stukas dies, it screams the most hideous noise.
43:57It's very, very frightening.
44:01And then the bombs began to fall.
44:08I kept going as long as I could.
44:11And suddenly my line went dead.
44:13And the building next to where I was was just a heap of rubble.
44:18Oh.
44:24The attacks on Chain Home had been feared since the Zeppelin spy mission.
44:29But after three days, they mysteriously stopped.
44:35This remained a very great puzzle because we knew the extent of the damage they'd done
44:39and we knew what they had to do to finish it.
44:41But they didn't.
44:42The returning airmen reported extensive damage to the towers.
44:52But when Martini's experts checked their frequencies, they were astonished by what they found.
44:59The radar signals were still there, a little fainter or on different wavelengths.
45:05Unknown to the Germans, the source of the signals were mobile radar vehicles
45:10that had been brought into operation when the main radar stations had been knocked out by the bombing raids.
45:19Despite the extensive destruction, the mobile stations had kept the radar chain on the air.
45:26The damage to the towers was rapidly repaired.
45:30We had all those four stations back in operation by midnight that night, plotting to find a command.
45:37Quite unintentionally, the mobile reserve had been a perfect deception.
45:44With the radar stations appearing undamaged, Martini's ideas were sidelined.
45:54Beppo Schmidt, the head of Luftwaffe intelligence, also had a strong view on the British radio towers.
46:00Major Beppo Schmidt was a long-standing Nazi Party member and a drinking buddy of Hermann Goering.
46:08He has never been accused of being an intellectual genius.
46:12And he considered that the tall radio masts were nothing other than radio direction finding, as used in the First World War.
46:21Goering called a conference on the 15th of August and instructed his Luftwaffe commanders to waste no more time on these radio installations.
46:33Get on and fight the war.
46:35Goering's frustrations were growing.
46:38He now had a plan that would call on every man and aircraft on the Western Front.
46:43The chain home stations began to track the gathering formations, extending from 5,000 to 20,000 feet.
46:55Hostiles 7-6, 100 aircraft, 16,000.
47:00And it was then that we began to get the very large numbers of aircraft.
47:06It was 100-plus had never been seen on a radar screen before.
47:15Adla Tag, or Eagle Day, was Goering's plan for a decisive hammer blow.
47:22The target soon became clear.
47:25Will you warn your controller that this looks like yet another attack on airfields?
47:29The thing was to assault the RAF, its airfields, its bases, depots, and aircraft production in southern England.
47:38Once you'd degraded the RAF, you then moved on to attacking communications and administrative centres, and then the invasion would take place.
47:47The RAF airfields were taking a pounding.
47:50Squadrons were broken up, and fighters became scattered across southern England.
47:55There were points in late August and early September 1940, where the system was almost on the point of collapse.
48:06With Dowding's ability to deploy his fighters fast disappearing, the Battle of Britain was on the brink.
48:18Then came a timely twist of fate.
48:20On the night of the 24th of August, the Luftwaffe attacked an oil refinery in the Thames estuary.
48:30But the raid went badly wrong.
48:33Crews got lost, and some jettisoned their payloads.
48:39For the first time, bombs fell on central London.
48:42Hitler had forbidden any attack on the capital, fearing a reprisal.
48:53He was right.
48:57Within 24 hours, Bomber Command was over Berlin.
49:00The Token Raid did little damage, but Hitler was outraged.
49:01The Token Raid did little damage, but Hitler was outraged.
49:17Goering changed his tactics again.
49:20Bepo Schmidt, head of German air intelligence, had been telling Goering over and over again that the RAF was finished, basically.
49:27Just a couple of hundred planes left.
49:28We've achieved air supremacy.
49:30And so it was possible to make this switch to the bombing of London without much danger.
49:37Late in the afternoon of the 7th of September, the chain stations plotted large formations grouping over France.
49:43Soon, Hermann Goering had assembled the largest air armada the world had ever seen.
49:53370 bombers headed directly to their target, London.
50:03Goering's daily bombardment continued for weeks.
50:06But shifting his attention away from the airfields proved to be a huge tactical error.
50:17Had the Germans sustained their attacks on the sector airfields and the sector controls in particular,
50:23it would have been impossible for Fighter Command to continue the defence of Britain.
50:28With the heat off the airfields, the RAF quickly returned to strength.
50:39As Goering continued to pound London, Dowding used his radar advantage to the full.
50:45There is a major raid developing to the south-east.
50:49He chose to intercept every raid with small numbers of fighters, rather than risk all in a pitched battle.
50:55This constant harassment left German intelligence only guessing at the strength of the RAF.
51:03They were told that Fighter Command was more or less finished.
51:06Every time they flew out, they were walking.
51:09As Bomber lost his sword, Goering ordered his fighters to fly in close escort.
51:15But they lost their advantage of height, and London was at the limit of their range.
51:22The Luftwaffe was forced to seek the cover of darkness.
51:30The daylight bombing raids were a disaster.
51:33Lost rates that the German Air Force simply couldn't support.
51:37And, of course, air supremacy had not been won.
51:41So sea arm was abandoned.
51:42The Battle of Britain had been won.
51:54But the mystery of the Zeppelin spy mission was still unresolved.
52:01Why had the Germans not destroyed British radar before the battle?
52:06The answer only came years later, after a chance encounter.
52:17It was only after the war, 1950, I, at the Farnborough Air Show, met General Martini,
52:23who was the chief sequence officer of the Luftwaffe.
52:27And I said to General Martini, why didn't you destroy the radar system when the war broke out?
52:32He said, you didn't have a radar system when the war broke out.
52:36I said, well, how did we track the Graf Zeppelin?
52:40He said, you track the Graf Zeppelin?
52:42Yes. And I described precisely.
52:44He said, I don't believe it.
52:46I said, you have to, we did.
52:49The astonishing truth dawned.
52:53The Zeppelin spies had failed to identify British radar.
52:59The Luftwaffe's top wireless experts would have had no trouble finding the powerful chain home signals.
53:06But what they found baffled them.
53:12They expected to hear high-pitched noises and musical tones,
53:15as you would get from an oboe in the middle range of the piano.
53:21The latest German radar equipment could transmit pulses between 500 and 1,000 times a second.
53:30Nothing like the crude signals they were now receiving.
53:36Listening to CH, all you would hear would be a dull sort of ticking, tick, tick, tick.
53:40Something they didn't recognise at all.
53:41German and British radars were of completely different designs.
53:51German radar generated its own pulses.
53:54British radar, by contrast, sampled the pulses of the national grid.
53:59The boffins had not just used the power cycle of the national grid as a simple economy.
54:06It was an ingenious way of synchronising the entire system.
54:10All the CH stations, all up the coast, were locked together on their repetition rates.
54:17They all produced 25 pulses per second, and they were all locked back to the mains frequency of 50 cycles per second,
54:23so that they were all transmitted in unison.
54:25To achieve a 100-mile detection range, Watson-Watt had used the most powerful transmitters then available.
54:36Each station produced more than 600,000 watts.
54:40And because they all derived their pulses from the national grid, the entire chain acted as one enormous and hugely powerful transmitter.
54:51So as the airship flew up the coast, it picked up the same radiation all the way up, tick, tick, tick, tick, tick, tick, tick, ticking, without change.
55:01This huge wall of radio power was creating further confusion.
55:06They had very sensitive receivers in the main beam of the CH stations, and they would have overloaded the receivers and broken through them into other wave bands.
55:18So no matter how they tuned their receivers, they would have had this curious ticking all the way.
55:22As the LZ-130 approached Scotland, the Zeppelin spies still struggled for an explanation.
55:33The signals appeared to have no direction, just a general widespread ticking.
55:39With British radar still blaring from their headphones, they decided the ticking could only have one source, the national grid.
55:56They were completely foxed by the fact that the repetition rate of the CH stations, 25 pulses per second, was quite unlike anything which they had used on their own radars.
56:08Which the Germans mistakenly took to be arcing and sparking from the British electrical distribution system.
56:15The Zeppelin spies had made the greatest intelligence blunder of the war.
56:29Ralph Zeppelin returned and the head of the mission reported that there was no sign of any radar transmissions.
56:36Watson Watson's basic, almost primitive system, had spoofed the finest technical minds in the Luftwaffe.
56:43Ironically, if Watson Watt had gone for anything more sophisticated than third best, the Germans would have been on to it immediately.
56:56Watson Watson's great wisdom had been to keep Chain Holmes simple.
57:01He knew there could be no delays in Britain's frantic race for radar.
57:07It was only just ready in time as it was.
57:11The Luftwaffe had botched the perfect opportunity to unravel all of the secrets of Chain Holmes a year before the Battle of Britain.
57:22The failure of the Zeppelin spy mission was a fundamental disaster for the Germans.
57:29They did not realise the effectiveness of British radar nor the substantial size of the organisation behind it on which the whole of British air defence hinged.
57:41I believe the failure of Martini to persuade Goring that the stations had to be destroyed effectively cost Goring the Battle of Britain.
57:55And that saved this country from a German invasion.
57:59a German invasion.
58:00The German invasion.
58:01The German invasion is pretty easy, it was not a German invasion.
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