THE ANNEX BLOGHow Did the Nazi Scientists Who Nearly Gave Hitler the Bomb React to Hiroshima? – 11.8.15
US soldiers dismantling the German experimental nuclear pile in a cave at Haigerloch, Germany

– US soldiers dismantling the German experimental nuclear pile in a cave at Haigerloch, Germany

          In the spring of 1945 the Allies arrested the physicists believed to have worked on the German nuclear programme during the Second World War, among them the renowned scientists Werner Heisenberg, Otto Hahn and Carl Friedrich von Weizsäcker. They were interned in a country house near Cambridge where their conversations were secretly recorded. MI6’s Operation Epsilon sought to determine how close Nazi Germany had come to building an atomic bomb, and it was in this remote setting that the German physicists first heard of the atomic bombing of Hiroshima.
          6 August 1945 was a day that changed the course of history. The terrible weapon unleashed on Japan caused unprecedented destruction and loss of life. Having worked under the assumption that nuclear fission was known only to them, the Germans were shocked that the Allies had such a bomb at their disposal. This is the story of the wartime race to develop an atomic bomb, and the genius, guilt, complicity and hubris of the Nobel Prize-winning scientists working to create a weapon that would undoubtedly have won the war for the Germans.
          Below is an extract from Night Of The Physicists – Operation Epsilon: Heisenberg, Hahn, Weizsäcker and The German Bomb written by Richard von Schirach.

On 6 August the German guests were blessed with one of those mild summer’s days that seem made for life in the country. As on previous days, the mellow atmosphere of a gently passing afternoon settles over an English country estate in Huntingdonshire.

Laue is writing his history of physics, Hahn is learning to type, Heisenberg is preparing for his recital of a Beethoven piano sonata, Bagge is penning a view of Farm Hall in his sketchbook, and Weizsäcker, a great admirer of Stefan George, at last finds the peace and composure to work on his Farm Hall sonnet:

The climbing rose that once my window framed
Has, rampant, reached the eaves and skyward strains,
Veiling my view with foliage; and I blamed
Not lack of pruning but the excess rains.
Small chestnut trees around the garden’s edge
Have, o’er the years, grown large and lush, and hide
The scene beyond more fully than a hedge.
Our home from home, where sadly we abide,
Is shaded by the five-fold leaves; concealed
Beyond, the village stands; its daily woes
Are shrouded by the trees, no more revealed.
The lawn in front is swept by wind, and knows
The benison of sun and rain; our views
And walks have limits, as our daily news.

Gerlach is scrutinising the rosebushes, and muffled conversation drifts out of the house, mingling with the crack of colliding snooker balls. The Major had organised a ramble the day before with some of the prisoners to a nearby wood, where they stumbled upon a surprising number of mushrooms. The cook has just announced that he will be serving omelettes filled with the fresh, butter-fried mushrooms as a starter at dinner that night. As yet, no one has the remotest idea that the coming hours will call all their lives and ideas into question.

It is after five when the phone rings in Major Rittner’s office. His department in London informs him that America has just detonated an atomic bomb over a Japanese military base. Before this news reaches the Major’s office, it has already spread like lightning around the globe and drawn a line between the world as it used to be and as it is now. Everyone who hears this piece of news will remember all their life where and when, in horrified fascination, they first heard of the event. The Major is requested to ensure that all the prisoners listen to the BBC’s six o’clock news. He is to observe their reactions and collect each man’s impressions. Under some pretext, the ‘guests’ are requested to leave their rooms so that the technicians can check all the microphones. They notice with satisfaction that evidently no one has taken the trouble to turn round the engravings and paintings.

As some of the ‘guests’ are already returning to their rooms, Major Rittner sits down for a moment to consider what he has heard. Then he pays a visit to the room of the one person who has done more than anyone else to lay the groundwork for this feat. ‘The Major knocks on my door,’ writes Hahn in his diary, ‘carrying a bottle of gin and two glasses and informs me that President Truman has just announced on the radio that the Americans have dropped an “atom bomb” on a Japanese city. I don’t want to believe him, but the Major emphasises that this was not a correspondent reporting but an official announcement by the President of the United States. I am losing some measure of self-control again at the thought of this great new misery.’

Hahn feels faint at the news, which hits him unexpectedly while his defences are down. The Major calms him with considerable quantities of gin, as he later notes in his weekly report. When Hahn has regained his composure, they go down to the dining hall together for dinner. When Hahn passes on the news, the hall falls silent. He captures the stunned, disbelieving attention of everyone in the room.

Soon afterwards the BBC reports on the six o’clock news, in brief and still imprecise terms, that America has detonated an atom bomb above ‘a Japanese military base’ and revealed its greatest military secret. The listeners sit in tense silence. Their worst fears associated with the words ‘atom bomb’ seem to have come true. Is this the end of all war, or the end of humanity – the apocalypse?

It takes a while for their agitation to spill into the open. An atom bomb? Out of the question! It is the technical aspects of this report that inspire the greatest scepticism among the assembled experts. Initially there is no discussion of the human disaster masked by the abstract casualty figures. In the first few days no one mentions the damaging effects of radiation either. It will be some time before the suffering of the tens of thousands of victims, their numbers swelling with each passing day after the bombing, bores its way into people’s consciousness.

The first generation of physicists had underestimated the danger of radioactive substances and had not taken them seriously. The two-time Nobel Prize laureate Marie Curie was its first known victim, and her daughter, the Nobel Prize winner Irène Joliot-Curie, also died from radiation damage at the age of 58. Otto Hahn, who had carelessly kept a paper bag with 50 kg of uranium salt in it under his desk for years, was lucky enough to live to a ripe old age. There were no safeguards for the scientists working in Haigerloch either. When the Americans advanced into the cellar in the rock and discovered this fact, they knew that the Germans must have failed in their efforts to get the reactor going; for had they succeeded, those involved would have been long dead.

Heisenberg thinks the news is a piece of propaganda. Max von Laue checks that he has heard properly and that ‘235’ – meaning the fissile U-235 isotope – was mentioned in connection with the bomb. Hahn confirms this: ‘Yes, 235.’ Everyone knows only too well that unimaginable efforts must have been necessary to produce this isotope. The man who knows best is the practically-minded Hahn. In 1939 one of his staff had spent months and months producing a fraction of a milligram of this rare isotope. And here they are talking about tonnes?

he same is true of 94 production, i.e. plutonium. Walther Gerlach comments that at least a tonne of the stuff would have been required – a quite incredible amount. Hahn once more emphasises how very complicated it is to produce 94; a machine would have to run for years. If, however, the Americans really do have a uranium bomb, the chemist berates the nuclear scientists in the group, ‘then you are all second-raters.

Poor Heisenberg!’ Laue adds, ‘The innocent!’

All eyes turn to Heisenberg. He is unquestionably the figure of authority from whom everyone now expects a decisive answer. Heisenberg asks again whether the word ‘uranium’ was used on the radio. The others say ‘No’, and he can enjoy a fleeting sense of being confirmed in his basic assumption that the Americans cannot have been in a position to take this step.

‘Then it’s got nothing to do with atoms, even though the equivalent of 20,000 tonnes of high explosive is terrific.’

None of the Farm Hall residents can or want to imagine yet that the Americans might actually have been capable of producing tonnes of fissile U-235, and Heisenberg concludes: ‘All I can suggest is some dilettante in America who knows very little about it has bluffed them in saying: “If you drop this, it has the equivalent of 20,000 tonnes of high explosive”, and in reality it doesn’t work at all.’

Once more Hahn pours his mild sarcasm over the head of the chief theorist of the German atomic bomb project: ‘In any case, Heisenberg, you’re just second-raters and you might as well pack up.’

Heisenberg reacts amiably in the same vein: ‘I quite agree’, and you can almost hear the two men’s relief that they have nothing directly to do with this weapon of mass destruction. Hahn assesses soberly that the Americans are 50 years ahead of them. Heisenberg, on the other hand, refuses to believe a single word for the time being: ‘They must have spent the whole of their £500 million on separating isotopes; and only then would it be possible.’

‘Good grief!’ Bagge writes in his diary of the huge sum mentioned on the radio, truly stunned. ‘What are our 15 million Reichmarks compared to that?’

Weizsäcker is initially sceptical too. ‘I don’t think it has anything to do with uranium.’

Hahn: ‘It must have been a comparatively small atomic bomb – a hand one.’

Heisenberg: ‘I am willing to believe that it was a high-pressure bomb, and I don’t believe it has anything to do with uranium, but that it is instead a chemical thing where they have enormously increased the speed of reaction and the whole explosion.’

Weizsäcker: ‘I think that it is dreadful of the Americans to have done it. I think it is madness on their part.’

Heisenberg: ‘One can’t say that. You could equally well say, “That’s the quickest way of ending the war.”’

Hahn: ‘That’s what consoles me.’

Heisenberg: ‘I still don’t believe a word about the bomb, but I may be wrong. I consider it perfectly possible that they have about 10 tonnes of enriched uranium, but not that they can have 10 tonnes of pure U-235.’ Heisenberg conjectures that the Americans might have a new kind of explosive with ‘atomic hydrogen or oxygen or something similar’.

Harteck asserts that it can only really be a uranium bomb: an explosive based on atomic hydrogen or oxygen could at best multiply the impact of current explosives by a factor of 10, but could never achieve the 20,000 tonnes that were mentioned.

Gerlach finds it all implausible.

In this climate of horror, mistrust and constantly resurfacing curiosity about how it might have been done, they pass the time until the BBC nine o’clock news in a state of nervous tension. The reports are now so concrete that there can no longer be any doubt that it was an atomic explosion of a completely new kind of bomb. However the bomb worked, nothing will ever be the same again.

Heisenberg, who as little as three months ago was convinced that the key to the atomic bomb would not be found without the Germans’ inquiring minds, is stunned and challenged. He is struggling to get his head round the technical aspects of what might have happened. The physicists are virtually paralysed by the confirmation that a hundred thousand civilians were burnt in seconds in an atomic furnace. The first application of Hahn’s discovery has led to a global disaster. The impact of this news provokes a range of reactions – downstairs in the living room and in one-on-one conversations up in the bedrooms. The six British surveillance specialists sitting in their cubicles with their headphones on witness a historic night of confessions, accusations, breakdowns, tears and the final spasms of self-delusion.

Otto Hahn feels particularly guilty this evening for having been the first to have pushed open the door into the atomic age. He will never truly rid himself of these self-reproaches.

‘I am to blame,’ he says during this night, and later, much, much later, Carl Friedrich von Weizsäcker will admit that for very few of his pronouncements did he ‘love Hahn so much as for saying that’.

None of these scruples are shared by the others who worked on the bomb, at least not that evening, nor are many words lost on the victims. Consciously or unconsciously, the others also see Hahn as the disaster’s innocent yet decisive initiator and keep a close watch over the marked man. As debate centres on bombing and omissions, Heisenberg calms the discussion with the words: ‘I think we ought to avoid squabbling among ourselves concerning a lost cause. In addition, we shouldn’t make things too difficult for Hahn.’ Weizsäcker seconds this.

‘It is a frightful position for Hahn. He really did do it.’

Harteck sums up the mood better when he says, ‘If we had worked on an even larger scale, we would have been killed by the British Secret Service. Let’s be glad that we are still alive. Let us celebrate this evening in that spirit.’

What seems like just a passing remark sparks a controversy that lays bare unsuspected emotions. Korsching comments that the Americans had demonstrated that they were capable of cooperation on a vast scale, something that wasn’t possible in Germany. Everyone claims that everyone else was incompetent.
Walther Gerlach, the head of the uranium project, takes great exception to this, and regarding the Uranium Club, he states, ‘You can’t imagine any greater cooperation and trust than there was in that group. You can’t say that any one of them said that the other was incompetent.’

When Korsching responds, ‘Not officially, of course’, Gerlach cannot restrain himself and shouts, ‘Not unofficially either! Don’t contradict me! There are many people here who know.’

He then falls silent as the conversation continues around him. How could the Americans have got a bomb without a ‘machine’, meaning an atomic reactor? That would turn all previous discoveries on their head. ‘They seem to have made an explosive before making the machine, and now they say, “In future we will build machines.”’

No one at Farm Hall knows that Enrico Fermi had triggered a chain reaction in Chicago back in 1942. But the discussion now revolves around the huge scale of American activities, which is becoming ever more apparent. It dawns on everyone that Germany could never have competed with this array of men and materials.
Heisenberg mentions that major funding was first available in spring 1942 after ‘we convinced him [Education Minister Rust] that we had absolutely definite proof that it could be done.’

He goes on to admit, ‘We wouldn’t have had the moral courage to recommend to the government in the spring of 1942 that they should employ 120,000 men just to build the thing.’

Weizsäcker: ‘I believe that the reason we didn’t do it was because all the physicists didn’t want to do it, on principle. If we had all wanted Germany to win the war, we would have succeeded.’

Otto Hahn immediately contradicts this: ‘I don’t believe that, but I’m thankful we didn’t succeed.’

Weizsäcker makes an odd additional remark the next day: ‘History will record that the Americans and the English made a bomb and that at the same time the Germans, under the Hitler regime, produced a workable machine. In other words, the peaceful development of the uranium machine was made in Germany, under the Hitler regime, whereas the Americans and the English developed this ghastly weapon of war.’

The reasons for their own failure keep coming up in snippets of conversation during a night when emotions boil over. Harteck puts his finger on a fundamental mistake: ‘Of course, we really didn’t do it properly. Theory was considered the most important thing and experiments were secondary, and then almost unintelligible formulae were written down. We did not carry out experiments with sufficient vigour. Suppose a man like [Gustav] Hertz had made the experiments, he would have done it quite differently.’

When Korsching sums things up thus: ‘If one hasn’t the courage, it is better to give up straight away’, Gerlach feels that these words are directed at him.

‘Don’t always make such aggressive remarks!’ he says, and receives by way of reply: ‘The Americans could do it better than us, that’s clear!’

Weizsäcker picks up on this: ‘Even if we had got everything we wanted, it is by no means certain that we would have got as far as the Americans and the English have now. It is not in question that we were nearly as far as they were, but the fact is that we were all con- vinced that the thing could not be completed during the war.’

Heisenberg disagrees. ‘Well, that’s not quite right. I would say that I was absolutely convinced of the possi- bility of our making a uranium machine, but I never thought that we would make a bomb, and in my heart of hearts I was really glad that it was a machine and not a bomb. I must admit that.’

Weizsäcker puts a positive spin on Heisenberg’s mistaken decision to commit them to heavy water from Norway: ‘If you had wanted to make a bomb, we would probably have concentrated more on the separation of isotopes and less on heavy water.’

The makeup of the small discussion groups is in constant flux, and the subjects they tackle mutate just as quickly. Many a sentence is left begging for an answer; when Hahn quits the small circle, Weizsäcker takes up his argument again that ‘we might have had the luck to complete it [the bomb] in the winter of 1944/45’.

‘The result would have been,’ Wirtz chips in, ‘that we would have obliterated London, but still would not have conquered the world. And then they would have dropped [the bomb] on us.’

Weizsäcker stands firm: ‘I don’t think that we ought to make excuses now because we did not succeed, but we must admit that we didn’t want to succeed. If we had put the same energy into it as the Americans and had wanted it as they did, we would still not have succeeded as they did because they bombed all our factories.’

He adds, ‘One can say that it might have been a much greater tragedy for the world if Germany had had the uranium bomb. Just imagine if we had destroyed London with a uranium bomb. It would not have ended the war, and even if the war had been ended, it is very doubtful whether it would have been a good thing.’

Wirtz’s interjection as to whether there would have been enough available uranium leads to fantastical digressions. ‘We would have had to equip long-distance aircraft with uranium machines to carry out airborne landings in the Congo or Northwest Canada. We would have had to capture and hold these areas by military force and produce the stuff from mines,’ is Weizsäcker’s sketch of an absurd scenario to overcome the hopeless scarcity of raw materials, before adding that this would have been impossible.

Heisenberg moves on to the threat of an American uranium bomb being dropped on Dresden. An official from the Foreign Ministry had alerted him to an American threat to bomb Dresden if Germany did not surrender soon. He had been asked at the time whether he thought this was possible, and he had answered ‘No’ with complete conviction.

When Wirtz comments that ‘it is characteristic that the Germans made the discovery and didn’t use it. I must say I didn’t think the Americans would dare to use it’, these words seem finally to cut Gerlach to the quick. He leaves the group and without a word goes to his room, from where, after a while, the remaining men hear loud sobbing. Gerlach, the plenipotentiary for the nuclear weapons project, is seized by a crying fit. Harteck and Laue go to try and console him. Major Rittner gets the impression that Gerlach sees himself in the hopeless role of the defeated general whose only choice is to put a bullet in his own head. Gerlach’s mood is anxious and agitated, and he sees a dark future stretching out before him.

‘When I took this thing over [the presidency of the Uranium Club],’ he explains, ‘I talked it over with Heisenberg and Hahn, and I said to my wife, “The war is lost and the result will be that as soon as the enemy enters the country I shall be arrested and taken away.” I only did it because I said to myself, this is a German affair and we have to see to it that German physicists are protected. I never for a moment thought of the bomb, but I told myself, “If Hahn has made this discovery, let us at least be the first to make use of it.” When we get back to Germany we will have a dreadful time. We will be looked upon as the ones who have sabotaged everything. We won’t remain alive long there. You can be certain that there are many people in Germany who say that it is our fault. Please leave me alone.’

Soon afterwards, Hahn also comes upstairs to console the gloomy Gerlach and asks him whether he is shaken because they didn’t make the uranium bomb?

‘Or are you depressed because the Americans could do it better than we could?’


‘Surely you are not in favour of such an inhuman weapon as the uranium bomb?’

‘No. We never worked on a bomb. I didn’t believe that it would move so quickly. But I did think that we should do everything to make sources of energy and exploit the possibilities for the future. When initial results showed that the concentration was much increased with the cube method, I first spoke to Speer’s right-hand man, as Speer was not available at the time, a Colonel Geist, and later Sauckel at Weimar asked me: “What do you want to do with these things?” I replied: “In my opinion the politician who is in possession of such an engine can achieve anything he wants.” About ten days or a fortnight before the capitulation, Geist replied: “Unfortunately we have not got such a politician.”’

When Harteck comes back into the room, Gerlach calls to him: ‘Tell me, Harteck, isn’t it a pity that the others have done it?’

Hahn, however, replied: ‘I am glad.’ ‘Yes, but what were we working for?’ ‘To build a machine, to produce elements, to calculate the weight of atoms, to have a mass spectograph and radioactive elements to take the place of radium.’

Gerlach’s fears that things might go badly for them in Germany and that their lives might be in danger dominate the rest of the conversation between the three physicists in Gerlach’s room. He assumes that they will spend a further two years at Farm Hall because their lives are under threat. Wirtz is worried about being tried by a German court for not succeeding. He claims that not everything went as harmoniously as Gerlach is making out. ‘If a German court were to investigate the whole question of why it did not succeed in Germany, it would be a very dangerous business. If we had started properly in 1939 and gone all out, everything would have been all right.’

The others do not share his fears. Heisenberg, by contrast, sees no reason why they should be kept detained any longer ‘as it is obvious that they are much further advanced than we were’.

And Hahn feels that he can go back to Germany without any risk. Heisenberg later pays Gerlach a visit in his room as well, and it turns into a long tête-à-tête. When Hahn had asked earlier why Gerlach had got so upset, Heisenberg had explained Gerlach’s peculiar state of mind by saying that he was the only one among them who had really wanted a German victory. Although he recognised the Nazis’ crimes and disapproved of them, he had felt obligated to serve his country.

Heisenberg once more resorts to the theory that the ‘completion’ of the final test reactor failed because of the raids on the heavy water plant in Norway, and he blames Hitler for the fact that ‘Hahn’s discovery has now been taken away from Germany’, but hopes that concentrating on uranium research will offer them a chance to work with the Allies.

‘I believe this uranium business will give the Anglo-Saxons such tremendous power that Europe will become a bloc under Anglo-Saxon domination […] I wonder whether Stalin will be able to stand up to the others as he has done in the past.’

Gerlach finds it hard to come to terms with the fact that the German option is gone, and he dwells on the thought of what an atomic bomb in German hands might have meant, as the threat of such a bomb could have achieved everything. ‘If Germany had had a weapon that would have won the war, then Germany would have been right and the others in the wrong, and whether conditions now are better than they would have been after a Hitler victory …’

Heisenberg comments tersely: ‘I don’t think so,’ and poses a different question: ‘Suppose Hitler had succeeded in bending Europe to his will and there had been no uranium available?’

However, not everyone speaks in the subjunctive this night. The contours of the Cold War are already becoming apparent. It is not Truman, who ordered the dropping of the bomb and whose voice could be heard on the evening news, who is at the centre of discussions, but Stalin. Heisenberg would like to know what the Soviet leader is thinking and doing at this moment. In any event, Weizsäcker is certain that Stalin doesn’t yet have the bomb. ‘If the Americans and the British were good imperialists, they would attack Stalin with the thing tomorrow, but they won’t do that; they will use it as a political weapon. Of course that is good, but the result will be a peace that will last until the Russians have it [the atomic bomb], and then there is bound to be a war.’

Most of the others share his opinion, as a war between America and the USSR seems unavoidable. Heisenberg is even convinced that there will be ‘five or six atomic wars’. This shift in the balance between the great powers restricts the scientists’ room for manoeuvre as well. Heisenberg remarks that ‘we have no possibility of switching over to the Russians even if we wanted to’. He advocates cooperation with the Anglo-Saxons, but would rather work in Russia than starve in Germany.

The dropping of the bomb has also diminished the scientists’ influence. With some delay, the military defeat is now followed by the bitter realisation that they have also failed scientifically. Unlike three months ago, when the members of the Uranium Club were convinced that the Americans and the British would scramble for their services, they are now prey to the insidious feeling that they are no longer of any use.

Wirtz asks Weizsäcker what can still be done now that the Americans have succeeded in separating isotopes. Heisenberg joins them and imagines that ‘we no longer appear to them as dangerous enemies’ and thinks they should now be released. No longer dangerous also means no longer interesting, offers Weizsäcker, adding: ‘It appears that they [the Americans] can get along perfectly well by themselves.’ Heisenberg mentions their knowledge and experience of heavy water in the hope that ‘perhaps they can learn something about heavy water from us’, but immediately qualifies this with: ‘But it can’t be much – they know everything.’

He also expresses one further aspect of the German failure: ‘The point is that the whole structure of the relationship between the scientist and the German state was such that although we were 100 per cent behind it, on the other hand we were so little trusted by the state that even if we had wanted to do it, it would not have been easy to push it through.’

In his diary, Bagge refuses to relinquish the hope that nuclear energy will ‘make people’s lives more pleasant, better and perhaps happier … All it takes is for people to be morally up to this development. And we believe they will be.’ He also bears in mind some words that Laue uttered late that day: ‘When I was young, I wanted to do physics and experience world history. I have done physics and I can now say, in my old age, that I have truly experienced world history.’ This is his epitaph on life as a physicist in his time. It is one o’clock, but things are not yet over for the night. An hour later there is a knock on Bagge’s door and Laue comes in.

‘We have to do something. I’m very worried about Otto Hahn. He has been shattered by the news, and I fear the worst.’ Together they put their ear to Hahn’s door and keep watch until they can be sure from the adjacent room that Hahn has finally fallen asleep.

Diebner and Bagge say very little that evening. But late that night the bedroom microphones pick up a tête-à-tête that sounds like an epilogue by the two observers. They wonder what is going to happen to them.

‘They won’t let us go back to Germany, otherwise the Russians will take us […] If a man like Gerlach had been there earlier, things would have been different,’ says Diebner.

‘Gerlach is not responsible; he took the thing over too late. On the other hand, it is quite obvious that Heisenberg was not the right man for it. The tragedy is that Korsching is right in the remarks he made to Gerlach. I think it is absurd for von Weizsäcker to say that he did not want the thing to succeed. That may be so in his case, but not for all of us. Von Weizsäcker was not the right man for the job either. Heisenberg couldn’t convince anyone that the whole thing depended on the separation of isotopes. The separation of isotopes was looked on as a secondary matter. When I think of my own apparatus – it was done against Heisenberg’s wishes. […] Do you remember how von Weizsäcker said in Belgium, “When they come to us we will just say that the only man in the world who can do it is Heisenberg.” […] You can’t blame Speer, as none of the scientists here forced the thing through. It was impossible, as we had no one in Germany who had actually separated uranium.’

Diebner: ‘They all failed. Walcher and Herzog wanted to build one [a bomb], but they didn’t succeed.’

The recordings break off with these resigned closing remarks from Diebner. It is half past one in the morning and all the guests have now gone to bed. The microphones capture nothing but deep sighs and the occasional voice calling out. From time to time the sound of opening and closing doors can be heard in the corridors – more frequently than on other nights. The effects of a day that has changed everything continue in their sleep and their dreams.

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