Farm Hall, in Godmanchester, played a key role at the end of the Second World War in identifying the extent of Hitler's nuclear capability and the likelihood of that knowledge being passed to Soviet Russia. When he was awarded the OBE in the New Year Honours, The Hunts Post asked the mansion's present owner, Professor MARCIAL ECHENIQUE, Professor of Land Use and Transport Studies at the University of Cambridge, to describe Farm Hall's history and the part it played in the history of the world. WHEN we bought Farm Hall from the National Trust 30 years ago, my wife and I had no idea that behind the classical Georgian facade of the Godmanchester mansion, there was an extraordinary piece of history that had been kept secret for many years. In 1979 my wife and I embarked on a large restoration programme involving the re-roofing of the house, rebuilding parapets and chimneys, as well as restoring the historic parkland to its former glory. The house, originally built at the end of the 17th century, was transformed at the beginning of the 18th century into a fashionable Palladian mansion by Charles Clarke, recorder of Huntingdon and Baron of Exchequer. During the Second World War the house was requisitioned and the first floor was subdivided, destroying the main reception rooms. The beautifully-proportioned main rooms of the house were in the 'piano nobile' (noble floor) in the first floor, as recommended by Andrea Palladio, the famous Italian architect of the 16th century, to allow better views over the parkland. We proceeded to restore the original rooms and, when the floorboards were lifted for spraying the timber against woodworm, we found hidden cables that were not connected to any electrical points. Our suspicion that these cables were part of bugging devices used for secretly recording conversations grew when we read the book entitled Most Secret War written by R V Jones in 1978. In the book it was explained that Farm Hall was in fact used to intern the top German nuclear scientists at the end of the Second World War. The combined Anglo-American operation "Alsos" captured these famous scientists, just before the Russians entered Berlin. Some historians argue that the capture of the scientists was the main reason for the Russians' push to take the city first. Later on, an American, Arnold Kramish, came to visit Farm Hall as he was writing a book called The Griffin that told the story of the secret operations conducted from the house by the Special Operation Executive (SOE), the predecessor of MI5. Among the stories in the book was the mission to destroy the German heavy water plant at Vermork in Norway, which was the subject of the 1965 film Heroes of Telemark, with the actor Kirk Douglas. Heavy water was used to enrich uranium, the essential ingredient for an atom bomb. Kramish gave us the names of the German scientists that were interned at Farm Hall. Amongst the 10 scientists there were three Nobel laureates, including Heisenberg of the 'uncertainty principle' fame in physics, and Hahn, who discovered nuclear fission in 1939. We wrote to the surviving scientists and we received replies from von Weizsacker, a scientist and philosopher, whose brother at that time - in the 1980s - was the president of West Germany, and from two other scientists, Wirtz and Bagge. The latter was engaged during the war in producing the first nuclear reactor. Bagge came later to visit Farm Hall as part of an advisory team to the German production of a film called The End of Innocence, which told the story of the scientists interned at Farm Hall. The big question in everybody's mind was: why didn't the Germans, who were much more advanced in nuclear developments than the allies, develop the atom bomb during the war? The answer given by Heisenberg in his autobiography Physics and Beyond was that they did not develop it for ethical reasons, but few people believed him. If there were secret recordings, as we suspected, of the German's conversations at Farm Hall, it might throw light on this issue. We tried to get a response from the Government, but it took a number of years for the transcripts of the recordings to be made public in 1993 and published in two books, one British entitled Operation Epsilon: The Farm Hall Transcripts, introduced by Sir Charles Frank, and one American entitled Hitler's Uranium Club by Jeremy Bernstein. With the publication of the transcripts of the secretly-recorded conversations at Farm Hall, many people came to the conclusion that the Germans did not know how to build a nuclear bomb and Heisenberg version was a latter fabrication. This idea comes from one of the conversations recorded in the present library at Farm Hall when the scientists heard the news from the BBC that the Americans had dropped the bomb in Hiroshima in 1945. The scientists were incredulous that the American could have fabricated a nuclear bomb that, according to Heisenberg, required several tons of pure uranium to make. This statement by Heisenberg has been used by many as evidence that Germans did not know how to make a bomb, because it was materially impossible to enrich that quantity of uranium in the available time. But, a few lines below in the same published transcripts, Hahn asks Heisenberg "But tell me why you used to tell me that one needed 50 kilograms of 235U [pure uranium]?" Incidentally, this was the amount used in the Hiroshima bomb. The interesting question is why did Heisenberg say this? One can only speculate now about his motivation. It could be that he had not worked out in detail, as he said, the required pure uranium needed or it was a deliberate ploy to justify himself in front of some of the scientists of his reluctance to embark in the development of the bomb. It must be said that amongst the scientists interned at Farm Hall there were not only some virulently anti-Nazi, such as the Nobel laureate Von Laue (who discovered the X ray) but also there were some pro-Nazi such as Gerlach (who was in charge of the German nuclear programme). It does seem that Heisenberg knew how to make a bomb, and there is further evidence in a report by the German Army Ordnance in 1942 that corroborated this calculation. If the Germans had decided to build a bomb at that time and dropped it on London, it would most likely have ended the war. The resources needed to develop the bomb were comparable to the 'V' rocket programme developed by Von Braun, but Heisenberg resisted the pressure exerted by the military to build the nuclear bomb by saying that it would take too long and by then the war would be over, with Hitler's victory. I, personally, give some credibility to Heisenberg's explanation that he did not want to develop it for ethical reasons. As told in his autobiography, he went in 1941 to see his friend and teacher, the Nobel laureate Niels Bohr, in Nazi-occupied Copenhagen to explain in secret (as it would have been considered treason by the Nazis) that the Germans will not build an atom bomb, and thus the allies should not build one either. Being a German, he would not be believed in the West, but Bohr, being a Dane of Jewish descendent, would be credible amongst scientists in the allied camp. The conversation between the two scientists was the subject of the award-winning play Copenhagen by Michael Frayn, which was acclaimed around the world. The Germans concentrated their effort instead on building a nuclear reactor to produce electricity and nearly succeeded in this endeavour. The prototype built in Germany during the war led to the development by the British Government of the first nuclear power station used for peaceful purposes at Calder Hall in 1947, now called Sellafield. The Germans were aware that a by-product of the nuclear reactor was the production of plutonium, which had an even bigger destructive power than uranium. As a matter of fact, the second American bomb dropped, on Nagasaki, was a plutonium bomb. The main purpose for the British reactor at Calder Hall was to obtain plutonium for the first British nuclear bomb. There is some evidence that a diagram of the German reactor was passed by Heisenberg to Bohr in their meeting in Copenhagen. But Bohr misunderstood Heisenberg and thought that he had been asked to collaborate in Germany's effort to make the bomb. Bohr was so concerned that he passed the message to the allies. Later he was whisked away by the Americans and collaborated in the development of the first nuclear bomb. The nuclear bomb was developed completely by Jewish scientists, who believed that unless they developed the bomb, Hitler's evil empire would succeed in doing so and thereby rule the world. Even Einstein wrote to President Roosevelt urging him to support the development of the nuclear bomb. It is ironic that the "goodies" ended up fabricating the most evil armament in the history of mankind, which killed hundred of thousands of Japanese civilians who had little to do with the suffering of the Jews. In contrast, the "baddies" - Germans - did the good thing of avoiding to give the power to an evil dictator and thus probably changed the course of history. There have been numerous books and documentary films about this episode, such as the BBC's Hitler's Bomb and ITV's Science in the Third Reich, and on many occasions I have been asked how we feel to live in a house that is associated with such dreadful artefact. My response has been that I not only love the place because of its architectural and landscape merits but, for me, Farm Hall represents how the ethical stance of a few individuals succeeded in getting good to triumph over evil. Perhaps we should all be grateful to these "good" Germans.