The second world war was the war of Hitler's state and a couple of aggressive dictatorships against the rest of the world. Nuclear fission having been discovered in 1938, each side in the conflict had a secret military "uranium project" to explore the possibility of producing big, even explosive nuclear reactions. The Allies succeeded in building a reactor and an atom bomb, while the German project stopped short of making the reactor. Hence Werner Heisenberg lost the "war" or "race" against Fermi and Oppenheimer - or so it has been said.

Historical facts, however, do not support such a simplified picture; they show that three aspects characterised the German uranium project. First, because of its early start, at a time when it was not even known that a chain reaction would work, it was not simply a bomb-making project. Second, all reports of the project related to the construction of a reactor. Third, Heisenberg was never director of the whole German enterprise.

At the end of the European war a group of ten leading German atomic scientists, including Otto Hahn (discoverer of nuclear fission), Max von Laue (who never worked on the uranium project), Heisenberg, Paul Harteck and some younger colleagues, together with Kurt Diebner and Walther Gerlach, the first and last director of the project, were captured and interned for six months at Farm Hall near Cambridge for interrogation and to keep them away from the former French and Soviet allies. From Samuel Goudsmit's book Alsos and from Leslie R. Groves's Now It Can Be Told - Groves was leader of the American bomb project - it became evident that the private conversations of the German detainees were "bugged" and that records of what was said existed. For more than 45 years some of the former "guests" (including Heisenberg) and others who were interested tried to obtain the material, but the British authorities refused, claiming to protect the rights of those involved.

Eventually the request of 15 fellows of the Royal Society and the British Academy succeeded: a few of the transcripts and English translations of parts of the conversations (with the comments of the British "hosts") were released on February 14 1992. These 22 reports represented weekly accounts dealing with items that interested the military British and American authorities most, namely possible secrets of the German uranium project, reactions of the detainees to the Hiroshima and Nagasaki bombs, relationships between the detainees and their relationship with the Nazi regime.

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The "Farm Hall reports" were published in 1993, in the "original" English version (The Farm Hall Transcripts) and in a German retranslation (Operation Epsilon), with suitable introductions on the historical background, and on technical and archival details. While the press and some historians spoke of sensational material throwing new light on the "German atom bomb project", others, such as myself, argued that the reports just added details to the picture obtained from previous documents. What then can be the reason for this new edition?

The editor, a professor of physics at (Stevens Institute of Technology (New York), explains: "When I first saw these transcripts I I had something of the feeling that Champollion must have felt in August of 1808 when he saw the newly produced copy of the Rosetta Stone." Having had teachers like Victor Weisskopf, Hans Bethe, Robert Oppenheimer and others connected with the American bomb project, having been "exposed [in 1957] as an intern at Los Alamos to some nuclear weapons technology", as he says, and so on, Jeremy Bernstein felt "safe in the 'culture' of nuclear weapons", especially competent to derive consequences from the Farm Hall reports on the German uranium project. His conclusions are that "the Germans seriously tried to work on nuclear weapons", and "it becomes painfully clear that Hahn, Heisenberg and the rest of the leading [German] nuclear scientists" knew practically nothing about the problem they were tackling.

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The editor supports such claims by piling up remarks, questions and statements inside square brackets. These remarks contain judgements about persons - mostly biased or wrong - and other "information", more than once contradicting the facts and misunderstanding technical details. The whole commentary exhibits how poorly Bernstein is acquainted with the history of the German project and the wartime situation in the Third Reich. Furthermore he relies on much later, hence weaker reminiscences rather than on contemporary documents; for instance, he quotes von Laue's 1959 letter to Paul Rosbaud instead of his immediate letter to Theodor von Laue, when dealing with the events of August 6 1945. But the main target is Heisenberg, to whom "a modest level of competence" is attributed. Overall, Bernstein is "struck by the intellectual thinness" of the German scientists compared with their Anglo-Saxon colleagues.

Bernstein's conclusions may be contrasted with opinions of better experts. Thus Edward Teller, having read the talk which Heisenberg gave a week after Hiroshima, concluded that the speaker got the facts mainly right except for a detail on which the Los Alamos scientists debated for several weeks: "The significance of this is that Heisenberg could not have worked on the atomic bomb seriously." With respect to his and others' competence concerning the reactor question, there is the judgement of Alvin Weinberg and Lothar Nordheim: "The fact remains that an independent group of scientists of much smaller size than ours, operating under much more adverse conditions, achieved so much."

Bernstein criticises and ridicules more careful and consistent treatments of the German uranium project (including Thomas Powers's account in Heisenberg's War). What is rather absurd is his own war against great scientists, whose procedure and arguments he cannot follow. This book puzzles the reader and harms the reputation of its editor. It should not have been written and certainly should not have been published.

Helmut Rechenberg, a former student of Heisenberg, is a physicist and historian of physics, Max Planck Institute for Physics, Munich, who edited Heisenberg's reports on the German uranium project.

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