Did Heisenberg undermine the German atomic bomb by deliberately hiding his expertise from the Nazis?

There were reviews of the documents recovered from Heisenberg's facility where, in his handwriting, equations he had derived, and which were used by the Manhattan Project, were very subtly wrong as well as testimony from other scientists in the project captured by allies and Soviets stating that Heisenberg ordered pointless experiments they could not ignore because he was the last first-rank physicist in Germany.

There is a relevant new publication on the topic:

Popp (2016) "Misinterpreted Documents and Ignored Physical Facts: The History of ‘Hitler's Atomic Bomb’ needs to be corrected"

"It is shown that until the end of the war the German physicists did not know that an atomic bomb can only be made with fast neutrons, except Heisenberg, who, however, discovered it rather late, did not communicate it clearly and did not study any bomb physics. The physically correct interpretation of the documents reveals that the German physicists worked unsuccessfully on a reactor, which would have been a prerequisite for a plutonium bomb. But they did not know how to build a bomb because they never worked on a realistic bomb theory."

J. Robert Oppenheimer's biographer Ray Monk thinks that Heisenberg played no such role (perhaps he "did" in convenient-to-some retrospect). See also here.

How did that different perspectives on Heisenberg occur ?

Robert Jungk published the (in my opinion excellent) book "Heller als tausend Sonnen" (Brighter than thousand suns) in 1956 about the fate of the atomic physicists working on the bomb. Jungk was strictly against the bomb and Heisenberg claimed in this book that he actively tried to prevent the building of the Bomb.

Now Niels Bohr had a talk with Heisenberg and after reading "Heller als tausend Sonnen" he said that Heisenberg had made the exact opposite impression: That Heisenberg supported the bomb and worked full-time on it to guarantee Germanys victory.

The Niels Bohr Archive in Kopenhagen has presented the letters of Niels Bohr under http://www.nba.nbi.dk/papers/docs/cover.html.

Heisenberg's letter can be found here (5,6,7): http://werner-heisenberg.unh.edu/

The question if Heisenberg did not made himself clear or if Bohr's interpretation is correct is unsolved. Fact is that the German physicists were not able to come up with a working design.

The German weapons development effort (including nuclear weapons) was fragmented among numerous competing groups, each jealously guarding their resources and not sharing information with other groups. German Secret Weapons of the Second World War, by Ian V Hogg, discusses this in great detail. As for the Bomb specifically, the evidence is that Heisenberg was somewhere between ambivalent and mildly enthusiastic. He was a patriot (but not a Nazi), and had to be careful not to offend the Gestapo (even though he was a Nobel Laureate). He did make some technical mistakes and (in hindsight) incorrect choices, but he did not deliberately sabotage the effort, nor was he incompetent in any sense of the word. Like most German scientists, he did a very poor job of communicating with political leaders, military leadership, and even with others in his field. He was first and foremost a scientist, not a military man working against time to develop the weapon. The Germans tried to get the Bomb, and they failed -- let us celebrate that.

No, he did not.

He very much wanted Germany to win the war. For example he was very excited about the offensive in the Ardennes. He met with Niels Bohr in attempt to gain more information about his work, which was described by Bohr himself.

The source of this information is the Niels Bohr's biography by Daniel Danin.

Heisenberg's speech notes from the 1942 Harnack Haus conference were recovered from KGB archives by Rainer Karlsch and published in 2005. These reveal that Heisenberg actively promoted development of an atomic bomb to fellow scientists, military chiefs and political leaders at that conference.

Luftwaffe General Field Marshall Erhard Milch recalled in his memoirs that when he asked Heisenberg at the conference how big such a bomb would need to be, Heisenberg replied no bigger than a pineapple. Heisenberg called for establishment of three different research projects

1. Uranium 235 Enrichment
2. Nuclear reactors to obtain Plutonium ("eka-Osmium")
3. Harvesting Protactinium 233

Heisenberg was personally involved with research to develop nuclear reactors but because of his expertise in Matrix theory of transmutation he was also employed as a consultant to Forschungsstelle-D at Bisingen. This was the connection between Heisenberg and Bohr. Before the war Bohr had been published for his experiments with transmutation of Protactinium from Thorium. Heisenberg was trying to acquire Bohr's knowledge for the German war effort.

Various OSS reports corroborated this based on intelligence smuggled to Switzerland from Reichstag official Dr Erwin Respondek during 1943.

On 22 April 1945 the US 1269th Engineers Battalion attached to ALSOS captured and dismantled an advanced 23 MeV syncrotron device at Bisingen. The ALSOS mission also captured a 1.8MeV Van der Graff generator at Tubingen not far away. These were involved with efforts by Otto Hahn to transmute Thorium which also involved use of the Paris cyclotron from 1941.

The informant of this was Dr Ing. Ernst Nagelstein [informant H-98] who was interrogated 1st November 1944 in Switzerland by Goudsmitt and Wardenberg.

Thus to suggest Heisenberg was trying to prevent Nazi development of the Bomb is either misleading or at best ignorant of the truth.

Heisenberg was not a central figure in the Nazi atomic bomb project. That accolade belongs to prof Kurt Deibner who headed a rival and far more secret project for Army Ordnance (Heereswaffenamt) to develop an atomic bomb.

Postwar focus on Heisenberg misses the point entirely that Heisenberg himself was not key to the German Atomic bomb project and in fact was quite peripheral and largely unaware of Diebner's achievements. Heisenberg was a vain, arrogant man who thought himself superior to other scientists and thus he perhaps saw himself at the centre of Germany's nuclear efforts, but this was light years from the truth.

The argument for Heisenberg being intentionally incompetent is that he made two "incorrect" choices in which path to follow.

1. He selected heavy water as the reactor moderator, even though it is very unusual and requires a big plant to make it.

2. He selected plutonium as the fissile material, even though it doesn't occur in nature and have to be created in nuclear piles.

The argument is that Heisenberg, being a highly intelligent man, would not have made those mistakes, and that he therefore intentionally made those choices to delay or stop Germany from getting the bomb.

However, this ignores that Heisenberg was a scientist, not an industrialist. I think Heisenberg simply chose the options he thought had the greatest chance of succeeding. He didn't think uranium was a good candidate for a chain reaction, and that it would be easier to make a bomb out of plutonium. He also thought it would be easier to create a nuclear pile if it was moderated by heavy water.

He was definitely correct about the heavy water. Making a heavy water reactor is easier than a graphite or ordinary water reactor, and in addition, a heavy water reactor can work with non-enriched uranium. This means that although you need facilities to create heavy water, you don't need facilities to enrich the uranium, to some extent compensating for the need of heavy water.

And it's hard to claim that he was wrong with regards to plutonium. He rather was "too correct". The Manhattan project decided to pursue both plutonium and uranium bombs, and during the development of those bombs they had to come up with a more complex bomb design for the plutonium bomb, because plutonium turned out to be so reactive that it would probably explode to early in the process, making it likely to "Fizzle" if it had been used with the original simpler design, while the simple design could be retained for the uranium bomb.

So I think he rather chose the options that was the easiest for him. The "safe bet", so to speak. He probably either underestimated the time and effort required in creating enough heavy water and then enough plutonium to build a bomb, or he didn't make his choices with regards to the time frame at all, but based them entirely on what he thought would be easiest, as opposed to what would be quickest.