Why did the Germans fail to build a nuclear bomb?

When the war in Europe ended, one of the Allies’ main priorities was to round up German nuclear scientists. Ten of them were interned in Farm Hall,  a former ‘safe house’ for British intelligence close to Cambridge. The Hall was bugged, and the scientists’ conversations were recorded. The transcripts run to several hundred pages. They are not particularly interesting.

I shall therefore discuss only the three leading figures: Carl Friedrich von Weizsäcker, Werner Heisenberg and Otto Hahn.

Weizs äcker

Weizsäcker’s taped statement contains a bold line: “I believe the reason we didn’t create an atomic bomb was because all the physicists didn’t want to do it, on principle. If we had wanted Germany to win the war, we would have succeeded.”

What does this statement imply? Two things. Firstly: “You are the bad guys, we are the good guys. You killed at least 200,000 people in Hiroshima and Nagasaki. We Germans would have never done such a thing.” And secondly: “Don’t think that you are the smart guys, that you succeeded where we failed. Had we wanted to do it, we would have done it. Yes, we would have done it. Believe me, we would have done it.”

These were Weizsäcker’s claims. The facts tell a different story. German scientists didn’t produce an atomic bomb because they couldn’t. They couldn’t, because they made two big mistakes. German physicists dismissed graphite as the moderator, and  vastly overestimated the critical mass of uranium needed for the explosion. These scientific mistakes were compounded by a lack of sufficient support from the top.  Hitler was never an enthusiastic nuclear supporter. His priorities were the V1 and V2 rockets and the jet fighter; the possibility of a nuclear weapon in five years’ time was of little interest to him. The absence of motivation, it seemed, stemmed from the top, rather than a principled stand taken by German scientists.

Following these questionable musings, however, it is interesting to note that Weizsäcker became a notable philosopher and ethicist later in life.

Heisenberg

Let me now come to the second German physicist: Werner Heisenberg, recipient of the 1932 Nobel Prize. Heisenberg’s fame within the scientific community rests on the uncertainty principle,  which states that certain physical variables cannot be measured with arbitrary accuracy. He also achieved some recognition in artistic circles: his September 1941 visit to Denmark to meet Niels Bohr (the 1922 Nobel Laureate) was the subject of the play Copenhagen by Michael Frayn.

At the time of their meeting, Niels Bohr was considered the grand old man of European science, known as “the Pope”. He was Heisenberg’s teacher, one-time boss, mentor, and scientific guardian. It is a visit that still raises controversy: what did Heisenberg want?

Heisenberg’s answer to this question is that he wanted Bohr to ask British and American scientists not to work on the atomic bomb, on principle.

The background to the conversation may belie this claim. In September 1941, Denmark was under German occupation and the German invasion of Europe was at its height. Germany’s reach extended from the gates of Moscow to the Pyrenees (and the country beyond the Pyrenees was a fellow fascist state). Might Heisenberg have been entrusted with the task of recruiting Bohr to the German war effort, to help build the bomb?

The military situation at the time offers a plausible motive. “England is finished, America is neutral, Germany is in a fight with Asiatic hordes. You may not like how the NSDAP runs Germany, but if you have to choose between Germany and the Soviet Union you would surely want European culture to succeed. Come and join us!”

Assuming that this offer was made, what were the chances of Bohr accepting it? Nil! Bohr himself had some Jewish ancestry and his wife was of Jewish origin. The Third Reich was unlikely to be their dream home.

Hahn

The third German scientist of interest was Otto Hahn: the first man to split the atom. He learned of his Nobel Prize for 1944 while at Farm Hall. He was probably the least politically-minded of the ten, and the one who readily admitted: “I am glad we did not succeed.” His main interest was in rebuilding German science after the war, a task he helped to spearhead.

Hahn’s close collaborator for several decades was Lise Meitner. By the time of the crucial experiments, Meitner was at work in Sweden. What did she think of her erstwhile colleague? Her first communication to him after the war ended was rather bitter, and one she ultimately never posted:  “You all worked for Nazi Germany. And you tried to offer only a passive resistance. I and many others believe that you must publish an open statement that you are aware that through your passivity you share responsibility for what has happened and that you must work to make amends.”

What is the verdict? Did German scientists want to produce a bomb for Hitler? Yes. They did their best, but their best was not good enough. They could not even get a chain reaction going: a feat managed in 1942 by Fermi and Szilard at Los Alamos. The Germans failed. They failed miserably. Of course, the honourable thing was to fail. So by this measure, were Weizsäcker, Heisenberg and Hahn honourable? Only if we categorise it as honour through incompetence.

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