What part did Germany play in building the bomb?

At the end of 1938, the Berlin scientists Otto Hahn and Fritz Straßmann succeeded in splitting a uranium nucleus in the laboratory. Shortly thereafter, Lise Meitner gave a theoretical explanation of the phenomena observed. As a result, nuclear physicists all over the world knew that nuclear fission contained a new, enormous energy potential that could be used for peaceful purposes such as generating electricity and heat - but also for military purposes in the form of an atomic bomb.

Several Jewish physicists who had fled Europe feared that the National Socialists could also take advantage of these opportunities. So they persuaded Nobel laureate Albert Einstein to write a letter to Franklin D. Roosevelt asking him to start a US nuclear program. The US President followed the recommendation and started a project in top secret, which was eventually given the code name "Manhattan Project" and led to the construction of the first two functional atomic bombs.

The warning was not unjustified, because at the same time a group of highly qualified nuclear physicists gathered around the Nobel Prize winner Werner Heisenberg in Germany. Together they wanted to explore possible uses of nuclear fission, including a "uranium machine", i.e. a nuclear reactor. But the possibility of a uranium bomb was also discussed.

This means that two research groups are working in parallel on the possibility of a superbomb. In the USA they got all the support from the state, while Hitler allowed the various working groups of the Uranium Association to keep to a rather limited extent. Physicists in the USA soon overtook their German competitors, mainly thanks to their two most important minds, J. Robert Oppenheimer and Enrico Fermi.

But Heisenberg did not give up, even if after 1945 he claimed to have taken a restraining stance. In the summer of 1942, he explained to Albert Speer, the newly installed Minister of Armaments, that a uranium bomb that could destroy an entire city was only "the size of a pineapple". It is not clear whether he said this in order to be able to maintain his working group or because he actually wanted to build such a weapon.

From 1943 onwards, German nuclear physicists lagged hopelessly behind the American "Manhattan Project". This also had to do with successful Allied air raids on resources in German-occupied Europe, such as a heavy water factory in Norway.

At the beginning of 1945, the Germans moved their experimental reactor to Haigerloch in Swabia out of concern for the advancing Soviets. But even here they did not succeed in controlling nuclear fission, which Enrico Fermi had already achieved in Chicago at the end of 1942. Basically, the scientists of the Uranium Society calculated with wrong numbers, so they had no theoretical idea of ​​how a nuclear weapon works.

When US soldiers marched into south-west Germany in April 1945, the physicists quickly removed all traces of their work. They were nevertheless arrested by an Allied special unit and taken to a special camp in England, at Farm Hall, where they were bugged.

The transcripts of their conversations show that they had no insight into the practical problems of developing nuclear weapons - and therefore the scientists of the "Manhattan Project" could not benefit from them either.

This article was first published in 2012.