In the summer of 2013, Professor Timothy Koeth of the University of Maryland received an unusual birthday gift: a package containing a small black cube about five centimeters on each side and weighing about five pounds. An attached note explained as succinctly as it did enigmatically: “Taken from the reactor that Hitler tried to build. Gift from Ninninger”. The cube in question was uranium, one of those that were part of the Nazi regime’s attempt to build a nuclear reactor during World War II.
In late 1938, German physicists Otto Hahn and Fritz Strassmann succeeded in obtaining barium after bombarding uranium with neutrons, in what is considered the first demonstration of nuclear fission, a term coined by another scientist, Otto Robert Frisch, after confirming it experimentally a few weeks later. The following months were feverish as speculations arose about the possibilities this opened up, and a team of physicists was formed, officially named the Arbeitsgemeinschaft für Kernphysik but popularly known as the Uranprojekt or Uranium Project (in the English version, Uranvein).
Shortly afterward, a second team was organized, and the work was directed toward military applications, for which it was necessary to build a reactor. That was always the objective since Hitler was never able to understand the world of the atom and, therefore, was only given a brief outline of the potential of a bomb, in which he did not show much interest. The problem was time, as it was estimated that a reactor could not be built before five years, and the outbreak of war seemed increasingly imminent.
All available uranium for the project
Once the conflict began, the scientists were clear that they would not succeed in the short term, so the work was divided among nine institutes: some were dedicated to obtaining uranium, others to producing heavy water (about five tons a year were produced in Norway), some to isotope separation, and others to reactor construction. There were a total of about seventy specialists, with Hermann Göring as the supreme leader of the project.
However, the course of the war forced the prioritization of resources for the war effort, leading to a halt in the fall of 1942. By then, it was estimated that an atomic bomb could not be produced before 1947, so alternatives were proposed, such as developing a uranium motor for the Kriegsmarine. However, by the following summer, Albert Speer managed to restart the work and ordered all available uranium (about twelve hundred tons) to be used in the projects.
The problem was that the Uranprojekt already had a competitor in the United States, the Manhattan Project, which ended up getting ahead despite starting two years later. According to experts, this was because—in addition to having superior resources—the participants worked together in the same direction rather than dispersing their efforts like the Germans, who split into three groups working separately in three cities (Berlin, Leipzig, and Gottow) and competing for resources. This would be confirmed, as we will see.
Now let’s return to the University of Maryland, where Professor Timothy Koeth set out to investigate the origin of the peculiar package he received. The note mentioned the reactor planned by Hitler, which in the winter of 1944, with the Allies already entering Germany, seemed like an achievable goal compared to the failed bomb. Koeth, who had already verified the authenticity of the cube, recalled a name: Werner Heisenberg. He was the director of the Kaiser Wilhelm Institute and probably the most notable physicist involved in the Uranprojekt, which is why he was given leadership. However, he always maintained that he and his team focused their efforts on building a reactor and neglected the bomb due to ethical concerns.
Six hundred and sixty-four uranium cubes
The fact is that, with the enemy already on German soil, it was ordered that the work be moved from Berlin to Haigerloch, a small town in the southwest of the country, where they set up in the local castle, which now houses the Atomkeller Museum. There, they conducted the B-VIII experiment (the B referred to Berlin), described by Heisenberg in a work he published in 1953, Nuclear Physics.
In it, they stated that they had six hundred and sixty-four uranium cubes, each weighing about two and a quarter kilograms, which were submerged in a tank filled with heavy water, connected to each other by cables hanging in rows from the lid. A wall of graphite surrounded the assembly. This was the reactor in question, which never came to operate due to a lack of sufficient uranium; it would have needed 50% more, which would have also required a greater amount of heavy water.
The cube received in Maryland was one of those, as evidenced by its dimensions, weight, and appearance (each face has a surface with the voids left by bubbles during the rough casting process, the type of preliminary processing of the time). Additionally, there are notches on it made for threading the cable, and a high-resolution gamma-ray spectrometer analysis revealed that the composition is natural uranium, neither enriched nor depleted.
Moreover, -and this is important-, it also does not have fission products (cesium-137, for example), which confirms that the reactor did not operate. Another possibility is that, for some reason, that particular cube was not used, but in any case, it is clear that it is one of those from the Uranprojekt.
The big question was how the cube ended up in the U.S., and the answer was in Operation ALSOS. It was commissioned by Leslie Groves, the general in charge of the Manhattan Project, and involved sending a unit of soldiers and scientists to the front lines to gather information on the German atomic program in all its fields. As the Allies advanced toward Haigerloch, it became clear to the Germans that they no longer had time to continue their research, and they were ordered to make all the equipment disappear. The documentation was hidden in a latrine, the heavy water was poured into barrels, and the uranium cubes were buried in a nearby field. When the ALSOS team arrived in the town at the end of April 1945, they arrested the German physicists, but not all of them; Heisenberg had managed to escape at night on a bicycle, taking several of the cubes with him.
The Allies soon found the documents and the water, and they also dug up the buried cubes. All of this was sent to Paris and from there to the U.S. under the control of the CDT (Combined Development Trust), an Anglo-American entity created to prevent the Soviet Union from obtaining such material. It is believed that the cubes were destined for ORNL (Oak Ridge National Laboratory), the center created to house the massive facilities and workforce of the Manhattan Project, which was initially going to continue the nuclear weapons experiments (later redirected to science and medicine); however, it seems that not all of them arrived.
Timothy Koech’s research led him to discover a box stored in the National Archives labeled German Uranium. It contained hundreds of recently declassified documents revealing that, in addition to the Haigerloch cubes, there were another four hundred in Germany, specifically in Gottow, where Dr. Kurt Diebner was attempting to develop another reactor. This means that if the teams in Gottow and Berlin had worked together, they would have had enough uranium and likely would have managed to get a working reactor before the war ended.
How did the Maryland cube make its way to America?
All those cubes, previously unknown, were sold in Eastern Europe by a smuggling ring that took advantage of the growing demand for uranium on the black market during the postwar period. In fact, they also tried to sell this unique merchandise to Western countries for hundreds of thousands of dollars per unit, though they were unsuccessful because the U.S. had an excess of uranium and would only buy it at market price, which was around twelve dollars per kilo. However, sporadic offers kept coming, and in 1952, two Germans were arrested and sentenced to life imprisonment for possession of one of these cubes, proving the existence of the plot. Nevertheless, most of the units ended up in the USSR… and that’s where the trail ends, although a sketch of a German atomic bomb was recently discovered in Soviet archives.
We just need to revisit the earlier question: How did the Maryland cube make its way to America? Timothy Koeth was searching for books on the subject in a bookstore when he found a 1954 work titled Minerals for Atomic Energy. Its author was named Robert D. Nininger, the same surname that appeared on the mysterious note, but with one less ‘n.’ It seemed too much of a coincidence, so he followed the lead and, through a phone call, found out that the individual in question had passed away in 2004… in Rockville, Maryland. It turned out that Nininger had worked in the uranium acquisition section of the Manhattan Project and was therefore responsible for receiving the cubes sent from Europe. His widow said he had kept the cube all that time, but it then changed hands several times before arriving at the university.
This fascinating story was not unique, as there are at least ten other cubes in private and public collections in the United States (the Smithsonian Institution, Harvard University, etc.), each presumably with its own interesting story. As for Heisenberg, he was ultimately captured and interned, along with other scientists like Otto Hahn, in an English internment camp.
There, he heard the news of the Hiroshima atomic bomb explosion on the radio and spent the next two days calculating the critical mass and amount of uranium needed for it; his results were so close that it seems likely that, had circumstances and will been different, he and his team might have succeeded earlier.
This article was first published on our Spanish Edition on August 30, 2019: La historia de los misteriosos cubos de uranio del proyecto atómico nazi
SOURCES
Timothy Koeth y Miriam Hiebert, Tracking the journey of a uranium cube
Rainer Karslch, New light on Hitler’s bomb
Susanne Heim, Carola Sachse y Mark Walker, eds., The Kaiser Wilhelm Society under National Socialism
Bruce Cameron Reed, The history and science of the Manhattan Project
Natividad Carpintero Santamaría, La bomba atómica
Jesús Hernández, Enigmas y misterios de la Segunda Guerra Mundial
American Institute of Physics, Searching for lost WWII-Era uranium cubes from Germany
Wikipedia, Proyecto Uranio
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