Toward the end of World War II, when the Allies began the invasion of Germany, Nazi scientists scrambled to create a nuclear reactor.

The project, which was headed by physicist Werner Heisenberg, is made up of 664 uranium cubes, with each weighing about 5 pounds or 2.3 kilograms. As Germany collapsed, the scientists buried the uranium cubes and fled.

More than 70 years after the war, one of those uranium cubes mysteriously appeared in Maryland.

Adolf Hitler's Uranium Cubes

Tim Koeth, an associate research professor at the University of Maryland, in 2013 received the artifact. It was accompanied by a cryptic note.

"Taken from the reactor that Hitler tried to build. Gift for Ninninger," the note reads.

The mysterious appearance of the uranium cube sent Koeth, who collects radiological oddities, and Miriam Hiebert, a doctoral candidate, into an investigation to uncover its history, how it got to Maryland, and where the remaining uranium cubes are hiding.

An article published in the May 2019 issue of Physics Today recounts the desperate attempt of Nazi Germany to build a nuclear reactor that spurred the Manhattan Project, leading to the bombing of Japan.

"To me, this cube represents a relic of the program that catalyzed the Manhattan Project and subsequently, both good and bad — weapons, nuclear energy, nuclear medicine," stated Koeth. "It's the dawning of a new era in human existence, when for the first time, we either had the capacity to save ourselves, or completely destroy ourselves."

Nazi Germany's Nuclear Plans

The Manhattan Project was formed in 1939 by former U.S. President Franklin D. Roosevelt as the direct response to intelligence reports that Nazi Germany is creating a nuclear weapon. However, in the war's final days, authorities actually got their first look at Germany's nuclear efforts and found that instead of a weapons program, Heisenberg's team was building a reactor in a cave under a castle in southwestern Germany.

Aware that they are going to lose the war, the Germans thought that they could salvage their reputation by being the first to create a nuclear reactor.

However, the effort failed and Germany fell. In April 1945, U.S. troops unearthed the uranium cubes and shipped them to Paris.

What happened next was unclear, but the investigation of Koeth and Hiebert led them to the late Robert D. Nininger who served in the group tasked to procure uranium for the Manhattan Project. They discovered that the Nazi's uranium cubes were eventually shipped to the United States, but they were no longer needed.

One of those uranium cubes is at the Smithsonian Institute and another is used in science classes at Harvard University. One ended up in Koeth's desk.

Koeth and Hiebert will continue searching for the whereabouts of Hitler's uranium cubes.

German Uranium Documents

The investigation also led the researchers to recently declassified CIA documents labeled "Germany Uranium." It revealed that a competing project had another 400 uranium cubes in use at the time of the war.

Moreover, according to Koeth, if Nazi Germany forced two scientist groups to work on a nuclear reactor, they would have likely succeeded.