Such an attack was serious business in Nazi Germany and threatened internment in a concentration camp or worse. Heisenberg sought the assistance of friends and associates within the establishment, including Nazi Party members, to clear his name. Heisenberg’s mother, who had been an acquaintance of Heinrich Himmler’s father, passed on a personal letter from the physicist to the SS Reichsführer. After a thorough investigation by the SS, which included a terrifying interview at its Berlin headquarters, Himmler personally exonerated Heisenberg, effectively inoculating him from charges of treason until the end of the war.

The most nightmarish of World War II alternative history scenarios is the one in which Nazi Germany acquires atomic weapons. In fact, by the spring of 1945, when America’s massive nuclear program was reaching its culmination, the Nazi atomic program consisted of one experimental reactor in a cave in southern Germany, operated by scientists who lacked a clear conception of how to build an atomic weapon.

Even if the German scientists had known what they were doing, they still lacked suitable radioactive material to produce a weapon. One of World War II’s most remarkable and controversial stories is just how the Nazi atomic program came to this sorry pass.

The potential power of atomic energy is a corollary of Einstein’s famous Theory of Relativity equation, E = MC2. Simply put, the equation means that all matter is energy. To determine the energy contained in any bit of matter, one need only multiply its mass times the square of the speed of light. As the speed of light is somewhere in excess of 186,000 miles per second, the resulting number is correspondingly huge.

Early in the 20th century, physicists realized that if it was possible to release the atomic energy in a piece of matter, say a brick, they could create a doomsday weapon. Fortunately, the atoms in bricks, and in almost all ordinary matter, are quite stable and not likely to erupt in an atomic chain reaction. However, by the mid-1930s, experiments with the unstable element uranium revealed the potential to tap into its store of nuclear energy and create machines of awesome power.

Nazi Germany’s Rejection of “Jewish Physics”

Theoretically, by the 1930s Germany had a jump on the rest of the world in atomic research. Many of the world’s top nuclear physicists were German or Austrian, or worked closely with German or Austrian colleagues. It was a German scientist, Otto Hahn, who first split the atom in 1938. Although Hahn later tried to claim all the credit for his experiment, at the time he did not actually know what he had done.

It was Lise Meitner, an Austrian Jewish colleague, who realized the significance of Hahn’s discovery and described the processes involved. Meitner realized that Hahn, by bombarding a small sample of uranium with neutrons, had literally broken some uranium atoms apart, releasing powerful atomic energy. Incredibly, in accord with Nazi policy, Hahn and other “German” academics had recently driven Meitner from her post at the Kaiser Wilhelm Institute for Chemistry near Berlin to refuge in Sweden. Meitner was a brilliant scientist, but evidently socially and politically inept enough that she continued to assist Hahn despite his treatment of her and Nazi Germany’s policies toward Jews in general.

Although Meitner continued to assist her former colleagues in Nazi Germany for a time, most Jewish scientists were not so lucky or naïve. By the late 1930s almost all of Germany and Austria’s Jewish physicists, along with many others who rejected Nazism, had fled, mostly to Britain or America. Einstein was by far the most famous among them, but only one of a great many.

Nazi academics began to take over Germany’s great educational institutions, hungrily seizing positions and offices previously held by Jews, foreigners, or anti-Nazi German academics. Some of these newcomers were marginal teachers and scientists, envious of successes by those they considered racially or ideologically inferior. Many disdained theoretical physics and Einstein’s relativity theories.

These men and the Nazi hierarchy regarded Einstein’s relativity theories and their progeny as “Jewish physics.” For them, the only valid physics was “Deutsche” or “Volkish” physics, by which they apparently meant a classical experimental physics that could somehow ignore the realities Einstein described. Nonetheless, not all of Germany’s scientists disdained “Jewish physics,” and as war loomed and then broke out, even high-ranking Nazis came to appreciate the tantalizing prospect of an atomic super weapon.

Werner Heisenberg: Germany’s Top Physicist

In the late 1930s, the most famous physicist in Germany (Einstein having left Germany for New Jersey) was Werner Heisenberg. Heisenberg was internationally renowned for his work in quantum mechanics and the Uncertainty Principle that usually bore his name. He was a brilliant theorist and mathematician and prided himself on his practical abilities as a physicist, although in fact these were suspect. For a time he was Germany’s youngest full professor.

In 1932, Heisenberg was awarded the Nobel Prize for Physics for his work on the Uncertainty Principle, although the prize committee slighted several other physicists who arguably deserved as much credit as the charismatic Heisenberg. In 1937, Heisenberg was appointed to a senior professorship at Leipzig University.

While not a card-carrying Nazi, Heisenberg was a loyal and patriotic German. Like many German academics and professional soldiers of his time, he considered himself above politics, and so was willing to serve whatever government ruled Germany, even Hitler’s. He was the logical choice to lead the country’s atomic weapons program.

However, in July 1937, just months before Hahn split the atom, Heisenberg came under attack in an article that appeared in Das Schwarze Korps, an SS magazine. The instigator behind the article was Johannes Stark, a rabidly anti-Semitic experimentalist who resented Heisenberg’s success and his association with Jewish physicists, a practical necessity in Heisenberg’s field. The article accused Heisenberg of being a part of a “white Jewish” establishment that sought to keep true Germans from positions of importance, promoted Einstein’s relativity theory, and by implication sought to undermine the Nazi Party.

Such an attack was serious business in Nazi Germany and threatened internment in a concentration camp or worse. Heisenberg sought the assistance of friends and associates within the establishment, including Nazi Party members, to clear his name. Heisenberg’s mother, who had been an acquaintance of Heinrich Himmler’s father, passed on a personal letter from the physicist to the SS Reichsführer. After a thorough investigation by the SS, which included a terrifying interview at its Berlin headquarters, Himmler personally exonerated Heisenberg, effectively inoculating him from charges of treason until the end of the war.

In his letter clearing Heisenberg, Himmler permitted him to continue with his work, but with the proviso that Heisenberg could only apply relativity theory and the work of Jewish scientists without acknowledging them. Relieved, Heisenberg readily agreed to the conditions and began working in earnest on the German atomic project.

Heavy Water Reactor Project

While Germany began state-sponsored atomic research several years before the Allies, its efforts did not go unnoticed. Because so many physicists were driven from the Reich, Allied governments were quickly able to form a relatively clear picture of German efforts. America’s program was sparked in part by Einstein’s warning to President Franklin D. Roosevelt concerning possible German successes.

By 1941, the Germans were operating two experimental reactor projects, but German success had in fact been limited. Heisenberg’s team in particular made certain engineering decisions that put the German program almost immediately at risk.

Very basically, a nuclear reactor operates by inducing a chain reaction in masses of Uranium 238 within the reactor. To initiate a reaction, the flow of neutrons around the radioactive isotope must be moderated by another substance, such as graphite or deuterium (heavy water). The Germans chose to use heavy water, which is rare in nature and difficult to manufacture.

In 1940, the Germans captured a heavy water plant in Vermok, a Norwegian town 100 miles north of Oslo. British intelligence had learned the basic outline of the German reactor project and realized that the Norwegian heavy water supply was a weak link. By mid-1942, the Norwegian factory was producing up to 10,000 pounds of heavy water per year for Heisenberg’s teams in Leipzig and Berlin. An initial raid on the plant by British paratroopers ended in disaster when the gliders carrying the troops crashed far from the target.

The British were concerned enough about the plant to mount another operation. The second raid was more subtle than the first. A daring team of Norwegian commandos infiltrated the plant and blew up the water tanks. Later, British submarines interdicted further shipments. The loss of so much heavy water set the German project back but did not derail it. That, the Germans unwittingly did themselves.

The Challenges of U-235 Enrichment

Despite the continuing attacks on the heavy water supply line, by 1941 German scientists had come to several broad theoretical conclusions that mirrored American conceptions of how to build an atomic device: (1) an enriched uranium fission device, (2) a plutonium-based fission device, or (3) a “reactor bomb.” While the United States would build successful atomic reactors and both uranium and plutonium bombs by the end of the war, the German scientists never approached a working conception for actual production of a successful atomic machine.