Today the name Werner Heisenberg means little, even to highly educated people. But on the eve of World War II, he was a Nobel laureate with a reputation as possibly the world’s greatest atomic physicist. So when the community of physicists realized that an atomic bomb was theoretically possible, they also felt certain that if anyone on Earth could actually figure out how to construct such a weapon of mass destruction, it was Werner Heisenberg.

For that reason, as the Nazi regime inexorably nudged Europe toward war, Heisenberg’s British and American peers within the physics community encouraged him to emigrate. They knew that Heisenberg quietly disapproved of Nazism. But as he explained to those who urged him to defect, he remained a German nationalist. And if war broke out, Heisenberg would honor his duty to the fatherland.

Sure enough, in 1939 Heisenberg joined the Uranverein (Uranium Club), which took its name from the fact that the isotope U-235 offered the best prospect for achieving nuclear fission, the basis of an atomic bomb. The fundamental challenge, however, was that U-235 constituted just 0.7 percent of natural uranium, and would have to be extracted from hundreds of tons of uranium ore.

Nazi Germany, as the Allies well knew, had all the requisite materials to achieve a nuclear weapon, including ample uranium from Czechoslovakia. But the specter that haunted the Manhattan Project, the Anglo-American effort to build an atomic bomb, was the knowledge that Nazi Germany also had Heisenberg, who had quickly become the de facto leader of the Uranverein, a role roughly equivalent to that of J. Robert Oppenheimer, the American physicist who masterminded the Manhattan Project. Fear of Heisenberg drove that frantic project all the more fiercely.

In my last column, I examined a scenario that could have emerged if Germany had developed an atomic bomb. But as the Allies discovered to their amazement when the war ended, Germany never came close to developing the bomb. Why not?

Some have pointed to the organization of the Nazi regime, a Balkanized mess of competing bureaucracies, deliberately fragmented to maximize Hitler’s power because it made him the sole arbiter of all major disputes. And truly, such was the regime that Heisenberg served. Its built-in inefficiency hobbled the creation of a German Manhattan Project. Yet resolute scientists sometimes overcame this inefficiency, as Werner von Braun did in persuading the regime to pour resources into the development of ballistic missiles. Why didn’t Heisenberg emulate that example?

Heisenberg actually seemed to do just the opposite: he downplayed the likelihood of creating the bomb. His report on the prospects for an A-bomb was a sleep-inducing marvel of bland obfuscation. When Albert Speer, Germany’s minister of armaments, asked Heisenberg point blank if a bomb were feasible, he declared that “the technical prerequisites for production” would take at least two years to develop, “even if the program was given maximum support.”

Heisenberg did not mean that it would take at least two years to develop a bomb; he meant that it would take at least two years to develop the large cyclotrons required to extract enough U-235. When Speer objected that surely his ministry had the means to construct such cyclotrons, Heisenberg replied that German physicists lacked experience with cyclotrons. They would first have to experiment with a small cyclotron. Confronted with this appraisal, Speer abandoned all thought of resourcing a major nuclear weapons program.

After the war, Heisenberg claimed that he and other nuclear scientists had deliberately misled the Nazi government because “the idea of putting an atomic bomb in Hitler’s hand was horrible.” Luckily, “we [physicists] had a wonderful excuse, we could always say: ‘Please, it is quite certain that what we are doing cannot result in an atomic bomb for three or four years.’?” Moreover, he said that German physicists had channeled research away from weapons and toward work on a small-scale reactor that never came close to producing a nuclear reaction.

A number of writers have taken Heisenberg at his word, most notably journalist Thomas Powers in his best-selling book, Heisenberg’s War (1993). “Germany’s failure to build an atomic bomb was not inevitable,” Powers wrote. “If a serious effort to develop a bomb had commenced in mid-1940, one might have been tested in 1943.” Heisenberg’s deliberate lack of zeal to push through the Nazi bureaucracy “was lethal, like a poison that leaves no trace,” Powers insisted. “Heisenberg did not simply withhold himself, stand aside, let the project die. He killed it.”

By this logic, if Heisenberg had been a Nazi, Germany might well have obtained the bomb, and done so years before the Allies. But few close students of Germany’s atomic program believe this.

The smoking gun, so to speak, lies embedded in transcripts of discussions with Heisenberg that took place in the summer and fall of 1945, when he was interned at an English manor called Farm Hall. The discussions center on the Hiroshima bomb. To the non-specialist perusing these transcripts, Heisenberg seems to know what he’s talking about. But to the specialist, Heisenberg’s ignorance of what was required to produce an atomic bomb is jaw-droppingly evident. The transcripts for August 6, the date of the Hiroshima explosion, reveal a nuclear physicist utterly innocent of knowledge of the physics of nuclear fission as applied to an atomic bomb. It further reveals that Heisenberg estimated the amount of U-235 in the Hiroshima bomb at 900 kilograms (the actual amount was just 56 kilograms), and his arithmetic was so sloppy that had he done the calculation correctly, the estimate would have been a whopping 11,700 kilograms!

Within a few days, as more information about the Hiroshima bomb became available, Heisenberg backtracked to align his calculations with reality, and did this so artfully that his mastery of physics appeared complete. But it was smoke and mirrors. Thus, from the Farm Hall transcripts, the reason behind Germany’s failure to achieve an atomic bomb becomes evident. It wasn’t that Heisenberg could not abide Nazism. It was that he could not fathom what it took to create a bomb. Heisenberg the genius proved not genius enough.