CHAPTER FOURTEEN

HUNTING HEISENBERG

1943-02-09 BBC RADIO

ROBERT ROBINSON REPORTS: The triumphant conclusion of the battle of Stalingrad and the capture of eight more German generals and 45,000 other prisoners in the past two days has overshadowed the rest of the news from Russia. Our allies have kept up their great advance on the southern front.

THE MOMENTUM OF WAR WAS SHIFTING in the Allies’ favor. The German Sixth Army in Stalingrad and the vaunted Afrika Korps commanded by General Erwin Rommel in North Africa had both been defeated. But what should have been good news left many senior Manhattan Project scientists more anxious. What would Adolf Hitler do if cornered? Citing “recent reports from newspapers and secret service,” Manhattan Project physicist Edward Teller, Heisenberg’s former graduate student, warned Oppenheimer, “it is possible that the Germans will have by the end of the year, enough material to make a large number of bombs.” 114

Another émigré scientist urged General Groves to “warn the American people in an official broadcast that the United States might be hit by an atomic bomb.” 115 Groves declined, electing to send a message directly to Heisenberg instead, an airmail special delivery from the RAF.

In December 1943, waves of British long-range Lancaster bombers swept across the skies above the Institute of Theoretical Physics in Leipzig where Heisenberg conducted his research. Their bombs destroyed the Institute’s top floors and Heisenberg’s scientific papers along with them. They damaged the home of Heisenberg’s in-laws where he and two of his children were staying. But they failed in their primary mission: “the killing of scientific personnel employed therein.” 116 Heisenberg was in another part of town when the bombing started.

In a memoir written after the war, Heisenberg describes running to his in-laws’ home and stepping in liquid phosphorous from incendiary bombs that ignited his shoes. “I quickly stepped into a puddle and so saved my precious footwear.” At the house he discovered it had been “badly hit; doors and shutters were blown in, and to my horror I discovered that there was no sign of life inside.” 117 Racing through what was left of the front door and up to the attic, he found his mother-in-law desperately trying to beat out the flames of burning timbers. His children were safe with neighbors. His wife Elisabeth was out of town.

Allied bombers followed the Leipzig attack with a raid on Otto Hahn’s nuclear fission lab outside Berlin. Hahn also escaped injury. Germany’s atomic research laboratories were spread across the country in several different universities. After the raids, Germany dismantled the labs and moved their whole atomic research program to secret locations. As a consequence, the little bit of intelligence that had trickled in to General Groves’ office concerning Heisenberg “virtually ceased.” And, as historian Thomas Powers wrote, “in the soil of silence . . . grew the seeds of fear.” 118

IN SEPTEMBER ’43, GENERAL GROVES, his hands already full managing construction at Oak Ridge, Hanford and Los Alamos, took on another job: gathering intelligence on German nuclear fission research.

He accepted the assignment, in part, to calm the nerves of his émigré scientists. 119 According to one of the general’s aides, Heisenberg had become such a distraction that “Groves had difficulty keeping the scientists’ minds on [their] work.” 120

Ironically, British scientists, those most likely to be targeted by Hitler’s first bombs, were far less troubled. British intelligence knew that the Germans had accelerated heavy water production in Norway. But they had not discovered any giant uranium processing complexes similar to Oak Ridge. A source in Berlin, who had been monitoring Heisenberg’s comings and goings, reported no mysterious travels or long absences from Berlin. 121 And a review of German scientific journals turned up several atomic research papers that would certainly have been censored had the Germans been working on a bomb. All considered, British intelligence concluded that Heisenberg was most likely not a serious threat.

United States analysts disagreed. The British had failed to account for 51 of the 60 German scientists known to be working in the field of nuclear fission. U.S. analysts took the publication of nuclear fission related research as a cautionary sign: the Germans were trying to “deceive us about the extent and progress of his program, and so cause us to relax the pressure on our own.” General Groves concluded, “We couldn’t take the chance.” 122

Now his own intelligence chief, General Groves turned to Oppenheimer for advice. Oppenheimer did as British scientists had done two years earlier with their analysts. He gave General Groves a list of eminent scientists likely to be working on the bomb. He gave him the rough parameters of what bomb-making and uranium processing facilities might look like. They’d be larger than a city block, draw large amounts of electric power and be located a long distance from the Soviet border and out of range of British bombers. Plutonium reactors would be “operating . . . where water [to cool the plants] is plentiful and where the flow from the plant passes either through open country or through country inhabited by an ‘inferior race’ whom they do not mind killing off.” 123

Armed with that information, U.S. and Royal Air Force reconnaissance flights prowled German skies looking for Heisenberg’s uranium and plutonium processing plants. Specially equipped A-26 Invader bombers sniffed the air for radioactive gases produced by nuclear reactors. And Allied agents sampled German rivers searching for radioactive water. These were dangerous missions. The A-26 crews often had to fly within easy range of German anti-aircraft fire. Weeks of reconnaissance turned up nothing, but Manhattan Project officials were still not convinced.

Maybe Heisenberg didn’t need a large industrial plant like Oak Ridge to separate out U235. “[Heisenberg] might have come up with a way to do it in his kitchen,” Oppenheimer warned. 124 Perhaps Heisenberg found a different way to produce plutonium and didn’t need to build large nuclear reactors.

WHAT INTELLIGENCE AMERICA DID possess came chiefly from scientists fleeing Nazi-occupied Europe, men like the Danish physicist Niels Bohr, the man who had identified U235 as the source of atomic energy. Bohr, whose mother was Jewish, had returned to his home in Copenhagen after his stint at Princeton University. When the Nazis invaded in 1940, they chose not to roil the waters by arresting Danish Jews. But that changed in 1943, and Bohr, with the help of British intelligence, escaped to England.

On December 30, 1943, General Groves showed up at Los Alamos with a special guest traveling under the name Nicholas Baker. Oppenheimer immediately recognized the distinguished Dane, Niels Bohr.

Bohr had enjoyed a near twenty-year father-son relationship with Heisenberg. They had first met in the summer of 1922 in Göttingen where Bohr was a guest lecturer and Heisenberg one of his students. Bohr took a liking to the brilliant young German. In the decade that followed, the period when Heisenberg produced his greatest work, Bohr was his collaborator and chief critic.

The two had vacationed together at Bohr’s ski cottage and gone on long sailing trips together. Heisenberg had played with Bohr’s children, taking them on pony rides. 125 The war had severed Heisenberg’s relations with many friends on the Allied side. None of those lost friendships pained him more than the loss of Bohr’s friendship. After the war began, Heisenberg wrote his mentor an affectionate farewell: “Since I don’t know whether and when our destiny will lead us together again, I will once again thank you for . . . everything you have done for me.” 126

Niels Bohr and Werner Heisenberg

(Niels Bohr Archive, Copenhagen, courtesy AIP Emilio Segrè Visual Archives)

Two years later, in September 1941, unwilling to trust in destiny, Heisenberg scheduled a lecture in Nazi-occupied Copenhagen and used the occasion to reach out to his old friend. Bohr reluctantly agreed to meet, inviting his former protégé to dinner.

The get-together began on a sour note when Bohr asked Heisenberg about a comment he had reportedly made at a recent luncheon defending Germany’s destruction of Poland. Heisenberg responded that Poland was a tragic case and tried to excuse his countrymen, pointing out that Germany had not been as brutal in France. 127

What Heisenberg’s true intentions were in coming to Copenhagen would be much debated after the war. Heisenberg would say he came to warn Bohr that Germany was working on a bomb and to search for a way that scientists could join together to halt its development. Bohr believed that Heisenberg’s visit was anything but humanitarian, that he had come solely to pump him for information about the Allies’ bomb program. 128 When General Groves solicited Oppenheimer’s take on the meeting, Oppenheimer, still distrustful of Heisenberg, sided with Bohr.

During their dinner in Copenhagen Heisenberg had sketched a cylinder with a line sticking out to illustrate what he was working on. Bohr thought it was a bomb and brought the drawing with him to Los Alamos. Oppenheimer and colleagues saw instead a nuclear reactor and control rods. 129 Either way, Bohr’s story provided direct confirmation that Germany had a nuclear research program; that, at the very least, it was building a nuclear reactor and that Heisenberg was deeply involved.

After Bohr left Los Alamos, General Groves pulled Oppenheimer aside and told him about a recent intelligence report. Groves cautioned that the source might not be trustworthy, but according to the report, Germany was not building an atom bomb. The two men looked at each other. Oppenheimer shrugged and said nothing, but his message was clear: it didn’t matter whether the report was true. Oppenheimer and Groves were going to finish what they had started. 130