by Craig Nelson
On January 25, 1943, Niels Bohr was given a key in Copenhagen. Inside was a microdot, which revealed a letter from James Chadwick, asking Bohr to join the Anglo-American fission project. Bohr said that he still thought nuclear weapons were implausible because of the difficulty of producing U-235, but that he might change his mind in the future. This reply was also converted into a microdot and carried back to England, inside the filling of a courier’s tooth.
At that time, Bohr’s Denmark was under German control, but in a very different manner from the rest of occupied Europe. The Nazis so depended on Danish butter, meat, and other foodstuffs that they allowed the country to govern itself and left their eight thousand Jews alone. But after the shocking German defeat at Stalingrad revealed the Fascists as less than omnipotent, Danes began organizing regular labor strikes and acts of sabotage. The Germans retaliated by taking control of the royal palace and arresting Jews. A friend of the Bohr family’s was working as a clerk for the Gestapo in Copenhagen and came across the warrants for Niels and his brother, Harald. In the middle of the night of September 29, 1943, under cloud cover that rendered the darkness visible, around a dozen people, including the two Bohr brothers, Niels’s wife, Margrethe, and Harald’s son Ole, rode a fishing boat to cross the sound and find safe harbor in Malmö, Sweden. Simultaneously, two German freighters arrived in Denmark to begin ferrying Danish Jews to concentration camps.
Bohr went to Stockholm, where he soon learned that Sweden was overrun with Gestapo agents whose careers would be made if they caught or killed him. Though he needed to leave for England as soon as possible, the great Bohr instead went to the palace to beg King Gustav V to give refuge to Denmark’s Jews, saying he had learned that the Nazis planned to arrest all of them the following day. The Swedish government questioned the Germans, who insisted nothing of the sort was happening. This was a lie, but the Danes had been so well informed ahead of time that they hid nearly eight thousand Jews, and the countrywide Nazi anti-Semitic campaign resulted in 284 men and women being taken from a nursing home. On October 2, Sweden announced that it would grant refuge, accepting 7,220 Danish Jews over the next two months. At the same time, rumors began circulating that Niels Bohr was going to be assassinated.
Diplomatic pouches were flown between Stockholm and Westminster in a two-engine plywood Mosquito that cruised above the twenty-thousand-foot ceiling of German antiaircraft cannon on the shores of Norway. On October 6, the fifty-eight-year-old Bohr was suited up, given a stick of flares and a parachute, and strapped into the plane’s bomb bay. If the plane went down, he could use the flares to help rescuers find him in the North Sea. Bohr’s son Aage (pronounced Awa): “The Mosquito flew at a great height and it was necessary to use an oxygen mask; the pilot gave word on the intercom that the supply of oxygen should be turned on, but as the helmet with the earphones did not fit my father’s head, he did not hear the order and soon fainted because of lack of oxygen. The pilot realized that something was wrong when he received no answer to his inquiries, and as soon as they passed over Norway, he came down and flew low over the North Sea. When the plane landed in Scotland, my father was conscious again.”
At the Savoy in London, Chadwick told Bohr about the progress made with Tube Alloys and the Manhattan Project. The physicist was speechless. Then in New York, an entire contingent of FBI agents escorted Niels and his son and future Nobel laureate Aage from the docks to their hotel and were so pleased in getting Niels across town incognito. Then they noticed his suitcase, which had huge black letters on its side: NIELS BOHR.
Bohr was such a terrible jaywalker—a habit shared by Ernest Lawrence—that when Groves had a security team follow Niels and Aage in Washington, one reported, “Both the father and the son appear to be extremely absentminded individuals, engrossed in themselves, and go about paying little attention to any external influences. As they did a great deal of walking, this Agent had occasion to spend considerable time behind them and observe that it was rare when either of them paid much attention to stop lights or signs, but proceeded on their way much the same as if they were walking in the woods. On one occasion, subjects proceeded across a busy intersection against the red light in a diagonal fashion, taking the longest route possible and one of greatest danger. The resourceful work of Agent Maiers in blocking out one-half of the stream of automobile traffic with his car prevented their possibly incurring serious injury.” The physicist met with British ambassador Lord Halifax and Supreme Court justice Felix Frankfurter and insisted that, unless the Russians were told and involved with the atomic weapons program, a terrifying postwar arms race would ignite. Groves, at first leery of having the voluble and famous Bohr at Los Alamos, now wanted him there as soon as possible to keep him isolated, and quiet. Groves was so alarmed that he personally escorted Bohr on the train to New Mexico.
Using the name Nicholas Baker and called by everyone Uncle Nick, Bohr arrived at the mesa on December 30, 1943. He fell in love with the American Southwest, especially remembering his first encounter with a skunk, and listening, at dusk, to the hissing tails of rattlesnakes as they scissored through the brush. After learning of the immensities of the Oak Ridge and Hanford operations, Uncle Nick insisted to Edward Teller that he’d been right all along in doubting the prospect of nuclear weapons: “You see, I told you it couldn’t be done without turning the whole country into a factory. You have done just that.”
Bohr was so used to having wife Margrethe taking care of his day-to-day needs that his life at Los Alamos alternated between the inspired and the comic. One day he came to work wearing a rope to hold up his pants since he’d forgotten where he’d put his belts. He returned from one party with a hugely oversize coat, saying he must have taken it by mistake since there were keys in the pockets, and he didn’t have any keys.
Emilio Segrè: “When Niels and Aage Bohr arrived, one night in Oppenheimer’s house he told a few European scientists of the conditions prevailing in Denmark and his escape. For many of us this was the first eyewitness account of what was really happening in a Nazi-occupied country. Although conditions in Denmark at that time were relatively tolerable and the worst horrors of Nazism were unknown to Bohr, the account left us depressed and worried, and more determined than ever that the bomb should be ready at the earliest date possible.” Bohr’s meeting with Heisenberg had frightened him—Bohr showed everyone Heisenberg’s sketches of a heavy-water reactor that the German had brought with him to a meeting in Copenhagen—and Bohr told Oppenheimer that Germany planned to end the war with an atomic bomb.
While the Los Alamos refugees fretted almost continuously over Hitler’s taking control of nuclear weapons, Vannevar Bush and Franklin Roosevelt, however, left no trace to history that they thought about it whatsoever, beyond the initial meeting over Einstein’s letter between Alexander Sachs and the president. Neither made much effort to uncover information on the Nazi program. One officer involved at the time, Major Francis Smith, believed that “the Nazis’ work was held in such poor esteem by our military authorities that certain German laboratories whose locations we knew were left unbombed to enable Hitler’s experts to continue their failures.”
The German effort to produce atomic weapons centered on Werner Heisenberg, whose role was equivocal, peculiar, and damning. Nazi physicist Johannes Stark had published an article in the July 15, 1937, SS journal Das Schwarze Korps, “ ‘Weisse Juden’ in der Wissenschaft” (White Jews in Science). Its “main theme was that it was not sufficient to exclude all Jews from sharing in the political, cultural and economic life of the nation, but to exterminate the Jewish spirit, which is stated to be most clearly recognizable in the field of physics, and its most significant representative Professor Einstein. . . . Several men of science of international reputation were named in the article as followers of Judaism in German intellectual life, and it was remarked that ‘They must be gotten rid of as much as the Jews themselves.’ ” Stark called Heisenberg a “Jew lover” and a “Jewish pawn.” Heisenberg wrote a
letter to Himmler—which his mother gave to Himmler’s mother, as they were good friends—asking that Himmler publicly approve or disapprove of these attacks. Himmler launched an SS investigation that lasted eight months and included interrogations of Heisenberg, recording devices in his home, and spies in his classroom. Himmler then cleared him.
When Heisenberg toured America in the summer of 1939, he repeatedly defended remaining in Germany, even though Columbia had offered him a post, telling Ed Teller, “Even if my brother steals a silver spoon, he is still my brother,” and Laura Fermi, “People must learn to prevent catastrophes, not to run away from them.” When on September 26 he was then called to join the Uranverein in Berlin, he thought that he could use the Reich’s interest in physics for the purposes of science and eagerly agreed. In December 1939 he gave the Nazi War Office a report, “The Possibility of Technical Energy Production from Uranium Fission,” which called reactors “uranium burners” and calculated a successful burner of a ton of uranium and a ton of heavy water in a spherical container producing 800°C (1,472°F).
In January 1940, the Nazis replaced Peter Debye as head of KWI Physics with Werner Heisenberg; by October 1940, the Virus House construction was finished, and the Uranverein experimented with paraffin as a moderator, which did not work. Neither did graphite since, due to Szilard’s silence campaign, they didn’t know that the reason was its impurities. They then tried heavy water, which did work, but they could only now get eight liters of it from Norway’s Vemork. They needed fifteen tons.
By May of 1941, the British came to understand why the Nazis were so keenly interested in Norwegian heavy water. The construction superintendent of the dam that powered Vemork, Einar Skinnarland, took a two-week vacation in England, during which he was trained by the Special Operations Executive to be a key member of a commando team, the Norwegian Independent Company. On October 13, 1942, Combined Operations put into effect Operation Freshman. Advance ground party Grouse, nine natives of the region experienced in the local wilderness, were trained by the SOE in pistols, knives, poisons, explosives, hand-to-hand combat, breaking locks, and cracking safes. Led by the twenty-four-year-old Jens Pousson, Grouse would find a landing spot to welcome commandos floating in on gliders, and the combined team would disable the heavy-water plant and then hike 250 miles to the Swedish border. On October 18, Grouse was parachuted in, but the drop turned out to be thirty miles from where they were supposed to be. Terrible weather meant it took them fifteen days to reach their base near the dam. At the same time, Norsk Hydro’s chief of hydrogen research, Jomar Brun, was running a campaign of sabotage within his own plant, putting castor oil in the electrolyte, producing a foam that would stop the process for hours and sometimes days. He didn’t know that others were themselves adding cod-liver oil to achieve the same purpose. Of the five tons of heavy water that Heisenberg wanted by June 1942, Norway delivered one.
On November 11, Grouse informed SOE that they’d found a landing site, and on November 19, two British Halifax bombers towing Horsa Mk.I gliders each carrying seventeen men flew into Norway. These fragile plywood gliders landed in a “controlled crash.” The first Halifax released too soon, and her glider crashed into a mountain, killing seven. The second glider’s towline broke, and it crashed, killing eight. All of the survivors were captured by the Nazis, interrogated, and executed by firing squad. On one officer’s body, the Germans found a map of the Vemork plant. They stationed nine hundred troops in the vicinity, and now the Grouse team was cut off from rescue.
A six-man reinforcement, Operation Gunnerside, parachuted in on February 16, 1943. The Nazis had heavily reinforced the plant, but not its rail-line depot. From that direction, leader Joachim Ronnenberg snuck into the building, set up demolition charges, and blew up the tanks. Evading the Germans, they raced to an icy plateau and skied to the Swedish border. By August, the Germans had repaired the damages and had the plant running again.
On November 16, 1943, under orders from Leslie Groves, three hundred B-17 Flying Fortresses and B-24 Liberators from the Eighth Air Force took off from East Anglia to drop 700 thousand-pound and 295 five-hundred-pound bombs on Vemork, to end its production of heavy water once and for all. But only two bombs hit the plant directly, and neither took out the electrolysis cells that were the real target, while twenty-two civilians died. SOE agent Knut Haukelid learned that the Nazis were planning to move the whole of the plant and its heavy water to Germany on February 20, 1944, the cargo being railed and ferried through Denmark to Berlin. The SOE arranged an operation to sink the cargo’s Norwegian ferry in the middle of a fjord, ensuring the Nazis could never resurrect their cargo. On February 18, Haukelid snuck onto the ferry and improvised a bomb with two alarm clocks. It worked, and Hitler’s entire stock of heavy water was finally destroyed.
But before this difficult victory, there was the meeting that had so terrified Niels Bohr. On September 15, 1941, accompanied by fellow Uranverein member Carl Friedrich Freiherr von Weizsäcker, Werner Heisenberg took the train from Berlin to Copenhagen to visit his great mentor. After the war, a controversy arose over who said what in Denmark that autumn, a controversy that turned out to be one of many German attempts to rewrite history.
The rewrite began with letters Heisenberg sent to Robert Jungk after reading Jungk’s 1956 history of nuclear science, Brighter than a Thousand Suns. In these letters, Heisenberg claimed that he had gone to Copenhagen in 1941 to discuss with Bohr his moral objections about scientists working on nuclear weapons, but that he had failed to say this clearly before the conversation came to a sudden stop. Jungk published portions of the letters in the Danish edition of the book, conveying that Heisenberg suggested he had sabotaged the German bomb project on moral grounds:
With the beginning of the war there arose of course for every German physicist the dreadful dilemma that each of his actions meant either a victory for Hitler or a defeat of Germany, and of course both alternatives presented themselves to us as appalling. . . .
My visit to Copenhagen took place in the fall of 1941; I seem to remember that it was about the end of October. At that time, as a result of our experiments with uranium and heavy water, we in our “Uranium Club” had come to the following conclusion: It will definitely be possible to build a reactor from uranium and heavy water which produces energy [but] the production of nuclear explosives from reactors obviously could only be achieved by running huge reactors for years on end. . . . This situation seemed to us to be an especially favorable precondition as it enabled the physicists to influence further developments. For, had the production of atomic bombs been impossible, the problem would not have arisen at all; but had it been easy, then the physicists definitely could not have prevented their production. The actual givens of the situation, however, gave the physicists at that moment in time a decisive amount of influence over the subsequent events, since they had good arguments for their administrations—atomic bombs probably would not come into play in the course of the war, or else that using every conceivable effort it might yet be possible to bring them into play. That both kinds of arguments were factually fully justified was shown by the subsequent development; for, in fact, the Americans could not employ the atomic bomb against Germany. . . .
Because I knew that Bohr was under surveillance by German political operatives and that statements Bohr made about me would most likely be reported back to Germany, I tried to keep the conversation at a level of allusions that would not immediately endanger my life. The conversation probably started by me asking somewhat casually whether it were justifiable that physicists were devoting themselves to the Uranium problem right now during times of war, when one had to at least consider the possibility that progress in this field might lead to very grave consequences for war technology. Bohr immediately grasped the meaning of this question as I gathered from his somewhat startled reaction. He answered, as far as I can remember, with a counter-question: “Do you really believe one can utilize Uranium fission for the construction of weapons
?” I may have replied, “I know that this is possible in principle, but a terrific technical effort might be necessary, which one can hope, will not be realized anymore in this war.” Bohr was apparently so shocked by this answer that he assumed I was trying to tell him Germany had made great progress towards manufacturing atomic weapons.
In my subsequent attempt to correct this false impression I must not have wholly succeeded in winning Bohr’s trust, especially because I only dared to speak in very cautious allusions (which definitely was a mistake on my part) out of fear that later on a particular choice of words could be held against me. I then asked Bohr once more whether, in view of the obvious moral concerns, it might be possible to get all physicists to agree not to attempt work on atomic bombs, since they could only be produced with a huge technical effort anyhow. But Bohr thought it would be hopeless to exert influence on the actions in the individual countries, and that it was, so to speak, the natural course in this world that the physicists were working in their countries on the production of weapons. . . . Since 1933 Germany had lost a number of excellent German physicists through emigration, the laboratories at universities were ancient and poor due to neglect by the government, the gifted young people often were pushed into other professions. In the United States, however, many university institutes since 1932 had been given completely new and modern equipment, and been switched over to nuclear physics. Larger and smaller cyclotrons had been started up in various places, many capable physicists had immigrated, and the interest in nuclear physics even on the part of the public was very great. Our proposition that the physicists on both sides should not advance the production of atomic bombs was thus indirectly, if one wants to exaggerate the point, a proposition in favor of Hitler. The instinctive human position “As a decent human being one cannot make atomic weapons” thus coincided with an advantage for Germany.