Exactly 70 years ago, on September 29th, 1943, the Danish underground movement received the message. Brothers Niels and Harald Bohr – who had a Jewish mother but that wasn't the only sin – would have to be arrested and transferred to Germany.
So far, Bohr would be often invited to emigrate but he would be refusing it with words resembling Zeman's "Why should I leave? They should leave!"
But the new situation was way too serious so both brothers and all of their offspring and families had to escape Denmark. So Bohr and his wife Margareta are suddenly walking on a Copenhagen street and meet a biochemistry professor they know. He is a part of the resistance movement and gives them a secret sign, everything is fine.
They go to a Copenhagen dwellers' popular recreational beach with fancy buildings outside of the capital. Harald, his wife, and children are there in a moment, too. The boat needs two hours. The fishermen, also belonging to the underground, know the schedule of German patrols so they may optimize the trajectory. On Thursday, September 30th, they finally reached a Swedish village.
Margareta stays in the village. Niels Bohr has some extra work to do. He takes an express train to Stockholm. There he meets with the secretary of state and other officials. Ultimately, he has a meeting with the king, too. Bohr has almost certainly contributed to the official October 1943 publicly declared decision of Sweden to accept all refugees. Thanks to the friendly and courageous Swedish aristocratic reaction, about 60,000 Danes escape a German prison during October 1943.
Sweden is not quite safe for Bohr, either. Germany could send secret agents or soldiers to silence him. Britain and America are safer; they seem like a more practical place for Bohr to help the Allies to kick the German bastards into their socialist balls (or, in the leader's case, ball).
Bohr agrees with the British proposal. His condition is that his son Aage, a physics student, must accompany him. Now, the main technical task is to transfer Bohr from Sweden to Britain. In between these two countries, you find Norway which is occupied just like Denmark.
The solution is a British combat aircraft, a bomber called Mosquito. The model is fast and can reach great heights – and escape from most German aircraft into the clouds. At some points, it's actually crucial for the height to be above 10 kilometers to be mostly safe; this also requires the British pilots to teach Bohr to use the oxygen mask. Where would Bohr sit? Well, in the bomb bay! Aage would fly in another aircraft.
A small technical glitch forces Niels Bohr's aircraft to return. He wants to take the first yellow cab. The Swedish agents are pulling their guns. But OK, they force him to sleep at this airport and nervously await the invasion of some Germans who could just find out where Bohr is and make a "friendly visit" at every moment.
Mosquito's average speed is about 600 km/h which means that 1,200 km to Britain is a 2-hour trip. Things went fine and the Mosquito landed in Northern Scotland. The pilots immediately go to see Bohr in the bomb bay. A sleeping and tired man didn't hear any instructions because the helmet wasn't large enough for his quantum skull. Also, he failed to use the oxygen mask so he fainted somewhere in the clouds but survived. "Next time, it will be better," he promised.
A more luxurious commercial aircraft took the co-father of quantum mechanics to London. He met some similarly active British physicists like Chadwick. Niels Bohr was impressed by the progress made by British on their tube alloys project (British nuclear bomb). In December 1943, he would fly to the U.S. As guests of the Manhattan Project, Niels and Aage would be renamed as Nicholas Baker and James Baker, respectively, for security reasons. I doubt that this secret name enabled Aage Bohr to become Reagan's Secretary of State.
Bohrs would only spend some time in Los Alamos. Oppenheimer credited Bohr for contributing to modulated neutron initiators and for his being an inspiring role model for younger physicists like Feynman – although Feynman himself wasn't exactly obsessed about authorities of any kind.
Incidentally, Enrico Fermi started the nuclear age 10 months before Bohr fled Denmark. It just happens that Fermi would celebrate his 112th birthday today. Enrico Fermi was born on September 29th, 1901.