Niels Bohr’s escape from Denmark in 1943 was a dangerous passage from German-occupied Copenhagen to the Allied atomic-bomb effort. Smuggled out by sea and then flown to Britain in a rescue operation, he survived a near-fatal loss of oxygen before reaching safety in Scotland.

Escape from Copenhagen

On the night of September 29, 1943, Bohr was smuggled out of Copenhagen aboard a motor launch. He reached the Swedish coast safely and was taken to Stockholm. Even there, his safety remained precarious: German agents plotted his assassination. The escape was not a single flight to freedom but a sequence of movements through places where danger continued to follow him.

The rescue flight

On October 5, British airmen sent to rescue Bohr helped him into the bomb bay of an unmarked British Mosquito bomber. As the plywood aircraft climbed toward 20,000 feet, the pilot instructed him to put on the oxygen mask built into his leather helmet. Bohr did not hear the instructions; he later said that “the helmet was too small for his large head.” Without oxygen, he soon fainted. The bomber’s ascent, intended to carry him to safety, had briefly become a mortal danger.

Arrival in Britain and the next journey

Bohr survived the flight and landed in Scotland. He remarked that “he had had a pleasant nap,” a dry description of an episode in which he had lost consciousness at altitude. His friend and colleague James Chadwick greeted him on the tarmac, took him to London, and began briefing him on the British-American bomb project. The escape thus brought Bohr from a life threatened by German agents into direct contact with the Allied wartime enterprise; in December, he and his son Aage sailed for New York, on their way to the project’s secret site in New Mexico.