In May of 1945, the American astronomer turned soldier Gerard Kuiper stood in the remnants of Nazi Germany. His keen eyes, normally trained on the heavens, looked across the Elbe River to the east. Germany had just surrendered, but the region was not yet at peace. Enemy soldiers and homeless refugees wandered lawlessly through rubble, seeking food. Meanwhile, sweeping from the east, the Red Army eagerly claimed its new lands. Kuiper had survived the war and completed top-secret assignments. So why would he volunteer for one last dangerous mission?

Born in the Netherlands and fluent in German, Kuiper had ably served America’s classified Alsos Mission, a remote offshoot of the Manhattan Project. The small scientific team stayed behind the advancing Allied front, ferreting out key German scientists and assessing the progress of their atomic weapons research. Their work was largely complete, with Germany’s lead physicist Werner Heisenberg and his collaborators in custody. Alsos had completed an autopsy of Germany’s nuclear program, finding it surprisingly remedial.

Now Kuiper had a rumor in hand and time was short. He was thinking about saving the renowned physicist Max Planck, one of the most treasured scientific authorities in the world. A captured German claimed that Planck was nearby, a few miles east of the Elbe but in bad shape. Kuiper had no personal connection to Planck (that we know of), but in Kuiper’s student days, Planck and his younger friend, Albert Einstein, had stood together as twin titans with their theories reformatting the atom and the cosmos alike.

Gerard Kuiper in 1964. (Dutch National Archives via Wikimedia)

Planck was not an Alsos target, and saving him would mean leaving the safety of the American front lines, since General Dwight Eisenhower had stopped his advance at the Elbe. Meanwhile, coming from the east, the Russians were now within 100 miles. As described by historian Antony Beevor, the Soviet troops embodied a post-apocalyptic nightmare, “an extraordinary mixture of modern and medieval: tank troops in padded black helmets, Cossack cavalrymen on shaggy mounts with loot strapped to the saddle.” In repaying Germany’s brutal invasion of the motherland, they took to raping, looting and killing. The survival rate of Germans captured by the Red Army hovered around 50 percent, and within a few hours, it would overtake Planck and his wife.

Kuiper collected two fellow GIs, hopped in a jeep and crossed the Elbe at top speed. With luck, he could find the Plancks, ferry them to safety and avoid the Soviet juggernaut.

During my research for my book Planck: Driven by Vision, Broken by War, I translated German texts and letters that shed further light on Planck’s condition and Kuiper’s jaunt. Planck and his wife had been war refugees in Rogätz, a small town on the Elbe River, until it became an active warzone in April. Planck’s wife, Marga, wrote of German soldiers setting up machine guns and issuing warnings. As the battle arrived, the Plancks fled for their lives, hiding in forests and resting in barns. Planck, at 87, often cried out in agony, as any movement induced pain in his arthritic back.

After Germany surrendered, the Plancks found shelter several miles from the Elbe, with a kindly milk farmer. Crowded into a one-room hut with the farmer’s large family, the Plancks awaited whichever army might reach them first.

Kuiper and his jeep lurched to a halt outside the hut on May 16, 70 years ago today. The GIs initially found confusion and fear inside. The farmer’s family and their two unmistakable guests looked up from a meager lunch. Knowing the Red Army could overtake them any minute, Kuiper quickly and politely extended their offer: Let us escort you to safety in Göttingen, to the west. The Plancks happily accepted, since they had relatives there.

The lone jeep dashed back toward the Elbe, narrowly escaping an encounter with the Russians. The Americans took Planck directly to a hospital in Göttingen, where he recovered over several weeks. Planck was one of the few high-profile Germans admired by Germans and Allies alike. Germans knew him as the respected leader and spokesman for German physics, a proud emblem of their nation’s brightest days, before the wars. The Allies knew him as someone who had never embraced the Nazis and had, in the closing months of the war, lost a son to the Reich’s cruelty. Erwin Planck had conspired with the German resistance, and after months of interrogation and torture, the Gestapo executed him in early 1945.

The two unlikely jeep partners went their separate ways. Kuiper returned to his telescopes in America, where he pioneered observations of planets and moons. Planck remained in western Germany and volunteered to once again guide Germany’s top research organization, which now bears his name. Forever known as the father of quantum theory, Planck died in 1947, while Kuiper, the father of modern planetary astronomy, died in 1973.

Max Planck in 1946 in Göttingen. (Courtesy of the Archives of Max Planck Society)


D. P.  Cruikshank. “Gerard Peter Kuiper: 1905–1973, a Biographical Memoir.” National Academy of Sciences, 1993.

J. Heilbron. Dilemmas of an Upright Man: Max Planck and the Fortunes of German Science. Harvard University Press, 1996.

D. Hoffmann. Max Planck: Die Entstehung der modernen Physik. Verlag, 2008.

A. v. Pufendorf. Die Plancks: Eine Familie Zwischen Patriotismus Und Widerstand. Propyläen Verlag, 2006.