One of the Allies' greatest fears during World War II was that Adolf Hitler and his Nazi forces would unleash so-called Wunderwaffen, or “wonder weapons.” Some of the rumored weapons were outlandish, such as earthquake generators and death rays. But others, like bacterial weapons, rockets and new deadly gasses, were entirely feasible. Most concerning? The possibility that the Germans would manufacture—and detonate—an atomic bomb.

At the outset of World War II, Germany far outpaced other countries in atomic research. In 1938, German scientists discovered nuclear fission. The Germans had even organized a special scientific unit headed by quantum physicist Werner Karl Heisenberg to develop an atomic weapon, amassing stockpiles of uranium for the effort.

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To learn the truth, the Americans organized a covert special-ops unit in 1943, tasked with discovering Nazi nuclear secrets and capturing their top scientists. Code-named the Alsos Mission, and nicknamed “Lightning A,” the unit consisted of a small force of scientists and counterintelligence troops, headed by Colonel Boris T. Pash. A counterintelligence officer who had run security for America’s own nuclear-weapons efforts, the Manhattan Project, Pash had uncovered a ring of communist spies trying to steal U.S. nuclear secrets.

Colonel Pash and his team initially followed the Allies onto the front lines of Italy and France, interrogating scientists and capturing research. These efforts led American intelligence to conclude that Germany likely did not have the capability to develop a nuclear weapon. But they didn’t have proof, and with the world already beginning to evolve into a Cold War standoff between the Soviet Union and the United States, the Americans were doubly anxious that German nuclear research and scientists not fall into Communist hands.

To prevent that from happening, Pash led Lightning A on its most dangerous and audacious operation yet: across enemy lines and into Germany.

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When Pash’s small force entered enemy territory on April 22, 1945, on a mission code-named “Operation Big,” they were protected only by two armored cars, four Jeeps fitted with machine-gun mounts and a cache of captured German weapons. Even though the Nazi regime was collapsing, the unit faced threats from resisting military units and so-called Wehrwulf, or “Werewolf” bands of diehard Nazi youths.

Working ahead of advancing Allied armies, Lightning A scoured the countryside around Heidelberg, heading southward to the town of Haigerloch. Fortunately for Pash, the Germans in the town, believing the war would soon be over, surrendered to the small band of Americans, hanging white sheets from windows and poles.

In a cave not far from Haigerloch, Colonel Pash found the prize: a Nazi nuclear laboratory complete with a test reactor. The Americans began dismantling it the next day and then destroyed the site. Pash then divided his team in an effort to hunt down the German scientists who had gone into hiding. One Lightning A unit rolled into Tailfingen, barely escaping an attack by a Wehrwulf band. The other descended on Bisingen, where despite being attacked by locals, they subdued the town.

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On April 24, Pash’s team made another major find: a textile mill and surrounding buildings that had been converted into a laboratory for German nuclear-research efforts. There, they rounded up 25 scientists. Through interrogations, they learned that the German research files had not been destroyed as the scientists had previously claimed, but were sealed inside a watertight drum they had sunk into a cesspool.

Pash delegated the disgusting job of retrieving the documents to subordinates who, after wrangling through human waste, managed to recover the drum. He also found the Nazi uranium pile and heavy water (a form of water that contains a larger than normal amount of the hydrogen) buried in a nearby field. They even located Heisenberg’s office—but the scientist was long gone. A week prior, he had fled by train and bicycle to join his family in the mountains of Bavaria, almost 200 miles away.

Operation Big ended, but Pash wanted Heisenberg. Following the clues and full of foreboding—there were still nagging rumors that the Fuhrer would unleash a last Wunderwaffe against the Allies—Pash headed into the Bavarian Alps. After Wehrwulf youths sabotaged a critical bridge over a gorge, the Lightning A team had to abandon their vehicles, whereupon Pash led his 19 men across the ravine and up into the mountains.

When they came to the town of Urfeld near the alpine lake of Walchen, they found Germans surrendering to them en masse—about 700 SS troops giving way to his paltry passel of soldiers. Through a bit of chicanery, Pash led the Germans to believe his force was larger than it was and bluffed his way out of the precarious situation. He was not interested in surrendering soldiers—he was there for Heisenberg. After interrogating locals, Pash found the scientist and his family in a mountain cabin on May 2, 1945. Two days before, Hitler had committed suicide in his bunker.

The German scientists were eventually brought to a safe house called Farm Hall in England. The scientists for their part publicly stated that they were anti-Nazi and had been trying in their passive-aggressive way to undermine research so Hitler could not get the bomb. Secretly, British intelligence bugged Farm Hall and learned that the scientists were amazed that the Americans had successfully detonated an atomic bomb at Hiroshima. Otto Hahn, who had discovered nuclear fission, was anti-Nazi and did not take part in the German atomic-research effort, felt personally responsible that his early discoveries had led to so many gruesome deaths. And while the Americans couldn't conclusively infer the other scientists' motivations, it was clear that, ultimately, Germany had not been close to developing a working atomic bomb.

More information on the remarkable Alsos mission is coming to light as source material becomes declassified and is digitized. Colonel Pash’s papers, housed at the Hoover Institution Library and Archives in Stanford, California, contain a wealth of information about this daring episode of military history, including an annotated map created by Pash, an accompanying diary and film footage from the daring Alsos Mission.

Joseph A. Williams is the author of The Sunken Gold: A Story of World War I, Espionage, and the Greatest Treasure Salvage in History and Seventeen Fathoms Deep: The Saga of the Submarine S-4 Disaster.

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