Science: The Bomb That Didn’t Go Off

How close were the Nazis getting to making an atom bomb? This frightening question spurred U.S. bombmakers throughout the war. It also helped still their consciences.

The Germans never came very close to making a bomb, apparently. In a recent issue of Britain’s Nature magazine, German Nobel-Physicist Werner Heisenberg tells how they almost achieved a successful uranium pile; but they did not even try to make a bomb.

Heisenberg points out that all the world’s physicists knew, before the war, that atoms of uranium 235 (the rare isotope of uranium) would split in two with a large release of energy. They also knew the theory of a “chain reaction”: that splitting atoms give off neutrons which make other uranium atoms split too. These facts were the “secret” of the atomic bomb—a secret open to everybody.

No Tools. Almost as soon as the war started in 1939, the Germans learned (Heisenberg does not say how) that the U.S. had allocated funds to research on atomic energy. The Germans quickly set up their own project. But, says Heisenberg: “Public interest in the problems of atomic physics was negligibly small between the years 1933 and 1939.” [the Nazi prewar period]. Germany had no cyclotron, and only two “adequately equipped laboratories.” Lacking proper tools, her physicists were seriously handicapped.

They started the job, however, in about the same way as their rivals, and came to the same initial conclusions. One way to get atomic energy, they decided, was to separate the reactive U-235 from the other uranium isotopes. The U.S. did this successfully at Oak Ridge, Tenn., but the Germans soon concluded that the enormous industrial effort required would be too much for war-burdened Germany.

The other possibility was to construct a chain-reacting pile made of uranium combined with some substance to slow down the neutrons shot out by its fissioning atoms. Theory indicated that carbon or heavy water would serve as this “moderator.” The U.S. used carbon (graphite), but the Germans decided it would not do. This was a bad mistake; it led them to use heavy water, which could be produced only by a slow and costly process.

No Interest. The U.S. used its successful graphite piles to produce the explosive element plutonium. The Germans, according to Heisenberg, realized in a vague way that this was possible. But the Nazis did not build cyclotrons and other necessary instruments in time. So they did not even try to produce plutonium. The only use they saw for their piles was as sources of power.

The German atomic project was never very large. Heisenberg estimates that it cost only about 1/1000th of what the U.S. spent ($2 billion) on The Bomb. Anyhow, top Nazis were never completely sold on the idea. Says Heisenberg: “The undertaking [of making an atomic bomb] could not even be initiated against the psychological background of the men responsible for German war policy. These men expected an early decision of the war, even in 1942, and any major project which did not promise quick returns was specifically forbidden.”

In spite of multiple obstacles, the Germans almost achieved a working pile. Their experimental models, made of uranium plates separated by heavy water, got better & better.

But time was running out. The Germans’ only heavy water plant, in Norway, was destroyed by Commandos and bombing when only two tons of the vital water had been produced. Air raids slowed Germany’s industry, disrupted her communications. The pile-builders never got all the uranium they needed. They were forced to work in cellars and air-raid shelters. In 1945, they took refuge in a dugout hewn in the rock near the village of Haigerloch, about 32 miles from Stuttgart.

There they built a pile that almost worked. “On April 22,” says Heisenberg, “Haigerloch was occupied, and the material confiscated by the Americans.”