Could the Nazis have built the first atomic bomb?

When the first reports of fission came out in early 1939, people immediately thought that there was a potential to create a hugely destructive atomic bomb. The Russians were interested and they were doing work. The Japanese were interested as well, ironically. And there was a lot of interest in France and Germany.

In France, they were focused more on trying to develop a peaceful nuclear reactor to generate electricity. But in May 1939, they actually took out a patent on an explosive uranium device – so this was a patent for an atomic bomb. It would have weighed about 40 tonnes and it wouldn't have worked, but it did show that the French were thinking along those lines.

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The obvious participating party that one would be interested in would be the Germans. They were very interested initially in making an atomic bomb and started moving towards this goal very early on – the day, in fact, that Hitler invaded Poland on 1 September 1939.

Shortly before war was declared, the Germans had set up a group called the Uranium Club in Berlin, which would include people like Werner Heisenberg, who was the golden boy of German physics. He'd won his Nobel Prize at an incredibly young age and was one of the founding fathers of quantum mechanics. Very bright man.

The Germans were very interested initially in making an atomic bomb and started moving towards this goal very early on

There was also Carl von Weizsäcker who was again a very imaginative physicist, although not quite as bright as Heisenberg. There were worries about him because his father was a ‘career Nazi’, so he was viewed as something of a threat.

There were lots of other people involved, including some who'd worked with New Zealand physicist Ernest Rutherford in England. They started off moving very concertedly towards the bomb; two groups wrote independently to the Reich Research Council and to the German army very early in 1939 – so within just a couple of months of the reports of fission – to say that a hugely destructive bomb was a possibility and that Germany must exploit it before its potential enemies could.

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To begin with, they put a lot of time and effort into this idea, but then attention drifted away towards a nuclear reactor that would generate electricity. This wasn't necessarily a peaceful proposition either – because the first use that they thought of was actually for it to propel submarines and keep them under water for longer.

It all fell apart in 1942, when there were a series of presentations to high-ranking Nazi military commanders. It’s clear that Heisenberg, who was in charge, hadn't really thought things through. He presented lots of detailed diagrams of the reactor, but when he talked about the bomb, it was clear he hadn't even thought about what it might look like, how much it would weigh, anything like this at all.

There were two killer questions from the military people involved which effectively killed the bomb project. The first was an innocent question: how big will this bomb be? And Heisenberg said it would be about the size of a pineapple. There had been stories in the press about nuclear weapons that might be the size of a walnut or the size of a basketball or weighing a couple of tonnes – and nobody quite knows why Heisenberg thought of a pineapple.

He hadn't done the calculations, any of them, to try and work out how much U-235 you would need for an atomic bomb, so he just probably plucked the numbers out of the air. When he was asked to justify his answer, he couldn't. So it became obvious to these rather hard men – who were used to dealing in certainty and thousands of other people's lives – that this guy was an amateur.

The second killer question was: how much money do you need? I can’t remember how many billions of Reichsmarks were being spent per day, but it was an awful lot. When Heisenberg was asked this question, he said, “Oh, I need a couple of 100,000 Reichsmarks”. It was such a ludicrously low amount that the person who asked the question actually said, “You’re sure that you don't need more?” And Heisenberg said no.

At that point, von Weizsäcker chipped in and said, “Well, we could do with another couple hundred”. And it became immediately obvious that these two guys in charge of this bomb hadn't even discussed the budget.

Following this discussion, one of the military men went to see Hitler. This was in June 1942 – and he had a list of about 20 items to discuss with the Führer. The notion of the German atomic bomb was an item way down the list. Hitler said no.

The Germans carried on working on the uranium reactor to generate power and electricity until the end of the war. But they didn't even manage to get this to go critical. So the German bomb died in early in the middle of 1942.

Gareth Williams is Emeritus Professor and former Dean of Medicine at Bristol University. His previous books include Angel of Death: The Story of Smallpox and Unravelling the Double Helix: The Lost Heroes of DNA. His forthcoming book is The British Super-Bomb: The Forgotten Father of the Manhattan Project.