The Third Reich’s nuclear programme: Churchill’s greatest wartime fear

That Adolf Hitler’s Germany might win the race to build the world’s first atom bomb was arguably one of Winston Churchill’s greatest wartime concerns, and one that was shared with his good friend US president Franklin D Roosevelt. When Churchill flew across the Atlantic to meet Roosevelt to discuss this issue, they agreed no effort could be spared to stop Hitler from getting the bomb, for with it he would win control over the world. “We both felt painfully the dangers of doing nothing,” Churchill would later write. “We knew what efforts the Germans were making to procure supplies of heavy water – a sinister term, eerie, unnatural, which began to creep into our secret papers. What if the enemy should get the atomic bomb before we did! We could not run the mortal risk of being outstripped in this awful sphere.”

The term ‘heavy water’ referred to deuterium oxide, a refined form of naturally-occurring H2O that is used as a moderator in nuclear power plants, which can breed weapons-grade uranium and plutonium.

So great were the wartime leaders’ fears that Roosevelt demanded immediate action to sabotage Hitler’s nuclear efforts. Only Britain had the capacity to respond. Churchill ordered a series of dramatic raids by his ‘Volunteers for Special Duties’ – his commandos, Special Operations Executive [SOE] agents and Special Forces: unique fighting men and women ideally suited to such near-suicide missions. Those daring raids targeted the giant heavy water plant at Vemork, in German-occupied Norway, among other facilities, which formed a key element of the Germans’ nuclear programme, and was the only element deemed vulnerable to Allied sabotage.

Those desperate sabotage attempts, which claimed scores of British lives before ultimately proving successful, form the narrative of my new book. But so too does Churchill’s launching of a top-secret mission codenamed Operation Peppermint: a covert programme to prepare Britain for a Nazi ‘dirty bomb’ being exploded over London. Operation Peppermint, arguably the most secret project of the entire war, aimed to provide early warning and whatever protection might be possible in the event of a nuclear strike by Nazi Germany on Britain. Secrecy was paramount, for Churchill feared mass panic and a collapse of wartime morale.

Such fears were very real. Following German physicist Otto Hahn splitting the atom in December 1938, the Allies believed the Germans to be two years ahead in the race to build the atom bomb. Those fears were massively exacerbated when Germany seized Czechoslovakia, prior to war’s outbreak, for in the mountainous north of the country was Europe’s only uranium mine. Joachimsthal is an ancient spa town in what was then northern Czechoslovakia, situated in the Ore Mountains. Following the seizure of the Joachimsthal mines in 1938, the German metallurgy company Auer Gesellschaft began shipping uranium ore to Oranienburg, in northeast Germany, where it began industrial-scale production of high-purity uranium – the raw material required to build the atom bomb.

With Nazi Germany’s seizure of Norway in April 1940, Hitler’s Reich took control of the Norsk Hydro Vemork plant – the only facility in Europe making heavy water, the other key component for a nuclear reactor and for ‘breeding’ atom bombs. When added to uranium, deuterium oxide acts as a ‘moderator’ to optimise nuclear fission – the self-sustaining chain reaction of splitting the atom.

Just 24 hours prior to marching into Norway, Nazi General Nikolaus Von Falkenhorst had led his troops into Denmark, occupying the nation in a matter of hours. In doing so Nazi forces had seized Copenhagen, along with its Institute of Theoretical Physics, whose founder and key luminary was Niels Bohr, a man many considered to be the grandfather of atomic research. In 1922 Bohr had won a Nobel Prize for his work on atomic structure and quantum theory. Among the top scientists that Bohr had mentored during the pre-war years was Werner Heisenberg, a German physicist who was then the chief mover and shaker at the Uranverein: Nazi Germany’s ‘Uranium Club’, set up at war’s outbreak to perfect the Third Reich’s nuclear weapons programme.

The Canadian William Stephenson, a First World War flying ace who went on to be Churchill’s foremost spymaster in North America during the Second World War, alerted his close friend to the threat of Bohr’s unwitting collaboration. “One of the world’s great atomic scientists was lost inside the German fortress… In a spirit of scientific inquiry Bohr was discussing the atomic bomb with those who wanted to use it to conquer the world”. In Bohr, the “Germans had the man whose theoretical work was the basis of the bomb”.

In May 1940, German forces struck a further series of seminal blows in the race for nuclear supremacy. On 10 May their forces overran Belgium, seizing at Olen (a town in the north of the country) the largest remaining stocks of uranium in all of Europe and possibly the world. Olen was one of the refining centres for the Belgium mining firm Union Minière du Haut Katanga, a company that then held sway over the world’s richest uranium reserves. In what was then the Belgian Congo, in Central Africa, the mining company controlled most of the world’s proven uranium reserves. At Olen, German forces seized well in excess of 1,000 tonnes of uranium ore.

British intelligence reports on this potentially catastrophic development made for grim reading. “Since the fall of Belgium… much the largest stock of uranium has been available [to Germany], from the refinery of the Union Minière at Oolen [sic].”

The report went on to chronicle how “several hundred tonnes of crude concentrates had been removed from Belgium”. The destination for that ore was the Auer Gesellschaft refinery, at Oranienburg – the same facility that was receiving the Czech ore from the Joachimsthal mines. “If Germany conquers Britain,” Stephenson declared, “the way is clear for the development of this weapon with which Hitler can blackmail the rest of the world… Give him respite, and he will make this new weapon of horror”.

Allied research suggested it would require 20,000 workers, half a million watts of electricity and $150 million in expenditure to build the world’s first atom bomb. A totalitarian state run by a dictator who now controlled most of western Europe could demand such resources, and in the concentration camps Hitler had access to millions of slaves. In short, the Fuhrer could harness Germany’s foremost engineering capabilities to its scientific expertise and western Europe’s almost unlimited resources – all of which made an atom bomb a real possibility. Allied worries reached fever pitch as the feasibility of building the bomb became ever clearer. Citing cutting-edge research, Churchill’s wartime scientific advisor, the eminent physicist Frederick Lindemann, said: “It should be possible for one aeroplane to carry a somewhat elaborate bomb weighing about one ton, which would explode with a violence equal to about 2,000 tons of TNT”.

“Whoever possesses such a plant should be able to dictate terms to the rest of the world,” concluded Lindemann. “It would be unforgivable if we let the Germans develop a process ahead of us, by means of which they could defeat us in war or reverse the verdict after they had been defeated.”

As early as the winter of 1942, the American military prepared to issue public warnings and evacuate key cities – so great was the fear of a Nazi nuclear strike. As Samuel Goudsmit, a key US nuclear physicist, later explained: “Since the Germans had started their uranium research about two years before us, we figured they must be at least two years ahead of us. They might not have the bomb yet, but they must have had the chain-reacting piles going for several years. It followed they must have fearful quantities of artificial radioactive material available. How simple it would be for them to… sow death wholesale amongst us.”

Goudsmit had more reasons that most to fear a nuclear-armed Nazi Germany: his Dutch parents would be deported to the concentration camps and murdered there. Of the climate of fear in the USA he wrote: “Some of the men… were so worried they sent their families to the countryside. The military authorities were informed and fear spread… scientific instruments were set up… to detect the radioactivity, if and when the Germans attacked”.

Britain’s experts, working at the top-secret London-based Tube Alloys project – the codename for the UK’s nuclear initiative – likewise warned of the seemingly unthinkable. Britain needed to prepare for Luftwaffe strikes utilising “fission products” – the by-products of a working nuclear reactor engineered into crude (‘dirty’) bombs. “Precautions should be taken to avoid a surprise attack,” the Tube Alloys experts wrote, proposing, “regular operation of suitable means of detection and tests in large towns”. This had to be balanced with “special precautions to preserve secrecy,” for they agreed with Churchill that if news leaked there would be mass panic on Britain’s streets.

By the autumn of 1943, Churchill’s Operation Peppermint was in full swing, and specialist teams equipped with Geiger counters – radiation detectors – were dispatched to Britain’s key cities. Expert reports outlined the dangers of the “military use of fission products by the enemy” – in other words, highly radioactive by-products from nuclear reactors being spread over Britain’s streets. Such fears reached their zenith when Nazi Germany’s V weapons programme (V for Vergeltung – vengeance) geared up for the so-called Robo-Blitz in the autumn of 1943, wherein more than 3,000 V2 rockets would pummel London, Antwerp and other key Allied targets.

Over the autumn of 1943 intelligence on the V1 and V2 weapons seeped into Britain. Top-secret Allied reports spoke of “liquid air bombs being developed in Germany… of terrific destructive power”. Stephenson, the quiet Canadian and Churchill’s intelligence supremo, noted that these were very possibly Vergeltungswaffe rockets carrying nuclear warheads. The V1 “flying bomb” campaign was followed by the giant V2 rockets – the first man-made objects ever to enter space. The V2 plummeted to earth at speeds in excess of 5,000 kph. No anti-aircraft guns or warplanes could ever hope to intercept the V2s or to shoot them down.

The greatest fear was that the Nazis had mastered the technology to fit a nuclear or radiological charge to the V2s, in which case there would be no defence possible. Churchill ordered aerial surveys to forewarn of such attacks; dry-run rehearsals to prepare for such an ordeal; and for frontline doctors to be briefed on the symptoms of radiation poisoning. Secrecy was of paramount concern.

Details of Operation Peppermint and the measures taken to prepare for a Nazi nuclear strike were revealed in papers that I unearthed from the National Archives. This came as a great surprise to me, for I was unaware that the Allied wartime leaders viewed Nazi Germany’s nuclear programme as such a real and present threat. The wider story of the race to stop the Nazi bomb is told in my new book, including the series of daring raids aimed at sabotaging Hitler’s nuclear programme wherever it was vulnerable to the Allies.

That sabotage was ultimately successful, though at considerable cost. In the autumn of 1942, some 34 British commandos flew into occupied Norway on two Horsa (wooden-hulled) gliders, which were towed by Halifax bombers. Their target was a vast hydro-electric plant producing deuterium oxide (heavy water), a key component of the Nazi nuclear programme, along with uranium. Sadly, the hemp towropes attaching the gliders to the tow-aircraft froze solid in the icy conditions over Norway and they snapped. Those Commandoes not killed in the subsequent crash landings were captured, tortured by the SS and Gestapo and executed horribly.

The failure of that mission, codenamed FRESHMAN, led to a very different approach being adopted by the Special Operations Executive. The commander of the SOE’s Scandinavian section – former scoutmaster and clandestine operations supremo Major John ‘Skinner’ Wilson – sent in two further assault teams. Codenamed Grouse and Gunnerside, each consisted of a small contingent of Norwegian commandoes (who had been trained and equipped in Britain) carrying explosives, skis and survival gear. In an assault of unrivalled daring and bravery, those 12 SOE raiders led by Joachim Rønneberg, who like most of his men was still in his early twenties, managed to penetrate the plant’s supposedly impregnable defences and to blow the deuterium oxide apparatus to smithereens.

William Stephenson, Churchill’s spymaster, would later say of those raiders: “If it had not been for [the saboteur’s] resolve, the Germans would have had the opportunity to devastate the civilised world. We would be either dead or living under Hitler’s zealots”.

Damien Lewis is the author of Hunting Hitler's Nukes: The Secret Race to Stop the Nazi Bomb. The book, published by Quercus, is out now.

This article was first published on History Extra in December 2016