Oppenheimer: Is Christopher Nolan guilty of perpetuating a historical myth?

Roosevelt sets up the Manhattan Project under physicist Robert Oppenheimer and military engineer General Leslie Groves. Oppenheimer assembles a brilliant American team at Los Alamos, which designs and constructs the bombs. These destroy Hiroshima and Nagasaki, precipitating the Japanese surrender and ending the Second World War.

I believed it too, until one morning in May 2017 when I was digging into the archives at Churchill College, Cambridge.

By accident, I came across top-secret documents, recently declassified, which painted a completely different picture. It was like stepping into a parallel universe, with names I didn’t recognise – Frisch, Peierls, Oliphant, M.A.U.D. and Tube Alloys – and no mention of Oppenheimer, Manhattan or Los Alamos.

Then I realised that this was all happening in 1940, two and a half years before Manhattan was born, and decided to find out more.

• Read more | What happened to Hiroshima after it was bombed in 1945?

The real story of the bomb began in Birmingham with two young physicists, Otto Frisch and Rudolf (Rudi) Peierls, both hounded out of Nazi Germany because they were Jewish.

When war was declared, the Home Office classified them as ‘aliens’ and barred them from the secret war project (radar) which swallowed up all their colleagues.

They therefore turned their attention to the extraordinary ability of a single neutron to crack the massive nucleus of uranium in two. Soon after the phenomenon was discovered in Berlin over Christmas 1938, Frisch coined the name ‘fission’ and showed that it released a huge blast of energy, a million times greater than detonating high explosive.

Days before the war began, Danish physicist Niels Bohr suggested that fission only occurred in a rare form of uranium, the isotope U-235, which constitutes less than one per cent of the natural element.

This made Frisch wonder what would happen if neutrons were fired into a mass of pure U-235. His calculations predicted a massive, explosive nuclear chain reaction.

He and Peierls estimated that a ‘super-bomb’ containing a few kilos of U-235 would explode with the force of tens of thousands of tons of TNT, and could devastate a city centre. They convinced their boss, Professor Mark Oliphant, who told them to write up their findings.

The Frisch-Peierls memorandum of April 1940 transformed the atomic bomb from fantasy into a series of technological challenges. In 1914, HG Wells invented the ‘atomic bomb’ for his novel, The World Set Free, but the notion hadn't progressed beyond science fiction; the 40-ton 'explosive uranium device' in a 1939 French patent couldn't have worked.

A top-secret expert committee, including Nobel Prize winners, was set up in March 1940 to consider the Frisch-Peierls memorandum. It was cryptically named 'M.A.U.D.', from a garbled telegram about an old friend of Niels Bohr.

Being ‘aliens’, Frisch and Peierls were excluded and relegated to a technical subcommittee. In June 1941, the M.A.U.D. Committee's final report concluded that the U-235 super-bomb was entirely feasible and could be ready in two years, and that work must begin immediately to design the weapon and an industrial-scale process to extract U-235 from natural uranium.

But there was a catch: war-locked Britain lacked money and manpower, and was being pounded by the Luftwaffe. The super-bomb could only be built in collaboration with the Americans, and using a U-235 separation factory on American soil.

The M.A.U.D report was approved by the War Cabinet and forwarded to Winston Churchill, and a copy was sent to the secret Uranium Committee in Washington. Its work done, M.A.U.D was dissolved and replaced by the Directorate of Tube Alloys, a consortium of British atomic researchers and industrialists, notably from Imperial Chemical Industries (ICI).

Meanwhile, British Intelligence reported that the Nazis had established a ‘Uranium Club of top nuclear physicists before the war started, and were making progress towards making an atomic bomb.

The Americans were told this and had been sent copies of all M.A.U.D documents, but they didn't respond – and they ignored the final M.A.U.D report endorsing the U-235 super-bomb that could only be built in collaboration with the US. Their silence caused great concern and frustration in Britain.

In summer 1941, Oliphant flew to the US to advise on radar, and decided to find out why the Americans hadn't replied about the bomb. He was shocked by what he discovered.

The Advisory Committee on Uranium set up by Roosevelt in response to Einstein's letter was dysfunctional and populated by people incapable of understanding the bomb: military men who insisted that it took two wars to introduce a new weapon; physicists who were fixated on Enrico Fermi's nuclear reactor in Chicago and had written off the atomic bomb as too difficult and speculative; and a chairman, completely ignorant of nuclear physics, who locked the M.A.U.D report in his safe because he couldn't understand it, without showing it to his committee.

Oliphant was furious and went to argue the case for the bomb with an old friend, Nobel Prize winner Ernest Lawrence in Berkeley. Previously sceptical, Lawrence was converted by Oliphant into a fervent bomb believer, and in turn convinced key people above him that the British super-bomb must be taken seriously.

At last, the boulder began to roll. In October 1941, Roosevelt approved full Anglo-American collaboration to build the atomic bomb, and informed Churchill.

The collaboration made a slow start. At first, Churchill covertly stalled negotiations (he didn’t want the Americans to get ahead technologically), which made the Americans lose trust in the British. The American bomb project gained momentum without the British, culminating in September 1942 with General Groves’s appointment to run the top secret, $2-billion Manhattan Project.

This vast enterprise included the bomb-making base at Los Alamos, a huge U-235 separating factory in Tennessee, and a separate plant in Washington State to make plutonium, a man-made element created in Fermi's nuclear reactor which was even more explosive than U-235.

In October 1942, Groves appointed Oppenheimer to direct the scientists at Los Alamos. Oppenheimer soon realised that he needed British input and expertise, and against opposition from Groves, the ‘British Mission to Los Alamos’ was set up under James Chadwick, Nobel Prize winner for discovering the neutron.

The British made up fewer than one per cent of those at Los Alamos but punched far above their weight. U-235 would not have been ready for the Hiroshima bomb (Little Boy) without the theoretical input of Rudi Peierls and Klaus Fuchs, together with a British-made nickel membrane that was crucial to the U-235 separation process.

Otto Frisch also calculated how much U-235 was needed from a terrifying experiment (likened to “tickling the tail of a sleeping dragon”) which came “as close as we could possibly go towards starting an atomic explosion without actually being blown up”.

The plutonium inside the bomb destined for Nagasaki (Fat Man) had to be imploded – crushed by conventional high explosives. The work of Peierls, Fuchs and James Tuck was vital in designing explosive ‘lenses’ to focus the shockwave, while British physicist Ernest Titterton devised the electronic firing signal that triggered the complicated detonation circuit.

Their impact? Without the British Mission, neither Little Boy nor Fat Man could have been built by August 1945 – or even by November that year, when America was set to invade the Japanese homeland if Japan didn't surrender.

And without Mark Oliphant's dramatic intervention in late summer 1942, the Manhattan Project would never have been set up, because nobody in America would challenge the assumption that an atomic bomb couldn't be made in time to play any role in the War.

• Read more | How did J Robert Oppenheimer react to the first nuclear weapons test?

Immediately after Hiroshima and Nagasaki, President Truman and Churchill both acknowledged that the bombs had resulted from a highly effective Anglo-American collaboration which depended on both partners.

But as the nuclear ambitions of America and Britain diverged after the war, American accounts progressively squeezed out the British.

In 1946, Groves commented that “I cannot recall any direct British contribution to our success in achieving the bomb”. The official American history of the bomb – The New World (1962) – further minimised the role of the British; Titterton, who actually detonated the Trinity plutonium test bomb, was written out of the story.

Most people won't have heard of Frisch, Peierls, Oliphant or Titterton, and won't know that the M.A.U.D. Committee or Tube Alloys ever existed. Oppenheimer is great cinema and a powerful account of a partial truth. The full truth is even better.

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.