You have betrayed the hospitality and protection given to you by this country with the grossest treachery.’
The arrest of Klaus Fuchs for espionage in 1950 was a news sensation.
The renowned physicist had spent years at the very heart of Britain and the United States’ nuclear programmes.
But unbeknown to his colleagues or the security services in either country, Fuchs was passing every secret that fell into his hands on to the Soviet Union.
It was largely down to his double-crossing that Soviets were able to test their own atomic bomb months earlier – to the West’s astonishment and alarm.
Here, Metro looks back at the life of one of Britain’s most brilliant atomic scientists and how he was unmasked as ‘the most dangerous spy in history’.
Klaus Emil Julius Fuchs was born in 1911 near Frankfurt to a deeply religious family.
He studied maths and physics at the University of Leipzig and although initially a member of the socialist party, he joined the communists believing only they could defeat the rising Nazis.
But he was forced to flee his homeland after Adolf Hitler came to power in 1933, making his way first to France and then on to Britain just hours before he was due to be arrested by the Gestapo.
After graduating from Bristol University he began work at the University of Edinburgh, but was rounded up with other German refugees suspected of being Nazi spies and interned in Canada.
When he was released in January 1941, Fuchs was head-hunted to work on Britain’s clandestine atomic bomb project – codenamed ‘Tube Alloys’.
Fuchs became a British citizen the following August and signed the Official Secrets Act, promising not to pass state secrets to foreign governments.
But within months he was handing over classified information on the progress of Britain’s atomic bomb research to Soviet agents.
Similarly terrified at the prospect of the Nazis getting their hands on a nuclear weapon first, the US was also pursuing its own top secret atomic bomb programme.
Late in 1943, Fuchs was part of a delegation of British scientists sent to New York to work on the Manhattan Project.
He was transferred to Los Alamos, New Mexico, in August 1944, where he was involved in the construction of the first atomic bomb.
Fuchs was present at the Trinity Test – the first detonation of a nuclear bomb to which he had made a significant contribution – and was considered one of the best theoretical physicists on the project.
As well as passing on the programme’s secrets, he also leaked detailed information about bomb’s design – saving them around two years’ worth of research.
When he returned to the UK in 1946, Fuchs was offered a prestigious post at the UK Atomic Energy Research Establishment at Harwell, Oxfordshire, where he worked on developing nuclear energy.
Its importance and secrecy led to it being nicknamed ‘the holy of holies’.
MI5 investigated him but found nothing incriminating.
His treachery was only discovered when the US intercepted messages from the Soviet intelligence services which included reports of Fuchs’s meetings with his handler.
In his confession, he revealed how he managed his double life.
‘I used my Marxist philosophy to establish in my mind two separate compartments,’ he said.
‘One compartment in which I allowed myself to make friendships, to help people and to be in all personal ways the kind of man I wanted to be.
‘I could be free and easy and happy with people without fear of disclosing myself because I knew that the other compartment would step in if I approached the danger point.
‘I could forget the other compartment and still rely on it.’
He added: ‘Looking back at it now, the best way of expressing it seems to be to call it a controlled schizophrenia.’
Fuchs was arrested in January 1950 and charged with violating the Official Secrets Act.
He was found guilty at the Old Bailey of disclosing atom secrets ‘calculated to be directly or indirectly useful to an enemy’ in England in 1943 and 1947 and in the United States in 1944 and 1945.
The prosecutor, Attorney General Sir Hartley Shawcross, said his motivation had been his ‘unswerving devotion to communism’.
Sentencing him to the maximum 14 years in prison, Lord Chief Justice Lord Goddard said: ‘You have betrayed the hospitality and protection given to you by this country with the grossest treachery.’
A 1951 report by the US Congress stated Fuchs had ‘influenced the safety of more people and accomplished greater damage than any other spy not only in the history of the United States but in the history of nations’.
In the event, Fuchs only served nine years and was released on this day 65 years ago.
Stripped of his British citizenship, he left for East Germany, where he was later elected to the Academy of Sciences and became a member of the Socialist Unity Party central committee.
Fuchs was later appointed deputy director of the Central Institute for Nuclear Physics in Dresden, where he served until he retired in 1979.
The man who helped three countries develop a nuclear bomb died in January 1988 aged 76.
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