On this day: The Einstein - Szilárd letter

Was it a letter that changed the course of history? Albert Einstein's confidential missive to Franklin Roosevelt, penned along with Hungarian Jewish physicist Leó Szilárd and other scientists, called on the US President to support the development of a nuclear weapon.

Those behind the letter believed that as a Nobel Prize winner, Einstein would help convince the president that they were right.

The letter warned the president that "German scientists might win the race to build an atomic bomb" and argued that if he could, Adolf Hitler would be likely to use it as a weapon. They said it was conceivable "that extremely powerful bombs of a new type may thus be constructed".

After some difficulties, the letter eventually reached Roosevelt and he replied saying that he found it a "most interesting and important enclosure". He also said that he had convened a board to investigate the possibilities.

Whether in response to that plea or not – academics continue to debate the subject – US scientists did begin looking into nuclear technology.

Their research became the Manhattan project and the atomic bomb, dropped on Hiroshima and Nagasaki in August 1945 in an attempt to prompt a Japanese surrender.

Einstein, who was 60 when he signed the letter, said later that it went against his

pacifist leanings and he regretted it. But he also said that the danger that the Germans would make them meant there was "some justification

What the JC said: The fates which have cast Jews into the so-called "free professions" were particularly active one day just seven months before the Second World War began, when Leo Szilard escorted a fellow-Hungarian Jew to drive him out to Peconic Bay on Long Island, a suburb of New York, to see another refugee…Albert Einstein. Dr Szilard, an outstanding scientist, had, like other physicists in America, learned that the Germans had succeeded in producing atomic fission. He, and they, were worried that from the laboratory to the atomic bomb would-be a short step.

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