Finally remembered: the Polish codebreaker key to Bletchley Park cracking Enigma Henryk Zygalski’s crucial work will be recognised today when a memorial is unveiled, writes Demot Turing, nephew of famed codebreaker Alan

The British are rightly proud of the code-breaking centre at Buckinghamshire’s Bletchley Park, which famously cracked the Enigma cipher machine and, according to one historian, helped shorten the Second World War by as much as two years.

The story has almost passed into legend, perhaps tempting us to visualise the man most closely associated with this episode – Alan Turing, my uncle – battling alone against prejudice and a mountainous, intellectual problem.

The truth is a little more complicated, but just as interesting.

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The Poles who must be celebrated

The reality is that Turing had help from Poland – the country that Britain pledged to defend in 1939. It was there, seven years earlier, that a different team of code-breakers had already got to the bottom of the Enigma problem. One of them, Henryk Zygalski, will finally be celebrated in a discreet ceremony in Chichester on Saturday, when the Polish ambassador to the UK unveils a monument in his honour.

It was in 1932 that he and other Polish code-breakers recreated, through pure mathematical analysis, the way the military Enigma machine worked. From then on, the Germans made frequent changes to their Enigma machines – any one of which could have blinded the Poles to the content of the messages – but the code-breakers were able to find a way around each development.

They invented new machines called “bombas”, as well as manual techniques to tackle the code-breaking challenge. Among Zygalski’s inventions was a method involving perforated cardboard sheets, representing Enigma rotor settings, which were piled on top of a light-box, progressively blocking more perforations until only one – the likely set-up – was left.

At a crucial meeting in Warsaw in July 1939, the secrets of Zygalski’s sheets, the workings of the bombas, the wiring of the Enigma machines and much more were divulged to an incredulous group of intelligence officers from Britain and France.

It was this handover of priceless know-how that gave my uncle and his co-workers at Bletchley Park the information they needed to provide an Enigma code-breaking capability to the Allies for the rest of the war.

Myths and misunderstandings

Poland was overrun by the Nazis in September that year and the Polish code-breakers had to flee to France, where they were stationed with the intelligence division of the French Army. There, Zygalski’s sheets came into their own. After Turing delivered a set (1,560 in all) of these huge cardboard sheets to the Franco–Polish combined team in January 1940, the code-breakers were able to read German Enigma traffic once more.

Another myth has also developed: that the British turned the Polish code-breakers away from working at Bletchley Park. In truth, Bletchley Park made repeated efforts to have the Poles join them, but the French had got their offer in first.

Even after the fall of France in 1940, the Polish code-breakers continued working in the “free zone” under the Vichy Government administration. There they lived a dangerous double life, hiding behind fake names while trying to provide decrypted messages to the Polish government-in-exile in London. This went on until the Germans took over the free zone in late 1942 – when, once more, the Poles found themselves on the run.

Eventually some of them made it to Britain, including Zygalski. After the war ended, most of the code-breakers concluded that it was too dangerous for them, as ex-spies, to return to Poland, which was now under Communist rule. Zygalski was one of those who stayed, finding a new calling as a mathematics lecturer, as well as a happy family life in Sussex. Thursday marked the 40th anniversary of his death.

His role – and that of his colleagues – deserves much better recognition. Without them, Bletchley Park’s achievements might never have happened.

Dermot Turing’s ‘X, Y and Z: The Real Story of How Enigma Was Broken’ (£20, History Press) is out on Monday