Alternate history: what if Alan Turing and Bletchley Park had not cracked the Enigma code?

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Once in possession of vital intelligence about the enemy’s location, though, an Allied fleet could divert its route and avoid significant loss of life. “Knowing where the wolfpacks were allowed the Allies to simply sail around them,” confirms Michael Goodman, professor of intelligence and international affairs at King’s College London.

“But how do you conceal from the Germans that you’re reading these codes? You can’t just bypass every single submarine because then it becomes obvious. It’s a classic intelligence conundrum: at what point do you reveal your hand?”

Winning the battle of the Atlantic

Keeping their cards close to their chest gave the Allies an advantage in the Atlantic, allowing supplies to reach other theatres. “Enigma was a force enabler,” observes Professor Goodman. “It provided a window into what the Germans were thinking and doing, but it didn’t tell the Allies what to do. It still had to be applied – but in the Atlantic it saved ships and it saved lives.”

Without the cracking of Enigma, would Germany still have ruled the Atlantic’s waves? “I think that’s probably true,” confirms Professor Goodman, before positing another conundrum:

“Had Hitler succeeded in marshalling the Atlantic, would he then have pushed on to the US? Or might he have linked up with the other Axis powers to push into the Americas, not just the US? I’d have been surprised if he had been able to extend into another theatre, but it could have been an option.”

One significant likely consequence of continued German control of the Atlantic has been much discussed: had Enigma not been cracked, it’s unlikely that the war would have ended in 1945. “I absolutely believe Enigma shortened the war,” says Professor Goodman. “The general consensus is that it did so by two or three years.”

• Read more | Enigma before Bletchley: the German spies who betrayed Hitler to steal codes

Bletchley Park and D-Day

With control of the Atlantic wrested from Germany, the Allies could focus attention elsewhere – and the work of the codebreakers at Bletchley Park proved fundamental to the success of D-Day in 1944.

“The intelligence that preceded the landings was all about whether the Germans had swallowed the deception plan,” explains Professor Goodman. “Did they believe that it was going to happen farther north along the coast, near Calais rather than in Normandy? And what level of opposition could be expected when the Allies landed? This was totally based on the intelligence gathered. And that was down to cracking Enigma.”

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Would the Allies have risked an invasion the size and scale of D-Day without the intelligence that had been harvested? “By then, the war was very much going the Allies’ way, and it was absolutely a decision taken by them that there had to be an invasion of northwest Europe,” explains Professor Goodman.

“But would it have taken place in the way that it did? And would they have committed as many forces? Possibly not, because for such a deception to succeed, you have to know it’s been swallowed by the enemy. And you couldn’t know that without something like Enigma. Had the deception plan not worked, and had all those German forces still been in Normandy and not redeployed to Calais, the loss of life on the Allies’ side would have been truly horrendous. It was still bad on D-Day.”

Without a large-scale invasion like D-Day – or, at least, one at that particular juncture – it’s again likely that the war would have lasted longer than it did. And who knows what direction it would have taken in those extra years. Would it, for instance, have given Hitler more time to develop an atomic programme, with dramatic consequences for Europe and the wider world?

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Professor Goodman thinks probably not. “The main German scientists who were captured towards the end of the war were interned in a house in Cambridgeshire,” he explains. “When the atomic bomb was dropped on Hiroshima, the rooms they were in were bugged. It was very clear they didn’t really know how to develop an atomic bomb. Would they have got there in another three years?

“Perhaps they would have grown their V1 and V2 programmes instead. Hitler was certainly turning towards bigger types of weapons like those.”

So it can be suggested that the cracking of Enigma at least indirectly helped avert another devastating Blitz for the people of Britain. “Whether these German missiles would have made a strategic difference is another question,” concludes Professor Goodman, “but certainly the effect on the UK population, both physically and in terms of morale, could have been very significant.”

• Read more | The evolution of British code-breaking after the Second World War

Michael Goodman is professor of intelligence and international affairs at King’s College London and author of The Official History of the Joint Intelligence Committee, Volume 1 (Routledge, 2014). Nige Tassell is a journalist specialising in history.

This article was first published in the June 2023 issue of BBC History Revealed