D-Day: Interception, Intelligence, Invasion

Sandra Westbrooke has been to a new exhibition at Bletchley Park that marks the 75th anniversary of D-Day

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On June 6, 1944, the future of Europe hung in the balance. It was D-Day, and Allied forces were preparing to land on the beaches of Normandy in a bid to force their way through German defences. As dawn broke, the first of the 24,000 British, US, and Canadian troops made their way ashore.

They encountered heavy fire and many lives were lost. But the assault had a major advantage that led to ultimate success: the Codebreakers, tucked away at Bletchley Park in Buckinghamshire, had intercepted messages that helped build up an exact picture of the defences they were likely to meet, including the likely level of resistance, the location of landmines, and even the height of fences. They had also fed out false information which convinced Hitler any invasion would be further down the coast at Calais, which led to the bulk of his troops being stationed there. This exhibition is the story of their achievements.

The Victorian mansion and estate of Bletchley Park had become government property in 1938, bought to house the secret codebreaking and intelligence efforts of the Government Code and Cypher School (GC&CS). As war loomed, the first wooden huts were built in the grounds, and around 150 experts were recruited to collect enemy intelligence and evaluate it. It was demanding, frustrating and sometimes very boring work.

Their first major success, breaking the codes used by the German Enigma machine, is widely known and was the subject of the 2014 film, The Imitation Game, with Benedict Cumberbatch as Codebreaker Alan Turing. But the role played by Bletchley Park staff in the subsequent Operation Overlord and D-Day campaign remained unrecognised until recently when documents started to be declassified, and some of the veteran Codebreakers began talking about their experiences.

By 1944 the complex had become an intelligence factory, employing almost 10,000 people in hot, noisy and cramped conditions. Working in shifts around the clock, with the help of Colossus computers developed there, they decrypted messages sent by Nazi Germany’s Enigma and Lorenz machines. Codenamed ULTRA, this information provided early warning of German air attacks on British cities, located German U-boat submarines in the Battle of the Atlantic, and helped identify new weapons.

The exhibition tells how the system was able to build up a picture of the deployment of Hitler’s forces. By D-Day, there were 58 German divisions in France and the Codebreakers had detailed information on all of them. No communication, however trivial it seemed, was discounted. One intercept was an application for leave from a German soldier in a unit in Russia. Because this was rejected by Field Marshal Gerd von Rundstedt in Paris, the team in Hut 3, the main reporting centre for messages, deduced that the unit was now under his command and was therefore being moved to his territory in the west. Similarly, every request for aviation fuel, every journey of a troop train, was logged, indexed and cross-referenced – little bits of a jigsaw that, carefully pieced together, formed an overall intelligence picture.

ULTRA became so efficient that on D-Day itself, Allied commanders got word of enemy communications almost as soon as their Nazi counterparts. The exhibition has the precious transcription of one German naval message, dated 0430 on June 6, 1944, and decrypted by 0728. It reads: “Immediate readiness. There are indications that the invasion has begun.”

Hitler never knew about Bletchley Park or that his top-secret codes were being systematically broken, and it’s estimated GC&CS’s efforts shortened the war by two to four years. Without them, even the outcome would have been uncertain. This exhibition honours the role of these Codebreakers with an immersive film, shown on a 22m-long screen, along with short biographies of key players, original decoded messages and background information that has only recently become available. According to David Kenyon, Bletchley’s Research Historian, it portrays the vital link between the men and women who toiled there and their counterparts on the battlefield. “It sheds fresh light on the hidden history of these unsung heroes, and how their efforts gave the D-Day invasion the best chance of success,” he says.

Visitors can explore the rest of the park, including the mansion, restored huts, and even the garages where wartime vehicles are on display. There’s a recreation of Alan Turing’s WWII office and the museum has different cipher machines, including Enigma.

D-Day: Interception, Intelligence, Invasion is housed in the refurbished Teleprinter Building in the centre of the complex. Admission included with Bletchley Park admission tickets: £20, valid for a year. Concessions available.