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Bletchley Park Was the Center of Allied Code-Breaking

The full scope of its intelligence work remained a secret until the 21st century.

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  • Dorothy Du Boisson (left) and Elsie Booker operate a Colossus Mark 2 codebreaking computer, 1943.Photo Credit: Wikipedia

Today, the estate known as Bletchley Park is remembered primarily for a secretive yet vital role that it played during World War II, and is the site of museums and exhibitions on code-breaking and early computing. However, that was not always the case. Prior to its selection by MI6 for use during wartime, the house and grounds belonged to a financier named Sir Herbert Samuel Leon, who built the house that still stands there, and which modernist architect Landis Gores described as a “maudlin and monstrous pile.”

During its heyday, Bletchley Park was “humming with servants,” including as many as 40 gardeners, who could transform a bed of yellow daffodils into a “sea of red tulips overnight” (according to the book Enigma: The Battle for the Code by Hugh Sebag-Montefiore). Leon built the house in 1883, expanding on an existing structure that had been erected by architect Samuel Lipscomb Seckham. Though Leon himself passed away in 1926, his wife remained at the house until her death in 1937. It was not long afterward that Bletchley Park was purchased by Admiral Hugh Sinclair, the second man ever to be in charge of the British Secret Intelligence Service, better known as MI6.

Sinclair was the founder of the Government Code & Cipher School (GC&CS), which was eventually headquartered at Bletchley Park. At the time that he bought the property in 1938, however, he did so with his own money, paying some £6,000, which would be nearly $500,000 USD today. It would be a little more than a year from the time the park was purchased by Sinclair until the day when Britain would enter into World War II.

Once the war had started, the estate—which was comprised of some 58 acres, eventually converted to house dozens of smaller buildings, in addition to the mansion itself—began humming with a very different kind of activity. Here, Allied codebreakers from all walks of life worked together to try to crack the complex ciphers that were being used by German armed forces, including the notorious Enigma and Lorenz machine ciphers.

In order to recruit the types of people who would be needed to break these complex ciphers, the British government took sometimes extraordinary measures. On the day that Britain declared war against Germany, Commander Alastair Denniston, who was the operational head of GC&CS, wrote to his superiors about the need to recruit “men of the professorial type.” Nor were men the only ones the service recruited. The GC&CS also brought in young women of "high society,” as well as female mathematicians such as Joan Clarke.

Besides professors and mathematicians, the GC&CS also reached out to chess champions like Hugh Alexander and Stuart Milner-Barry. The Daily Telegraph was even asked to run a crossword competition, which was used as a recruitment tool. In fact, the crew at Bletchley Park was so eclectic that, during a 1941 visit, Winston Churchill himself is said to have remarked, “I told you to leave no stone unturned to get staff, but I had no idea you had taken me so literally.”

While the most famous of the various codebreakers employed at Bletchley Park is probably Alan Turing,  also among the ranks were Jack Good, Harry Hinsley, John Jeffreys, Mary and Valerie Middleton, Max Newman, Derek Taunt, Peter Twinn, Gordon Welchman, and many others. By 1945, some 10,000 people were working at Bletchley Park and at various outlying stations, working to decrypt enemy codes. Of those, nearly 75% were women.

The earliest female recruits were mostly skilled typists, linguists, and radio operators who could perform the kinds of quick processing of data that was necessary. As the needs of the operation grew, however, the program brought in female mathematicians, physicists, and engineers, such as Eleanor Ireland, Ruth Briggs, Mavis Lever, Margaret Rock, Rozanne Colchester, Cicely Mayhew, and many others. Though often overshadowed by the names of some of their more famous male counterparts, they played vital roles in the Allied code-breaking process, including working on some of the first computers.

Indeed, while the work that went on at Bletchley Park was central to the Allied war effort and considered so important that a new classification—Ultra Secret—was devised for the intelligence it produced, computers may be the most lasting legacy left behind by the work that was done here. Beginning with a relatively simple machine called “the bombe,” designed by Alan Turing and Gordon Welchman, the codebreakers at Bletchley Park devised increasingly complex mechanical methods to assist them in their decrypting procedures.

This culminated in the device known as Colossus, a massive set of machines that has been called the world’s first programmable, electronic, digital computer. Designed by Tommy Flowers, a telephone engineer working for the General Post Office, Colossus was programmed via switches and plugs, very differently than any computer we know today. And yet, it was a definite beginning, and by 1944, it was in use at Bletchley Park.

One such computer proved not to be enough, however, and by the end of the war, there were 10 in operation, with more on the way. However, despite their importance to early computing, the very existence—let alone design—of these machines was considered top secret, and remained so until the 1970s. At the end of the war, all but two of the machines were dismantled so that their purpose could no longer be discerned, and Tommy Flowers was ordered to destroy all documentation.

“I was instructed to destroy all the record,” he said later, “which I did. I took all the drawings and the plans and all the information about Colossus on paper and put it in the boiler fire. And saw it burn.”

In fact, it was not until the 21st century that the British government fully acknowledged the work of the thousands of people who contributed to the Allied victory in World War II through their work at Bletchley Park. In 2009, a commemorative medal was struck for those involved. 

Today, Bletchley Park and its grounds still stand, having been rescued from demolition on at least one occasion. It houses a number of museums and exhibitions dedicated to its role in the war, including the National Museum of Computing, which features rebuilt examples of the Colossus computer and other early mechanical decryption machines.