...and Never Cackled

The work carried out at Bletchley Park was of immense importance to the war effort and, as such, was extremely top-secret. It seems that none of those involved squealed about the important breakthroughs, and the Germans remained unaware that every message they transmitted via the Enigma was being deciphered and read by the British. Towards the end of the war, a common joke among top-level intelligence staff was that if Hitler wanted any information about the movements of his admiralty, he need only ask the British, who knew more about German naval movements than the Germans themselves!

Winston Churchill famously referred to the workers at Bletchley Park as “my geese that laid the golden egg and never cackled”. The work at Bletchley Park was so secretive that details of the important codebreaking carried out there were not made public until the 1970s. And important it was: the intelligence produced at BP was so crucial to the Allied war effort it has been said that without this, the war may have been up to two years longer (some believe it may have been up to 4 years longer).

Enigma

We saw these Enigma machines in the Science Museum in London.
It was an exhibit on Alan Turing, one of the brains at BP.

In the early 1920s, a German engineer was having much success with his machine that could code and transmit secure information, the Enigma machine. Enigma used electrical connections to encrypt messages, and so the process was much quicker than it had been when an operator had needed to perform encryption by hand, using a table of codes. Most importantly, the resulting encrypted messages were considered impossible to crack. For this reason, by 1933, all of the German armed forces were using their own variants of the Enigma.

An Enigma machine looks like a typewriter, but with some extra features. The operator types in their message, then the machine uses three to five rotors (depending on the version of the machine) to scramble the text and produce different letters of the alphabet. This is known as a substitution cypher, as one letter is substituted for another. The receiver of the message needs to know the exact settings of the rotors in order to reconstitute the text. Over the years the basic machine became more complicated as more rotors were added and as German code experts added plugs with electronic circuits.

One key point of difference with the Enigma is that when an operator inputs a letter, that letter will never be enciphered as itself.  That is the weakness that eventually enabled the machine’s codes to be ‘cracked’. There were certain words that would generally appear in a message, for example ‘to’ at the start, and yet the letters from those words never appeared in the encrypted messages. 

 By 1932, the Polish had managed to decipher Enigma messages. At that stage, the cypher was only altered every few months, but as the 1930s rolled on and German military operations began to increase in frequency, so did the number of messages being transmitted. It wasn’t long before the cypher was being changed at least once per day. This gave 159 million million million possible settings to choose from! It is no wonder the Germans considered the machine to be unbreakable. 

 As the encryption became more complicated, the Poles were unable to continue deciphering the messages. In 1939, they handed their data to the British, and Bletchley Park became the new centre for efforts to decrypt the Enigma. 

 The first break into Enigma came in January 1940, when a team worked out the key used by the German Army. Soon after, they also unravelled the key used by Luftwaffe officers who coordinated air support for army units. BP staff based in a neighbouring hut turned the deciphered messages – known as Ultra - into intelligence reports. As the cracking of Enigma was extremely top-secret, the resulting reports were made to look like they had been produced by an MI6 spy, codenamed Boniface, with a network of imaginary agents inside Germany.

 At this stage, there were some amazing minds working at BP. Dilly Knox, Alan Turing, Gordan Welchman, and Max Newman knew that deciphering Enigma messages by hand was taking too much time. By the time the messages were unravelled, the intelligence was of little operational use. Alan Turing, with the support of the others, created a device that would run through all possible Enigma wheel configurations, in order to reduce the possible number of settings that could have been used to encrypt the message. This reduced the amount of codebreaking work that had to be done by hand. The machines were known as Bombes, and were generally operated by Wrens, members of the Women’s Royal Naval Service. 

(Unfortunately we couldn't get any pictures of a Bombe, as that part of BP was closed for renovations. You can find a picture of it here: http://www.theregister.co.uk/2009/03/23/bletchley_bombe/)

The resulting intelligence – Ultra – was extremely valuable to the Allies. Throughout the First Battle of the Atlantic, Ultra gave the navy vital information about the positions of German submarine packs (‘wolfpacks’) and the Admiralty was able to fight off the U-Boats which attacked merchant ships bringing supplies to Britain from North America. Ultra also enabled the Allies to discover if the Germans had swallowed deception plans they had planted, such as those for the invasion of Sicily in July 1943. Before the operation, secret agents planted false intelligence suggesting that plans to attack Sicily were only a ruse, and that real landings would take place elsewhere. Ultra revealed that the Germans had fallen for the false intelligence and believed an Allied operation in Sicily would only be a ruse for real attacks elsewhere. The resulting invasion of Sicily was a success, and was one of the main turning points in the war. Ultra also played a key role in the success of the D-Day landings in June 1944. Ultra intercepts showed that the Germans had believed the deception campaigns, and were convinced a landing was to be made in the Pas de Calais. This meant that when the eventual landings took place in Normandy, and over 150,000 Allied troops arrived by air and sea, German resistance was low and the Allies were able to finally re-gain a foothold in Europe. Right to the end of the war, the Germans did not believe that the Enigma had been broken and they continued to send sensitive information which was promptly deciphered by a select few at BP.

Lorenz

Another triumph of Bletchley Park was the deciphering of messages sent using a Lorenz cypher. Before the war, the High Command of the Germany Army had requested the construction of a teleprinter cypher machine that would enable them to send secret messages via radio. The Lorenz Company designed a machine that featured up to twelve wheels all with a different number of cams, or pins, in them. From here, it all gets a bit complicated for me, but I understand that this means the possible encoding options are huge. (Wikipedia it or use Tony Sale’s amazing website - http://www.codesandciphers.org.uk/index.htm - if you want to know more: )

The Lorenz machine used a combination of dots and crosses and Boolean 0s and 1s to print a message. It then used the Vernam system of adding a random set of obscuring characters before transmitting the message. At the receiving end, the random set of obscuring characters would be added back on to the message, they would cancel themselves out, and the original message characters could then be printed. This cypher system, which uses one-time purely random obscuring characters, is unbreakable. Until you factor in human error.

On August 30, 1941, the Germans made a terrible mistake. An operator had a long message of nearly 4,000 characters to be sent from one part of the German Army High command to another. He set up his Lorenz machine, sent a twelve letter indicator to the receiving operator – this would tell the receiver which settings to put onto his Lorenz machine - and keyed in his long message. The receiving operator then signalled that he had not received the message and to send it again. Both operators then put their Lorenz machines in the same start position they had used for the original message – even though this was forbidden. The second time around, the sending operator made some abbreviations and mistakes. The interceptors at Knockholt realised that the same message was coming through, as it was using the same one-time obscuring sequence. However, the message was slightly different and this set off alarm bells. The incoming text was quickly sent to Bletchley Park, where one of the top codebreakers, John Tiltman began to study it.

 Eventually Tiltman was able to work out a chunk of the obscuring character sequence that the cipher machine generated. After three months, his team had failed to make any further headway, and 24 year old mathematician Bill Tutte was brought in. In two months, Tutte worked out the complete logical structure of the cypher machine. Without ever seeing a Lorenz machine (in fact, the British would not come face-to-face with one until 1945), Tutte managed to reverse engineer the cypher machine. This was a huge breakthrough, possibly one of the greatest intellectual feats of the War.

Soon, the team had constructed a machine, known as the Tunny, using Tutte’s calculations. Further developments produced a family of machines known as the Robinsons, though these were still too slow to be of much use to the war effort. It was time to call in the big(ger) guns.

Above, Tunny and Heath Robinson machines

 Max Newman, a mathematician, and his engineer sidekick Tommy Flowers soon designed and constructed THE COLOSSUS. (*Cue dramatic music*) The Germans enciphered a message with the Lorenz, transmitted it by radio, when it was intercepted and recorded on to paper tape at BP. The tape was joined into a loop with special punched holes at the beginning and end of the text. Colossus was able to read the tape at 5,000 characters per second. 

(For computer geeks, “At 5,000 cps the interval between sprocket holes is 200 microseconds. In this time Colossus will do up to 100 Boolean calculations simultaneously on each of the five tape channels and across a five character matrix. The gate delay time is 1.2 microseconds. Colossus is so fast and parallel that a modern PC programmed to do the same code-breaking task takes as long as Colossus to achieve a result.” According to Tony Sale, the former curator at BP.)

By Christmas 1943, a Mark 1 Colossus was assembled at Bletchley. The machine could break Lorenz messages in hours, which was a huge advance. It was just in time to decipher messages related to D-Day, and the resulting deciphered messages revealed that Hitler had fallen for the deception campaigns (such as the phantom army in the south of England, phantom convoys moving across the Channel – look it up, it’s very exciting stuff!) and was convinced that an attack would be launched on the Calais area of northern France, rather than at the correct location of Normandy. This was extremely valuable knowledge to possess, and it was all thanks to the hardworking teams at Bletchley Park. 

By the end of the war, nine more Colossuses (Colossi?) had been built, and 63 million characters of German messages had been decrypted.

Knockholt

While we were in the Computing Museum, we were excited to come across some information about Knockholt. Knockholt is our neighbouring village, and in it sits a large farm house called Ivy Farm. This house was recently for sale at £1.25 million, and it hides an exciting past. 

During WW2, Ivy Farm was requisitioned by GC&CS and was used as a wireless intercept station. There was a wireless room at BP, but concerns around German detection of the site soon dictated that other stations should be created in numerous locations throughout the United Kingdom. One of the most important of these was at Ivy Farm in Knockholt. The Farm served as a Radio Intercept Station for messages transmitted by means other than Morse Code, e.g. such as those that had been enciphered using the Lorenz.

The 815 workers were either billeted to families in surrounding villages, or accommodated in huts built on the land around Ivy Farm. From November 1942 to May 1945, the Knockholt staff worked tirelessly, collecting 167,727 messages, of which 27,631 were sent to Bletchly Park where 13,508 were successfully deciphered. 

Isn't that exciting?! Living just minutes from one of Britain's most important intelligence locations of WW2?

Well that concludes the story of our trip to Bletchley Park - a place I've wanted to visit for many years. It was wonderful to walk on the ground where such exciting history unfolded, and to picture the many Wrens and genius codebreaking minds engaged in their valuable work. Sometimes I feel like I was born in the wrong era, as the excitement and mystery of the 1930s and 1940s appeals to something deep inside of me. Being at Bletchley Park for the 1940s festival with so many remnants of the war, and so many people dressed in costume was an amazing experience. 

Of course, we know how truly lucky we are not to have to experience the fear, death, and dishonour that was the reality of life in war-torn Europe. As we stood on that ground, rich with history, we also said thanks to the men and women who served their country with their valuable intelligence work and helped secure a better future for all of us.

(For the information about Enigma and Lorenz machines, I have relied heavily on the website of Tony Sale, who was the original curator at the Bletchley Park Museum. Thank you to Mr Sale for his interesting website and the informative reports on codebreaking at Bletchley Park. He describes the mechanisms of Enigma and Lorenz in depth on the website, so if you want to know more, go to Mr Sale's website - http://www.codesandciphers.org.uk/index.htm.)