Bletchley Park
"Bletchley Park didn't win the war, that was won by people with guns and bullets and things out in the field, but I think Bletchley Park is a great exemplar, particularly to the younger generation now, of brains over bullets. You can defeat an enemy intellectually, and that was shown here." (Tony Sale - Decoding Nazi Secrets Documentary)
By mid 1940, the German Army had conquered all of western Europe. Hitler was tightening the noose around Britain. In the Atlantic, German U-boats were decimating Allied convoys, threatening to cut off Britain's only lifeline. But Churchill had a secret weapon, the strangest military establishment in the world. Commanded by Alastair Denniston, the Park was given the cover name Station X, being the tenth of a large number of sites acquired by MI6 for its wartime operations.
Crossword fanatics, chess champions, mathematicians, students and professors, Americans and British, all came here with one common aim: to unlock the secrets of the Enigma, a machine that concealed Germany's war plans in seemingly unbreakable code. If Enigma could be penetrated, everything Hitler plotted would be known in advance. At Bletchley Park there unfolded one of the most astonishing exploits of the Second World War. Many here had never seen a code before, yet it was their job to find a way to crack Enigma. In the process, they devised ingenious codebreaking machines that were forerunners of the modern computer.
Step 1 - The Recruitment Process for Codebreakers
Codebreaking was a somewhat esoteric profession. But it wasn't clear exactly who would make a good codebreaker. People who were recruited were asked whether they did crossword puzzles. And if they said they did and enjoyed doing them, and did them well, that was generally enough to get you in. People of a whole variety of backgrounds did very well: Anthropologists, Egyptologists, paleontologists, and even an occasional lawyer turned out to have the knack. Bletchley Park evolved into a unique operation in which military discipline, uniforms, and rank no longer mattered. The sole imperative was to break the Enigma, and break it as quickly as possible.
In time, mathematicians were mainly enlisted to take on the daunting complexity of the Enigma. Only a completely new approach to codebreaking could help to penetrate its secrets. But if the work at Bletchley Park were to succeed, absolute secrecy was essential. Some of the recruits had no idea of the purpose of their work.
After meticulous preparation and a series of trial runs, the codebreakers arrived in earnest in August 1939. They masqueraded as 'Captain Ridley's Shooting Party' to disguise their true identity. It was to be the first installment in one of the most remarkable stories of the Second World War.
Humans vs. Machine
The German authorities believed in the absolute security of the Enigma. However, with the help of Polish mathematicians who had managed to acquire a machine prior to the outbreak of WW2, British code breakers stationed at Bletchley Park managed to exploit weaknesses in the machine and how it was used and were able to crack the Enigma code. At the beginning, the Government Code and Cipher School at Bletchley Park initially broke Enigma by hand. As they studied the intercepts, it became clear that the Germans kept repeating certain set phrases. It was soon possible to predict which message contained a particular phrase. Bletchley Park called these phrases "cribs."
"I remember "Nieder mit die Englander," down with the English. And of course "Heil, Hitler." "Heil, Hitler" was enormously valuable, I mean you should never inculcate in your military, anyway, the tendency to have exactly the same phrase opening every statement of a great victory."(Peter Hilton - Decoding Nazi Secrets Documentary)
In August 1940, they started using their own Bombe, designed by Alan Turing and Gordon Welchman. It was also a rotary electro-mechanical device but it worked on an entirely different principle. All information, retrieved by cryptanalysis had the codename “Ultra” and played a very important and sometimes decisive role during the entire war, mainly in the Battle of the Atlantic. All Ultra information was used very careful, to avoid suspicion in German forces. Special liaison officers, trained to deal with this valuable but delicate knowledge, were placed in Headquarters and other strategic places. Moreover, Ultra was never used, unless it could be confirmed by a second source - this was to avoid the German Command from noticing that their communication might be broken.
Apart from the Atom Bomb, there was no greater secret in World War II than the work of the codebreakers of Bletchley Park. Their breakthroughs gave the Allies a vital edge in the U-boat war, the tank battles against Rommel, and the D-Day invasion. But their impact was felt far beyond the battlefield. Eavesdropping and decryption won a new prominence in the minds of politicians as well as generals. The transatlantic alliance, that took its first hesitant steps at Bletchley Park, would mature and prove critical during the Cold War. And the roots of today's computer era trace back directly to the dazzling inventiveness of Turing, Flowers, and their wartime colleagues. In the end, though, Bletchley Park's greatest achievement lay not in broken ciphers but in the hundreds of thousands, perhaps millions, of lives it saved.
Enigma & the German Navy
The inability to read the Navy Enigma messages finally ended in May 1941 when Britain captured the German submarine U-110 with its encryption equipment intact. U-boat commander Fritz-Julius Lemp, fearing that the sub was sinking rapidly and that it was about to be rammed, ordered his crew to abandon ship. The radio room crew, believing they were in great peril of drowning and obeying the order to abandon, did not destroy the Enigma or codebooks before donning their life vests and jumping overboard.
With the German submarine crew treading water in the cold Atlantic, the British ship Bulldog sent a boarding party to the U-110. They found a treasure trove of secrets. The boarding party collected all books, charts, logs, and other important documents and equipment. Among the captured material were codebooks, instructions, and key lists for several different German Navy and submarine codes. It also included an Enigma machine with the daily settings in place and each of the eight rotors.
Representatives arriving from Bletchley were astonished at the find. Britain had at last acquired the missing rotors. With the rotors and the keys through June, Bletchley didn’t even need the Bombes in order to read the messages. But those two months would pass quickly, and the Bombes needed to be ready when the keys ran out. BP began wiring drums for the Bombes to match the wiring of the three new rotors.
Fortunately, Admiral Doenitz did not realize that the U-110’s Enigma rotors and other vital communications information were now in the hands of the Allies. Had he known, he certainly would have changed the system. The U-110 was boarded in sight of some of the survivors, so Britain went to great lengths to convince them that the submarine sank before it could be boarded. Word got back to Admiral Doenitz that the code was safe.
However, despite the assurances he received concerning the U-110, Admiral Doenitz suspected the Allies could read his fleet’s Enigma messages. When he asked the German High Command of this possibility, they assured him that the Enigma could not be broken. They proposed other reasons as to why his U-boats were less effective, including Allied direction finding capabilities, aerial reconnaissance, or even a German traitor. In truth, even when the Navy Enigma messages could not be read, British direction finding combined with traffic analysis did have substantial successes.
Certainly the Germans’ faith in the Enigma was not unfounded because of the astronomical mathematical possibilities. However, to encourage this unquestioned confidence, Britain went to great lengths to disguise how Enigma information had been obtained.
Alan Turing
Turing is considered one of the two or three best mathematicians of the twentieth century, and spent the entire war working in cryptanalysis. He has also been described as the "father" of the modern computer. While at Cambridge University Turing delved deep into the burgeoning world of quantum mechanics. It was there that he developed the proof which states that automatic computation cannot solve all mathematical problems. This concept, also known as the Turing Machine, is considered the basis for the modern theory of computation.
During WWII Turing and his colleagues used their mathematical skills to improve on a machine the Poles had first built that enabled the British to compare, in a relatively rapid fashion, the numerous possible keys with portions of messages they thought the Germans were sending. Curiously, Bletchley Park called it the "bombe," perhaps because of the ticking noise it made while operating. Turing's machine was vastly more powerful than the Poles' earlier device.
The Bombe was an array of electromechanical drums that simulated the rotors of the Enigma machines. The drums clicked round letter by letter, testing the thousands of possible Enigma settings - 20 every second - until the correct one had been found. These machines radically sped up the pace of decoding. By the end of the war there were 200 of the devices at six different locations, enabling Bletchley Park to decode 90,000 messages a month.
Colossus
Building on Turing's success, other members of the Research Section eventually redesigned Turing's machine in to the Colossus, the first electronic computer. Designed by the telephone engineer Thomas Flowers, the Colossus could read a coded message at high speed and then search for the settings of the Lorenz code wheels; it could accomplish this in minutes instead of a month.
The computer was as big as a room - 5 meters long, 3 meters deep and 2.5 meters high - and was made mainly from parts used for post office telephone and telegraph systems. It was a development from the mechanical Bombes. The timing of the D-day landings was based on intelligence produced by Colossus.
Colossus was not like a modern computer: to set the machine up for a new job, it was necessary to change some of the machine's wiring manually, by means of switches and plugs. The key idea of storing programs of instructions in memory, now almost as familiar to us as the wheel, was Turing's. Flowers said that, once Colossus was in operation (proving for the first time that large-scale digital electronic computing machinery was feasible), it was just a matter of Turing's waiting for the opportunity to put his idea into practice. In 1945, at the National Physical Laboratory, Turing drew up a groundbreaking design for an electronic stored-program computer, to be called the 'Automatic Computing Engine' (ACE).
A complete Mark 2 Colossus machine has recently been rebuilt and is on display at Bletchley Park.
- Image of one of the very few surviving documents from Bletchley Park’s massive code reaking operation. It is an example of the teleprinter code used by the German High Command, dubbed “Fish” by the British:
fishintercept.pdf
Enigma Press and Propaganda during WWII
Bletchley Park -
Enigma Stolen (Sept. 2000)
Enigma Cipher Machine Homepage: Jamie Brownell
References
