Grant Musick
SN: 8931827
CSEP 590
Final Project
Origin and Nature of the Allied Cryptographic Advantage During World War II
One of the more interesting stories of World War II was how the Allied powers (consisting primarily of the United States, Great Britain and the members of the British Commonwealth) were able to so successfully break large quantities of encrypted messages of the Axis powers (consisting primarily of Germany and Japan). This extra intelligence often allowed the Allies to decide when and where to pick their battles and thus gave them significant strategic and tactical advantages. As can be seen below, this Allied advantage came about as a combination of foresight, hard work, organization, cleverness, serendipity and industrial might.
Although there were several different encryption machines the Axis used during the war, the Enigma family of machines and their variants were most widely used. They were the primary means of encryption by the Germans and an important secondary means of encryption for the Japanese. Many of the strengths of the Allied powers’ cryptanalysis efforts can be seen by how they managed to crack these encryption devices. Thus most of the examples below will focus on the Enigma family of machines, with some examples of efforts against the Japanese Imperial Navy code JN-25 and the Japanese diplomatic codes.
The Allied advantage in the cryptographic war started off well before there were any “Allies.”The Germans (and many others) were using Enigma machines in the 1920s, primarily for encrypting commercial traffic.[1] The encryption on them was so difficult that the British and the French considered them unbreakable and effectively gave up trying to crack the codes.However, the Poles were able to “obtain” a copy of one of the machines in 1929 by intercepting some mislabeled German baggage. By 1932, Marian Rejewsky had a major break-through and deciphered Enigma encrypted traffic. Two other Polish mathematicians, Henryk Zygalski. and Jerzy Różycki, who were colleagues of Rejewsky, created additional attacks for Enigma encrypted traffic. By 1938, Rejewski made another significant break-through by creating a “cryptologic bomb,” an electromechanical computing device, to aid in cracking the messages.[2]
In the Pacific, the United States was already actively preparing for possible conflicts with Japan. Throughout the 1920s the U.S. acquired various versions of the Imperial Japanese Navy codebook.[3]During this time the U.S. sent its naval officers to Japan for two year stints to gain an increased familiarity with the language (something the Japanese were also doing in reverse by sending citizens to the U.S.). This turned out to be very important because to effectively break codes you have to know the likely plain-text and Japanese is an extremely nuanced language.
Back in Europe, war was closing in on the Poles. In 1939 they decided to share their knowledge on breaking the Enigma codes with the French and the British. This is the first example of another Allied advantage...the ability to cooperate with each other across nationalities and across governmental organizations.
Work on breaking the Enigma code was moved to PC Bruno near Pariswhere it continued until the Fall of France. Then it moved to England where the British took almost exclusive control of it at their code-breaking facility BletchleyPark where luminaries such as Alan Turing continued the work of breaking codes.
In what was probably the most significant advantage for the Allies, the British and later the United States tended to concentrate and coordinate their cryptographic talent in central facilities. The British chose to physically concentrate their efforts at BletchleyPark while the U.S. had several facilities that all worked together with reasonable cooperation.
"The [German] army, the navy, and the air force each had its own unit, though there was rather more justification for that. But this multiplicity spread the available manpower, which was scarce to begin with, very thin. And it diffused the codebreaking effort. Contrast this with the concentration of effort at Bletchley Park, Britain's sole codebreaking agency, and with that in America, where the army and navy codebreaking units worked in the closest co-operation. There was some co-operation in Germany, of course. But it did not overcome the lethal effects of dispersion, which stemmed ultimately from Hitler's assigning duplicate responsibilities to his underlings so that he could retain ultimate control. The charismatic nature of his leadership enabled him to do this in many areas of government. It facilitated his rule - but it devastated his war effort, including codebreaking. . . . The Allies put better men into cryptology than the Germans. BletchleyPark was an unbelievable galaxy of talent. All American recruits were given an IQ test; those who scored the highest were proposed for cryptologic work. This resulted in extraordinarily high brainpower in codebreaking units. The American army agency could have staffed a first-class university in all departments, one of its leaders said. No such recruiting seems to have taken place for German codebreaking."[4]
The Allies created places where many good, great and brilliant minds were able to pool their resources to come up with ways to break the Axis codes. Neither the Germans nor the Japanese took advantage of havinga few, concentrated cryptographic centers or of recruiting people specifically for the job.
Another huge advantage that the Allies had was a combination of automation and industrialization. The invention of the “cryptologic bomb” (or bombe as it will be referred to from here-on) was just the beginning of automated attacks on encoded messages. With the U.S. entry into the war, the industrial might of the nation was also put into breaking coded messages and the U.S. churned out much larger versions of the bombe that could test thousands of keys rapidly.[5] The British invented the “Colossus” series of computers which were used to completely break the German stream cipher (code-named TUNNY).[6]
In the Pacific, the Allies were able to break both the Japanese diplomatic codes and the main Japanese naval code JN-25. Information obtained from the Japanese diplomatic intercepts was code-named MAGIC. Many of these codes were sent through a machine dubbed PURPLE, which used stepper switches (like a telephone exchange) instead of rotors. As in the case with the Enigma family of machines, it was broken through a combination of mathematical insights and electro-mechanical automation.[7] The Japanese naval code JN-25 was a much harder nut to crack because of its use of “false addition” and random numbers. Code breaking on it doesn’t appear to have been automated like that of the Enigma family, but through increased intercepts and manpower, it was sufficiently broken by May of 1942 to provide hints of the upcoming move by the Japanese again on Midway.[8]
There were several other less technical, but no less important, factors in the Allied advantage. One of the most important was an Allied effort to target Germanships for capture. This allowed the Allies to get their hands on no less than fifteenEnigma devices (seven from U-boats and eight from surface ships) during the war.[9] Just like the original lucky break of the Poles, this allowed the Allies to keep up with German cryptographic advances throughout the war.
Another advantage was strategic initiative. The Allies were able to make several attacks and raids just to prompt the Germans to send radio traffic. They would do this because the Germans would have known procedures for dealing with attacks; afterwardthe Germans would flood the air with radio chatter and the Allies would listen in. Since the allies already had a good guess as to what the Germans were saying, they were able to reverse engineer the encryption codes. This process was referred to as “gardening” by the British.[10]
Lastly, the Allies were able to count on good old-fashioned incompetence to help them out. There were many cases of German signal operators sending out encrypted test signals that just used the same repeated physical key, e.g. “t,”over and over again. They would also use the same cryptographic keys over and over, such as using their initials or their names of their girlfriends. This gave the Allies a good shot at guessing the rotor settings for the day and decrypting all the other traffic for a short period of time.[11]
So were the Axis members just cryptographically incompetent? The evidence presented here makes them look like idiots, but they were not. Part of the problem for this paper is a lack of good source material detailing the Axis efforts. However, their own cryptoanalytic departments apparently had many successes, such as repeatedly cracking the British Naval codes.
The Japanese were adept at cracking encrypted tactical communications (which were more lightly encrypted).They were so good at it, the U.S. rolled out one of its secret (no pun intended) weapons of the war…the Code Talkers. These were Navajo Indians who were assigned to Marine units in the Pacific. They would relay tactical reports in code in Navajo. Since the Japanese didn’t understand that the base language being used wasn’t English, and Navajo was an obscure, unwritten language, they were never known to have broken a message encrypted by this technique.[12]
In conclusion, the Allied advantage in cryptography appears to have been a combination of several factors that were mentioned above.However, the primary advantage can be summed up as the Allies considered cryptography and cryptanalysis to be very important to their war effort and devoted the appropriate resources to them.
“After the war, American TICOM project teams found and detained a considerable number of German cryptographic personnel. Among the things the Americans learned was that German cryptographers, at least, understood very well that Enigma messages might be read; they knew Enigma was not unbreakable. They just found it impossible to imagine anyone going to the immense effort required. When Abwehr personnel who had worked on Fish cryptography and Russian traffic were interned at Rosenheim around May 21, 1945, they were not at all surprised that Enigma had been broken, only that someone had mustered all the resources in time to actually do it. Admiral Dönitz had been advised that that was the least likely of all security problems.”[13]
General References:
[1] Answers.com -
[2] Answers.com -
[3]Naval War College Review, Autumn 1995, Vol. XLVIII, No. 4 vis-à-vis
[4] Text quoted from David Kahn at the website Originally taken from "Codebreaking in World Wars I and II: The Major Successes and Failures, Their Causes and Their Effects," in The Historical Journal, Volume 23, Issue 3, Sep., 1980, pp. 617-639.
[5] Answers.com -
[6] Answers.com -
[7] Answers.com -
[8] Wikipedia -
[9] Answers.com -
[10] Answers.com -
[11] Answers.com -
[12] Wikipedia -
[13] Answers.com -