German Code Breaking of WWII
By Arvo L. Vercamer

Before proceeding into the topic of German code breaking efforts during the Second World War, we should first cover some of the basic elements of codes and secret means of communications. Explanations here may help to place some of the later cited examples into a more optimal perspective.

In the below examples, a code is essentially a form of substitution. It can be comprised of any combination of letters, numbers, phrases, symbols, etc., which represent a plaintext message. A code does not have to have an association with its plaintext counterpart; in fact, it really should not.

Plaintext: - - - - - - - Code:
Jason - - - - - - - - - - Feldgrau (Fieldgrey in German)
Berlin - - - - - - - - - - Jelly Doughnut
Estonia - - - - - - - - - jäääär (meaning “the edge of the ice” in Estonian)
Latvia - - - - - - - - - - Sveiks (Hello in Latvian)
Mt. Rainier - -- - - - - +<^>+ (use of symbols)
Germany- - - - - - - - 1871 (use of numerics)

Naturally, one can get very elaborate with such a setup.


Ciphers (U.S.)/Cyphers (UK) In the very simple 8x3 matrix example above, the plaintext is “Jason is the webmaster ruler”. To securely transmit this message, the plaintext will need to be “enciphered”. First, one will need a “key” to help us encipher and decipher the plaintext, in the above case “FELDGRAU”. The numbers below the key represent the numeric equivalent of the letters of the English alphabet; F=06; E=05; L=12; etc, but in more complex systems, the variables are more elaborate. In the end, the receiver and the transmitter have agreed in advance to the same “key” to understand the plaintext.

The next step is to read all of the letters under the number 01 (the letter A) - SAE. In alphabetical order, our cipher-text thus reads - SAE OER AEE JHT NBU SWR IML TSR. The recipient takes the “key” (FELDGRAU) and constructs an 8x3 matrix. The recipient knows that the first transmitted cipher group “SAE” is placed under the “A” column of the key (the “A” in FELDGRAU)), the “OER” letter group under the next alphabetically ordered letter in the English alphabet - in our case “D” (since the key FELDGRAU does not have a “B” or a “C”). The matrix is then completed. The recipient knows that the message has been created the way one reads; from left to right, so:


JASONISTHEWEBMASTERRULER - the recipient also knows where to place the appropriate spaces after every word.

As can be imagined, there are many possible ways in which to encipher plaintext messages. The above example is but one of these. Of note is that one can encipher codes; logically, this makes the crypto-analysts work that much more difficult.

The Soviet Union developed the “one-time pad” system back in the early 1920’s. This communications medium proved very difficult to compromise; though they were compromised, to a lesser extent by the Germans, to a large degree of success by the Finnish Intelligence Service. One-time pads essentially work like this:


The plain-text is “FELD”. Each letter receives a numeric equivalent (in this case, its sequence in the English alphabet; A=01; B=2; C=3; D=04; E=05; etc.). Now the message transmitter would consult a key. The key is comprised or randomly selected groups of numbers (they can be in groups of two, three, four or most commonly, five).

39574 40126 95633 01284
29001 75640 39393 10475
83345 80001 28934 93452

The numeric equivalent of the plaintext message would now be added to the randomly generated groups of numbers.

39574 40126 95633 01284 (random number group taken from the one-time pad)
00006 00005 00012 00004 (add the letter equivalent)
39580 40131 95645 01288 (sum - the transmitted number group)

The message receiver would then record the number he/she heard via wireless onto a piece of paper. Then, one would consult one’s one-time pad which contained the original random number groups; subtract the difference and then compare the resulting number to a table which would indicate which number represented which letter of the alphabet. Our short message was the word “FELD”. Then both the transmitter and the receiver would securely dispose of the used one-time numbers and go on to the next sheet of paper containing more “random” number groups. Check digits would ensure that both the transmitter and the receiver started and ended on the same “random” number group.

Some of the earliest known forms of “secret” writings can be traced back to the ancient Egyptian civilization when Egyptian priests and scribes “modified” the standard hieroglyphs a bit (they made them more artistic or “fancy” looking) so that sacred/special texts and writings would be harder for the average laymen to comprehend.

The ancient Chinese civilizations also experimented with altering their ideographs to represent secret texts. Regretfully, simply changing a stroke or line within an ideograph or in several ideographs really did not conceal anything. Government, merchant and military couriers essentially memorized their special information as they conducted affairs. However, by 1000 AD, the Chinese were well on their way to inventing ingenious ways to transmit “secret” communications. One means was to write plaintext onto silk paper, then rolling up the paper to resemble a ball and then covering that “ball” with a layer of wax.

At about the same time, 1000 AD, Indians were transmitting covert communications by using a myriad of techniques, such as phonetic substitutions (switching vowels for consonants and consonants for vowels), reversed letters, writing texts in unnatural angles, etc. Of interest is that knowing how to conceal plaintext was one of the 60+ skills an Indian woman had to master in the Kama-Sutra.

One of the most famous uses of covert communications can be found in the Bible; Daniel 5:5-28. Daniel’s crypto analysis of the plaintext phrase “Mene Mene Tekel Upharsin” - was interpreted by him as meaning the end of the Babylonian Empire. Shortly thereafter, Cyrus, a Persian military commander did indeed conquer and defeat the mighty Babylonian Empire. I humbly stand corrected should the above item be in variance with the data available to other, more subject knowledgeable readers.

The Greeks used encoded and enciphered languages quite extensively. For example, Leonidas’s wife Gorgo (of Spartan fame and, Leonidas being also the name of one of the best Belgian confectionaries around today IMHO) gained fame as being one of the first female crypto-analysis in the world. The Greeks in fact also invented a very intricate signaling system for maritime navigation based on positioning lamps and torches in high sites.

Gaius Julius Caesar, while campaigning against Asterix and Obelix (smile), corresponded via coded letters with his friend Marcus Tullius Cicero in Rome. His system basically shifted every plaintext letter by three places (a=d; b=e; c=f; etc.). To the layperson, the jumbled letters meant nothing. But to Ceasar and Cicero, the messages were of great importance. With the demise of the Roman Empire, like with many other fields, the art and science of cryptography went into a serious state of decline.

Things got back on track in the renaissance era. Italy’s Leon Battista Alberti (*1404-+1472) in the 1400’s invented the Alberti’s disc (a copper disc containing two wheels each containing the Latin alphabet - one would align the wheels per a pre-arranged setting and voila - read the enciphered message!). In1462, Johannes Trithemius of Germany developed the code list, the “tabula recta”. Covert communications were used very effectively by France’s “Sun King” (he issued color coded “passports” to separate certain categories of domestic and foreign visitors, etc.). The U.S. Civil War also saw many uses of secret writings, codes, etc. In one respect, they gave General Grant a decisive edge in defeating the forces of the Confederate States of America.

One can go on and on here, but suffice it to say that already in the early days of human civilization, the concept of converting plaintext into encoded or enciphered materials was alive and well.

No study of codes and ciphers would be complete without a quick look at the famous German “Zimmerman” telegram. In short, Germany proposed a military alliance with Mexico; if she joined, Mexico could “regain” its lost territories from the United States. The Kaiser and the German High Command agreed and Germany sent a two-part telegram to its Embassy in Mexico City. Germany used a code system it numbered as “0075”. This system contained upwards of 10.000 phrases and individual words. One codebook was required to transmit the message, another book to decode a message. Secure enough, the Germans thought.

But Britain had an ace up its sleeve - Room 40 OB (Old Block) and Captain William Hall. In short, Captain Hall and his staff worked hard and decoded the Zimmerman telegram and the rest is now history.

But the Germans were not done yet. Knowing that system “0075” was now compromised, the Germans developed a second encipherement system - ADFGX. This system, developed by Oberst Fritz Nebel, allowed for these five letters (A-D-F-G-X) to be substituted for any plaintext. His initial enciphering matrix looked as follows:

# A D F G C
A l r m e i
D k f v w t
F c s a u z
G h x g j n
X b p o q d

As can be seen from the above, each plaintext letter would thus receive two enciphered letters; a=FF, b=XA, c=FA, etc. The letter “y” was omitted.

Now, a “super-encipherement” was added to the original enciphered text. Then, the final message was written with groups of five letters; FDFAX FDFAD XAAFX, etc.

Initially, both the American and French crypto analysts were stumped by the German code. However, by matching up German rear area activities, wireless transmissions, etc. The French believed that a German attack was imminent between the towns of Compiegne and Montdidier; both towns are located approximately 50 miles north of Paris. 09 June 1918, Kaiserschlacht began at that very location and thanks to Allied preparations, the Americans, British and French had essentially plugged an otherwise open hole. On 11 November 1918, Germany surrendered.

World War One also saw a catastrophic failure in the field of cryptography - the Imperial Russian defeat at Tannenberg. Ignoring regulations and often transmitting vital troop movements and strategic/tactical information in plaintext, the Russians essentially told the Germans what they were going to do in East Prussia and how they were going to do it. The result was a resounding German victory in the first few months of the war. In addition, the Germans also gained valuable insights into the makeup of Imperial Russian secure communications efforts. Interestingly, German radio traffic security measures were also less than optimal at the time of Tannenberg.

Despite the fact that the Russians lost at Tannenberg, it was also the Russians who gave the British one of the best prizes of the war in 1914. They turned over the codebook they had found on the German cruiser “Magdeburg” to the Royal Navy. This gave the British great insights into German secure communications efforts for most of the First World War.

Did the Germans (or other Axis nations) successfully compromise the secure communications of other nations during WWII? The answer here is yes. The Finnish Intelligence Service was indeed very successful in compromising not only Soviet secure communications, they were also able to compromise the classified transmissions of other, non-Axis nations as well. Of interesting note is that members of the Estonian Military Intelligence Service worked with the Finnish Intelligence Service before and during the Second World War and they also worked with their Japanese counterparts; primarily against the Soviets.

The Japanese had more success compromising Soviet codes and ciphers than they had in compromising American or British ones. The Japanese never were able to break the Navajo codes (the Navajo code-based system used words of the native Navajo language to represent war items; owl=recon aircraft, etc.), nor for that matter any Chippewa, Comanche, Hopi or Menominee codes used by the U.S. Armed Forces from 1941-1945 (American Indian “code talkers” were also used in the First World War and their efforts too were never compromised by the Germans). During the interwar period (but only up to 1933), Lithuania and Germany worked closely together to compromise Polish codes and ciphers; a number of successes were registered. The Americans were able to compromise the Japanese Orange, Red and Purple systems.

As far as Germany goes, they did have many successes in reading the secure traffic of other nations. Regretfully, Germany somewhat missed the proverbial boat in terms of securing its own communications. Hitler’s Germany was convinced that its Enigma technology could not be compromised. It was; by the Polish Intelligence Service even before the Second World War began! All of the major branches used the Enigma machine; each branch having its own variant.

However, while the British enjoyed greater successes in compromising Luftwaffe and Wehrmacht secure wireless transmissions, the British had a harder time with those of the Kriegsmarine (KM). This is because the KM was the most security conscious of the three services. The German navy used landlines whenever possible to facilitate communications (and the landlines used an entirely separate means of encryption and encipherment than used by KM wireless transmission) and the KM also modified its Enigma machines extensively, making it harder for the British and Poles to obtain the key. That said, the following list represents the major KM ciphers used during the war:

  • Aegir - used by surface warships completing missions outside of German home waters.
  • Bertok - used for secure communications between OKM and the German Naval Attache in Tokyo, Japan.
  • Freya - used by OKM to communicate with its naval shore commands when the use of landlines was not possible.
  • Hydra - initially, this system was the main cipher used by all operational U-Boats; by 1941, it also was the main cipher used by German naval ships when they were operationally active in occupied territories.
  • Medusa - the primary cipher used by OKW to command/control all U-Boats in the Mediterranean Sea.
  • Neptun - primary cipher used by KM capital ships only (in use by the Bismarck during Rheinübung when she broke radio silence and was thus D/F’ed and used during the channel dash).
  • Potsdam - primary KM cipher used in the Baltic Sea for naval operations against the Soviet Union.
  • Sleipner - the primary cipher used by the KM while engaged in torpedo-firing excercises in the Baltic Sea.
  • SoChi 100 - Special cipher 100 - used by the KM raiders (Atlantis, etc.).
  • Süd - primary cipher used by all KM surface ships operating in the Black Sea and in the Mediterranean Sea.
  • Tetis - the primary cipher used by OKW to communicate with all U-Boats training in the Baltic Sea.
  • Tibet - a very early, pre-war cipher issued to German merchantmen and naval tankers who found themselves outside of German waters after 01 September 1939.
  • Triton - primary cipher used by the B.d.U. to command/control all active U-Boats in the Atlantic.

    All German naval ciphers were changed on a monthly basis, except for the “Aegir” and “SoChi 100” systems (they were changed once a year).

    Shortly after 1918, Germany established a new crypto-analysis capability. One of the first tasks of the Reichswehr’s new code unit was to break the British Government’s telegraph code. This code advised the British Admiralty what every non-British warship was doing, where it was located, etc. in the world.

    By 1932, the Germans were reading British, French and even Italian naval communications (naturally, the Germans never advised the Italian navy that their secure transmissions had been compromised). By 1934, Germany was working loosely with the Finnish Intelligence Service to compromise Soviet secure communications. Generalissimo Franco allowed Germany to establish a number of wireless surveillance posts in Spain (these were primarily directed against the Royal Navy operating in the Atlantic and in the Med).

    Prior to the start of the Second World War, the Germans traded information with the Italy’s Servizio Informazione Militare re French secure naval communications efforts. The Ilaians also read British and Jugoslavian naval traffic with ease. On the eastern front, Germany, Hungary and Romania often traded information they had collected against Soviet secure communications efforts. But then the Soviets were also reading German traffic with minimal problems. Interestingly, Admiral Golokov, the Soviet CinC in the Arctic, wrote in his 1960 memoirs that he knew that Admiral Fraser was planning to send the Scharnhorst to sea in December of 1943. The Americans and the British did not advise the Soviets of this - thus, how did Admiral Golokov know what Germany planned on doing if it did not read its secure traffic?

    Like in many other fields (R&D, mfg, security, etc.), the Germans also had many duplicate efforts in place in the field of cryptography. There were no less than 9 separate entities tackling the myriad of problems. Each component guarded its secrets jealously and there were few instances where two or more components pooled their talents to get the job done more efficiently:

  • The Deutsche Reichspost (DRP censorship efforts included)
  • The Forschungstelle (Kurt E. Vetterlein’s telephone intercept unit - DRP)
  • The Forschungsamt (under Reichsmarschall Göring)
  • Auslandsamt, Abteilung Z
  • OKW/Chiffrierungsabteilung (OKW/Chi) (focusing on army/military issues)
  • OKH/12. FHO
  • OKH/3. FHW
  • OKW/Abwehr
  • OKL (focusing on aviation issues)
  • OKM (focusing on maritime issues)
  • The Reichssicherheithauptsamt (RSHA)

    Prior to America’s entry into the war in 1941, Germany’s Naval B-Dienst (Beobachtungsdienst - Surveillance Service) was reading a number of American encoded communications systems. This capability essentially ceased after April of 1942 when the U.S. adopted a new system; but before the U.S. switched systems, reading U.S. naval traffic helped the second Paukenschlag to be a huge success.

    Of note is that the Deutsche Reichspost was able to break the scrambled voice transmission of the American-British transatlantic telephone system. Specifically, German technical experts built a de-scrambling device, set up shop in the town of Noordwijk in the Netherlands and by 1940/1941, were (routinely) listening to classified telephone conversations between U.S. President Roosevelt and PM Churchill. By 1944, the Germans had to relocate their telephone intercept facility from the Netherlands to Bavaria - and as a result of the much poorer intercept potentials, they were no longer able to compromise all Allied telephone conversations. As a whole, Germany had not gained immensely valuable insights into the Allied camp. Most of the intercepted telephone conversations did not yield the Germans optimally suitable intelligence primarily because the Allies knew their system was not secure and most individuals did practice good security measures when talking.

    B-Dienst (a part of OKM) was very successful in compromising the Royal Navy’s secure communications for most of the war; specifically, B-Dienst compromised the 5-digit Royal Navy code. The British 4-digit naval code was harder to break, but in time, it too was compromised by the German Navy’s B-Dienst. By 1941, B-Dienst applied German city names to British naval codes as an easy way to distinguish one British naval system from the next. “Köln” was one cover name; “München-Blau” and “München-Braun” were two others. A four-digit American-British naval communications system was codenamed “Frankfurt”. Of note is that Germany was never able to break secure British diplomatic communications.

    In addition to the above, OKM’s B-Dienst was able to compromise five French naval communications systems, four Soviet systems (though the Germans never were able to break the Soviet diplomatic code) and three Danish systems by 1939.

    But in the end, very little really mattered. The Germans lost the “cipher” and “code” war. American and British efforts to compromise German secure communications were far better than German efforts to compromise Allied efforts. This is not to say that the Allies were perfect. The British misinterpreted much during the German invasion of Norway. Both the Americans and the British failed to correctly interpret the German position at Arnhem and they failed to recognize the German attack of the Battle of the Bulge in 1944. And the Germans too had their share of successes. But the Allies had more successes than the Germans did. Among the major reasons for failure (in the field of cryptography or code-breaking), one can cite the fact that the Germans were overly arrogant in their beliefs, they were pre-occupied with petty political infighting and they were subservient to a bizarre political structure, a political system which wanted to see only what it wanted to see and which truly neglected to invest in a good intelligence service when it should have - in 1933.