The Combined Cipher machine - 1942-1962

Cipher machines were extensively used by both the Axis and the Allies during WWII.

The Germans had the Enigma, the Lorenz SZ 40/42 and the Siemens T-52.

The Japanese had the Type B Cipher Machine (Angooki Taipu B).

The Americans had the Converter M-134-C (SIGABA) and the Hagelin M-209.

The British had the Typex.

Another machine that became increasingly important for the Allies, in the period 1943-45, was the Combined Cipher Machine - CCM. Unfortunately, this machine has not received a lot of attention from historians because there is limited information available on its internal operation and use in the field.

Here I have attempted to present information on the CCM from various sources that are not easy to find (the timelines section has detailed sources): 

SRH-368 ‘Evaluation of the Role of Decryption Intelligence in the Operational Phase of the Battle of the Atlantic’

The very interesting Special Research History SRH-368 ‘Evaluation of the Role of Decryption Intelligence in the Operational Phase of the Battle of the Atlantic, U.S. Navy OEG Report #68’ is available from the NSA website.

I’ve also uploaded the pdf to my Google drive and Scribd accounts.

Google drive link.

Scribd link.

Enjoy!

Naval Enigma compromise and the spy in the United States Department of the Navy

Signals intelligence and codebreaking played an important role in WWII. British and American codebreakers solved many important Axis crypto systems, such as the German Enigma machine and the Japanese Navy’s code JN25. 

The solution of the German military’s plugboard Enigma was mostly carried out at Bletchley Park with Hut 6 attacking Army and Airforce ‘keys’, while Hut 8 worked on the naval traffic. During the Battle of the Atlantic the German U-boats relied mostly on the Enigma for their communications with U-boat Command, so the solution of these messages was a top priority for the Allied codebreakers.

Unfortunately the fact that the Navy used stricter procedures than the Army and Airforce plus their introduction of a separate 4-rotor Enigma machine in 1942 meant that in the period March 1941- September ‘43 the successes of Bletchley Park were spasmodic and suffered from time lag. Things changed in September since the new 4-rotor ‘Bombes’ built by the Americans were introduced and they could solve the Enigma settings reliably and in a timely manner (at least until the introduction of individual Enigma keys for U-boats in late 1944).

According to several books and articles the Germans never suspected that their codes were being read and they thought that the Enigma was unbreakable. The reality was a slightly more complex than that as can be seen from the numerous security measures they implemented during the war. Would they have taken so many precautions if they considered Enigma unbreakable?

Since the Enigma was used in huge numbers it was accepted that during the war both cipher machines and valid keylists had fallen into Allied hands. Thus current traffic could be compromised but only until new settings were introduced.

Another question is whether the Germans considered the Enigma to be vulnerable to cryptanalysis. After all it wasn’t every day that Enigma machines and keylists would fall into enemy hands. Here the story diverges since the different codebreaking departments in the Army (Inspectorate 7/VI), Navy (B-Dienst), Airforce (Chi Stelle) and Armed Forces High Command (OKW/Chi) had different opinions on the matter. Unfortunately we don’t know the full story of their security investigations as the relevant files have not been studied in detail but it is clear that they constantly researched ways of solving the Enigma.

In this area the Army codebreakers proved more suspicious than their counterparts in other departments and they always worried about the possibility of solution of the machine by the enemy. During the war they not only studied the Enigma but also interrogated Polish personnel regarding their solution of the prewar Enigma, known to the Germans as case ‘Wicher’.

The analysts of the naval cipher security department on the other hand seems to have shown a lack of imagination when it came to researching the Enigma. For some reason they constantly downplayed the possibility of cryptanalytic solution and attributed enemy successes to captured cipher material.

This can be seen from one of their reports found in NARA-RG 457- Entry 9032- box 1279 – NR 3775 ‘German Navy U-boat logs’. In the summer of 1943 the military intelligence service Abwehr learned from a Swiss-American working in the US Department of the Navy that the operational orders to U-boats were decoded by the Allies and all messages read.

According to google translate:

At 10.8. received the following message via KO Switzerland :

‘‘For several months, deciphering German naval codes with regard to operating Uboat commands succeeded. All commands are read.

Additional: Source Swiss-American secretary in high position in the U.S. Navy Department.‘’

It is not clear if this person was an Abwehr agent or someone who revealed this information to Swiss diplomatic or intelligence authorities and they in turn shared this information with the Germans.

The response of the security department was that the continuous reading of their communications by the Allies was out of the question. There was however the possibility of losing cipher material in one of the sunken U-boats. For that reason they instituted a change of the Enigma settings using the keyword ‘Andromeda’.

The emergency key-‘Stichwort’, worked on the following system according to the study ‘Cryptographic History of Work on the German Naval Enigma’, p6:

"Stichwort".

19. The "Stichwort" was a device used when the enemy suspected that the keys had been captured, or wished to protect himself from the danger of this happening. An example will make its nature and method of use clear.

20. All holders of the machine (at the time of this example) held a sealed envelope labelled PERSEUS. An order was sent out "STICHWORTHEFEHL PERSEUS". The holders opened their envelopes and found the word DANZIG inside (the "Kennwort"). They then "applied" DANZIG to the key as follows (1) D = 4 was added to the number of each wheel in the W.O. (2) A, N, Z respectively were added to the three letters of the Ringstellung. (3) I = 9 was added to each letter in the Stecker. This change was applied to all keys until further notice.

21. Suppose for instance the key for the day had been W.O. 275, Rings. BYL, Stecker A/F, B/J, D/X.... . The modified key would then be W.O. 631, Ring. CML, Stecker J/O, K/S, M/G .... .

22. This is a security measure with some "nuisance value" but is clearly not equivalent to a new key. Given that a key has been captured (the assumption on which the Stichwort is based) then - once we have discovered what is happening - there are 8 W.O.'s and 26 sets of Stecker to try; this might certainly be tiresome but does not compare with the 336 W.O.'s and 140 million million stecker on a completely unknown key.

The naval codebreakers would change their minds regarding the theoretical solution of their 4-rotor Enigma in late 1944 when one of their analysts named Hans-Joachim Frowein showed that it could be solved on a ‘crib’ of 25 letters (suspected plaintext in the ciphertext).

 

This report is TICOM I-38 and is available from Ticom Archive.

US Military Strip Ciphers

The US Armed forces made extensive use of the strip ciphers M-94 and M-138 in the 1930’s and during WWII. Although authors focus on the SIGABA machine initially only a handful of these were available.  In late 1941 there were around 10.000 M-94 devices, 1.500 M-138 strips and 120 SIGABA. It would take years to build large numbers of cipher machines and during that time it was the strip ciphers that had to hold the line.

Overall about 10.000 M-94 cylinders and 17.000 M-138 strip ciphers were built from the 1920’s till 1944.

The strip ciphers have gotten little publicity but their use was vital for the US forces in WWII, especially in the period 1941-43. The M-94 cylinder was used at division level and was eventually replaced by the M-209 cipher machine. The M-138 (and M-138-A) was used for high level messages by military units and diplomatic attaches. During the war it was replaced by SIGABA but It continued to be available as an emergency system till the 1960’s.

The British Interdepartmental Cypher

One of the high level British cryptosystems exploited by the Germans in WWII was the Interdepartmental Cypher. This was a 4-figure codebook enciphered with 5-figure subtractor tables.

The ID Cypher was used by the Foreign Office, Colonial, Dominions and India offices and the Services. Also used by the Admiralty for Naval Attaches, Consular Officers and Reporting Officers.

The Germans captured the codebook from the British consulate in Bergen in May 1940 and subsequently ‘broke’ the encipherment. Although their success was mainly based on cryptanalysis, they also received some enciphering tables from the Japanese in 1941.

All the German agencies (OKW/Chi, Forschungsamt, Pers Z plus the cryptanalytic agencies of the German Army, Navy and Airforce) worked on the ID Cypher and they exchanged results. During the period 1940-43 they were able to gain valuable diplomatic and military intelligence by reading the messages.

The Navy’s central cryptanalytic department OKM/SKL IV/III (Oberkommando der Marine/Seekriegsleitung IV/III) was able to decode the British Admiralty’s weekly intelligence summaries sent to naval attaches. In addition messages from the Freetown Area were decoded and provided intelligence on the movement of heavy ships and convoys. Traffic between the Admiralty and Consular Officers and Reporting Officers gave information on convoys and independently routed ships in the Atlantic. From ADM 1/27186 ‘Review of security of naval codes and cyphers 1939-1945’, p75-76

The Luftwaffe’s Chi Stelle read the communications of air attaches in the Near East, Portugal, Sweden and Switzerland. Maximum daily traffic was about 100 messages according to Ferdinand Voegele, the Luftwaffe’s chief cryptanalyst in the West. From TICOM IF-175 Seabourne Report, Vol. XIII. ‘Cryptanalysis within the Luftwaffe SIS’ Part 1, p21

Diplomatic messages were solved by OKW/Chi, the Forschungsamt and Pers Z. Interesting information was received regarding negotiations between Britain and Turkey.

The German efforts were assisted by poor British cipher practices. A security investigation in 1942 showed that the tables were overloaded, leading to heavy ‘depths’ and the indicators were not selected correctly.

The German success finally ended on 15 June 1943 when the codebook was changed.

Sources: ‘British intelligence in the Second World War’ vol2, TICOM reports I-12, I-22, I-172, I-119, HW 40/75 ‘Enemy exploitation of Foreign Office codes and cyphers: miscellaneous reports and correspondence’, HW 40/85 ‘Exploitation of British Inter-Departmental cipher’, ADM 1/27186 ‘Review of security of naval codes and cyphers 1939-1945’, ‘European Axis Signal Intelligence in World War II’ vol5, TICOM IF-175 Seabourne Report, Vol. XIII. ‘Cryptanalysis within the Luftwaffe SIS’

WWII Myths - U-boat tankers and ULTRA intelligence

Several books and articles mention that in the summer of 1943 the Allies were able to sink the majority of the German U-boat tankers thanks to decrypted Enigma messages. I have to admit I thought it was a historical fact. However it seems it is not true.

From ‘Hitler's U-Boat War: The Hunted, 1942-1945’ by Clay Blair, p356

Many historians of the Battle of the Atlantic write that the Allies, acting on naval Enigma decrypts, wiped out the U-boat tanker force in the summer of 1943, thereby crippling the operations of the Type VIIs. This is a myth. The Allies did indeed virtually wipe out the U-tanker force that summer, sinking nine of twelve boats at the front (including XB minelayers). However, according to a recently declassified top-secret postwar American study, only two of the nine U-tankers were sunk with the help of Enigma decrypts. Most boats were sunk or forced to abort by Commonwealth and American aircraft engaged in the intense Bay of Biscay anti- U-boat campaign (Derange/Musketry/Seaslug) and by American "jeep" carriers, mostly as a result of ill-advised personal orders from Karl Donitz for all U-boats to remain surfaced and fight back if detected and attacked by aircraft.

Blair was referring to Special Research History SRH-368 ‘Evaluation of the Role of Decryption Intelligence in the Operational Phase of the Battle of the Atlantic, U.S. Navy OEG Report #68, 1952’.

These are the relevant pages from that study:

Italian codebreakers of WWII

Fascist Italy was one of the main Axis powers. At the start of WWII Mussolini remained neutral but he joined the war in 1940 after it was obvious that France would be defeated. From then on Italian troops fought in the Balkans, against the Soviet Union and in North Africa.

Mussolini’s adventurism led to military reverses as the Italian economy was not mobilized for war and the military did not have modern equipment and training. This forced the Germans to come to their aid in the Balkans and in North Africa. However that does not mean that the Italian military didn’t fight bravely. In the Mediterranean it was the Italian navy that successfully transported troops and supplies to the Axis forces led by Rommel. Italian troops fought bravely in North Africa even though they were deficient in modern weapons and lacked mobility. The Italians may have lacked modern weapons however they did have a small but effective cryptologic capability.

The Italian Army and Navy had separate codebreaking agencies that managed to exploit important foreign crypto-systems. The Army's codebreakers could read the codes of several foreign countries, including the communications of US military attaches and especially those of a mr Fellers in Cairo. The Navy's codebreakers were very successful with Royal Navy codes and cyphers. The Italian codebreakers were assisted in their efforts by the good work of a special undercover squad that entered foreign embassies and copied the codes.

Army agency

The Italian army’s intelligence agency SIM (Servizio Informazioni Militari) had a cryptanalytic department that attacked foreign crypto-systems. This section was headed by General Vittorio Gamba and was located in Rome. Personnel strength was roughly 50 people (half cryptanalysts-half linguists and clerks).

The cryptanalytic department was divided into three sub-sections:

1). Diplomatic

2). Military and Research

3). Commercial

Personnel were moved from section to section based on the current priorities. The diplomatic section was subdivided into nine groups. The military and research section had 5 cryptanalysts. The research section was responsible for the initial ‘break’ into hard systems. Results were sent to field units. The commercial section’s task was to check Italian commercial codes for irregularities.

On average 8.000 messages were intercepted each month, 6.000 were studied and out of these 3.500 translated. The codes of several countries were read including France, Turkey, Rumania, USA, Britain, Yugoslavia and the Vatican. According to post-war reports there was a serious shortage of foreign speaking personnel and a lack of funds. There was also lack of IBM equipment for statistical work. The Italians used a small number of IBM punch card machines for cryptanalysis. Initially IBM machines were used only at the offices of the Watson Corporation in Rome. However it was only in the last stages of the war that these machines were used regularly.

Intercept section

The intercept section of SIM was the one that provided messages for cryptanalysis. It had 4 stationary intercept stations in Italy and 7 mobile units in Italy, the colonies and the occupied territories.

There was poor liaison between the intercept section and the cryptanalytic department and all requests had to go through SIM headquarters.

The Sezione P unit

The Italians were often able to read foreign codes without the use of cryptanalysis. Their secret? They had a very efficient undercover team that entered foreign embassies and copied codes and ciphers.

This was the Extraction Section (Sezione Prelevamento), headed by colonel Manfredi Talamo of the Carabinieri (military police). Its operatives were experts in entering guarded areas and opening locks. It was this unit that copied the Military Intelligence code No11 used by the US attaché in Cairo colonel Bonner Fellers.

Cooperation with foreign countries

Cooperation with Germany

General Gamba arrived unannounced at OKW/Chi in 1938 and requested cooperation in the cryptanalytic field. The Germans initially agreed to share results on French diplomatic and military systems. This collaboration was expanded and provided the Germans with important cryptologic material like the US Military Intelligence code, however relations between OKW/Chi and SIM were not as close as with the Finns and the Hungarians. According to Fenner, head of the cryptanalysis department of OKW/Chi, the Italians took too long to respond to requests or did not send the agreed upon material. An even greater problem was their resistance regarding the change of their weak cipher systems. As the war went on relations became strained since the Germans came to distrust the Italians.

Cooperation with the German army‘s signal intelligence agency - OKH/In 7/VI seems to have been poor as the Germans had little respect for Italian cipher security.

Cooperation with Hungary

According to ‘European Axis Signal Intelligence in World War II’ vol8, there was cooperation between the Hungarian cryptologic service and the Italians.

In page 21 it says:

Liaison with the Italians on cryptanalytic matters appears to have been very good. The Hungarians maintained liaison officers in Rome and made the results of their work available to the Italians.

Cooperation with Finland

Some intercepted traffic was sent to the Finnish cryptologic service.

Notable successes

Fellers code

In late 1941 the Sezione P unit managed to infiltrate the US embassy in Rome and copied crypto material. One of the systems copied was the Military Intelligence Code No11 used by military attaches. This allowed the Italians to decode the messages of US attaches from embassies around the world.

The most important transmissions were those of colonel Fellers US ,attaché in Cairo. Fellers was a graduate of West Point and former assistant of General Douglas MacArthur. He was posted to Cairo in October 1940. His job was to provide Washington with detailed information on all important military operations. The British gave him access to their facilities and shared sensitive information on upcoming operations. All this information was extremely important for the Axis side. The Italians shared the Military Intelligence code with the Germans.

According to Fenner, head of the cryptanalysis department of OKW/Chi, the Italians sent him a copy of the codebook in 1941 but not the encipherment tables. He got these from the Hungarians. Both sides were able to read the Fellers messages during the first half of 1942.

Yugoslav Army code

In 1940 the Italian forces in Albania invaded Greece. The Greek army was able to drive them back and hard fighting ensued.

Practically all the Italian forces were concentrated in the south of Albania. This meant that the Albanian-Yugoslav border was not well protected. A sneak attack by Yugoslav troops had the potential to destroy the Italian forces.

In April 1941 this operation was put in motion by the Yugoslav high command. The Italians were in a tight spot however they were able to cope with the situation through their mastery of Yugoslav codes.

The Italian codebreakers sent two messages to the Yugoslav divisions, written in the correct format and ‘signed’ by General Dusan Simovic, head of the new government. These said:

1). To the Cetinje divisional headquarters:

Subordinate troops will suspend all offensive action and retire in the direction of Podgorica, organizing for defense.

2). To the Kosowska Mitrovica divisional headquarters:

Withdraw immediately with all subordinate troops back towards Kosowska Mitrovica.

Since the messages were enciphered with the Yugoslav army code and had all the signs of a real order they were accepted by the divisions and the offensive was halted! The Cetinje division requested confirmation from HQ but none came and it too retreated. When the next day HQ responded that no retreat had been authorized it was too late. Italian military units had occupied the abandoned areas and the Yugoslavs had bigger problems to handle as the German invasion had led to the collapse of their military forces.

Naval agency

The naval intelligence agency SIS (Servizio informazioni Speciali della Royal Marina) was divided into 4 branches. Branch B (Beta) was tasked with signals intelligence. It was subdivided into cryptanalysis, interception and direction finding, security and clandestine radio intercepts.

The cryptanalytic department was located in Rome and headed by Commander Mario De Monte. In the 1930’s they solved several French naval systems. During the war the emphasis was on British naval and naval aviation codes. Low level British naval codes were easily solved. The Italians also read the Royal Navy’s Administrative Code (used from 1934 till August 1940), the Naval Code No1 and No2 (used from August ‘40 till March ’43) plus the Naval Cypher No1 and No2 (used from 1934 till January ‘42). They acquired Naval Cypher No3 (Anglo-American Cypher used from June ’41 till June ‘43) from the Germans and were able to solve the encipherment. For speeding up their work they used punch card equipment in 1942.

The Italian Air Force Intelligence Service (Servizio Informazioni Aeronautica) relied on the Navy department for interception and cryptanalysis. In 1941 the Airforce set up its own intercept station and sent the messages to the Navy.

Intercept section

The interception and direction finding department of Branch Beta supplied messages and had 7 main stations in Italy and its possessions. The intercept network was comprised of the following stations:

- Monte Rorondo, near Rome with subcentre at Licola.

- Tirrenia, with substations at Arma di Taggia and Toulon.

- Porto Palo, Augusta with substation at Favignana.

- Pula, Sardinia with substation at Porto Torres.

- Rhodes, Greece.

- Tripoli, Libya.

- Benghazi, Libya

Additional material was received from the Germans. The daily average was 3,000 messages. Special intercept units were also based onboard flagships (squadrons, divisions and convoy escorts) so that the intercepted messages could be exploited as quickly as possible and the information communicated to the naval commanders.

Cooperation with the Germans

During the 1930’s liaison was established with the German Navy’s cryptanalytic service B-Dienst and some information on French codes was exchanged. The Germans also gave information on the British Administrative code but did not share their work on other systems.

After Italy’s entry into the war relations became much closer and information was exchanged on the Naval Cypher and Naval Code. Finally in 1942 the Naval Cypher No3 (Convoy Cypher) was shared.

There was a daily exchange of recovered code groups via teleprinter and every week a written report was sent. Branch Beta also received messages from German intercept units.

Battle of the convoys

In the period 1940-1943 the naval codebreakers concentrated on the codes and ciphers of the Royal Navy. The call signs, messages and volume of traffic of British units were analyzed in order to build up the British order of battle and identify the movement of units in the Mediterranean. Branch Beta summarized this information in a daily bulletin submitted to all naval commands.

The value of codebreaking and signals intelligence was recognized by the Navy’s high command and there was close cooperation between Branch Beta and the operational command of the Italian Navy. According to Admiral Franco Maugeri, head of the SIS:

‘The departure of an enemy naval force or a convoy from East or West never escaped the SIS, and it was almost always possible to establish within a few hours its composition and even its objectives; which permitted immediate counter measures on the part of our naval command, and the most Important naval encounters (Battle of Punta Stile, of Cape Tulada, of Cape Matapan, the two actions off Sirte, and that of Pantellaria) originated through information from the SIS’.

Another advantage from reading British naval codes was gained by learning of their plans to attack Italian convoys to N.Africa. Messages from British naval aircraft (Fleet Air Arm) could be decoded very quickly and these gave an insight into British operations, especially against Italian convoys. In those cases the Italian command quickly warned the convoys by sending them top priority messages called PAPA (Precedenza Assoluta sulla Precedenza Assoluta) so they could alter their course.

Work after the surrender of 1943

In September 1943 the Italian government surrendered to the Allies and tried to exit the war. Unfortunately the Germans were expecting such a move and quickly occupied the country.

Mussolini was established as head of the Italian Social Republic covering the German occupied areas. This state continued to use a small number of SIM codebreakers. They mostly exploited systems already broken before the surrender. The main emphasis was on diplomatic messages in order to get information about conditions in the liberated areas.

The Germans were not helpful and they did not exchange results with the codebreakers of the Social Republic.

Conclusion

Italy entered WWII hoping to exploit Germany’s victory for its own gains. When the war dragged on the Italian economy and the military forces were unable to deal with the new situation and the country tried to surrender to the Allies in 1943. Despite these shortcomings Italian army units and the Navy fought well in the Mediterranean and North Africa.

In the cryptologic field the Italians were hampered by the lack of personnel and resources. Still they were able to exploit several important enemy systems and provided the Italian leadership with the confidential messages of several foreign countries. In the case of the Fellers messages and the Yugoslav Army code their efforts truly had a strategic effect. Their naval codebreakers successfully solved the codes of their main opponent, the Royal Navy, and took advantage of this in several naval engagements.

Considering the resources at their disposal it would be hard to ask more of the Italian codebreakers.

Sources:

HW 40/75 ‘Enemy exploitation of Foreign Office codes and cyphers: miscellaneous reports and correspondence’, TICOM DF-187D ‘Relations of OKW/Chi with foreign cryptologic bureaus’, ‘The codebreakers’, ‘European Axis Signal Intelligence in World War II vol8’, Cryptologia article: ‘The cryptographic services of the Royal British and Italian Navies’, International Journal of Intelligence and Counter-Intelligence article: ‘Left in the Dust: Italian Signals Intelligence, 1915-1943’, TICOM I-12 ‘Translation of the Preliminary Interrogation of O.R.R. Tranow of 4/SKL III/OKM, carried out at Flensburg on 24-25 May 1945 by TICOM Team 6’, Wikipedia, Naval War College Review article: ‘The Other Ultra: Signal Intelligence and the Battle to Supply Rommel's Attack toward Suez’,
‘Italian Communications Intelligence Organization’-Report by Admiral Maugeri with U.S. Navy Introduction, TICOM D-71 'German and Italian Correspondence on Miscellaneous Cyphers', CSDIC/CMF/Y 29 ‘First detailed interrogation of Samarughi, Giuseppe’, CSDIC/CMF/Y 4 ‘First detailed interrogation of Bigi, Augusto’, CSDIC (main)/ Y 12 ‘First detailed interrogation of Vassalio Todaro’

Soviet naval codes and the Arctic convoys

Overview

Histories of the war between the Soviet Union and Nazi Germany focus almost exclusively on the land battles and devote a smaller part for the airforces of the two countries. The naval engagements of the war are usually given very little space.

This is understandable since the Soviet Navy was mostly ‘bottled’ up in the Baltic and there were few interesting operations in the Black sea. From their side the Germans only used limited naval forces against the SU (mainly gunboats and mine-layers).

The German side was however interested in the plans and operations of the Soviet navy and especially on the convoys between the UK and the SU. These convoys carried Lend Lease supplies that were vital for the Soviet economy and armed forces.

Through signals intelligence and codebreaking the Germans were able to monitor Soviet operations and especially the route and speed of the Allied convoys. This allowed them to take a heavy toll on commercial shipping and cause a crisis in the arctic convoys.

The systems they exploited were Soviet naval codes and in the case of the convoys the code used by the Soviet naval aviation.

Soviet naval codes

The German naval codebreakers divided the Soviet naval systems geographically (North Sea, Baltic, Black Sea) and according to whether they were main or subsidiary systems.

The main systems were 4 and 5-figure codes (superenciphered or substitution) and they were used by shore stations and large units.

The subsidiary systems were 2 and 3-figure codes enciphered with a simple substitution table. They were used by small ships.

North Sea and Baltic

The 5-figure codes used in these areas were mostly enciphered with OTP. However in summer ’44 the Chabarovo station traffic was revealed to be 4-figure with the 5^th figure taken from the subtractor table. This book was partially reconstructed but there were no other compromises after September ’44.

Several 4-figure codes were read during the war. The most important ones were those used by the Northern and White Sea fleets as they were ‘broken’ without much difficulty.

High level codes were read till late ’43. From that time on it seems the Russians used OTP extensively. Low level codes were solved throughout the war.

The German success with Soviet naval codes became known to the Brits through Enigma decrypts. Report HW 40/7 ‘German Naval Intelligence successes against Allied cyphers, prefixed by a general survey of German Sigint’ gives an overview of the intelligence that the Germans got through codebreaking:

Messages from Leningrad gave information on the activities of mine-sweepers and patrol boats in the Baltic. The time lag in 1942 was from 2 days to a few hours.

Also in 1942 medium to high grade ciphers used by the Northern Fleet gave the German navy considerable information on the activities and disposition of Soviet surface vessels and submarines as well as British shipping off North Russia.

Black Sea

Pre-war a 5-figure superenciphered code was used. At the beginning of the war this was replaced by a 4-figure subtractor system. The subtractor was not taken from a pad but was generated using a substitution table from the text of the ‘History of the Communist Party’ ( three different letters= 1 figure).

This was replaced by a 4-figure subtractor system, this time the subtractor taken from a pad. This system was used extensively by the Soviet naval air arm but was only partially solved.

The next system in line was a 5-figure doubly enciphered code that was not solved.

Finally there were several 5-figure systems, including a 4-figure disguised as a 5-figure that were not completely solved.

Low level codes were read till summer ’44.

In general work on Black sea systems was given a lower priority compared to the North Sea and Baltic which were more important for operations.

Soviet naval aviation codes

The code used by the planes of the Soviet naval air arm was a simple substitution table. This was easily solved by the codebreakers of the Luftwaffe’s signal intelligence service.

Since the naval planes had the mission of escorting the Allied convoys they constantly transmitted their position, strength and route. One can only imagine the importance of this traffic for the Germans.

The exploitation of the naval aviation code is mentioned in several postwar reports:

From HW 40/7 ‘German Naval Intelligence successes against Allied cyphers, prefixed by a general survey of German Sigint’, p11

Besides the purely naval traffic broken by OKM, the G.A.F. Sigint Service was exploiting some Russian Fleet Air Arm cypher during the Autumn of 1942, which constituted a dangerous source of intelligence on Allied convoys between the U.K. and North Russia. On 8th September, for example, a G.A.F. Sigint report was seen in Special Intelligence containing decodes of three signals relating to the 95th Air Regiment of the Russian Northern Fleet of which the first, dated 7th September, gave the scheduled movements of convoys PQ 18 and QP 14 for the period 10th to 20th September, and the other two contained instructions for air escort of these two convoys.

PQ18 lost 13 ships for 76,000 tons while QP14 lost 2 escorts and 4 merchant ships for 20,800 tons. [Source: ’Hitler’s U-boat War vol2’, p21]

From TICOM DF-292 ‘The Cryptologic Service in WWII (German Air Force)’, p46

In another case the destruction of a convoy near Murmansk was involved. This time during the course of several days messages were intercepted and decrypted in which a convoy of some 40 vessels was reported which was on its way to Murmansk. In those messages the position of the convoy was given repeatedly. All the messages were enciphered with a simple substitution table and could be deciphered in full, very quickly. The Air Fleet in the North could be alerted in time. A large number of bombers was ready to start. Then when additional decrypted massages announced the approach of the convoy to Murmansk the German bombers were ordered to start. The exact position of the attack was known. Here again the attack came as a surprise and destroyed nearly all the ships. From these two examples one might assume that the enemy did not count on the possibility that the German Intercept Service could decrypt the enciphered messages in time. But why this important massage was enciphered in such primitive fashion is hard to explain.

Report DF-292 was written by Edwin von Lingen, head of the Luftwaffe Chi Stelle’s Soviet cryptanalysis department.

The compromise of the routes of PQ17 and PQ18 from reading Soviet naval aviation codes is confirmed from another source. The Swedish codebreakers were able to decode German messages travelling through their telephone network, even if they were enciphered with the Siemens T-52 cipher teleprinter. Some of these reports mentioned the decoded Soviet messages dealing with the northern convoys. The Swedish codebreaker Sven Wasstrom, who examined these messages, became distraught at this drama.

Cooperation with the Finnish codebreakers

According to TICOM I-16 the German naval codebreakers exchanged material with the Finns but did not cooperate closely. The Finns had excellent interception of Baltic traffic and had solved a doubly enciphered 5-figure code.

Conclusion

The codebreakers of the B-Dienst and the Luftwaffe were able to exploit several Soviet Navy and Naval air arm codes.

The operations of the Red Navy in the Baltic and the North Sea were monitored through codebreaking. The Russians used several insecure systems until late ’43. From then on however it seems that at least their high level codes were secure.

Still the compromise of the Naval Aviation code and the effect it had on German operations against Allied shipping was a serious defeat for the Soviet side.

Sources:

HW 40/7 ‘German Naval Intelligence successes against Allied cyphers, prefixed by a general survey of German Sigint’, TICOM reports DF-292 and I-16 (the last one available through TICOM Archive), Codebreakers: Arne Beurling and the Swedish Crypto Program During World War II 

B-Dienst vs Bletchley Park - The invasion of Norway and the Battle of the Atlantic

The use of secret intelligence and codebreaking during WWII, by both the Allies and Axis, is a fascinating subject. For the German side some of their greatest successes were achieved by the Navy’s signal intelligence agency B-Dienst (Beobachtungsdienst).

In the field of naval codes this organization was able to read the principal Royal Navy cryptosystems from 1938 to end of 1943. The advantages of reading this traffic were of immense importance for the German side.

In 1940 decoded British naval messages alerted the Germans to the movement of troops to Norway and allowed them to preempt the Allied plan.

During the Battle of the Atlantic most of the intelligence supplied to the U-boats came from codebreaking.

Admiral Doenitz considered it the best source of Naval intelligence and often the only source of operational information.

The Battle of the Atlantic was the longest campaign of WWII and it involved the German navy’s U-boat command versus Allied commercial shipping and the surface forces of the British, Canadian and US navies which escorted them.

The German strategy was to exploit Britain’s lack of self sufficiency in raw materials and agricultural products. If they managed to sink the majority of supplies crossing the Atlantic then Britain would be economically strangled and would have no choice but to sue for peace. Even if this did not happen the lack of military supplies would make it impossible to launch heavy attacks on continental Europe.

The head of the U-boat service, Admiral Doenitz knew he needed large numbers of submarines in order to achieve victory. His operational strategy was to overwhelm convoys with a large number of U-boats. These wolfpacks could evade the few escort vessels and sink the majority of commercial ships. The rest would disperse and could be picked off at a later time.

In order for the wolfpack strategy to work the Germans needed to know the route and speed of the convoys in advance. Their main ways of gaining this information was through aerial reconnaissance and signals intelligence.

According to post war reports D/F (direction finding) was not very helpful in locating the convoys.

Aerial reconnaissance was the job of the Luftwaffe and was hampered by the lack of a long range bomber aircraft that could search the Atlantic. The planes that the Germans used in that role were the Focke Wulf 200,the Heinkel 177 and the Junkers 290. The Fw 200 was a modified commercial airliner and its structure could not absorb all the weight of weaponry and equipment. So accident were frequent. More important however was the fact that at any given time only a handful were available for naval recon operations. The Ju 290 was also used in tiny numbers and the He 177 had many development problems that delayed its operational use.

In the end naval reconnaissance was never an important mission for the Luftwaffe and few resources were invested in it.

This left only codebreaking. Thankfully the naval codebreakers were able to solve the Royal Navy’s systems, both the high level Cypher and Code plus the Merchant Ships code.

The central cryptanalytic department OKM/SKL IV/III (Oberkommando der Marine/Seekriegsleitung IV/III) was based in Berlin and had roughly 1,000 people working on foreign codes. Around 800 were assigned to the British section. This was quite an investment in terms of manpower! Still the results justified the expenditure. From summer 1942 they were also aided in their efforts by IBM /Hollerith punch card equipment.

In order to access the successes of the B-Dienst it is imperative that we understand the cryptologic systems used by the Royal Navy in WWII.

At the start of the war the main systems were:

1.     Naval Cypher No1, a 4-figure book used since 1934.

2.     Administrative Code, a 5-figure book used since 1934.

3.     Auxiliary Code No3, a 4-letter book used since 1937 by small units.

Merchant ships used their own codebook. During 1939 this was the International Code and Naval Appendix. From January ’40 to April ’42 it was the Merchant Navy Code and for the rest of the war the Merchant Ships Code.

All these codes and cyphers were reciphered with special tables. There were different sets of tables depending on the geographic area and the level of traffic (Commander in Chief table, Flag Officer’s tables, General table etc).

The reciphering tables were changed at frequent intervals.

These security measures did not stop the Germans from ‘breaking’ the naval codes. They were greatly aided in their efforts by the poor British decision to use the Administrative and Auxiliary codes unreciphered for non-confidential traffic. This allowed them to recover the true values of the codebooks and then focus only on breaking the enciphering tables.

In 1935-6 the Administrative Code was solved and in 1938 the Naval Cypher followed. At the start of the war the Auxiliary Code was also read with little difficulty.

By the spring of 1940 the work of the B-Dienst had progressed so far that they were able to read virtually everything of importance in connection with the Norway operation. For example their success rate was 30-50% of intercepted cypher traffic.

There is no doubt that the German victory in Norway owed a great deal to the efforts of the B-Dienst.

British cipher security was upgraded on 20 August 1940 when new editions of the Cypher and Code were introduced. The Auxiliary Code was discontinued and instead small units used the Naval Code enciphered with Auxiliary Vessels tables.

These changes hindered the German effort but could not defeat it. The German naval codebreakers, after hard work, managed to ‘break’ in back into these systems.

However from June 1941 their main effort was directed at the new Naval Cypher No3 used in the Atlantic by the British, American and Canadian navies.

This was a 4-figure book originally created for the Royal Navy but since no other system had been prepared for inter-allied naval traffic it was shared with the US navy and the Canadians. The Germans called it ‘Frankfurt’.

The subtractor tables used with Cypher No3 had 15,000 groups. Since traffic was much heavier than anticipated (M table-General: 218,000 groups in August ’42, S table-Atlantic: 148,000 groups in October 1942 and 220,000 in November), code-groups were reused several times and the Germans used these ‘depths’ to reconstruct the tables. The British tried to limit ‘depths’ by introducing new tables. Originally these were changed every month but from September ‘42 every 15 days and in ‘43 every 10 days.

Naval Cypher No3 was introduced in June ’41. The Germans were able to ‘break’ into the traffic in December ’41. By February ’42 they had reconstructed the book and till 15 December ’42 they were reading a large proportion of the traffic (at times up to 80% of intercepted messages). In December an indicator change set them back but from February ’43 they were again able to read the messages.

Their greatest success with the convoy cypher was achieved in 1943. From February till June they often read signals 10-20 hours in advance of the actions mentioned in them. Also from February ‘42 to June ‘43 they could decode the daily Admiralty U-boat disposition signal nearly every day.

In the Atlantic they also exploited the Naval Code and the merchant ship codes.

Naval Code versions 1-3 (valid from August ’40 to January ’44) were read by the B-Dienst and some of the messages from the Atlantic and Western approaches areas were decoded.

The Merchant Navy code and the Merchant ships code were captured from commercial ships. Their enciphering tables were solved throughout the war. The official history ‘British intelligence in the Second World War’ says that these two systems ‘were a prolific source of information to the B-Dienst second only to the Naval Cypher No3 in their importance to the battle of the Atlantic’.

Taken together, these successes meant that from the start of the war till the summer of 1943 the German High Command had the upper hand in the field of intelligence. Thus Doenitz could place his U-boat groups at the time and place where they would do the most damage.

German fortunes declined after summer ’43. In June ’43 Naval Cypher No5 replaced No3 in the Atlantic. It was recyphered by a new system called the ‘Stencil Subtractor’. In November the Combined Cipher Machine was also used by Allied warships in the Atlantic. In December the Auxiliary vessels tables transferred to the Stencil system. During the same month the Merchant Ships code was used with enciphered coordinates.

By January 1944 the Germans had lost all their high level sources of information. They did not give up though. They assigned a large staff to research the new stencil system and managed to ‘break’ the Auxiliary Vessels traffic of December ’43 in early ’44. They were able to do so because they had already reconstructed the Naval Code No3 which was used at the time. This was changed in January with Naval Code No4.

Their conclusion was that without having the new Naval Code and Cypher books they could not hope to solve the traffic. If however they managed to get hold of the codebooks then solution would not be hard. Unfortunately for them they did not manage to get their hands on the Royal navy’s codebooks. Their only remaining successes would be with low level codes.

These cryptologic changes were not by accident. The Brits suspected that their codes were not secure but they got definitive proof only when they started ‘breaking’ the Enigma again in 1943. For various reasons it took them quite a long time to upgrade their security but once they did B-Dienst was effectively defeated.

Since I’ve covered the main achievements of the German side it’s important to also go through the British operations.

The other side of the hill:

Doenitz needed to be kept informed of the operations of his submarines at all times. This meant that the U-boats sent daily reports of their sightings, route and fuel situation. The U-boat command also sent its orders daily.

In order to protect this traffic the Germans enciphered it with the naval Enigma M3 and from February 1942 the 4-rotor M4.

The M3 Enigma used by the German navy had additional security measures compared to the standard Wehrmacht Enigma. Apart from the 5 rotors, used by all services, it had an additional 3 that were used only by the navy. These had two notches (compared to one for the standard ones) making movement more irregular.

The M4 had one more (non moving) rotor position that was used with two additional rotors. These however could not be used in the other three positions. Cryptographically the M4 was much more secure than the 3-rotor Enigma and its use caused a crisis in the Anglo-American agencies.

Signaling procedures were also much stricter than those of the other services. For example indicators were not selected by the operator but from a book (Kennbuch) and they were enciphered with a bigram table. Both Kennbuch and bigram tables were changed several times during the war thus complicating the work of Hut 8.

Coordinates were taken from a grid table. From June ’41 coordinates were further disguised by using fixed reference points on the grid table. From November ’41 an Adressbuch was used to encipher the grid references.

These security precautions on behalf of the Navy meant that their Enigma traffic was much harder to decode that the Airforce version which was read regularly.

The section of Bletchley Park that attacked naval Enigma traffic was Hut 8 headed, in the beginning, by the mathematician Alan Turing. During the period 1939-41 they did extensive research on the indicator system and the naval Enigma. They were aided by the capture of the 3 extra rotors. Two from U-33 in February 1940 and the last one in August 1940.

Despite the excellent work done in studying the naval Enigma and the indicator system, by March ’41 their only operational success had been the solution of the Enigma ‘key’ for 5 days of 1938 and 6 days in April 1940.

Obviously something had to be done to force this deadlock! This ‘something’ would be a commando operation against the German forces in the Norwegian Lofoten islands. The goal was to capture cipher material that could be used by Hut 8. The operation took place on 4 March 1941 and was a resounding success. The keylists for February were captured from the German armed trawler Krebs. This material allowed Hut 8 to decrypt the February traffic during March. Then thanks to the intelligence gained from this ‘break’ they were able to solve the April and May traffic cryptanalytically.

After decrypting the February and April traffic it was discovered that the Germans were keeping weather ships north of Iceland and in mid-Atlantic. The next operations targeted these ships as they would have cipher material onboard.

On 7 May ’41 the weather ship München was captured and the June keylists captured. On 28 June ’41 the weather ship Lauenburg was captured with the July keylists.

Another ‘pinch’ took place on 9 May when the U-boat U-110 was captured. The material seized included the Officer’s Enigma settings and the short signal code book (Kurzsignale).

These captures allowed Hut 8 to break into the Naval Enigma currently and familiarize itself with the structure and content of the messages. This information could then be used for cryptanalysis without the help of captured material.

In the second half of 1941 the Enigma decrypts allowed the British to route their convoys around the U-boat concentrations. Only 5 of 26 SC convoys, 2 of 31 HX convoys and 3 of 49 ON convoys were attacked. They were aided in this regard by the small number of U-boats operating in the Atlantic (16 for 4^th quarter ’41). They also benefited from the German navy’s diversion of U-boats to the Mediterranean and the Baltic.

The drastic reduction in sinkings had baffled the Germans. They must have suspected that something was wrong since in February 1942 the 4-rotor M4 Enigma was introduced for the Atlantic U-boats. This was much more secure than the 3-rotor version and immediately put an end to the British success. British and American efforts to solve it failed again and again.

By December 1942 only 3 days traffic had been broken. This failure had strained relations between British codebreakers and the US navy’s OP-20-G. It was obvious that new 4-rotor ‘bombes’ were needed but the British reassurance that these would be soon introduced failed to materialize. The Americans then decided to build their own ‘bombes’ at the National Cash Register Corporation under engineer Joseph Desch. It was a good thing they did because the British 4-rotor ‘bombe’ design turned out to be problematic.

The introduction of the new ‘bombes’ took place in September 1943. From then on the naval Enigma settings would be solved within 24-48 hours.

However while the ‘bombes’ were being built the war was still going on. The Allies needed to break the new Enigma machine or their convoys would face horrible losses. Thankfully on 30 October 1942 the U-boat U-559 was heavily damaged of Port Said in the Med and before she sunk three British sailors managed to recover the Enigma and the short signal weather book. Two of them drowned when they went back to find more material.

Thanks to this material the Hut 8 codebreakers discovered a fatal flaw in the use of the Enigma by the Germans. When sending short signals they set the M4 ‘s fourth rotor at neutral position. This made the machine perform like the 3-rotor version. The Germans had built it this way so they could exchange messages between M3 and M4 versions (since the other services only had the 3-rotor version). Immediately the British work was dramatically reduced as they could use the short signals (such as weather reports) to find the position of only the 3 rotors. Once they did they could then find the position of the fourth rotor by checking the possible 26 positions by hand!

Thanks to these insights the Naval Enigma was once again being read. Still even with these advantages work was laborious and it took several days to recover the daily ‘key’. This limited the tactical value of the Enigma information. The official history says that messages older than three days could not be used in the field as the information was too old. This table from SRH-009 breaks down the days decoded by the time it took to break them (notice that the emphasis is on 2 days):

U-boat key Atlantic
	Days not broken	Days broken	Broken in 2 days or less	Between 2-5	Over 5
Dec-42	12	19	5	3	11
Jan-43	3	28	5	12	11
Feb-43	1	27	18	5	4
Mar-43	5	26	8	11	7
Apr-43	11	19	12	7	0
May-43	3	28	9	5	14
Jun-43	9	21	1	6	14
Jul-43	2	29	2	1	26
Aug-43	6	25	1	9	15
Sep-43	4	26	3	16	7

The majority of the days were ‘broken’ too late for the information to be of use in the field. During the period December ’42 –May ’43 only one third of the ‘keys’ were solved in 2 days or less.

Even when the messages were decoded the coordinates they carried were enciphered with an additional system. In 1943 the grid system could be broken only with ad hoc analysis and with frequent mistakes.

Looking at the information presented so far it is obvious that in the period December ’42 to May’43  the value of Enigma intelligence cannot have been decisive. Moreover there were so many U-boats operating in the Atlantic that it was practically impossible to route the convoys around them (50 for 1^st quarter ’43 compared to 16 in 4^th quarter ‘41).

Instead other factors such as the use of new D/F equipment by the escort ships and radar by long range aircraft were decisive.

Conclusion:

Overall it is clear that the German naval strategy was to starve Britain of supplies. This required advance knowledge of the convoys routes and schedule.

The only way this could be achieved was through codebreaking. The B-Dienst was able to solve the Royal Navy codes in the Atlantic and there is no doubt that without this advantage the U-boats would not be able to locate the Allied convoys.

At the same time the codebreakers of Bletchley Park could not decode the naval Enigma or could decode it with considerable time lag. The only exception is the second half of 1941 when they indeed had a great success. In 1942 however they were blinded by the introduction of the 4-rotor Enigma.

In the first half of 1943 the German codebreakers had their greatest success against the convoy cypher. They could decode messages fast enough for the information to be used by the U-boat Command.

Their counterparts at Bletchley Park could also read their enemy’s communications but with too many problems and significant time lag. Even when the messages were decoded, use of enciphered coordinates by the Germans meant that Hut 8 had to spent additional time against this code. Clearly in this battle it was the B-Dienst that triumphed. Why did the U-boats lose then?

The answer is that by 1943 the U-boats were technologically obsolete. In the surface they could not survive against the Allied escorts. The Allied ships were equipped with new high frequency direction finding equipment and new mines. Escort carriers provided air cover. Long range recon planes with radar also hounded the U-boats forcing them to submerge or be destroyed. Their speed when submerged however was too slow to keep up with the convoys. The U-boats were not true submarines but submersible surface vessels.

No amount of codebreaking could change these facts. The last major effort by the U-boat command was clearly defeated by the Allies in May 1943. The catastrophic losses forced Doenitz to recall his U-boats from the Atlantic.

They would never again seriously threaten the Allied shipping routes.

Still their successes and the effect they had on Allied operations and strategy were definitely worth the effort.

The winner in the secret intelligence war in the Atlantic was the German side. The fact that they were defeated shows that even the greatest codebreaking successes cannot win wars on their own.

Sources: ADM 1/27186 ‘Review of security of naval codes and cyphers 1939-1945’ , HW 25/1 ‘Cryptographic History of Work on the German Naval Enigma’ by C.H.O'D. Alexander, British intelligence in the Second World War (4 volumes on operations) , SRH-009 ‘Battle of the Atlantic: Allied Communication Intelligence December 1942 - May 1945’ , Enigma Message Procedures Used by the Heer, Luftwaffe and Kriegsmarine , Memoirs: Ten Years And Twenty Days , TICOM I-143 'Report on the Interrogation of Five Leading Germans at Nuremburg on 27th September 1945', ‘The German Naval grid in WWII’- Cryptologia article, Eagle in flames: the fall of the Luftwaffe, NSA history - ‘Solving the Enigma: History of the Cryptanalytic Bombe’, Bitter Ocean: The Battle of the Atlantic, 1939-1945, ‘Breaking Naval Enigma’ (Dolphin And Shark) , Wikipedia, SRH-368 ‘Evaluation of the Role of Decryption Intelligence in the Operational Phase of the Battle of the Atlantic, U.S. Navy OEG Report #68’ 

Acknowledgements: I have to thank Ralph Erskine for the S table statistics and for answering my many questions on naval codes.