Update

In the essay The French War Ministry’s FLD code I’ve added the following information:

Identifying the FLD codes

We can try to identify the cryptosystems used in the FLD radio network by looking at Huettehnain’s statements and various TICOM documents.

According to Army cryptanalyst dr Buggisch (7) the designations F90 and F110 referred to French Army ciphers, read during the period 1939-1940:

‘F90 and F110 were German designations for French Army cipher systems before and during the campaign in FRANCE. Both were based on a four figure code, in one case the recipher consisted of a periodic adder [or subtractor] of length 11; in the other it was ordinary transposition, the transposition key being obtained from a key word which itself was taken from the code and shown by an indicator group. Both systems were being read from the winter of 39/40 to the end of the French campaign. Solution was by methods generally known in cryptanalytic circles. One of the codes turned, up again for a short period in De Gaullist traffic.’

Note that Buggisch’s description of the systems is similar to Huettenhain’s from ‘Einzeldarstellungen aus dem Gebiet der Kryptologie‘.

In the TICOM collection of the German Foreign Ministry’s Political Archive there are documents that have more information on the ciphers F90 and F110:

1). The TICOM documents T3611 and T3612 (8) have information on cipher F90, however document T3611 is not available due to deterioration.

According to document T3612 the cipher F90 was a 4-figure code enciphered with short additive sequences of 5, 7 or 11 digit length. It seems that the codebook consisted of 20 pages, each with 100 entries, totaling 2.000 code groups.

This system was used by the network FLD (Paris) in communications with stations fla, flb, flc, flf, flg, fak, fam, flq and others and it was solved thanks to a major cipher clerk error committed in September 1937.

It seems that the same message was sent twice, first without encipherment (so only the code groups were transmitted) and then with additive encipherment. Clearly this gave the German codebreakers an opportunity to identify the basic code groups and then solve the additive sequence used for encipherment. This success allowed them to correct their own relative code findings (from previous decipherments) into the actual French code values.

The information in TICOM document T3612 matches Huettenhain’s statements about a high level code enciphered with short additive sequences being solved completely in the years prior to WWII.

2). The TICOM document T3684 (9) describes system F110 (F4ZCW110 - French 4-figure code with simple transposition) and it says than from February 1938 the radio network of the French 14^th Army, with stations in Lyon, Grenoble, Modane, Briancon, Chambery, Jausiers and Beurg-Saint-Maurice, started using this transposed code. The indicator was 55555 and the transposition key was created from the plain meaning of one of the codegroups. The example given in the report was:

p   e   r   m  i  s   s   i  o  n   o  n   n   a   i   r   e 

13 2 14  7  4 16 17  5 11  8 12  9 10  1  6 15  3

The details in the report match Huettenhain’s statements about a French military district adjacent to Italy using a transposed code, with the transposition keys being created from the codegroups of the codebook and the first breakthrough coming in 1938.

The successors to systems F90 and F110

From the available TICOM documents it seems that in September 1939 both systems were changed. Cipher F90 was replaced by a new 3-figure code plus additive, while cipher F110’s successor used the same underlying code but with a new encipherment procedure.

1). TICOM document T3661 (10) contains a report by the cryptanalyst dr Ludwig Föppl, dated 18 December 1939. In the report Föppl says that the code F90, which was used in the military command radio network FLD (Paris), was changed in September and replaced by a new system.

The new system was a 3-figure code enciphered by additive sequences. It seems the encipherment consisted of a 20-digit number that was composed of two 10-digits parts. A peculiarity of the encipherment was that each 10-digit number was composed of all the ten digits from 0 to 9 used only once (11). This system was solved and it seems that the German designation for it was F135.

2). In the notes of dr Huettenhain there is a report from November 1939 that describes the solution of the successor to system F110 (12):

‘Report on the attachment to Army Group C evaluation section

On 2 September 1939 the French Army Code F110 was replaced by a new code so that traffic could no longer be broken currently.

On 3 September 1939 I was seconded to FRANKFURT-ON-MAIN in order to take part in the task of breaking this new code. The task was accomplished at the beginning of October so that all the September material could be read retrospectively.

This success was made possible in such a short time by the fact that

1) the necessary data (Code etc) was obtained by months of work in peace time, chiefly by Herrn TRAPPE (Chi OKW) and SCHMIDT (Chi OKW)

2) a close co-operation between the above named gentlemen and me could be established.

It was therefore, still possible in October to work on the October material with success. In addition to the above named gentlemen Herr Professor Dr. FOPPL was of great assistance in the solution of this system.

As the system was not changed on 1 November 1939 this code could be read currently again from the date when the October key was broken. On 3 November 1939 at the finish of my attachment in FRANKFURT-0N-MAIN I was sent to BERLIN.’

From Huettenhain’s report it seems that the underlying code remained the same (as in system F110) but the encipherment procedure was changed. By having the code the German codebreakers only needed to attack the encipherment and this was quickly achieved according to Huettenhain.

Update

In the essay French Hagelin cipher machines I made a correction regarding the solution of the Hagelin C-36 by the German Army codebreakers. 

I had written that the device proved secure in 1939-40 but in TICOM report I-78 Mettig (head of the Army’s codebreaking department for the period 1941-43) stated that it was read by July 40 (thanks to captured machines).

I’ve also added the following paragraph at the end of the essay:

Solution of the Hagelin C-36 at OKW/Chi:

The Hagelin C-36 cipher machine was not a secure device and it seems that in the 1930’s the codebreakers of OKW/Chi (codebreaking department of the Armed Forces High Command) developed methods of solving it.

According to the NSA report ‘Regierungs-Oberinspektor Fritz Menzer: Cryptographic Inventor Extraordinaire’, p21 in 1936 Fritz Menzer developed two methods for solving the C-36.

Also in TICOM report I-31, p7 dr Huttenhain (chief cryptanalyst of OKW/Chi) stated that the French C-36 type could be solved cryptanalytically (without the use of stereotyped beginnings).

Unfortunately, there is no information on the work they did on the C-36 during the late 1930’s and in 1940. Considering their statements on the security afforded by the device it is possible that at OKW/Chi some French Hagelin C-36 traffic was solved during that time.

Information on French codes and ciphers of WWII

Two very interesting articles from the ‘Bulletin de l’ARCSI’:

1). Bulletin N°3 1975: Essai d'historique du Chiffre (Add. N°3) by Général Ribadeau-Dumas.

2). Bulletin N°4 1976: Essai d'historique du Chiffre (N°5) by Général Ribadeau-Dumas.

The French War Ministry’s FLD code - More clues…

I’ve written about the compromise of the French War Ministry’s FLD code by the codebreakers of the German High Command's deciphering department – OKW/Chi, however up to this point I hadn’t been able to find the official designation of this cryptosystem.

Recently I’ve discovered some clues that might clear things up.

According to the available sources this cryptosystem was used for ‘the cypher traffic between the French War Ministry and the army groups, armies and home authorities’.

The new finding aid to the TICOM collection of the German Foreign Ministry’s Political Archive has certain entries that read:

NR 3684 – ‘F4ZCUW 110’ German notes on the above French Defense Area cipher

NR 3615 – F4ZCUT’ German notes, 1931, on French code as above, used by the Defense Areas HQ’s from Schliersee.

The finding aid also mentions the French code F-90 which might have been the predecessor to F-110.

The French code F-110 is mentioned in one of Erich Huettenhain’s reports:

What was the French designation for the system that the Germans called F-110?

Possibly Code R.A.

The finding aid says:

NR 1736 – Code RA, French military code sheets and instructions for use. Various dates 1933-39 March and July 1940-42 from Schliersee.

Why do I think that Code RA was used by the French War Ministry and the Army Groups?

In the book ‘KODY WOJNY. Niemiecki wywiad elektroniczny w latach 1907–1945’, p1.046 there is a copy of a French report dated 16 April 1940.

It says:

Un code R.A. avec additif et son procede de surchiffrement (clef ZERO S.2.) pour permettre de correspondre a l'Intérieur de la Métropole avec les Autorités et Etats-Majors dotés de ce document (notamment commandants d' armes).

Google translation:

R.A. a code with additive and process for its super-encryption (key ZERO S.2.) To allow a match the interior of the metropolis with the authorities and with staffs of this document (including commanders of weapons).

I hope my friends in France will look into this case. I can’t solve everything by myself!

Allied agents codes and Referat 12

In the course of WWII both the Allies and the Axis powers were able to gain information of great value from reading their enemies secret communications. In Britain the codebreakers of Bletchley Park solved several enemy systems with the most important ones being the German Enigma and Tunny cipher machines and the Italian C-38m. Codebreaking played a role in the Battle of the Atlantic, the North Africa Campaign and the Normandy invasion. 

In the United States the Army and Navy codebreakers solved many Japanese cryptosystems and used this advantage in battle. The great victory at Midway would probably not have been possible if the Americans had not solved the Japanese Navy’s JN25 code.

On the other side of the hill the codebreakers of Germany, Japan, Italy and Finland also solved many important enemy cryptosystems both military and diplomatic. The German codebreakers could eavesdrop on the radio-telephone conversations of Franklin Roosevelt and Winston Churchill, they could decode the messages of the British and US Navies during their convoy operations in the Atlantic and together with the Japanese and Finns they could solve State Department messages (both low and high level)  from embassies around the world.

Radio intelligence and codebreaking played an important role not only in the military and diplomatic fields but also in the shadow war between the Allied intelligence agencies, the European Resistance movements and the German security services. In the period 1939-41 German troops conquered most of continental Europe and the occupied countries were forced to contribute to the Axis effort by sending raw materials, agricultural products and forced labor to Germany. Thanks to the blockade of German occupied Europe by the Royal Navy and the harsh demands of the German authorities life in the occupied areas was bleak. Discontent over German occupation led many people to join resistance movements and oppose the authorities, either by printing and distributing anti-Axis leaflets and books, by sabotaging war production or by directly attacking the German troops and their collaborators in the government and the civil service.

The codes of the Polish Intelligence network in occupied France 1943-44

In WWII Poland fought on the side of the Allies and suffered for it since it was the first country occupied by Nazi Germany. In the period 1940-45 the Polish Government in Exile and its military forces contributed to the Allied cause by taking part in multiple campaigns of war. Polish pilots fought for the RAF during the Battle of Britain, Polish troops fought in N.Africa, Italy and Western Europe and the Polish intelligence service operated in occupied Europe and even had agents inside the German High Command.

Although it is not widely known the Polish intelligence service had spy networks operating throughout Europe and the Middle East. The Poles established their own spy networks and also cooperated with foreign agencies such as Britain’s Secret Intelligence Service and Special Operations Executive, the American Office of Strategic Services and even the Japanese intelligence service. During the war the Poles supplied roughly 80.000 reports to the British intelligence services (1), including information on the German V-weapons (V-1 cruise missile and V-2 rocket) and reports from the German High Command (though the agent ‘Knopf’) (2).

In occupied France the intelligence department of the Polish Army’s General Staff organized several resistance/intelligence groups tasked not only with obtaining information on the German units but also  with evacuating Polish men so they could serve in the Armed Forces. These networks obviously attracted the attention of the German security services and in 1941 the large INTERALLIE network, controlled by Roman Czerniawski, was dismantled.

Another large network was controlled by Zdzislaw Piatkiewicz aka ‘Lubicz'. The book ‘Secret History of MI6: 1909-1949’, p529 says about this group: ‘Some of the Polish networks were very productive. One based in the south of France run by ‘Lubicz' (Zdzislaw Piatkiewicz) had 159 agents, helpers and couriers, who in August and September 1943 provided 481 reports, of which P.5 circulated 346. Dunderdale's other organizations were rather smaller’.

From German and British reports it seems that the radio communications of the Polish spy groups in France (including the ‘Lubicz' net) were compromised in the period 1943-44. Wilhelm Flicke who worked in the intercept department of OKW/Chi (decryption department of the High Command of the Armed Forces) says in ‘War Secrets in the Ether’ (3):

The Polish intelligence service in France had the following tasks:

1. Spotting concentrations of the Germany army, air force and navy.

2. Transport by land and sea and naval movements.

3. Ammunition dumps; coastal fortifications, especially on the French coast after the occupation of Northern France.

4. Selection of targets for air attack.

5. Ascertaining and reporting everything which demanded immediate action by the military command.

6. Details regarding the French armament industry working for Germany, with reports on new weapons and planes.

The Poles carried on their work from southern France which had not been occupied by the Germans. Beginning in September 1942 it was certain that Polish agent stations were located in the immediate vicinity of the higher staffs of the French armistice army.

In March 1943 German counterintelligence was able to deal the Polish organization a serious blow but after a few weeks it revived, following a reorganization. Beginning the summer of 1943 messages could be read. They contained military and economic information. The Poles in southern France worked as an independent group and received instructions from England, partly by courier, and partly by radio. They collaborated closely with the staff of General Giraud in North Africa and with American intelligence service in Lisbon. Official French couriers traveling between Vichy and Lisbon were used, with or without their knowledge, to carry reports (in the form of microfilm concealed in the covers of books).

The Poles had a special organization to check on German rail traffic to France. It watched traffic at the following frontier points: Trier, Aachen, Saarbrucken, München-Gladbach, Strassburg-Mülhausen and Belfort. They also watched the Rhine crossings at Duisburg, Coblenz, Düsseldorf, Küln, Mannheim, Mainz, Ludwigshafen, and Wiesbaden. Ten transmitters were used for the purpose.

All the Polish organizations in France were directed by General Julius Kleeberg. They worked primarily against Germany and in three fields:

1. Espionage and intelligence;

2. Smuggling (personnel);

3. Courier service.

Head of the "smuggling service" until 1.6.1944 was the celebrated Colonel Jaklicz, followed later by Lt. Colonel Goralski. Jaklicz tried to penetrate all Polish organizations and send all available man power via Spain to England for service in the Polish Army.  The "courier net" in France served the "Civil Delegation", the smuggling net, and the espionage service by forwarding reports. The function of the Civil Sector of the "Civil Delegation" in France was to prepare the Poles in France to fight for an independent Poland by setting up action groups, to combat Communism among the Poles, and to fight against the occupying Germans. The tasks of the military sector of the Delegation were to organize groups with military training to carry on sabotage, to take part in the invasion, and to recruit Poles for military service on "D-Day". The "Civil Delegation" was particularly concerned with Poles in the German O.T. (Organisation Todt) or in the armed forces. It sought to set up cells which would encourage desertion and to supply information.

Early in 1944 this spy net shifted to Northern France and the Channel Coast. The Poles sought to camouflage this development by sending their messages from the Grenoble area and permitting transmitters in Northern France to send only occasional operational chatter. The center asked primarily for reports and figures on German troops, tanks and planes, the production of parts in France, strength at airfields, fuel deliveries from Germany, French police, constabulary, concentration camps and control offices, as well as rocket aircraft, rocket bombs and unmanned aircraft.

In February 1944 the Germans found that Polish agents were getting very important information by tapping the army telephone cable in Avignon.

In March 1944, the Germans made a successful raid and obtained important radio and cryptographic material. Quite a few agents were arrested and the structure of the organization was fully revealed.

Beginning early in June, increased activity of Polish radio agents in France became noticeable. They covered German control points and tried to report currently all troop movements. German counterintelligence was able to clarify the organization, its members, and its activity, by reading some 3,000 intercepted messages in connection with traffic analysis. With the aid of the Security Police preparations were made for the action "Fichte" which was carried out on 13 July 1944 and netted over 300 prisoners in all parts of France.

This, together with preliminary and simultaneous actions, affected:

1. The intelligence service of the Polish II Section,

2. The smuggling service,

3. The courier service with its wide ramifications.

The importance of the work of the Poles in France is indicated by the fact that in May 1944 Lubicz and two agents were commended by persons very high in the Allied command "because their work was beginning to surpass first class French sources." These agents had supplied the plans of all German defense installations in French territory and valuable details regarding weapons and special devices.

Flicke’s statements on the solution of Polish intelligence codes in 1943 can be confirmed, in part, by the postwar interrogation of Oscar Reile, head of Abwehr counterintelligence in occupied France. In his report 'Notes on Leitstelle III West Fur Frontaufklarung' (4) he said about the Polish intelligence communications:

CODE-CRACKING BY FUNKABWEHR

107. Leitstelle III West also benefited from the work done by the code and cipher department of Funkabwehr, which studied all captured documents connected with codes and ciphers, with the object of decoding and deciphering the WT traffic of agents who were regarded as important and could not be captured. 

108. Valuable results were often obtained by Funkabwehr. During the winter of 43/44, the above-mentioned code and cipher department succeeded in breaking codes used by one of the most important transmitters of the Polish Intelligence Service in FRANCE. For months thereafter WT reports from Polish agents to ENGLAND were intercepted and understood; the same applied to orders they received from ENGLAND. The Germans also learnt that important military plants were known to the Allies, and a considerable number of names and cover names of members of the Polish Intelligence Service were discovered.

Flicke also said ‘Early in 1944 this spy net shifted to Northern France and the Channel Coast. The Poles sought to camouflage this development by sending their messages from the Grenoble area and permitting transmitters in Northern France to send only occasional operational chatter’. This statement can also be confirmed by other German and British reports.

The monthly reports of Referat 12 (Agents section) of the German Army’s signal intelligence agency OKH/In 7/VI (5) mention spy messages from Grenoble in May and July 1943 as links top and 71c (9559, Grenoble), so it is possible that these are the Polish intelligence messages that Flicke says were solved in summer 1943. Unfortunately these reports are difficult to interpret since they use codewords for each spy case.

More information is available from messages found in the captured archives of OKW/Chi (since Chi also worked on Polish military intelligence codes). The British report DS/24/1556 of October 1945 (6) shows that messages on the link London-Grenoble were solved and these were enciphered with the military attaché cipher POLDI 4.

The same report mentions that in August 1944 the British authorities became aware that decoded Polish military intelligence messages from Grenoble were sent from Berlin to the Abwehr station in Madrid, Spain:

‘In August 1944, a series of decoded Polish ‘Deuxieme Bureau’ messages between London and Grenoble were seen by us in ISK traffic being forwarded by Berlin to Abwehr authorities at Madrid. The time lags varied between 5 and 43 days. S.L.C. Section at headquarters informed us that this was a properly controlled leakage, and that no cypher security action was necessary or desirable.’

Some of these messages can be found in the British national archives (7):

It is interesting to note that the response of the higher authorities was ‘this was a properly controlled leakage, and that no cypher security action was necessary or desirable’, without however giving more details.

Conclusion

During WWII the Polish intelligence service operated throughout Europe and was able to gather information of great value for the Western Allies. These activities were opposed by the security services of Nazi Germany and in this shadow war many Allied spy networks were destroyed and their operatives imprisoned or killed. In their operations against Allied agents the Germans relied not only on their own counterintelligence personnel but also signals intelligence and codebreaking. Fixed and mobile stations of the Radio Defense Corps (Funkabwehr) monitored unauthorized radio transmissions and through direction finding located their exact whereabouts.

The Agents section of Inspectorate 7/VI and OKW/Chi analyzed and decoded enciphered agents messages, with the results passed to the security services Abwehr and Sicherheitsdienst. Both agencies solved Polish intelligence communications including traffic from Switzerland, France, Poland, the Middle East and other areas. The Polish intelligence networks in France were an important target for the Germans not only because they were a security risk but also because they would undoubtedly assist the Allied troops in their invasion of Western Europe in 1944. In that sense the compromise of the communications of the Polish military intelligence network was an important success since it allowed the Germans to dismantle parts of this group and also learn of what the Allied authorities wanted to know about German strengths and dispositions in France.

According to Flicke the success started in summer 1943 and from the British reports we can see that they continued to solve the traffic till summer ’44 (when France was liberated). It is not clear of when the Brits first learned that the Polish communications had been compromised and what measures they took to prevent the leakage of sensitive information. It is also not clear of whether they chose to inform the Poles about all this…

Notes:

(1). Journal of U.S. Intelligence Studies article: ‘England's Poles in the Game: WWII Intelligence Cooperation’

(2). War in History article: ‘Penetrating Hitler's High Command: Anglo-Polish HUMINT, 1939-1945’

(3). ‘War Secrets in the Ether’, p230-1

(4). CSDIC SIR 1719 - 'Notes on Leitstelle III West Fur Frontaufklarung', p15

(5). War Diary of OKH/In 7/VI - May and July 1943

(6). British national archives HW 40/222

(7). British national archives HW 40/221

Sources: ‘Secret History of MI6: 1909-1949’, Journal of U.S. Intelligence Studies article: ‘England's Poles in the Game: WWII Intelligence Cooperation’, ‘War Secrets in the Ether’, CSDIC SIR 1719 - 'Notes on Leitstelle III West Fur Frontaufklarung', HW 40/221 ‘Poland: reports and correspondence relating to the security of Polish communications’, HW 40/222 ‘Poland: reports and correspondence relating to the security of Polish communications’, War in History article: ‘Penetrating Hitler's High Command: Anglo-Polish HUMINT, 1939-1945’, War Diary of OKH/In 7/VI

Update: German decodes of the London-Grenoble traffic can be found in pages 793-877 of ‘KODY WOJNY. Niemiecki wywiad elektroniczny w latach 1907–1945’. They date from July 1943 to October 1944 and are signed ‘Szef II Oddzialu Sztabu’, ‘Marian’, ‘Alfred’, ‘Szef Ekspozytury II Oddzialu Sztabu’, ‘Lubicz’, ‘Vox’, ‘Los’, ‘Rawa’, ‘Klemens’, ‘Major Zychon’, ‘Mikolaj’, ‘Bernard’, ‘Biz’, ‘Zenon’.

Sonderkommando Rote Kapelle and the radio network of the French Communist Party

The Soviet Union was a secretive state convinced that the capitalist world was plotting to invade and destroy it. In order to avert such a development the Soviet government financed and organized the creation of spy networks throughout Europe. These penetrated military, economic, political and diplomatic circles. Many of the agents were devoted communists who thought they were working for the creation of a better world.

Germany was a major target of the Soviet spies, especially after power was seized by the NSDAP party. The Red Orchestra was the name given by German intelligence to the Soviet spy networks operating in Europe during WWII. These networks had been set up in the 1920’s and had managed to infiltrate government departments and business circles of every country in Europe. Through their spying activity they kept Moscow informed of important events in Europe.

Their means of communication was the radio and it was this means that led to their downfall. The German Radio Defence agency (Funkabwehr) was able to locate one of the sites used for radio transmissions in 1941 and by apprehending the cipher clerks and their cipher material they were able to read this traffic. By decoding messages they uncovered the names of many Rote Kapelle members and of course these were arrested, interrogated and more people were incriminated. By late 1942 the main networks in Western Europe were destroyed.
 
However after exposing and dismantling these networks the Germans took measures to continue their transmissions to Moscow, so that they could pass false information to the Soviets and also receive information on new spies sent to the West.

The unit tasked with dismantling the Rote Kapelle networks and handling the radio deception (funkspiel) was the Sonderkommando Rote Kapelle, headed in 1943-44 by Heinz Pannwitz.

Operations Eiffel and Mars

In the period 1943-44 the Sonderkommando Rote Kapelle/ Sonderkommando Pannwitz was based in Paris and handled the radio-games between captured Soviet agents and Moscow. The Germans had managed to capture the leaders of the organization Leopold Trepper (Grand Chef) and Anatoly Gurevich (Petit Chef).

After a short period in captivity Trepper managed to escape but Gurevich was used by the Germans to report disinformation to Moscow and convince them that their spy networks were operating normally.

Radio messages were sent from Paris (operation Eiffel) and from Marseille (operation Mars).

The radio network of the French communist party

Another success of the Sonderkommando Rote Kapelle concerned the undercover radio network of the French communist party. According to a recently declassified CIA report, written by Pannwitz, the French CP had prepared a network of undercover radio stations, ready to be used when the party leadership ordered it.

 

These stations had been located by the Germans and they were eliminated thus preventing direct communications with Moscow. However Pannwitz knew that eventually the communists would replace these stations with new ones and risk exposing his operations in France. In order to preempt such a move the Sonderkommando established a new French CP radio network that was in reality under its complete control.

Using the cover of the Rote Kapelle, the resistance leader Paul Victor Legendre was persuaded to set up this radio network. The Germans managed to build up this organization and inserted their own men as radio operators. By operating this network they got a large number of daily espionage reports and were able to keep track of the resistance and stop acts of sabotage.

 

According to Pannwitz an added benefit of running this network was that during the Normandy campaign some of the radio stations continued to transmit information, this time on the strength and operations of the Allied forces.

 

The operations of the network concluded in the summer of 1944 when the Germans had to evacuate Paris. Till that time however the German intelligence agencies got information of great value through the French CP radio network.

Sources: CIA Report - PANNWITZ, HEINZ   VOL. 2_0042, CSDIC/CMF/SD 80 - 'First Detailed Interrogation Report on LENTZ, Waldemar, and KURFESS, Hans'

The French War Ministry’s FLD code

In May 1940 Germany shocked the world by defeating the combined forces of France, Britain, Belgium and Holland in a short land campaign. Unlike World War I that had ended in millions of deaths and a stalemate in the West, this time the German forces were able to quickly defeat their opponents. After France’s defeat several theories were promoted, trying to explain this strange outcome. Some focused on the supposed superiority of the Germans in manpower and armaments, while others tried to point to the German Panzer divisions that supposedly had a big advantage over the similar French units.

General Gamelin who commanded the French forces told Churchill that the defeat was due to: ‘Inferiority of numbers, inferiority of equipment, inferiority of method’. In fact both sides had roughly similar strength in troops and aircraft while in tanks it was the Franco-British alliance that had the advantage, both in terms of numbers and of quality.

However the German were able to overcome their tank inferiority by grouping their armored divisions together, supporting them with ample airpower and providing them with dedicated infantry, anti-tank, artillery and communication units. At the same time their radio communications system was much more advanced than the French Army’s and orders could be dispatched quickly and securely to all units.

The German leadership also took a big risk by attacking through the Ardennes area with the purpose of cutting off the northern part of the Allied front.

Another area where the Germans had the advantage was in signals intelligence. Unfortunately historians have focused almost exclusively on the German Enigma cipher machine and its solution by the codebreakers of Bletchley Park thus neglecting the many successes of the German codebreakers.  

The German victories during the period 1939-1942 in France, N.Africa, Atlantic and in the Eastern Front were achieved at least in part thanks to their ability to read their enemies communications.

French military codes and the Battle of France

The French military and civilian authorities used for their secret communications several codebooks, both enciphered and unenciphered. Individually these systems did not have a very high degree of security but it seems that the French strategy was to overwhelm enemy codebreakers through the simultaneous use of a large number of different codebooks (1). Additionally, it is possible that the French Army’s cipher bureau overestimated the security of the encipherment procedures used with the codebooks.

According to the available sources the following cryptosystems were in use in 1939 (2):

For high level networks (Army High Command and Army Corps) the machine cipher B-211 and 5-figure/5-letter dictionaries enciphered with transposition methods.

For mid level networks (Armies and Divisions) the machine cipher C-36 and the 4-figure/4-letter codebooks RA, ATM and 69.

For low level networks (small Army units like battalions and regiments) codebooks enciphered with short additive keys (9-13 digits long) plus 3-letter dictionaries.

From recently released TICOM reports and various books it is clear that the Germans could read French Army tactical codes (3), the Navy’s main cipher system (4) and the Airforce’s ‘Aviation Militaire’ (5). By exploiting these systems the Germans obviously got valuable intelligence. However their main success that directly contributed to their victory in 1940 was achieved against high level enciphered codes used by the French War Ministry.

The code of the French War Ministry

From the early 1930’s the German codebreakers could read the code used between the French War Ministry and the various military districts. This was a 4-figure codebook of 10.000 values enciphered with additive sequences. In September 1939 there was a change in the method of encipherment and columnar transposition was used instead of addition. Unfortunately for the French this method had been used by one of their military districts prior to September 1939, thus allowing the Germans to solve it and figure out how the transposition keys were chosen. Thanks to this compromise the Germans could read messages of the War Ministry and the military districts till June 1940. The information gained concerned the French army’s order of battle, the weak point of the Maginot Line, the mood of the troops and the population in France and in the colonies, the order of battle of the British troops stationed on the mainland and their movements.

Information on the compromise of the FLD code is available from several sources.

Colonel Mettig, head of the German Army’s signal intelligence agency Inspectorate 7/VI in the period 1941-43, said in TICOM report I-128 ‘Deciphering Achievements of  In 7/VI and OKW/Chi’, p2

‘In assessing the value of Signals Intelligence PW considers that the deciphering of messages of strategic importance is more valuable than deciphering those of tactical importance. He therefore rates most highly the solution of the French ciphers in the FLD military network radiating from Paris. The deciphering of this traffic before and during the war gave a clear picture of the order of battle of the French and Belgian armies and also of the British army.’

This success was accomplished by the codebreakers of the German High Command's deciphering department – OKW/Chi. Wilhelm Fenner, who was head of the cryptanalysis department of OKW/Chi, said in TICOM DF-187B, p7

‘Even before the military action with France began, the military systems of French higher staffs were solved. This was a 4 or 5-figure code that was systematically transposed (tableau carve) .In the cryptograms a few parallel passages (repetitions) were discovered .The interval between these passages was constant and must therefore correspond to the width of the transposition box as cryptanalytic studies have shown.If I am not mistaken the keys (Loesungen ?  ? ? )  ? ? the box itself were taken from the same code book. Despite all the cunning of this cryptographic system, the occurrence of short parallel passages proved fatal. By the aid of these deciphered messages tabs could be kept on the French Army far back into the homeland.’

Colonel Randewig, head of the intercept organization in the West during the 1940 campaign wrote in the report FMS P-038 ‘German radio intelligence’:

‘As early as December 1939 the Germans broke a special cryptographic system used by the French command in radio messages to the armies and military district headquarters. It had been used contrary to regulations prior to the opening of hostilities in September 1939. The Germans were able to solve this system because the radio station guilty of the violation was reprimanded and thereupon repeated the same messages in the proper system. Their contents revealed a certain amount of organizational information, for example, the fact that the French 2d and 3d Cavalry Divisions had been reorganized into the 1st and 2d Armored Divisions and were due to move into their assembly area northeast of Paris by 1 January 1940. However, this type of incomplete information could generally be considered only as a supplement to and confirmation of other intelligence concerning the enemy. It was not possible to deduce the enemy's order of battle from radio intelligence alone.

Nevertheless, the Germans could identify the probable concentration areas of the French and British armies from the practice messages sent by the field radio stations, although the boundaries of army groups, armies, corps and divisions could not be established with any certainty. Greater clarity prevailed about the fortified area behind the Maginot Line in the south. Enemy forces stationed near the Frenco-Swiss and Franco-Italian borders were not observed according to any regular plan. Spot-check intercepting failed to pick up the French Tenth Army in the place where it was presumed to be by the German command. However, radio intelligence did indicate the presence of the French Sixth Army.’

The importance of this intelligence is even admitted by the official history ‘British Intelligence in the Second World War volume 1’, p163-4

‘It later became clear that, until the fall of France, Germany enjoyed not only the strategic initiative but also the advantage of good operational intelligence………. During the planning and the carrying out of the attack on France the work of the enemy intelligence department of the General Staff of the German Army was of crucial importance and its value fully justified the prestige which the department had always enjoyed. The work has been described by General Ulrich Liss, head of the department from 1937 to 1943. He emphasizes that partly on the basis of British army documents captured in Norway, which provided all it needed to know about the British order of battle, and partly from the cypher traffic between the French War Ministry and the army groups, armies and home authorities, most of which it read from soon after the outbreak of war until 10 May, the department had a very comprehensive and accurate knowledge of the dispositions and qualities of the Allied forces………… During the campaign its intelligence continued to be good, and Sigint continued to be the best source.’

However the person who can give the most accurate account of the work done on the FLD code was the chief cryptanalyst of OKW/Chi, Erich Hüttenhain. According to Hüttenhain’s manuscript ‘Einzeldarstellungen aus dem Gebiet der Kryptologie‘, p14-16 (6) the code used between the French War Ministry and the military districts was a 4-figure codebook of 10.000 values, enciphered with short additive sequences. Since this method of encipherment offered limited security and the underlying code remained in use for years these messages could be read by the Germans. However a different system was used by the military district in the border with Italy. Here the code was transposed based on codewords. After finding two messages with parallel passages the German codebreakers were able to solve this system in 1938 and they realized that the transposition keys were created by using the codegroups of the codebook. Thus from mid 1939 the traffic of this military district could also be solved. In September 1939 when WWII broke out the French War Ministry instead of changing the cipher procedures, ordered that this system of transposition was to be used by all the military districts. Since the 4-figure codebook remained in use the Germans could read this traffic up to June 1940 and Hüttenhain says that the German leadership was informed of all significant operations within the French armed forces.

Among his conclusions about this case were that a country should not adopt for its main cipher a system that is already known to the enemy and thus possibly compromised and that indicator groups should be independent of the cipher.

’Das französische fld-Netz 

Beim Anfang der dreißiger Jahre benutzte das französische Kriegsministerium im Verkehr mit den französischen Wehrkreisen zur Verschlüsselung der Nachrichten einen 4Z-Code, der mit einer endlichen Additionszahl überschlüsselt wurde. Fast alle 10.000 Gruppen des 4Z-Codes waren belegt. Der Code wurde im Laufe der Jahre nicht geändert oder gar abgelöst. Die Additionszahlen wurden in kürzeren Zeitabschnitten abgelöst. Es waren jeweils gleichzeitig mehrere Additionszahlen im Gebrauch. Die Längen der einzelnen Additionszahlen waren ungerade und schwankten zwischen 7 und 13 Ziffern. Die mit dieser Geheimschrift,also mit dem 4Z-Code verschlüsselten Nachrichten wurden in den letzten Jahren vor dem 2. Weltkrieg vollständig mitgelesen. In dem Verkehr mit dem an Italien angrenzenden französischen Wehrkreis verwendete das französische Kriegsminister rium ein anderes Chi-Verfahren. Im vorangehenden Studium des gesamten Spruchmaterials dieses einen Verkehrskreises wurden 2 Sprüche gefunden, die eine größere Anzahl von fast gleich langen und über die ganzen Spruchlängen fast gleichförmig verteilten Ziffernfolgen enthielten; lediglich die Reihenfolge der diese 2 Anfangszeilen bildenden Ziffernfolgen in den beiden Sprüchen war verschieden. Diese Feststellung führte zur Erkenntnis, daß ein Ersatzverfahren mit einem Würfel überschlüsselt wurde. Mit Hilfe von 2 Anfangsreihen konnte die Würfellosung rekonstruiert und das Ersatzverfahren als 4Z-Code erkannt werden.-Es war also in den beiden Sprüchen, die zum Einbruch in das Verfahren führten, eine längere, sich über mehrere Zeilen des Würfelkastens erstreckende gleiche Textstelle vorhanden.

Der 1. Einbruch gelang im Jahre 1938. Im Laufe der nächsten Monate wurden weitere dieser Parallelstellen-Kompromisse gefunden. Es wurden die in Wortlosungen umgewandelten Würfellosungen als die Klarbedeutungen der Codegruppen des verwendeten 4Z -Codes erkannt. Und es wurde erkannt, da als Kenngruppen für die Würfellosungen 4Z -Gruppen des Codes gewählt wurden, deren Klarbedeutung jeweils die Wortlosung des Würfels war. Auf diese Weise lieferten gedeutete Codegruppen neue Würfellosungen und rekonstruierte Würfellosungen neue Codegruppen. Mitte 1939 wurde der gesamte Verkehr zwischen dem französischen Kriegsministerium und dem an Italien angrenzenden Wehrkreis, der also mit der Geheimschrift 4ZCüW verschlüsselt wurde, mitgelesen.

Als am 3. September der Krieg mit Frankreich ausbrach, verfügte das französische Kriegsministerium, daß die bisher nur im Verkehr mit dem an Italien angrenzenden Wehrkreis benutzte Geheimschrift 4ZCüW unverzüglich auch in allen anderen Wehrkreisen verwendet wurde. Es blieb der Code derselbe, und es wurden die Würfellosungen nach wie vor aus den Klartextbedeutungen der Codegruppen genommen. Es wurden lediglich an den jeweils folgerden Monatsersten geringfügige Änderungen an den Kenngruppen vorgenommen, Änderungen, die in kurzer Zeit erkannt und nach einigen Wechseln sogar vorausgeahnt wurden.

Dieser Zustand blieb bis zum Ende des Frankreichfeldzuges im Juni 1940 unverändert bestehen. Jeder aufgenommene Spruch dieses militärischen Führungsnetztes, das als fld-Netz bekannt war, wurde mitgelesen. Die deutsche militärische Führung war über alle wesentliche Vorgänge innerhalb der französischen Wehrmacht unterrichtet. Neben der Gliederung in der französischen Wehrmacht klärten die mit gelesenen Sprüche die Bewaffnung der einzelnen Einheiten auf, die schwächste Stelle der Maginot-Linie, die Stimmung der Truppe und der Bevölkerung in Frankreich und in den Kolonien, die auf dem Festland stationierten englischen Truppen und deren Bewegungen usw.

Es erscheint angebracht, an Hand dieses für Frankreich und für Deutschland folgenreichen Entzifferungs ergebnisses einige Folgerungen zu ziehen:

1. Es ist falsch, ein Chiffrierverfahren, dessen Sicherheit nicht bewiesen ist, zum Hauptverfahren zu machen, wenn es bereits als Nebenverfahren als beim Gegner bekannt vorausgesetzt werden muß.

2. Ein Chiffrierverfahren, dessen Sicherheit von der Struktur der Klartexte-Anfängen, Schlüssen,  Parallelstellen, Spruchlängen u.a. - abhängig ist darf nicht verwendet werden.

3 Kenngruppen müssen vom Chiffrierverfahren unabhängig sein; sie dürfen keine doppelte Bedeutung haben.

4. Die Erfassung des Spruchmaterials sollte vollständig sein, um auch die kompromittierenden Sprüche finden zu können.

Anm.: Rekonstruierte Seite einer Kopie, deren 12 Anschläge links unlesbar waren. Hier sind also die ersten 12 Anschläge erraten,-allerdings sinngemäß! Ausnahme: Zeile 12, wo die Zahl 13 willkürlich ist,für die allerdings 2 Bedingungen stehen: 1) >7 und Zweistelligkeit (in den 12 Anschlägen).’

Identifying the FLD codes

We can try to identify the cryptosystems used in the FLD radio network by looking at Huettehnain’s statements and various TICOM documents.

According to Army cryptanalyst dr Buggisch (7) the designations F90 and F110 referred to French Army ciphers, read during the period 1939-1940:

‘F90 and F110 were German designations for French Army cipher systems before and during the campaign in FRANCE. Both were based on a four figure code, in one case the recipher consisted of a periodic adder [or subtractor] of length 11; in the other it was ordinary transposition, the transposition key being obtained from a key word which itself was taken from the code and shown by an indicator group. Both systems were being read from the winter of 39/40 to the end of the French campaign. Solution was by methods generally known in cryptanalytic circles. One of the codes turned, up again for a short period in De Gaullist traffic.’

Note that Buggisch’s description of the systems is similar to Huettenhain’s from ‘Einzeldarstellungen aus dem Gebiet der Kryptologie‘.

In the TICOM collection of the German Foreign Ministry’s Political Archive there are documents that have more information on the ciphers F90 and F110:

1). The TICOM documents T3611 and T3612 (8) have information on cipher F90, however document T3611 is not available due to deterioration.

According to document T3612 the cipher F90 was a 4-figure code enciphered with short additive sequences of 5, 7 or 11 digit length. It seems that the codebook consisted of 20 pages, each with 100 entries, totaling 2.000 code groups.

This system was used by the network FLD (Paris) in communications with stations fla, flb, flc, flf, flg, fak, fam, flq and others and it was solved thanks to a major cipher clerk error committed in September 1937.

It seems that the same message was sent twice, first without encipherment (so only the code groups were transmitted) and then with additive encipherment. Clearly this gave the German codebreakers an opportunity to identify the basic code groups and then solve the additive sequence used for encipherment. This success allowed them to correct their own relative code findings (from previous decipherments) into the actual French code values.

The information in TICOM document T3612 matches Huettenhain’s statements about a high level code enciphered with short additive sequences being solved completely in the years prior to WWII.

2). The TICOM document T3684 (9) describes system F110 (F4ZCW110 - French 4-figure code with simple transposition) and it says than from February 1938 the radio network of the French 14^th Army, with stations in Lyon, Grenoble, Modane, Briancon, Chambery, Jausiers and Beurg-Saint-Maurice, started using this transposed code. The indicator was 55555 and the transposition key was created from the plain meaning of one of the codegroups. The example given in the report was:

p   e  r   m  i   s   s   i   o   n  o   n   n  a  i   r   e 

13 2 14  7  4 16 17  5 11  8 12  9 10  1  6 15  3

The details in the report match Huettenhain’s statements about a French military district adjacent to Italy using a transposed code, with the transposition keys being created from the codegroups of the codebook and the first breakthrough coming in 1938.

The successors to systems F90 and F110

From the available TICOM documents it seems that in September 1939 both systems were changed. Cipher F90 was replaced by a new 3-figure code plus additive, while cipher F110’s successor used the same underlying code but with a new encipherment procedure.

1). TICOM document T3661 (10) contains a report by the cryptanalyst dr Ludwig Föppl, dated 18 December 1939. In the report Föppl says that the code F90, which was used in the military command radio network FLD (Paris), was changed in September and replaced by a new system.

The new system was a 3-figure code enciphered by additive sequences. It seems the encipherment consisted of a 20-digit number that was composed of two 10-digits parts. A peculiarity of the encipherment was that each 10-digit number was composed of all the ten digits from 0 to 9 used only once (11). This system was solved and it seems that the German designation for it was F135.

2). In the notes of dr Huettenhain there is a report from November 1939 that describes the solution of the successor to system F110 (12):

'Report on the attachment to Army Group C evaluation section

On 2 September 1939 the French Army Code F110 was replaced by a new code so that traffic could no longer be broken currently.

On 3 September 1939 I was seconded to FRANKFURT-ON-MAIN in order to take part in the task of breaking this new code. The task was accomplished at the beginning of October so that all the September material could be read retrospectively.

This success was made possible in such a short time by the fact that

1) the necessary data (Code etc) was obtained by months of work in peace time, chiefly by Herrn TRAPPE (Chi OKW) and SCHMIDT (Chi OKW)

2) a close co-operation between the above named gentlemen and me could be established.

It was therefore, still possible in October to work on the October material with success. In addition to the above named gentlemen Herr Professor Dr. FOPPL was of great assistance in the solution of this system.

As the system was not changed on 1 November 1939 this code could be read currently again from the date when the October key was broken. On 3 November 1939 at the finish of my attachment in FRANKFURT-0N-MAIN I was sent to BERLIN.’

From Huettenhain’s report it seems that the underlying code remained the same (as in system F110) but the encipherment procedure was changed. By having the code the German codebreakers only needed to attack the encipherment and this was quickly achieved according to Huettenhain.

Conclusion

The German victory in the Battle of France shook the world in 1940 and countless theories were formed in order to explain this unusual event. Up to 1940 the French Army was thought to be the most powerful and best equipped force in Europe. Supported by the small British Expeditionary Force, the powerful British Fleet and with military supplies coming in from the United States the Franco-British alliance had every reason to expect a victory over Germany thanks to its superior economic resources. 

The German leadership took a huge gamble by concentrating all their armored divisions and using them to encircle and destroy the northern flank of the Allies but this gamble paid off. In a victory of such magnitude it is not possible to attribute success to only one factor. Obviously the German advantages in training, doctrine, leadership, communications etc were decisive. However the German victory also owed a lot to signals intelligence and codebreaking. 

Especially the solution, during the late 1930’s and in 1940, of the French military command’s ciphers gave the Germans valuable information on the location of the Allied units and was obviously used during the planning stage for the attack.

Notes:

(1). TICOM report DF-187B, p6 and SRH-349 ‘The Achievements of the Signal Security Agency (SSA) in World War II’, p31.

(2).  ‘Bulletin de l’ARCSI’ article: Bulletin N°3 1975: Essai d'historique du Chiffre (Add. N°3).

(3). EASI vol1 – ‘results of European Axis cryptanalysis’

(4). ‘Delusions of intelligence: Enigma, Ultra and the end of secure ciphers’, p44

(5). TICOM report I-112, p6

(6). Bayerische Staatsbibliothek: ‘Einzeldarstellungen aus dem Gebiet der Kryptologie’ - BSB Cgm 9304 a

(7). TICOM report I-176, p2

(8). German Foreign Ministry’s Political Archive - TICOM collection - file 3612 ‘Frankreich 1938 Arbeiten u.Notizen zu Code F90’

(9). German Foreign Ministry’s Political Archive - TICOM collection - file 3684 ‘Frankreich 1938 ''F4ZCUW110'', Notizen zu Chiffre f. Verteidigungsbereich, m. Beispielen’

(10). German Foreign Ministry’s Political Archive - TICOM collection - file 3661 ‘Frankreich 1939 Bericht betr. Entschlüsselung F90 Arb.-Blätter zu F135’

(11). TICOM document T3661 - Föppl report, p5

(12). TICOM report D-60, p4

Acknowledgments: I have to thank Jean-François Bouchaudy for referencing the ‘Bulletin de l’ARCSI’ articles and Frode Weierud for his analysis of the TICOM reports T3612, T3684 and T3661.

Additional information:

The US report SRH-361 ‘History of the Signal Security Agency volume two - The general cryptanalytic problems’, p136 mentions a French cryptosystem solved in 1944 that was similar to that solved by the Germans in the 1930’s. This was a transposed code, with the transposition keys created from the codegroups of the codebook.

Link to chapter VI – ‘The French systems’ of SRH-361