German intelligence on operation Overlord

In the summer of 1944 the German army suffered two horrific defeats that sealed the fate of the NS regime. In the West the Anglo-Americans were able to invade France and after hard fighting in Normandy they routed the German forces in the West and liberated France.

In the East a huge Soviet offensive against Army Group Centre in Belorussia resulted in a crushing defeat for the Germans and the liberation of the last part of occupied Soviet territory.

Operation Overlord was the Anglo-Americans plan to invade and liberate France. It had been planned thoroughly and huge military forces were assigned for it.

One of the most interesting questions of WWII history is whether the Germans could have taken measures that would lead to a defeat of the Allies in the West. Many authors and historians claim that the Germans had huge forces in the West but were prevented from moving them to Normandy because of a deception plan. I have criticized this belief here and here. The problem is that the positioning of German divisions in the West does not correspond with that theory.

During the first half of 1944 the Germans had not only moved new units into Normandy but out of their best divisions 3 out of 4 were close to it and only 1 near Calais. It was these forces that held the Allies contained in Normandy for two months.

Specifically out of their 4 operational Panzer divisions in the West 3 ( Pz Lehr, 12 SS ‘Hitlerjugend’ and 21^st Pz) were positioned close to Normandy and only 2^nd Pz close to Calais.

Also many units had been moved to Normandy during May ‘44. The 91^st Air Landing Division was posted to the Cotentin peninsula along with Parachute Regiment 6, 101 Werfer regiment, 206 Pz battalion, 70 Army Assault battalion, 17 machine gun battalion and 100 Pz training battalion. Total strength of these units was more than 14.000 men plus 70-80 French tanks and 54 rocket launchers. [Sources: ‘British intelligence in the Second world war’ vol3 part 2 - Appendix 9 and ‘Normandy 1944: German Military Organization, Combat Power and Organizational Effectiveness’]

In addition the 352 Infantry Div was moved to the shore and the 21^st Pz close to Caen. The last minute movement of these two units was not identified by Allied intel with serious consequences on D-day.

Why did the Germans place new units in Normandy? Why did they position powerful mobile units close by? Weren’t they expecting an Allied assault against the Calais area?

It seems that by May ’44 their attention had definitely shifted towards the Normandy-Brittany areas.

Hitler in a talk with Japanese ambassador Oshima on 27 May 1944 said that diversionary attacks would take place in Norway, Denmark, the Southern part of Western France and the coasts of the French Mediterranean. A major allied assault would come in either Normandy or Brittany. This would be a serious operation but once the Allies had consolidated their position it would probably be followed by the main invasion in the Calais area.

From NARA archives RG 457 SRDJ Nos 59973-5:

Another report FMS B-675 ‘Army Group B-Intelligence Estimate (1 Jun 1944)’ By Oberst i. G. Anton Staubwasser (head of intelligence for Army Group B in 1944-45) says that the German high command became convinced that Normandy would be the site of Allied landings in April/May ’44:

It is important that - for the first time in April/May - Hitler informed OB West, through General O. JODEL, as follows: "The Fuehrer has definite information that Normandy is endangered." It has not become known from, what source this news originated. This message was immediately and also later repeatedly passed on to A Gp B and all armies of the west, that is, approximately 4 weeks before the beginning of the invasion. This is also the reason for the transfer of the 91 Luftwaffe Division, several armored battalions and antitank battalions to the COTENTIN peninsula and for the assembly by OKW of the Pz Lehr Division.

General Alfred Jodl, Chief of the Operations Staff of OKW said the following in TICOM I-143 ‘Report on the Interrogation of Five Leading Germans at Nuremburg on 27th September 1945', p3

3. Signals Intelligence, however, provided very little definite information regarding the invasion before ‘D. Day’. They had not much idea where the schwerpunkt was going to be but thought it would probably be at Cherbourg, with a second attack in the Pas de Calais.

General Walter Warlimont, deputy chief of the Armed Forces Operations Staff, said in report ETHINT-1 that the last minute movement of German units to Normandy and Brittany was a response to intelligence reports showing the concentration of Allied forces in Southeast and Southwest Britain.

How could the Germans have correctly identified the invasion area at that time?

I’ve tried to look into all the Germans sources of secret intelligence during the period late ’43-mid ’44:

Luftwaffe reconnaissance:

By 1944 the Luftwaffe was hopelessly outnumbered both in the East and in the West. Allied fighter defenses made long range recon missions over Britain very dangerous. According to an official British study called ‘The Rise and Fall of the German Air Force, 1933-1945’, p323 the German effort was extremely limited in extent. The main effort was over the South and South-West coasts but Scapa Flow and Northern Scotland were also covered. German planes did not penetrate overland and there was no frequent coverage.

Another book ‘Eagle in flames: the fall of the Luftwaffe’ by E. R. Hooton, p284 gives more details. According to Hooton recon missions were very dangerous since the RAF had standing fighter patrols over the assembly areas, so most photographs were of targets within 40km of the coast. A Bf-109 was able to take pictures of Portsmouth harbor shortly before D-day but was destroyed when landing in France. However the Germans were able to take more photos by using a captured P-47 Thunderbolt. Recon units in France flew missions over Southern England and those in Norway covered Scotland.

David Kahn in ‘Hitler’s Spies’, p499 says that on 25 April Luftwaffe recon showed 234 LCT’s, 254 small and 170 auxiliary landing boats and 15 transports in Portsmouth, Southampton and Selsey Bill. These were judged capable of transporting 70.000 men.

Cicero spy:

The valet of the British ambassador to Turkey was a German spy and provided them with classified reports held in the ambassadors safe. Through these reports the Germans learned the codename Overlord:

Thanks to Cicero, Hitler was soon reading the British ambassador’s enraged telegram to Churchill on December 13, reporting that the Turks were demanding impossible amounts of armaments before they would agree to terms – a ploy familiar to the Führer from his dealings with the Italians. Eden accepted temporary defeat and cabled the following to his ambassador:

To sum up. Our object is to get Turkey into the war as early as possible, and in any case to maintain a threat to the Germans from the eastern end of the Mediterranean, until Overlord is launched… We still have not given up the idea that our squadrons should fly in on 15th February. [Source: ‘Hitler’s War’, p641]

However no details of the actual operation were betrayed.

Royal Navy low level codes:

Low level codes used by small ships were easily read by German naval codebreakers and they allowed them to identify the movement of landing ships from the Med and the Scottish coast to the Southern and East coasts of the UK. [Source: ADM 1/27186, p85 and 91]

British railways code:

According to ‘Delusions of intelligence’, p46:

This same Heer station had broken into the British railroads codes by late November 1943 and claimed a 98 percent success rate in reading the two thousand plus signals produced by twenty-six keys in December 1943. Although not considered vital in peacetime, such intelligence on Britain proved important by providing information on the movement of troops and supplies.

From the reports of Inspectorate 7/VI and NAAS 5 it is stated that the radio network of the railways was investigated since August 1943, the cipher system was solved in November and in the months of December 1943 and January 1944 the traffic was read with almost 100% success . However from February this traffic could no longer be identified.

The traffic of the railways organization could be used to monitor the movement of troops and supplies in the UK. In combination with the RN codes mentioned earlier it could have revealed to them the concentration of forces in the South.

Allied airforce radio traffic:

Creation of Allied Expeditionary Air Forces - AEAF:

The Luftwaffe signal intelligence service was able to ascertain that the call sign procedure of the US 9^th Airforce was changed to be similar to that used by the British 2^nd TAF (Tactical Air Force). This meant that the British and American ground support airforces had combined under one Command.

Conclusion of practice traffic:

Practice traffic of military units in Britain had been monitored for years. In March 1944 after exercise ‘Spartan’ all practice traffic stopped. This was an obvious sign that actual operations were imminent.

Transfer of units of the RAF’s 2^nd TAF:

The units of 2^nd TAF were monitored through traffic analysis and direction finding. In April/May most of the units were being transferred to Southern England, specifically the Portsmouth-Tangmere and Reading-Odiham areas.

Reinforcement of IX and XIX tactical air commands:

In the middle of May units of the US 8^th AF were moved to the 9^th AF. This was revealed when they changed their frequencies to those used by 9^th AF. The traffic of 9^th AF units showed a large concentration in the Middle-Wallop area in South England and a smaller one in South East England.

US Transport Command code:

The codebreakers of the German airforce were able to solve the Bomber code used by units of the US Transport Command. Bomber code was a daily changing 2-letter code table.

This allowed them to identify that the aircraft used was the C-47 transport. The bases of these units were found in the following areas through D/F (direction finding):

1.     Grantham-Cottesmore

2.     Aldermaston

3.     Exeter

Also through statistical analysis and D/F they established that the transport command had a very large number of aircraft (around 1.000) and it was assumed that they would take part in air-landing operations during the upcoming invasion

Preparation of RAF 38th Group for air landing operations:

The 38^th Group of the RAF worked with the intelligence service SOE and SIS in secret operations. Their main function was to transport spies and saboteurs into occupied Europe as well as airdrop weapons for the resistance movements.

The Luftwaffe’s signal intelligence service was able to find out (through cryptanalysis of the Bomber code and traffic analysis and D/F) that the 38^th Group was preparing for air landing operations in cooperation with the 2^nd TAF.

Practice traffic between aircraft control stations and Air Support Parties:

In the second half of May ’44 the practice traffic between aircraft control stations aboard warships and Air Support Parties was intercepted. Through D/F this traffic was located in the area off Plymouth and Southampton. The appraisal of the signal intelligence service was that embarkation had begun and the allied operation was imminent.

The endangered area was from Calais to Cherbourg.

The source on airforce codes is TICOM I-109 ‘Translation of a Report by Lt. Ludwig of Chi Stelle OB.d.L, based on questions set for him at ADI(K)’, p15-8:

Slidex used by British ALO’s (Army Liaison Officers):

The SLIDEX referred to by the Germans as the EC 30/3 was reconstructed by 9 Fixed Intercept Sta in May 44. Traffic intercepted had been originated by ALOs links (FLIVONETZE) in UK. Control of these links was always at Corps level and reading of traffic gave an insight into Corps O of B, etc. PW states that traffic was British and not American and that as far as he could make out the ALOs were Army and RAF officers.

[Source: CSDIC/CMF/Y 40 - 'First Detailed Interrogation on Report on Barthel Thomas’, p3]


M-209 used by US armed forces:

The M-209 cipher machine was used extensively by the US armed forces in the period 1943-45. Army units in England sent training messages on the M-209 which the Germans decoded. The USAAF used it in operational and administrative networks.

From the war diary of Inspectorate 7/VI and the reports of NAAS 5 it is clear that in the first half of 1944 M-209 messages from US forces in the UK were solved and valuable intelligence was gathered on the groupings of US military forces. In the period February-May ’44 the USA section of Inspectorate 7/VI issued 47 reports based on 678 decoded messages. Also the report E-Bericht Nr. 3/44 der NAASt 5 (Berichtszeit 1.4-30.6.44), pages 3-8 shows that NAAS 5 solved 1.119 messages during April-May ’44 and got intelligence on the assembly of US troops.

 

Activity report before the invasion

…………………………………………

1). AM1:

Focused on decoding the AM1. Ten absolute settings were recovered, which brought the deciphering of 1,119 messages. This cipher-material, mostly composed by the U.S American Expeditionary Corps, gave valuable insights into the location of enemy groups.

After the Allies landed in Normandy a significant number of M-209 messages continued to be read revealing the Allied order of battle. The messages for the days of 6-9 June were solved thanks to captured cipher material.

Division Field Code of the 29th Infantry Division

The US Division Field Code was a 4-letter codebook of approximately 10.000 groups, used primarily for training purposes. In 1944 the 29th Infantry Division, stationed in the UK, was using the 28th edition of the DFC for training messages. Some of these messages were solved by NAAS 5 which was the cryptanalytic centre of KONA 5 (Signals Intelligence Regiment 5), covering Western Europe. The reports of that unit show that these decoded messages allowed the Germans to identify the 29th Infantry Division and considering the unit’s rule during operation Overlord it is possible that they gave the Germans vital clues about the upcoming invasion of France.

 

Bell Labs A-3 speech scrambler:

The A-3 speech scrambler was used on the Washington-London radiotelephone link during the war. Two separate German teams were able to solve it and eavesdrop on sensitive Allied talks. One of these talks is described by General Walter Schellenberg of the SD security service in his memoirs:

Early in 1944 we hit a bull's eye by tapping a telephone conversation between Roosevelt and Churchill which was overheard and deciphered by the giant German listening post in Holland. Though the conversation was scrambled, we unscrambled it by means of a highly complicated apparatus. It lasted almost five minutes, and disclosed a crescendo of military activity in Britain, thereby corroborating the many reports of impending invasion. Had the two statesmen known that the enemy was listening to their conversation, Roosevelt would hardly have been likely to say good-bye to Churchill with the words, 'Well, we will do our best-now I will go fishing.' [Source: ‘The memoirs of Hitler’s spymaster’, p418]

In summer 1943 another speech privacy system, called SIGSALY, was introduced and this was secure, however it didn’t become fully operational till April ’44 and even after that time officials preferred to use the A-3 since the only Sigsaly link could be accessed at the Cabinet War Rooms. Perhaps some important detail passed on the A-3 link. [Source: ‘The woman who censored Churchill’, p112-3]
.

US diplomatic codes:

In 1943 till mid ’44 the Germans could read the State Department codes Gray, Brown, A1, C1 and M-138 strip. Could there be details of op. Overlord in the diplomatic messages? The Germans already knew of the codename Overlord through their spy ‘Cicero’.

In ‘Swedish Signals Intelligence’, p208 an interesting episode is described. On 30 May 1944 the Finnish codebreakers decoded a US message on the M-138 strip that said Ira Hirschmann would be in Europe with ‘Overlord’ on 6 June. The Finns realized this referred to the major Allied operation but did not tell their German Allies.

Could the Germans have decoded similar messages dealing with Overlord? No concrete details are known.

Polish codes:

The Polish government in exile was a close ally of the British and its secret service provided the Allies with countless important reports. In exchange for this work Polish communications did not have to adhere to the same rules as other small Allied nations. Specifically they were allowed their own communication facilities and their own codes with no interference from the British authorities.

Because of its close relation to the Anglo-Americans and the efficiency of its secret service the Polish government was exceptionally well informed on important events.

The Germans were able to take advantage of this by decoding Polish codes. According to postwar reports they got information of great value from Polish diplomatic, secret service and resistance movement communications.

Let’s take a look at the relevant cases.

Polish resistance movement code London-Warsaw:

From TICOM I-115 'Further Interrogation of Oberstlt METTIG of OKW/Chi on the German Wireless Security Service (Funkuberwachung)’, p9

It was possible, moreover, to crack all wireless traffic which the Polish government in LONDON carried on with its organizations in Poland. The methods by which these transmissions were compromised are not known to PW. This activity was kept very secret indeed, owing to the importance of the source, which furnished the German Government with up to date information on the situation in POLAND and the development of the Polish question. To preserve secrecy and partly to ensure quicker delivery of the decodes, members of the Polish section of Referat VAUCK, which was then in DORF ZINNA near JUTERBOG, were transferred in autumn 43 to the Polish Referat of OKW/Chi, Gruppe V (angestellter BERND) in BERLIN. The clear text was published by OKW/Chi as "VN" (Verlässliche Nachrichten) and given extremely limited distribution. Simultaneously, Polish wireless traffic was also intercepted by FNAST LAUF, an intercept station of OKW/Chi. This double-interception was ordered deliberately, on account of the value of the traffic. A further success against the cipher systems of the Polish Government in exile was achieved over the link LONDON - TURKEY (ANKARA). PW does not know if this system was solved by Referat VAUCK or by the Polish section of OKW/Chi

47. Results in this field were almost sensational when, just before the Allied invasion of France a ban on all WT transmissions from ENGLAND was instituted which included even diplomatic channels; the wireless traffic of Polish agents to ENGLAND, however, continued to operate.

In ‘Hitler’s Spies’, p508 it is stated that a message was intercepted from the Polish government in London calling for all Poles to take up weapons against the Germans on 15 May.

Polish diplomatic link London-Washington:

From TICOM I-159 ‘Report on GAF Intelligence based on Interrogation of Hauptmann Zetzsche’, p3

9. Intelligence concerning foreign diplomatic exchanges was received from the Forschungsamt (subordinated directly to GOERING) through Ic/Luftwesen/Abwehr, and was given a restricted distribution. It consisted of intercepted Allied radio-telegrams (e.g. London-Stockholm), ordinary radio reports (e.g. Atlantic Radio) and intercepted traffic between diplomats and ministers on certain links, e.g. Ankara-Moscow (Turks), Bern-Washington (Americans), London-Washington (Poles).

10. The last-mentioned source was of great value before and during the invasion and after the breaking-off of Turkish-German relations. In general the Forschungsamt reports contained a great deal of significant information concerning economic and political matters.

Polish secret service link London-Grenoble:

The Polish secret service operated many networks in occupied France. In 1943 their communications on the link London-Grenoble were decoded by OKW/Chi. The code used was a version of the British Stencil Subtractor Frame.

From report CSDIC SIR 1719  'Notes on Leitstelle III West Fur Frontaufklarung’, p15

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.

109. The code and cipher dept of Funkabwehr succeeded only rarely in breaking codes used by Allied agents in cases where no document containing the code or cipher was available. It more frequently succeeded in breaking codes when documents containing them were captured.

However British report DS/24/1556 says that this link was ‘a properly controlled leakage’. This probably means that when the Brits found out about the German success they sold out the Poles in order to protect Overlord.

Overview of Polish communications:

Could the Poles have transmitted information on op. Overlord? It’s not unlikely. They were after all very well informed on military and political events. British report DS/24/1556 admitted that no one knew what kind of information passed on Polish links.

Uncontrolled spies:

The spies that the Germans sent to Britain were all(?) identified and controlled by the British. This meant that the information they sent back to Germany was designed to mislead the German high command.

However in 1944 two spies existed that were not controlled by the Allies and they transmitted interesting information to the Germans. One was in Sweden, the other in Portugal.

From Stockholm Karl Heinz Krämer provided a steady stream of maritime and aviation intelligence allegedly obtained in Britain by agents code-named HEKTOR and JOSEPHINE. A British investigation showed that he did not really have agents in the UK but rather got his intel from the press and conversations with Swedish officers and foreign envoys, notably the Japanese military attaché Makato Onodera. [Source: Historical dictionary of German intelligence, p244]

From Lisbon the agent Paul Fidrmuc sent a report correctly identifying the endangered area ‘the plan of attack favored by the Allies was an assault on La Manche (Cherbourg) peninsula’. According to his postwar interrogation he got this information from his agent ‘TOR’ in the UK.

 

[Sources: ‘British intelligence in the Second world war’ vol3 part 2, p61 and KV 2/198 ‘Paul Georg FIDRMUC, alias FIDERMUTZ, RANTZAU, codename OSTRO’]

SIS-SOE codes:

From TICOM I-115 'Further Interrogation of Oberstlt METTIG of OKW/Chi on the German Wireless Security Service (Funkuberwachung)’, p5

26. PW cannot give any accurate details of playing back activities in which Referat VAUCK participated. Dr VAUCK told him that shortly before the beginning of the invasion twelve links, operated either by German personnel or by agents turned round, were running from FRANCE to ENGLAND. Of these twelve links, the Germans intended in six cases to reveal in the course of transmission that the cipher had been broken and that the agent was being played back. It was hoped thereby to confuse the British Intelligence Service, so that they would begin worrying which other of their many links were compromised. PW does not know whether, and if so with what success, this operation was carried out.

The Agents section of OKH/in 7/IV (later moved to the Funkabwehr) was able to decode agents transmissions, usually through physical capture of the cipher material but sometimes through cryptanalysis.

German intelligence agencies like the Abwehr and the Sicherheitsdienst had many agents inside Western European movements and especially in France they controlled whole resistance groups.

In June ’44 they were aware that the BBC had issued secret orders for the resistance movements to prepare for the invasion.

Could they have identified the Allied interest in Normandy through their agents? A report dated 20 March from the evaluation center Foreign Armies West said:

…………Continuing observation of enemy air attacks, agents activities and agents wireless networks in the occupied areas of the West unanimously and  clearly show concentrations in the areas Pas de Calais, Paris, Tours, Loire estuary and the south coast of France. [Source: ‘British intelligence in the Second world war’ vol3 part 2, p54]

Normandy is not mentioned. Could they have received new information in the period April-May?

It seems so, as the Sicherheitsdienst intercepted messages to the underground  Armée Secrète in the Le Havre area. This resistance group was ordered on 15 May to go on full alert on 20 May. Prealarm messages were analyzed by the Reich Main Security Office-RSHA and the majority were addressed to groups in Brittany, Normandy and the Lille-Amiens area. [Source: ‘Hitler’s Spies’, p510-1]

Conclusion:

In 1944 the German high command knew that a major landing operation would come in the West. Although they expected diversionary operations in Norway, Southern France and the Balkans they believed that the main invasion would take place in the Northern coast of France. The area they considered most likely to be invaded was from Calais to Cherbourg.

Initially their belief was that the area around Calais was the most likely target.

However by May ’44 the Germans had shifted their attention to the Normandy-Brittany areas. New units were moved there and they were the reason that the fighting in Normandy was hard for the Allies.

It is not clear on what information they based this change in strategy. It is reasonable to assume that some or all of the intelligence that alerted the Germans came from a combination of codebreaking with traffic analysis and D/F.

The Allied units in Britain took many security measures but could not keep 100% radio silence. Their decoded messages and their radio emissions gave vital clues regarding the concentration of forces in the South.

Low level naval codes gave excellent intelligence on the movement of landing ships. 

Radio traffic of the Allied air forces showed the movement of units to the South of England.

Did the Germans learn more specific details of ‘Overlord’? How could Hitler have ‘definite information’?

The Polish resistance movement and diplomatic codes could have revealed information on Overlord. Unfortunately details are lacking. The problem for the Allies was that Polish communications were not monitored nor were they forced to share their codesystems with the British.

US diplomatic communications were also vulnerable in the first half of 1944.

Despite the Allied effort to fortify their codes even in 1944 many of their systems were insecure. The intelligence gathered from secret Allied communications must have been the reason that the Germans moved units to Normandy. The battle of attrition was finally won by the Allies but if the difference of forces was more tolerable then the outcome of the battle might have been different.

More research is needed to identify if ‘Overlord’ was compromised from signals intelligence. Instead we’ll probably get more books and articles on how the Germans had millions of troops in the West but were tricked into holding them back.