German signals intelligence successes during operation Barbarossa

On June 22 1941 the military forces of Nazi Germany attacked the Soviet Union, thus starting the largest land campaign in history.

Codebreaking and signals intelligence played a major role in the German war effort. Army and Luftwaffe units relied on signals intelligence in order to monitor enemy units and anticipate major actions.

For a summary of German signal intelligence operations read Compromise of Soviet codes in WWII.

Information on the Enigma cipher machine found in the War Diary of Inspectorate 7/VI

During WWII the German Army made extensive use of signals intelligence and codebreaking in its operations against enemy forces. German commanders relied on signals intelligence in order to ascertain the enemy’s order of battle and track the movements of units.

The German Army’s signal intelligence agency operated a number of fixed intercept stations and also had mobile units assigned to Army Groups. These units were called KONA (Kommandeur der Nachrichtenaufklärung - Signals Intelligence Regiment) and each had an evaluation centre, a stationary intercept company, two long range signal intelligence companies and two close range signal intelligence companies.

The KONA units did not have the ability to solve complicated Allied cryptosystems. Instead they focused on exploiting low/mid level ciphers and even in this capacity they were assisted by material sent to them by the central cryptanalytic department in Berlin. This was the German Army High Command’s Inspectorate 7/VI. 

The War Diary of Inspectorate 7/VI

Some files of the German army signal intelligence service survived WWII and were retrieved in 1947 from a camp in Glasenbach, Austria, where they had been buried at the end of the war.

The War Diary of Inspectorate 7/VI for the years 1939-45 can be found in the US National Archives, in collection RG457 and in the TICOM collection of the German Foreign Ministry’s Political Archive.

The reports of departments 1, 7, 13 and F occasionally have information on the Enigma cipher machine (both commercial and plugboard versions).

Initially department 1 was responsible for general cryptanalytic research but in 1941 department 7 was created to look into the security of German cipher systems. For a time both 1 and 7 did general crypto research. In November 1942 department 13 was created and from then on department 7 dealt solely with German hand systems, while department 13 was responsible for German cipher machines. In 1943 department F (Forschung/Research) was created to do general cryptanalytic research.

I’ve copied the relevant passages from the War Diary and used google translate. However many terms were not translated correctly so it was up to Frode Weierud, an expert on Enigma history, to correct these passages.

Thus I present the War Diary entries dealing with the Enigma machine for the years 1941-45 (I’m afraid I don’t have the files of 1939-40):

Secure ciphers - Insecure messages

In the construction and use of tactical cryptosystems there are two conflicting requirements. One is security and the other is ease of use. If a system is highly secure but hard and time consuming to use then important messages might be secure from cryptanalysis but they could arrive too late, with disastrous consequences. On the other hand if a system is extremely easy to use but insecure then the messages will get through on time but the enemy will also be able to read them.

The Slidex code, used by the US and British armies in WWII was easy to use but it could be solved in a few hours by the German codebreakers.

However the British Army’s double transposition cipher and the US Army’s M-209 cipher machine were basically secure systems, since they could only be solved through mistakes in encipherment. It seems that contrary to regulations the Allied troops did not always use these systems in the field since it took too long to encipher their messages.

UK example

Letter from the War Office to the Commanders in Chief 21st Army Group, Home Forces, Middle East, Persia-Iraq (dated February 1945):

‘Sir,

I am commanded by the Army Council to inform you that further consideration has been given to the suitability for operational purposes of the Low-Grade cipher "Double Transposition" which was introduced for use throughout the Army by War Office letter 32/Tels/943 dated 5th November, 1943.

2. Experience shows that while this cipher affords adequate security, unit personnel find it difficult and slow to operate. There is, therefore, a tendency to avoid the use of cipher with a consequent possibility of overstrain of other safe means of communication or the use of wireless in clear to a dangerous extent.

3. It has, therefore, been decided to adopt a new Low Grade cipher, called LINEX, details of which are given in appendices A to D, in place of Double Transposition.’

US example

Report of interview with S/Sgt, Communications Section 79 Inf Div, 7th Army. (dated March 1945):

"The US Army code machine #209 was found to be something that hampered operations. It would take at least half hour to get a message through from the message center by use of this code machine and as a result the codes of particular importance or speed, for instance mortar messages, were sent in the clear."

Sources: British national archives WO 193/211 ‘Wireless, cable and signal (including cipher) communications: policy and codes: action from report of Godwin-Austen Committee’, US national archives - collection RG457 - Entry 9032 - box 1.024 - US COMSEC reports.

6 June 1944 – Allied plans, German intelligence and allocation of German units

With the anniversary of the Allied landings in Normandy coming up, it’s time to read up on some aspects of the battle that have been overlooked by historians:

German intelligence on operation Overlord

Normandy 1944 - Allied estimates of German power

Normandy 1944 – What-if scenarios and the Fortitude deception

The Jellyfish radio-teletype link

German fuel reserve - Normandy 1944