The German Radio Intelligence Operation were signals intelligence operations that were undertaken by German Axis forces in Europe during World War II. In keeping with German signals practice since 1942, the term "communication intelligence" () had been used when intercept units were assigned to observe both enemy "radio and wire" communication. When the observation of only enemy "radio" communication was undertaken, the term was "radio intelligence" (). The term "intercept service" () was also used up until 1942.
Towards the end of the war, about 12,000 troopers of the German Army were engaged in German Intercept Station Operations during World War II against increasingly powerful enemies. With the decline of information gained by intelligence through aerial observation, prisoner of war interrogations, and reports from enemy agents, communication intelligence became increasingly important.German radio intelligence, by Albert Praun, pp. 3–5 As a result of communication intelligence, German commanders were better informed about the enemy and enemy intentions than in any previous war.
While this form of electronic warfare was being waged, another aspect also gained steadily in importance, on the high-frequency battlefield of Radar in World War II. Radar used Microwave transmission for the location and recognition of enemy units in the air and on the sea, and each side adopted defensive measures, especially in air and submarine warfare.
The third aspect of this electronic warfare, was the radio broadcasters' war, in which propaganda experts endeavored to influence by providing propaganda against the enemy, through foreign language broadcasts over increasingly powerful transmitters. These three aspects of the radio war continued as a "cold war of the airwaves", even when the guns were silent.
Radio intelligence operations
In addition to the intelligence gained from interception of routine radio traffic in peacetime and the activity intercepted during maneuvers, the political and military events which preceded World War II offered abundant material for interception. The reason for this was the increased traffic between nation-states and the larger number of messages, transmitted by communications equipment in an evolving field. During this period, the German signals intelligence organizations and the specialists employed therein gathered an enormous amount of information. The activities of the Reichswehr intercept service from 1933 to 1939 centered around the various international crises that arose.
Intercept operations during interwar period
Austrian Revolt of 1934
In 1934, at the time of the Austrian revolt, Munich was given the task of monitoring all Austrian communications traffic including internal communications.IF-181, Page 6 In its earliest stage, the monitoring and capture of intercepts were intended only to thoroughly acquaint the Reichswehr cipher bureau personnel with Austrian traffic. However, after the revolt began, warrants for the arrest of political offenders appeared in the customs and police traffic, thus giving the Nazi Party information concerning the fate of its partisans across the border. At the same time, the intercept service monitored Italian communications. Its discovery that the Italians were massing a multitude of divisions at the Brenner Pass brought about the timely withdrawal of Germany from the affair.
Occupation of the Rhineland 1935
Ever since 1930, the Munich and Stuttgart intercept stations had, during the summer months at the time of the occupation of the Rhineland, reconnoitered the Demilitarized Zone for suitable intercept sites for use against France. After sites had been selected, the construction work was completed with the help of trustworthy civilians. Several weeks before the Remilitarization of the Rhineland, intensive monitoring of France was ordered. As a result of the intelligence, German troops marched in without fear of reprisal.IF-181, Pages 6–7
The Abyssinian War 1933–1936
From 1933 to 1935, during the period of the Abyssinian War, intercept stations of the Army High Command, monitored Italian traffic without cessation.IF-181, Page 7 During the Abyssinian War, the intercept stations and the Wehrmacht cipher bureau were able to follow all Italian traffic very closely because, with one exception, it was in possession of all Italian codes. The strength, organization, and locations of the Italian peacetime army were accurately known, and it was possible to keep abreast of the movements of each unit. The SIS also possessed a roster of all Italian officers, from Commander-in-Chief, Benito Mussolini, down to the youngest second lieutenant. Locations, strength, and armament of the Italian Colonial Troops were also known in detail.
The Spanish Civil War 1936–1939
From 1936 to 1939, the Munich and Stuttgart intercept stations monitored both factions during the Spanish Civil War.IF-181, Page 8 To facilitate this task, an advanced intercept station was created on the Wendelstein in Bavaria. From the traffic intercepted, it was realized that intercept sites in Spain itself were indispensable. Accordingly, when the Condor Legion was founded, a signals intelligence company was added to it, with personnel count eventually reaching approximately 230 men. With the company, Signals Intelligence took to the field for the first time. However, a mistake was made in placing the unit in the hands of officers who were opposed to the very existence of the signals intelligence apparatus, and who had an unfavorable effect on the work. In spite of this, the unit quickly assumed its role as the most important instrument of intelligence to the Legion Command, the more so because the signal procedures of the Communists were considered very primitive.
The monitoring of the Spanish Civil War was an opportunity to conduct a "war by proxy" against the Soviet Union, as the Republican Armies communications equipment was of mostly soviet origin and design.
Czechoslovakia 1938
For a long time during the interwar period, the entire radio net traffic of Czechoslovakia was considered easy to intercept and evaluate. It was observed by fixed listening posts and intercept companies in Silesia and Bavaria and subsequently also by stations in Austria. Towards the end of May 1938, one of the key radio stations in Prague, attached to the Czechoslovak War Ministry, suddenly transmitted a brief unusual message, which was believed to be an order for mobilization. This message was immediately followed by changes in the radio traffic characterized by the use of new frequencies and call signs, and by regrouping of radio nets which had been prepared for the event of mobilization. During the next few days, very primitive and simple radio nets appeared along the border and then disappeared again when the tension was relaxed, whereupon the entire radio net resumed its original characteristics. The Intercept Control Station was able to report that the mobilization order had been revoked.German radio intelligence, by Albert Praun, pp. 6–7
Czechoslovakia radio efficiency
During the middle of 1938, the Czechoslovakia war ministry repeated the same procedure as happened in Spring 1938. Again another announcement for mobilization order was repeated by radio and within a few minutes, the message was forwarded to Berlin. The same primitive radio nets appeared along the border with almost the same call signs on the same radio frequencies.
German signal intelligence considered it a practical object lesson in how to run an inept radio operation. The reason for the two partial mobilizations by Czechoslovakia was considered by the Professor of History, Igor Lukeš, who has studied this event at length, stating that it was a possible deception operation by the Soviet Union, where disinformation was fed to the Czechoslovaks, causing the partial mobilization. The reason was that Joseph Stalin feared not war but a diplomatic arrangement between the western allies and Hitler leading to the collapse of Czechoslovakia. Certainly at that time Hitler had no plans to invade Czechoslovakia, although it seems the mobilization seemed to cause a change of mind.
Intercept operations during World War II
Polish Campaign 1939
Polish radio communications were well known to the Intercept Control Station, as a result of long observation during the interwar period, and were intercepted from points in Silesia and East Prussia. During the summer of 1939, the intercept service and cipher bureau observed not only the regular traffic but a large number of field messages which increased daily and was far out of proportion to the known organisation and radio equipment possessed by the Polish Army. As was later confirmed after the Invasion of Poland in September 1939, the purpose of this was to camouflage Polish radio communications by using three call signs and three frequencies for each station. Intelligence officers engaged in the evaluation of traffic and D/F data were unable to derive any detailed tactical results from the intercepted messages. It was impossible for officers to determine if Polish efforts to disguise their efforts were to simulate stronger forces than they possessed. In any case, the lack of radio silence in the assembly area was a grave mistake.German radio intelligence, by Albert Praun, pp. 8–9
In 1939, German intercept was still mostly immobile. Intercept companies were mostly motorized but there was no close cooperation between them and the army group and HQ. The Polish radio communication system failed after the second day of the campaign when it attempted to take the place of the wire landlines destroyed by bombing. Perhaps as a result of the intercept successes they had achieved in the 1920s, they had restricted peacetime radio activity to a minimum. As soon as they ramped up radio communications, their communication nets collapsed completely. The system was unable to keep pace with the Polish retreat, and they were seized by a kind of panic. Clear-text messages revealed that some stations would not transmit, lest they be bombed. The lack of information meant that the leading source of information regarding the situation became the German OKW communique (). This mistake was corrected by the OKW in 1940.
A Commander of Intercept Troops East () was left in occupied Poland to continue monitoring the Soviet Union from the intercept posts in Königsberg/Cranz and Striegau with the 3rd/7 and 3rd/18 intercept companies.
Soviet Union 1939–1940
After the conclusion of the Polish Campaign, the intercept company FAK 610 (KONA 6), stationed in Galacia region, in the Sanok-Jaroslav-Sandomir area was charged with intercepting radio traffic from the officially friendly Soviet Union units, in eastern Poland, while the Soviet Union was undertaking the invasion of Poland.