The Miracle of the Marne
On the Western Front, a German attack was made through Belgium as part of the Schlieffen Plan, which was designed to sweep onward through northern France to crush the French Army. This theatre of war became one of rapid movement, but signals intercepts were going to decide much of the battle’s outcome as well. The French Deuxième Bureau on the Western Front was well prepared for the signals war and were determined that they were going to defeat the German Army’s attack, even though they did not have the benefit of the plain text messages that Hindenburg enjoyed reading during his campaign in the east. However, they were able to decipher the German messages quite easily. The Miracle of the Marne was not the miracle it was made out to be as it was primarily due to the French practising their skills in intercepting and deciphering enemy signals well before war began. The German High Command had planned their army’s advance through Belgium with a great sweep east around Paris to surround the French Army and destroy it. On their right wing, the First Army was commanded by General von Kluck. His subordinate, General von der Marwitz, commanded a cavalry corps that made good use of their radio equipment in the German fast-moving advance. Von Kluck’s rapid advance through Belgium and then into France used radio extensively to co-ordinate the units of his army according to plan. However, German radio operators had little training in signals operations and their skills in the new discipline were slim. They sent transmissions correctly in cipher to begin with, but as the heat of battle increased, messages were sometimes sent in plain text and security procedures began to flag. The French intercept service began monitoring the German Army’s radio traffic even before they began to cross the Belgian border, and this enabled them to track regularly and with increasing detail the positions and movements of their advancing enemy.
The Cabinet Noir was the cryptographic department of the Deuxième Bureau and intercepted over 350 radiograms transmitted by the German cavalry corps over a two-week period during the campaign. The Bureau called their interceptions the ‘Marwitz Telegrams’ as the German wireless operators disguised their call-signs less and less effectively, as the stress of battle made them more lax in their wireless security disciplines. Messages were hurriedly enciphered (or otherwise) by the radio station officers, who often had little understanding of the reasons for them. Radio station staff had no clear instruction on wireless security so the call-signs of each station in the army invariably started with the same letter and remained unchanged as their advance progressed, nor was there any change in wavelength of the broadcasts. The French were able to establish the wireless stations of every German Army division by their individual call-signs. Cavalry units were the worst offenders, probably due to stress of their fast-moving formations, although some infantry divisions and even corps developed bad security habits as well. Each German cavalry control station, for instance, had an identifying letter: ‘S’ was the designation of units in Belgium, ‘G’ in Luxembourg, ‘L’ in the Woëvre and ‘D’ in Lorraine. Confirmation from some messages came in plain text and could even be clearly signed by the sender with their rank and name. After a few intercepts, it became known that General von der Marwitz commanded the corps using the ‘S’ letter in Belgium and General Richthofen commanded the corps using the letter ‘G’ in Luxembourg. A clear message with a call-sign ‘L’ stated that two cavalry divisions had forced their way into the Woëvre Valley and were moving towards Verdun via Malavillers and Xivry-Circourt. This kind of information was extremely valuable to the French general directing his battle. After a few days of these interceptions, the Deuxième Bureau were able to describe to the French General Staff the operational structure of the enemy forces they were facing in detail. The Bureau followed the movements of von Kluck’s First Army as it advanced through Belgium and from this were also able to extrapolate and deduct the structure and strength of Second Army under General Otto von Bulow. These two armies were unable to keep in touch with each other as they wheeled in a great arc across France and a widening gap began to appear between them.
Von der Marwitz’s cavalry were ordered by radio to provide a thin screen of lancers to cover the widening gap between First and Second armies. The French identified this as a weak spot in the German front that began to stretch for miles as the two armies advanced at an uneven pace. Using signals intelligence gleaned by the Deuxième Bureau on 8 September, the French general struck at the critical point between the two German armies’ line of advance. They soon began to threaten the German First Army with encirclement and outflank von Bulow’s Second Army in the process, causing both German armies to retreat. The German High Command was blamed for ordering the retirement when the Battle of the Marne was ‘almost’ won in the minds of the German public. Frontline French soldiers were surprised by the change; the German Army retreating in the face of a desperate French resistance became known as ‘The Miracle’ in public parlance. The French High Command and the Deuxième Bureau, however, knew better.
The Race to the Sea
The British had formed an Army Signal Service in 1912 as part of the Royal Engineers at a time when there was little money or resources available from the War Office. They did not envisage the size or complexity of the conflict that was to come, so wireless communications were not a priority and were rarely used by staff officers who probably did not fully understand, and even mistrusted, the new-fangled codes and ciphers. The intercept services of the British Expeditionary Force (BEF) in France were, therefore, under-used in the war’s opening stages so operators had time to listen to enemy transmissions in a similar way that the German operators had done in Thorn Fortress on the Eastern Front. Operators began to intercept enemy transmissions and gauge the intentions of the enemy, so transmissions were restricted or being sent by the more traditional means of runners or riders to keep the airwaves clear. It is unlikely that they used Hindenburg’s innovation of sending despatches by aeroplane, but one novelty that the BEF did have was a ‘wireless compass’ device which was issued to them in 1914. This was a direction-finding receiver made by Marconi and further developed by Professor Sir John Fleming (who coined the word ‘electronic’). The newly instituted Direction Finding Service started using its new equipment in locating enemy transmitters for the BEF, and this was later taken up with good effect by the Royal Navy. Radio stations were invariably attached to the headquarters of an army formation and it was possible to locate German formations by ‘wireless compass’ as the message was being transmitted. The ability to spot the source of enemy transmissions and thus piece together their order of battle became increasingly important during the course of the war.
General von Kluck found himself checkmated at the River Marne, north of Paris, so he switched his attack further west to outflank the French, British and some Belgian forces that were positioned nearer to the French coast. The Germans probed the French and British line of defence in the direction of the Channel in a deadly dance of men and guns while trying to find a vulnerable flank. Massive German troop movements were constantly monitored by the Deuxième Bureau and the less experienced intercept service of the BEF as the opposing armies manoeuvred around each other.
The previous experience of British military intelligence had been formed during the Boer War some fifteen years earlier. Even at that time they had realised that the gathering, analysis and use of intelligence information needed method and had developed a three-tier reporting structure: intelligence officers collected information from frontline troops; this was sent on to staff officers to be collated; and the results were then analysed by a Field Intelligence Department to assess the enemy’s strength and intentions. This proved quite successful in action, but the little signals experience that British Army operators had of SIGINT was when the Boers captured some of their few radio transmitters: the main lesson learned was not to leave your wireless sets lying about when the enemy are near. As the war in South Africa ended, the memory of the intelligence structure the army had worked out for itself began to fade. The experience would have been entirely lost but for a manual written in 1904 entitled Field Intelligence: Its Principles and Practice by Lieutenant Colonel David Henderson. This document proved invaluable to the War Office in its sudden and unexpected mobilisation in 1914 as they realised that an intelligence system was needed by the BEF within its command structure. This was the new intelligence handling system into which the signals intelligence operators began to feed their intercepts, in addition to those of the Deuxième Bureau, to provide British staff officers with a clear picture on the strong German forces in front of the BEF.
After the war, an analysis of German signals intercepts by Colonel Cavel of the French Deuxième Bureau, correlating intelligence evaluations with movements of Allied forces, showed that counter-measures and effective actions taken in the 1914 battles of movement were almost all due to signals intelligence. Another of the colonel’s findings was how quickly the French and British operators learned to use the skills of electronic warfare to counter the enemy in the early months of the war. The same could not be said of the German signals intelligence, who took almost a year to develop an effective intercept and decryption service. By 1916, however, both sides on the Western Front had developed comparably efficient signals intelligence services as the levels of wireless traffic increased and skills in decryption and security improved. The German Army had learned a lesson about signals security at Tannenberg on the Eastern Front, but the victors were slow to apply that lesson to the security in signals transmissions in the west. The German General Staff showed a lack of awareness of the wireless security faults that had betrayed the Imperial Russian Army and this would now act as a weak point in their own conduct of the war for over a year. The war of movement gave way to a war of entrenched positions along a 350-mile-long front by 1915. A fundamental change in the nature of the signals intelligence war began to evolve as the conflict went into its second year. Trenches and barbed wire entanglements now extended from the Belgian coast, across the fields of France and to the borders of Switzerland. No major change in those emplacements would occur in the years to come until the war of movement began again in 1918.