The Mechelen incident of 10 January 1940, also known as the Mechelen affair, took place in Belgium during the Phoney War in the first stages of World War II. A German aircraft with an officer on board carrying the plans for Fall Gelb (Case Yellow), the German attack on the Low Countries, crash-landed in neutral Belgium near Vucht in the modern-day municipality of Maasmechelen (Mechelen-aan-de-Maas) within the Province of Limburg. This prompted an immediate crisis in the Low Countries and amidst the French and British authorities, whom the Belgians notified of their discovery; however, the crisis abated relatively quickly once the dates mentioned in the plans passed without incident. It has been argued that the incident led to a major change in the German attack plan, but this hypothesis has also been disputed.
The crash
The incident was caused by an error by the German aviator Major Erich Hoenmanns, the fifty-two-year-old base commander of Loddenheide airfield, near Münster. On the morning of 10 January 1940, he had been flying a Messerschmitt Bf 108 Taifun, an aircraft used for reconnaissance, liaison, and other miscellaneous roles, from Loddenheide to Cologne when he lost his way; extensive low fogbanks obscured his view of the landscape. In response he changed course to the west, hoping to regain his bearings by reaching the River Rhine. However, having already crossed over the frozen and indistinguishable Rhine at the moment he changed direction, he left German territory flying all the way to the River Meuse, the border in this area between Belgium and the Netherlands, and ended up circling Vucht.
At that moment, Hoenmanns seems by mistake to have cut off the fuel supply to the plane's engine by moving a lever inside the cockpit. The engine spluttered, then stopped, and Hoenmanns was forced to land in a nearby field at about 11:30 AM. The aircraft was severely damaged. Both wings were broken off when they hit two Canadian poplar trees as he sped between them; the heavy engine tore off the nose section. The plane was damaged beyond repair, but Hoenmanns survived unscathed.
Had Hoenmanns been alone in the plane, nothing of great significance would likely have happened, apart from his internment for landing without permission in a neutral country. However, he had a passenger, Major Helmuth Reinberger, who was responsible for organising the 7. Flieger-Division's supply, the formation that was to land paratroopers behind the Belgian lines at Namur on the day of the coming attack. Reinberger was going to Cologne for a staff meeting. The previous evening, over a drink in the mess, Hoenmanns had offered to fly him there. Usually, Reinberger would have had to make the tedious trip by train, but Hoenmanns needed some extra flying hours anyway and wanted to take his laundry to his wife in Cologne. Hoenmanns was unaware that Reinberger would be carrying documents related to the German plan for the attack on The Netherlands and Belgium, which on the day of the flight was decreed by Hitler to take place a week later on 17 January.
Only after landing did Hoenmanns become aware that Reinberger was carrying secret documents when they asked a farmhand, Engelbert Lambrichts, where they were, to be told that they had unknowingly crossed Dutch territory and landed just inside Belgium. On hearing this, Reinberger panicked and rushed back to the plane to secure his yellow pigskin briefcase, crying that he had secret documents that he must destroy immediately. To let him do this Hoenmanns, as a diversion, moved away from the plane. Reinberger first tried to set fire to the documents with his cigarette lighter but it malfunctioned; he then ran to the farmhand who gave him a single match. With this Reinberger hid behind a thicket and piled the papers on the ground to burn them. But soon two Belgian border guards, Sergeant Frans Habets and Corporal Gerard Rubens, arrived on bicycles. Seeing smoke coming from the bushes, Rubens rushed over to save the documents from being completely destroyed. Reinberger fled at first but allowed himself to be taken prisoner after two warning shots had been fired.
The two Germans were taken to the Belgian border guardhouse near Mechelen-aan-de-Maas (French: Malines-sur-Meuse). There they were interrogated by Captain Arthur Rodrique, who placed the charred documents on a table. As a diversion once more, Hoenmanns asked the Belgian soldiers to let him use the toilet; Reinberger then tried to stuff the papers into a burning stove nearby. He succeeded but yelled with pain when lifting the extremely hot lid of the stove. Startled, Rodrique turned and snatched the papers from the fire, badly burning his hand in the process. The documents were then locked away in a separate room. The failure to burn them made Reinberger realise that he would surely be shot, for letting the attack plan fall into the hands of the enemy. He decided to commit suicide and tried to grab Rodrique's revolver. When the infuriated captain knocked him down, Reinberger burst into tears, shouting 'I wanted your revolver to kill myself'. Hoenmanns supported Reinberger saying: 'You can't blame him. He's a regular officer. He's finished now.
Two hours later officers from the Belgian intelligence service arrived, and brought the papers to the attention of their superiors in the late afternoon.
Initial German reaction
Late in the evening of 10 January news of the incident reached Berlin via press reports about a crashed German plane. In the Oberkommando der Wehrmacht, the German armed forces high command, it caused general consternation, as it was soon deduced that Reinberger must have had papers revealing parts of the attack plan with him. On 11 January an enraged Hitler fired both the commander of Luftflotte 2, General Hellmuth Felmy, and Felmy's chief of staff Colonel Josef Kammhuber. It was nevertheless decided to proceed with the attack as originally planned, while the Luftwaffe attaché in The Hague, Lieutenant-General Ralph Wenninger, and the military attaché in Brussels, Colonel Friedrich-Carl Rabe von Pappenheim, would investigate whether the plan had been fatally compromised or not. On 12 January, the day of the attachés' first meeting with Reinberger and Hoenmanns, General Alfred Jodl, the Wehrmacht's Chief of Operations, gave Hitler a worrying assessment of what the Belgians might have learned from it. A note in Jodl's diary on 12 January summed up what he had said to Hitler: 'If the enemy is in possession of all the files, situation catastrophic!' However, the Germans were initially falsely reassured by Belgian deception measures.
Deception
The Belgians decided to try tricking Reinberger into believing that the papers had been destroyed and give him the opportunity to pass this information on to the German authorities. There were two parts to the deception: in the first the Belgian investigators asked Reinberger what was in the plans and told him that he would be treated as a spy if he did not tell them. Later Reinberger testified saying: "From the way this question was asked, I realised he [the interrogator] could not have understood anything from the fragments of the documents he had seen." The second part of the plan was to let Reinberger and Hoenmanns meet the German Air and Army Attachés, Wenninger and Rabe von Pappenheim, while their conversations were secretly recorded. During this meeting Reinberger informed Wenninger that he had managed to burn the papers enough to make them unreadable. This act of deception was fairly successful, at least in the short term. After the meeting at the police station, Vicco von Bülow-Schwante, Germany's ambassador to Belgium, telegraphed his superiors: 'Major Reinberger has confirmed that he burnt the documents except for some pieces which are the size of the palm of his hand. Reinberger confirms that most of the documents which could not be destroyed appear to be unimportant.' This appears to have convinced General Jodl. His diary for 13 January included the entry: "Report on conversation of Luftwaffe Attaché with the two airmen who made forced landing. Result: despatch case burnt for certain."
Belgian reaction
During 10 January the Belgians still doubted the authenticity of the documents, which had been quickly translated by the Deuxième Section (military intelligence) of the general staff in Brussels. Most had indeed been badly damaged by Reinberger's consecutive attempts to burn them, but the general outlines of an attack against Belgium and the Netherlands were clear from the remaining passages, although the date of the attack was not mentioned and most of the text was concerned with specific instructions to 7. Flieger-Division only. As their content conformed to earlier warnings from the Italian Foreign Minister, Count Galeazzo Ciano, about a German attack to take place around 15 January, on 11 January General Raoul Van Overstraeten concluded that the information was basically correct. That afternoon King Leopold III of Belgium decided to inform his own Minister of Defence, General Henri Denis, and the French supreme commander, Maurice Gamelin. At 17:15 the French liaison officer, Lieutenant-Colonel Hautcœur, was given a two-page abstract of the contents, albeit without any explanation of how the information had been obtained. Lord Gort, the commander of the British Expeditionary Force, was also warned, and Leopold personally telephoned Princess Juliana of the Netherlands and Grand Duchess Charlotte of Luxembourg, telling the former "Be careful, the weather is dangerous", and the latter "Beware of the flu", both predetermined code phrases indicating the Belgians considered a German attack to be imminent.
French reaction
On the morning of 12 January, Gamelin held a meeting with the highest French operational army commanders and the Chief of Military Intelligence Colonel Louis Rivet. Rivet was sceptical of the warning but Gamelin considered that, even if it were a false alarm, this would be an excellent opportunity to pressure the Belgians into allowing a French advance into their country. Gamelin intended to execute a decisive offensive against Germany in 1941 through the Low Countries; their neutrality would however, be an obstacle to these plans. If this invasion scare would make the Belgians take the side of France and Britain, this awkward problem would be partially solved and strategically vital ground from which to launch the attack effortlessly gained. On the other hand, if Germany really went ahead with the invasion, it was very desirable that the French forces could entrench themselves in central Belgium before the enemy arrived. Both to intensify the crisis and to be ready for any occasion that presented itself, Gamelin thus ordered 1st Army Group and the adjoining Third Army to march towards the Belgian frontier.
The warning by Sas
That their deception plan seemed to prove that the documents were genuine, that day further increased Belgian anxiety; the next day they became convinced the situation was critical. In the evening of 13 January, a message from Colonel Georges Goethals, Belgium's Military Attaché in Berlin, included these words: "Were there tactical orders or parts of them on the Malines plane? A sincere informer, whose credibility may be contested, claims that this plane was carrying plans from Berlin to Cologne in relation to the attack on the West. Because these plans have fallen into Belgian hands, the attack will happen tomorrow to pre-empt countermeasures. I make explicit reservations about this message, that I do not consider reliable, but which it is my duty to report." The "sincere informer" was the Dutch Military Attaché in Berlin Gijsbertus Sas who spoke with Goethals at about 17:00; his information always had to be carefully considered because he was in contact with a German intelligence officer who was an opponent of the Nazi regime, known today to have been Colonel Hans Oster.