Hönmanns and Reinberger attempted at once to destroy the documents. While the pilot made off to divert attention, Reinberger attempted to set fire to the contents of his attaché case, at first with a lighter which failed to work, and then with a match the farmer had given him. Two Belgians soldiers, Sgt. Frans Habets and Private Gerard Rubens, saw the smoke and suspected immediately that an attempt was being made to destroy something important, and ran to the scene. Reinberger attempted to escape but gave up when the Belgians fired shots in the air as a warning to stop.

Reinberger and Hönmanns were taken to the border post at Mechelen-aan-de-Maas for interrogation by Capt. Arthur Rodrique. He placed the slightly charred documents on the table before them, and when Hönmanns requested to use the toilet, Reinberger grabbed the papers and tried to burn them in the stove. In the attempt he burned himself and alerted Rodrique with his howl of pain. The Belgian officer retrieved the papers from the fire and took them to another room. A struggle then ensued in which Reinberger tried to relieve Rodrique of his pistol to shoot himself but failed. He had realized that in Hitler’s eyes his mistake would be unforgiveable. During the afternoon the Belgian General Staff was informed about the documents.

When Hitler was informed of the incident he dismissed the Commander-in-Chief, Luftflotte 2, General Hellmuth Felmy, and his Chief of Staff, Oberst Josef Kammhuber, but did not amend his planning.

Initially the Belgians doubted the authenticity of the invasion plans. Although Reinberger had managed to damage some of the documents, the main parts remained legible: the Germans were planning to attack Belgium and the Netherlands, but no date was given. The possibility of this being a ruse was not discounted until the Italian Foreign Minister, Ciano, warned the Belgians that Germany was preparing to attack on 15 January. From their initial scepticism, the Belgians now felt certain that the seized documents were genuine.

On 11 January King Leopold decided to inform his Minister of Defence, General Henri Denis, and the Commander-in-Chief of the French Army, Gamelin. The King also warned Lord Gort, commander of the British Expeditionary Force, personally of the seriousness of the situation. Princess Juliana of the Netherlands and Grand-Duchess Charlotte of Luxemburg were also warned, although all he said to the princess in his telephone conversation was, “Take care, bad weather.”

After the Belgian secret service had analyzed the situation it was decided to dupe Reinberger and Hönmanns into believing that the documents were badly charred and illegible. This was successful, for on 12 January when the two captives were allowed to see the Luftwaffe attaché in The Hague and the Military attaché in Brussels, Reinberger assured them that he had succeeded in making the documents illegible. The German ambassador in Brussels informed Berlin personally that it was confirmed the documents were unreadable “apart from some insignificant fragments”. Even General Jodl, given the task of heading the investigation into the matter, and who had been very doubtful about the details of the incident, telling Hitler that the situation was catastrophic if the Belgians had all the information, believed this version.

For Gamelin, the whole thing was “fabulous”. There was nothing better for convincing the Belgians that their neutrality was in danger and obtaining their agreement to station French troops in Belgium. Gamelin had been planning to invade Germany through the Netherlands in 1941. He could not do this if these two small countries adhered rigidly to their neutrality. The Mechelen incident was so favourable for his intentions that he ordered 1.Corps/3.Army to head for the Belgian border.

Although the Belgians had handled the Mechelen incident well at the beginning, possession of the knowledge began to make them uneasy. The Belgian military attaché in Berlin, Colonel Goethal, informed Brussels on 13 January that a “reliable source” had assured him the documents were authentic and the Germans would invade next day. His informant was the Dutch military attaché in Berlin, Gijsbertus Sas, who received his information from a traitor within the German Abwehr, Oberst Hans Oster. This unsettled the Belgian General Staff since they did not know whether they were victims of a ruse or actually did face imminent invasion.

The Chief of the Belgian General Staff, Lt-General van de Bergen, informed the commander of the Belgian forces that an attack the next day “was as good as certain”. Then he announced on national radio the “activation of Phase D”, the immediate recall to their units of all troops on leave. This brought 80,000 men to a state of readiness to resist a German invasion. In so acting, van de Bergen went over the head of the King, the official Commander-in-Chief of the Belgian Army, and the head of the secret service, General van Overstraeten.

As a result of this mishandling of the situation, doubts began to arise. The Gemans were not attacking and the weather (heavy snowfall along the border) made it highly unlikely that they would. The anger of the King and van Overstraeten was now so apparent that the Germans knew the Belgians had their plans. The feared and expected invasion never came and now the Belgians withdrew from the British and French their offers of cooperation. At midday on 14 January, van Overstraeten ordered the borders closed “to prevent any attempt to enter the country by foreign troops no matter who they are”. The Belgian Government adhered to its policy of neutrality as if it had never been involved in the whole business and rejected all offers of help from the British and French who were, of course, both at war with Germany. Belgian neutrality had to be a premise to which no man could find objection.

Belgian troop movements clarified the situation for the Germans. When Jodl took the bait and believed the documents were illegible, he postponed the invasion to the 15/16 January. The nervous posture of the Dutch and Belgians convinced him that his plan was known. After he recommended Hitler to suspend the invasion, the latter made the decision to do so on 16 January.

When the invasion finally went ahead on 10 May, the Germans had had plenty of time to amend their strategy. Thus the January troop movements were cloaked as a feint. The documents seized from Reinberger and Hönmanns⁶ convinced the Allies that the Germans were intending to invade near the Dutch and Belgian coast. Operation Fall “Gelb” as corrected meant that the main German thrust would come through the Belgian Ardennes towards Sedan, as Hitler had personally ordered.

The Second Warning: The Invasion of Denmark and Norway

There was gloom along the borders of Belgium particularly when the Germans invaded Norway and Denmark on 9 April 1940. This move was logical: before he proceeded against the Western Powers, Hitler needed to secure the northern flank. The Belgian Government anticipated that Belgium would be next, but there was nothing to be done but prepare to defend. On 1 May 1940 the highest state of alert was raised in the train of German troop movements along the border. On 7 May the Apostolic Nuntius in Belgium, Monsignore Clemente Micara, warned the Government that the invasion of Belgium, the Netherlands and Luxemburg was imminent. On 9 May twelve divisions were stationed along the Albert Canal between Antwerp and Liège. An Army corps occupied the so-called “Liège strongpoint”: two divisions protected the bridges over the Meuse near Liège, and the border with France: two others were spread throughout the wooded region of the Ardennes, and four divisions remained as a reserve in the interior of the country.

It was clear that the Germans would pounce, but not in the way the Belgians had expected. Between 0510 and 0535 hrs on 10 May 1940⁷ gliders carrying paratroopers landed at four places along the Albert Canal: at Fort Eben Emael and the bridges at Kanne, Vroenhoven and Veldwezelt near Maastricht and the Dutch border. The Germans had arrived silently behind the Belgians’ backs, and this had not been anticipated in any defence plan.