A little something they do not teach in history class.
Losing your secret invasion plans.
Human carelessness can cost a lot. In early 1940, it cost Nazi Germany its secret invasion plans against France.
On January 10, 1940, Major Erich Hoenmanns, base commander of Loddenheide airfield in Germany, took to the skies in an unarmed Messerschmitt Bf 108. This, in itself, was no big deal. Hoenmanns had a civilian pilot’s license and was allowed to fly a plane to check the camouflage od the airfield from above. He was trying to escape his desk job and become a fighter pilot, taking every chance to log extra flying hours. He also lived away from his wife in Cologne and regularly flew there to give her the laundry. He also had a mistress in Loddenheide, but reasonably couldn’t expect her to do it.
This time, however, was different. The night before, Hoenmanns bumped into an old friend, Major Helmuth Reinberger. Reinberger was supposed to take the train to Cologne for a staff meeting, but Hoenmanns offered to fly him there instead the next day. Reinberger should have known better: he was carrying secret documents that he was forbidden to take onboard any aircraft.
Reinberger was in charge of supply for Germany’s secret paratrooper division. The documents with him contained supply-related instructions for Germany’s planned surprise attack against France through Belgium and the Netherlands, slated to begin on January 17, 1940 only a week after the flight. Though he wasn’t carrying specific invasion plans, any military expert would have been able to look at the documents and get a good idea of Germany’s intentions.
On January 10, Hoenmanns’ plane flew into heavy fog near Cologne. The River Rhine, which flows through the city, was frozen and covered with snow and the major failed to spot it in the bad weather. He continued flying westwards until he got into Belgian airspace. Over Belgium, the engine started sputtering, likely after Hoenmanns accidentally hit a lever and shut off the fuel supply. Whatever the case, the two German officers had to make an emergency landing in one of the neutral countries they were about to invade in a week, near Mechelen-aan-de-Maas, which lent the incident its name.
The plane was wrecked on landing, but the men escaped unscathed. A local farmer told them where they were, causing Reinberger to panic: he hadn’t told Hoenmanns about the documents and was also convinced he would be executed if he let the plans fall into Belgian hands. They asked the farmer for a match, ostensibly to light their cigarettes, and Reinberger tried to burn the papers behind some bushes.
By this time, however, two Belgian soldiers had already reached the scene on their bikes. Seeing the smoke, they overcame the Germans, saved the paperwork and took the men to a watchhouse. During their interrogation, the Germans tried to destroy the remaining papers as well. Hoenmanns drew the soldiers’ attention by asking to go to the toilet. When the guards turned away, Reinberger scooped the papers off the table and threw them into a burning stove. The lid of the stove, however, was hot, causing him to drop it with a clang, warning the guards and giving one time to reach into the fire for the remaining scraps. This failure despaired Reinberger so much he first asked the soldier for his pistol to commit suicide with, then tried to grab it anyway when the request was refused.
The Belgian authorities easily predicted the coming invasion from the surviving pages and were naturally concerned. However, there was disagreement over whether the plans were genuine or a ruse deliberately allowed to fall in Belgian hands. In order to make the Germans believe they were still clueless, they played a ruse of their own. First, they interrogated the two majors, pretending that too much of the document was burned to decipher the rest. Then, they allowed them to speak with German attachés, (mistakenly) telling them the orders were successfully destroyed in time.
Up to this point, the Germans thought the two majors might have been traitors who deliberately delivered the documents to Belgium. Hoenmanns and Reinberger were even tried and sentenced to death in absentia. The sentence was never carried out: the men remained in Belgian hands, then Allied custody until they were returned to Germany in a 1943-44 prisoner exchange, after which they were pardoned back home.
The documents stirred up a diplomatic storm. Belgium and the Netherlands were neutral countries, but France and Britain were pushing them for permission to station their troops on their land near the German border. The discovery of the plans, leaked to the Allies and also supported by warning both from the Italian foreign minister and an anti-fascist officer in the German Intelligence Service, caused them to redouble their lobbying. In the end, however, nothing came of it: the Allies couldn’t give the guarantees Belgium was demanding. Some measures were taken to defend against a German invasion, but the suspected date came and went and the state of alert was stepped down.