A German plane had crash landed near Mechelen in Belgium on 10th January. One of the German officers was carrying documents which he was discovered attempting to burn. They proved to be comprehensive plans for the invasion of Belgium, to be conducted in the near future. Whilst the Belgians pretended to the Germans that the maps had been almost completely burnt and they had learnt little from them, they simultaneously set about preparing for an imminent invasion and warned their putative allies, the British and the French.
General Alan Brooke had been alerted on the 12th to expect an invasion and ‘heavy parachutist attacks’, which he found implausible given the extremely cold weather conditions. He was awoken at 3.30 am on the 14th and told to prepare to advance into Belgium. Later that day he attended a GHQ conference where he learnt of the reasons for the alert: the crashed plane and the documents.
We discussed the whole evidence and came to the conclusion that the whole affair looked like a ‘plant’ on the part of Germany. It was not likely that officers would fly over Belgium with a plan of that kind in their possession. It seems probable that the whole affair was staged with the object of trying to induce Belgium to call on France and England for military support in the face of a threat, and thus to provide Germany with an excuse for violating the frontier of Belgium and Holland. We may or may not have been right and so as to leave nothing to chance we are now at 4 hours notice to move.
In fact the plans were genuine, Hitler had ordered the attack to commence on the 17th January. Initially the German High Command was concerned that their plans had been discovered, but they were persuaded to believe the Belgium pretence that the smouldering documents had been so badly burnt that nothing confidential was revealed. It was the weather that proved to be the vital factor that led Hitler to agree to postpone his plans.
Meanwhile in the face of the categorical warning of Germany’s intention that they had now received, the Belgians continued to cling to their declared neutrality, for fear of ‘provoking’ Germany.