A World War I example showing the danger of deceiving your own side

The following is a summary of the short article The Avenger Ignored by Charles Sanders, published in Military History Magazine.

French Intelligence bought what turned out to be partial German military plans for WWI around a decade before the outbreak of the war. The plans detailed a German invasion of Belgium for the obvious purpose of then attacking France from the North. French intelligence compared map to territory finding that the plans explained much German construction which until then had seemed “random and unthreatening”. Many in the French high command came to correctly believe in the plans’ authenticity and by 1907 French military strategy reflected this.

In 1913 many in the French military wanted to take an offensive posture with respect to the German threat. This posture would be more justified if Germany intended to directly attack France rather than go via Belgium. Therefore, French military officer Lt. Col. Edmond Buat falsely claimed to have found a copy of a German military document “under his seat during a train trip in Germany” that showed this. This imaginary document purportedly outlined a direct German attack on France that would largely ignore Belgium.

Buat described but never showed the document to anyone. His hoax was still believed and France based its military deployment on the imaginary document, to disastrous effects. When the French military command received reports of an actual gigantic German attack on Belgium (consistent with the real military plans French Intelligence bought a decade ago) an important French General telephoned French commanders to say “reports on German forces in Belgium are greatly exaggerated. There is no cause for alarm.” France went ahead and executed its existing military strategy “as if the massive, deadly threat now clearly sweeping down from the north did not exist.”

In 1915 Buat admitted his deception, but this didn’t stop him from going on to hold “numerous important assignments in the postwar army.”

I found The Avenger Ignored article through a History According to Bob Podcast.