When the target failed to materialize, the commander of German defenders, Hermann Göring, sent a sarcastic telegram to all concerned, congratulating them and himself on "the successful defence of the fortress of Koepenick", a reference to the 20th century hoax, Captain of Köpenick.
[1][2] On 20 October, just a week later, the 8th Air Force sent 119 bombers to attack the western town of Düren, near the border city of Aachen, but the German defenders assumed it was really a return to the earlier target.
In 1973, Alfred Price wrote that this was based on the noise of aircraft, though they were not seen; Adolf Galland attributes this to chaff dropped by the bombers drifting on the wind and registering on German radar.
With the disappearance of the threat, Göring freely admitted that the joke was on him, that he had sent the Luftwaffe on a tour of their own airspace and sent an ironic telegram to all concerned congratulating them and himself on "the successful defence of the fortress of Koepenick", a reference to the Captain of Köpenick, a hoax of the early 20th century.
Price and Galland pointed out the difficulties of discriminating between friend and foe in confused circumstances; both observed that neither side managed to resolve the problem during the air war.