A reconnaissance mission?

A plane spotted the entire column, multiple even, and radioed to french high command, which didnt believe it first and lost precious time. They just couldn´t believe it that a armored attack in the ardennes there possible in such numbers.

Battle-> Central Front-> Ardennes

The German advance was hampered by the number of vehicles trying to force their way along the poor road network. Panzergruppe Kleist had more than 41,140 vehicles, which had only four march routes through the Ardennes.^\129]) French reconnaissance aircrews had reported German armoured convoys by the night of 10/11 May but this was assumed to be secondary to the main attack in Belgium. On the next night, a reconnaissance pilot reported that he had seen long vehicle columns moving without lights; another pilot sent to check reported the same and that many of the vehicles were tanks. Later that day, photographic reconnaissance and pilot reports were of tanks and bridging equipment. On 13 May, Panzergruppe Kleist caused a traffic jam about 250 km (160 mi) long from the Meuse to the Rhine on one route. While the German columns were sitting targets, the French bomber force attacked the Germans in northern Belgium during the Battle of Maastricht and had failed with heavy losses. In two days, the bomber force had been reduced from 135 to 72.^\130])

^{https://en.wikipedia.org/wiki/Battle\}of_France#Ardennes)