Having arrived by train in the region of Zagan on Saturday, the Second Armored Brigade Combat Team, 1st Infantry Division, had planned to start firing practice the same day in a restricted zone set up by the Polish authorities.
However, the military's plans were dashed when it transpired that local Poles were in no mood to put off their annual mushroom picking bonanza.
Ignoring the warning signs around the area, they flocked into the forest to forage for porcini, a prized funghi which has grown particularly well this season.
Amid foggy weather, the army was forced to postpone its firing practice to avoid potential accidents, the battalion's commander John Donlin told the German newspaper Tagesspiegel.
The battalion is just one of a 3,300-troop force sent by the US to Poland, where they are holding drills before dispersing around Poland and the Baltic countries.
The units were deployed as part of the "Atlantic Resolve" operation to boost NATO's military presence in in Lithuania, Latvia, Estonia and Poland following the eruption of the Ukrainian crisis in 2014. NATO's increasing presence along Russia's western borders, which has increased eightfold in the last ten years, is regarded as a security threat by Moscow.