In the fight against the German invasion, KOP units took part among other battles in the battle of Węgierska Górka. After Soviet invasion on 17 September, Korpus Ochrony Pogranicza which had 25 battalions were unable to defend the eastern border and were further ordered by Edward Rydz-Śmigły to fall back and not to engage the Soviets. This however did not prevent some clashes and small battles, including Battle of Szack (28 September) and Battle of Wytyczno (1 October).