By mid-1939, thousands of Polish Volksdeutsche had been secretly prepared for sabotage and guerrilla warfare by the Breslau (Wrocław) office of the Abwehr; the purpose of their activities was to provoke anti-German reprisals that could be claimed as provocations by the Germans.[14] Those German agents indeed cooperated with the German forces during the invasion of Poland, leading to some reprisals, which were highly exaggerated by the German Nazi propaganda.[14][15][16] One of the most notable cases of such a scenario was reportedly carried out during Bydgoszcz Bloody Sunday.