that up to 20,000 Germans living in Poland belonged to organizations involved Cause_to_be_included in various forms of subversion. < ref name= '' polityka.pl/historia '' > < /ref > Operation Tannenberg was followed by the `` Intelligenzaktion '' , a second phase of the `` Unternehmen Tannenberg '' directed by Heydrich 's `` Sonderreferat '' from Berlin , which lasted until January 1940 .