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 .

Intelligenzaktion ( , `` Intelligentsia action '' ) was a secret mass murder Killing conducted Action by Nazi Germany against the Polish intelligentsia ( teachers , priests , physicians , `` et al . '' )

The mass murder operations of `` Intelligenzaktion '' killed Killing 100,000 Polish people ; by way of forced disappearance , the Nazis imprisoned Arrest and killed Killing selected Choosing citizens of Polish society , identified Check before the war as enemies of the Reich ; they were buried in mass graves at remote places .

The `` Intelligenzaktion '' was a major step to implementing Action `` Sonderaktion Tannenberg '' ( Operation Tannenberg ) , the installation of Nazi policemen and functionaries — from the SiPo ( composed of the Kripo and Gestapo ) , and the SD — to manage Hold the occupation and facilitate Cause_to_make_progress the realisation of `` Generalplan Ost '' , the German colonization of Poland .

Among the 100,000 people killed Killing in the `` Intelligenzaktion '' operations , approximately 61,000 were of the Polish intelligentsia , whom the Nazis identified Check as political targets in the Special Prosecution Legality Book-Poland , compiled before the war began in September 1939 .

The `` Intelligenzaktion '' occurred Coming_to_be soon after the German invasion of Poland ( 1 September 1939 ) , and lasted from the autumn of 1939 until the spring of 1940 ; the mass murder of the Polish intellectuals continued with the operations of German AB-Aktion operation in Poland .