After the invasion of Poland, which started World War II, Kartuzy was occupied by Germany, where it was administered as part of Reichsgau Danzig-West Prussia, Regierungsbezirk Danzig. In mid-September 1939 the SS Wachsturmbann "Eimann" and "Einsatzkommando 16" entered the town to carry out mass arrests and massacres of local Poles as part of the "Intelligenzaktion Pommern". Around 4,000 Poles from Kartuzy and the county were arrested in September 1939. That same month, many local pre-war Polish activists, as well as railway, post and court employees, were murdered in massacres in the forests in Gmina Somonino and at the Wzgórze Wolności, while 10 Polish priests were murdered in the forest near Kartuzy. Dozens of Poles from Kartuzy, including local officials, teachers, merchants, postmen, restaurateurs, policemen were murdered in October and November 1939 in the nearby forest and in Piaśnica. Poles from the village of Egiertowo were also murdered in the Kartuzy forest. At the end of World War II Karthaus was captured by the Red Army and afterwards it was restored to Poland.