In August 1940 Bischoff was reassigned to the newly-annexed territory of "Reichsgau Wartheland" where he served under "SS"-"Brigadeführer" Ernst Damzog as commander of the "Sicherheitsdienst" and "Sicherheitspolizei" (KdS) for the city of Poznań (Posen). In this capacity Bischoff was also the commandant of the Fort VII concentration camp, which was initially called "KZ Posen" and in 1939 became "Übergangslager (transit camp) Fort VII". While primarily a detention center, Fort VII also served as a regular execution site for many local Poles, Jews and the physically or mentally disabled. Prisoners usually remained in the camp for about six months, before being sentenced to death, a long prison term or transfer to a larger concentration camp.