[2] Behrens was most notable for being a member of the Berlin-based anti-fascist resistance group, that was later called the Red Orchestra by the Abwehr.

Behrens acted as a courier for the group, passing reports between Arvid Harnack and Hans Coppi who was the radioman.

[3] Behrens was also active in a resistance group at the AEG turbine factory power together with Walter Homann and others.

[8] In 1935, he was arrested for selling the communist newspaper, Gegenangriff (Counterattack) but was released as there was no firm evidence.

[7] In 1938, Behrens began working as a design engineer at the giant AEG turbine factory[1] in Brunnenstrasse in Berlin.

[10] Through his work at the AEG factory as a designer and his contacts with former KPD officials, he was able to provide political, economic and military information to the Soviet People's Commissariat for State Security (NKGB), where he was assigned the code name, Lutschisti (Shining One, Ray of Light or Beamer).

[1] Owing to Behren's having children, Arvid Harnack decided in 1941 not to use him as a radio operator for a planned connection with the Soviet Union.

[3] In the same year, Behrens was arrested for forging exit papers for his Jewish brother-in-law, Charly Fischer.