[6][8] Thiessen was the main advisor and confidant to Rudolf Mentzel, who was head of the chemistry and organic materials section of the Reichsforschungsrat (RFR, Reich Research Council).

The objectives of their pact were threefold: (1) prevent plunder of their institutes, (2) continue their work with minimal interruption, and (3) protect themselves from prosecution for any political acts of the past.

Hertz was made head of Institute G,[16] in Agudseri (Agudzery),[14][15] about 10 km southeast of Sukhumi and a suburb of Gul’rips (Gulrip’shi).

[18] In Institute A, Thiessen became leader for developing engineering design techniques for manufacturing porous barriers for isotope separation using the gaseous and centrifugal technologies.

[19] In 1949, six German scientists, including Hertz, Thiessen, and Barwich, were called in for consultation at Sverdlovsk-44, which was responsible for uranium enrichment using the gaseous diffusion.

[21] He is credited with founding the field of tribochemistry, which he formulated when encountering problems to make the gaseous diffusion method feasible for the Soviet nuclear weapons.