Gisbert Hasenjaeger

Gisbert F. R. Hasenjaeger
Picture of Gisbert_Hasenjaeger in his identity papers during his time at OKW/Chi
Born	June 1, 1919 (1919-06) Hildesheim
Died	September 2, 2006(2006-09-02) (aged 87) Münster, Westphalia
Citizenship	German
Fields	Mathematics Logic
Institutions	Münster University University of Bonn University of Princeton
Alma mater	Münster University
Doctoral advisor	Heinrich Scholz
Doctoral students	Alexander Prestel Ronald Jensen
Known for	Testing the Enigma encryption machine for cryptographic weaknesses. Developing a proof of the completeness theorem in 1949.
Influences	Alan Turing

Gisbert F. R. Hasenjaeger (June 1, 1919 – September 2, 2006) was a German mathematical logician. Independently and simultaneously with Leon Henkin in 1949, he developed a new proof of the completeness theorem of Kurt Gödel for predicate logic. He worked as an assistant to Heinrich Scholz at Section IVa of Oberkommando der Wehrmacht Chiffrierabteilung, and was responsible for the security of the Enigma machine.

Gisbert Hasenjaeger went to high school in Mülheim, where his father Edwin Renatus Hasenjaeger^[] was a lawyer and local politician. After completing school in 1936, Gisbert volunteered for labor service. He was drafted for military service in World War II, and fought as an artillerist in the Russian campaign, where he was badly wounded in January 1942. After his recovery, in October 1942 Heinrich Scholz got him an employment in the Cipher Department of the High Command of the Wehrmacht (OKW/Chi), where he was the youngest member at 24. He attended a cryptography training course by Erich Hüttenhain, and was put into the recently founded Section IVa "Security check of own Encoding Procedures" under Karl Stein, who assigned him the security check of the Enigma machine. At the end of the war as OKW/Chi disintegrated, Hasenjaeger managed to escape TICOM, the United States effort to roundup and seize captured German intelligence people and material.