[2][3] 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.

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[5] got him employment in the Cipher Department of the High Command of the Wehrmacht (OKW/Chi), where he was the youngest member at 24.

[6][7] 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.

In 1964/65, he spent a year at Princeton University at the Institute for Advanced Study[8] His doctoral students at Bonn included Ronald B. Jensen, his most famous pupil.

[9] In October 1942, after starting work at OKW/Chi, Hasenjaeger was trained in cryptology, given by the mathematician, Erich Hüttenhain, who was widely considered the most important German cryptologist of his time.

Hasenjaeger was put into a newly formed department, whose principal responsibility was the defensive testing and security control of their own methods and devices.

He crucially failed to identify the most important weakness of the Enigma machine: the lack of fixed points (letters encrypting to themselves) due to the reflector.

When he had solved the problem in late 1949, he was frustrated to find that a young American mathematician Leon Henkin, had also created a proof.

Although Hasenjaeger's work on UTMs was largely unknown and he never published any details of the machinery during his lifetime, his family decided to donate the machine to the Heinz Nixdorf Museum in Paderborn, Germany, after his death.

Hasenjaeger UTM contained 3-tapes, 4 states, 2 symbols and was an evolution of ideas from Edward F. Moore's first universal machine and Hao Wang's B-machine.

The fact that the Germans had so comprehensively underestimated the weaknesses of the device, in contrast to Turing and Welchman's work, was seen by Hasenjaeger today as entirely positive.