He worked with Professor Aurel von Szily [de] in Münster during the 1930s and, with him, pioneered an electrical treatment for retinal detachment.

[1] He joined the German army at the outbreak of the Second World War in the hope of winning a first class Iron Cross bravery medal.

In 1929 in Freiburg, he worked on a doctorate (on amphibian development) under the supervision of Prof. Hans Spemann (later Nobel prize winner) and was promoted Nov. 1929 to Dr. phil.

In June 1932, Erna became aware that she might have Jewish ancestry, which she knew could be an issue due to the rise of the anti-Semitic Nazi Party.

[5] Anti-Semitic discrimination escalated under the Nazis and Szily, as a Jew, was forced from his position at the clinic, with Machemer also losing his job there.

[2] Machemer was unable to set up his own practice as the Association of Statutory Health Insurance Physicians refused to grant a permit because of his marriage.

[6] Under these laws, Machemer's wife was classified as "mixed-race" and "half-Jewish" and the family became subject to much more stringent restrictions and discrimination.

[2] He noted this in a letter home to his wife and Erna's reply was that he "shouldn't consciously put yourself in danger again, it seems to me like a challenge to fate".

[7] Helmut also wrote to Erna of his concern that he might be withdrawn from the front line and placed in a field hospital where he would be unlikely to be recommended for a bravery award.

Machemer appealed the decision in March 1942 and, after sending a family tree and confirmation that Erna had no contact with her Jewish relations, was promoted to the rank of Oberarzt and approved for the Iron Cross, first class on 14 May 1942.

[6] Hans worked with historian Christian Hardinghaus [de] to catalogue and assess the material and also produced a documentary film and a book, Wofür es lohnte, das Leben zu wagen ("What it was worth risking life for") published 2018 in German by Europa Verlag.

[6] Besides Hans the other sons were Peter and Robert Machemer (1933–2009), also an ophthalmologist and sometimes called the "father of modern retinal surgery".

[5][11] Hans Machemer appeared in the BBC documentary "Lost home movies of Nazi Germany" explaining his father's self-sacrifice, through film footage taken by Helmut himself.