When we think of the crimes of Nazism, concentration camps and the Holocaust come to mind. However, what we might bitterly call the "rehearsals" for such horrors took place slightly earlier, with the victims being patients in hospitals and institutions who suffered from mental illnesses, genetic disorders, and severe physical disabilities - in short, those who were collectively deemed "lives unworthy of living".

Aktion T4 was the program through which the Nazis planned and carried out the extermination of these individuals, including children. T4 stands for "Tiergartenstraße 4", the address of the public health authority under the Nazi regime. The program began in October 1939 at Hitler's command, with Karl Brandt, his personal physician, and Philipp Bouhler, head of the Führer’s Chancellery. In reality, the program had already started in August 1939, first targeting children and then adults. It was conducted in secrecy, with six institutions set up for the task. Patients were often brought in under the guise of receiving "new treatments", but were instead executed using methods (such as gas and crematoria) that would later be used in the extermination camps. The families of the victims often suspected the truth but remained silent. Despite this, rumors spread, and protests, especially from Protestant and Catholic communities (notably Bishop Clemens von Galen of Münster), led to the program being officially halted at the end of August 1941.

In reality, Aktion T4 continued until the end of the war, and it is estimated that well over 200,000 people were killed. Nazi propaganda had long prepared the German population for this operation with both racial justifications (the claim that these individuals "infected the healthy stock" of the nation) and economic arguments (the cost of maintaining such lives).

But this was not a uniquely German issue. Across Europe, the debate over eugenics and "euthanasia" was very active, and some views were not confined to Germany alone. Many of those responsible for Aktion T4 were never punished, and certain eugenic practices continued well beyond the war. Aktion T4 is a Nazi crime that was long forgotten but deserves to be remembered.