The project that carried out the extermination of children and adults with disabilities was known as "T4." The initials came from Tiergartenstrasse 4, Berlin which was the full address of the Fuhrer Chancellery. The T4 Project included four organizations: the Realms Work Committee in charge of collecting information on candidates for euthanasia from questionnaires sent to hospitals, the Realms Committee for Scientific Approach to Severe Illness Due to Heredity set up exclusively to apply euthanasia to children, the charitable company for the transport of the sick which transported patients to the killing centers, and the Charitable Foundation for Institutional Care, in charge of final disposition of the victims' remains.
At Hadamar Mental Institution, the victims were stripped, dressed in paper shirts and taken to a gas chamber where they were murdered with hydrocyanic acid gas, and the bodies moved to crematoriums by conveyer belts, six bodies to a furnace. The psychiatrist in charge at Hadamar was Dr. Adolf Wahlmann, an active member of the German Mental Hygiene Movement.
After information about the exterminations began to filter down to the German public, some members of the clergy started speaking out against the program. Hitler ordered the T4 program to stop killing patients in gas chambers. Instead the program went underground and victims were poisoned or starved to death. On May 8, 1945, the war ended in Germany. In the extermination institutes, they either kept on killing, or let the patients starve to death. As late as May 29, 1945, a four-year-old feebleminded boy was murdered in Kaufbeuren. Estimates of how many disabled people died under the Nazis range up to 250,000.
The extermination program in Nazi Germany caused eugenics theorists in the
United States and Europe to backpedal on their beliefs about eliminating
mental illness and congenital disabilities through euthanasia. However
sterilization of people with disabilities continued to be a widespread
practice well into the 1970s.