T4 was codename for euthanasia activities performed by Nazi doctors during WWII. T4 was a program of forced euthanasia on the mentally and physically disabled, including children. Children of mixed marriages, disabled soldiers, the sick and anybody else considered “unworthy of life” were also killed. At first, the program’s personnel killed people by starvation and lethal injection, but they later chose asphyxiation by poison gas. 

Between 1939 and 1945, 200,000 people died under T4 guidelines.