The Nazi Regime under Adolf Hitler imposed some of the most insane forms of eugenics the world has ever seen. Between 1939 and 1945, at least 70 medical research projects, involving cruel and often lethal experimentation on human subjects, were conducted behind the walls of Nazi concentration camps. These supposed research projects were carried out by established institutions within the Third Reich and fell into three main areas; research aimed at improving the survival and rescue of German troops, testing of medical procedures and pharmaceuticals, and experiments that sought to confirm Nazi racial ideology. More than seven thousand victims of these medical experiments have been documented, but the official number remains unknown. The Nazis justified the murder by claiming the victims were 'undesirables', people they viewed as a drain on national resources. Adolf Hitler signed a secret authorisation in order to protect participating physicians, medical staff, and administrators from prosecution.