15. Himmler decided to eliminate unproductive prisoners in 1941
By the spring of 1941 all of the labor camps were overcrowded, the result of Hitler’s armies overrunning Western Europe. An increase in the influx of slave labor was also anticipated from the east once the invasion of the Soviet Union was launched. Himmler extended a program designated Action T-4 to cover the labor camps. T-4 was an official Nazi euthanasia program which had been implemented to clear the hospitals and homes for the infirm of those unable to work or otherwise undesirable in the minds of the senior Nazi hierarchy. These included the mentally ill, criminal recidivists, disabled, and others.
Himmler’s extension of the program to the camps included homosexuals, those suspected of other deviant behaviors, those physically unable to work, those unwilling to work, and others. As the daily life in the camps gradually weakened the prisoners to the point of physical exhaustion they became conduits to the execution camps. In April 1941 Sachsenhausen began the execution of prisoners using carbon monoxide gas. Prisoners executed by gas were entered into the efficient German documentation system as being retired. Known as Action 14f13 in the camps, the program continued until late 1944, when the Nazis decided to destroy as much of the evidence of their activities as they could.