Under this extermination program, known to S.S. bureaucrats by the code Action 14f13, some sixty-five hundred prisoners were killed in the course of a year. By early 1942, it had become obsolete, as the scale of death in the camps increased. Now the killing of weak and sick prisoners was carried out by guards or camp doctors, sometimes in gas chambers built on site. Those who were still able to work were increasingly auctioned off to private industry for use as slave labor, in the many subcamps that began to spring up around the main K.L. At Ravensbrück, the Siemens corporation established a factory where six hundred women worked twelve-hour shifts building electrical components. The work was brutally demanding, especially for women who were sick, starved, and exhausted. Helm writes that “Siemens women suffered severely from boils, swollen legs, diarrhea and TB,” and also from an epidemic of nervous twitching. When a worker reached the end of her usefulness, she was sent back to the camp, most likely to be killed. It was in this phase of the camp’s life that sights like the one Loulou Le Porz saw at Ravensbrück—a truck full of prisoners’ corpses—became commonplace.
Uniquely at Auschwitz, prisoners were tattooed with a serial number, on their left breast for Soviet prisoners of war[97] and on the left arm for civilians.[98] Categories of prisoner were distinguishable by triangular pieces of cloth (German: Winkel) sewn onto on their jackets below their prisoner number. Political prisoners (Schutzhäftlinge or Sch), mostly Poles, had a red triangle, while criminals (Berufsverbrecher or BV) were mostly German and wore green. Asocial prisoners (Asoziale or Aso), which included vagrants, prostitutes and the Roma, wore black. Purple was for Jehovah's Witnesses (Internationale Bibelforscher-Vereinigung or IBV)'s and pink for gay men, who were mostly German.[99] An estimated 5,000–15,000 gay men prosecuted under German Penal Code Section 175 (proscribing sexual acts between men) were detained in concentration camps, of which an unknown number were sent to Auschwitz.[100] Jews wore a yellow badge, the shape of the Star of David, overlaid by a second triangle if they also belonged to a second category. The nationality of the inmate was indicated by a letter stitched onto the cloth. A racial hierarchy existed, with German prisoners at the top. Next were non-Jewish prisoners from other countries. Jewish prisoners were at the bottom.[101]
But individual deaths, by sickness or violence, were not enough to keep the number of prisoners within manageable limits. Accordingly, in early 1941 Himmler decided to begin the mass murder of prisoners in gas chambers, building on a program that the Nazis had developed earlier for euthanizing the disabled. Here, again, the camps’ sinister combination of bureaucratic rationalism and anarchic violence was on display. During the following months, teams of S.S. doctors visited the major camps in turn, inspecting prisoners in order to select the “infirm” for gassing. Everything was done with an appearance of medical rigor. The doctors filled out a form for each inmate, with headings for “Diagnosis” and “Incurable Physical Ailments.” But it was all mere theatre. Helm’s description of the visit of Dr. Friedrich Mennecke to Ravensbrück, in November, 1941, shows that inspections of prisoners—whom he referred to in letters home as “forms” or “portions”—were cursory at best, with the victims parading naked in front of the doctors at a distance of twenty feet. (Jewish prisoners were automatically “selected,” without an examination.) In one letter, Mennecke brags of having disposed of fifty-six “forms” before noon. Those selected were taken to an undisclosed location for gassing; their fate became clear to the remaining Ravensbrück prisoners when the dead women’s clothes and personal effects arrived back at the camp by truck.
In most camps, prisoners were forced to wear identifying overalls with colored badges according to their categorization: red triangles for Communists and other political prisoners, green triangles for common criminals, pink triangles for homosexual men, purple triangles for Jehovah's Witnesses, black triangles for asocials and the "work shy", yellow triangle for Jews, and later the brown triangle for Romanis.[30]

On 26 June 1933, Himmler appointed Theodor Eicke commandant of Dachau, who in 1934 was also appointed the first Inspector of Concentration Camps (CCI). In addition, the remaining SA-run camps were taken over by the SS.[14][15][16] Dachau served as both a prototype and a model for the other Nazi concentration camps. Almost every community in Germany had members who were taken there. The newspapers continuously reported on "the removal of the enemies of the Reich to concentration camps" making the general population more aware of their presence. There were jingles warning as early as 1935: "Dear God, make me dumb, that I may not come to Dachau."[17]