The ghettos, and the slow death they brought, were only part of the overall plan. In the months following the Wannsee Conference, three specialized killing centers, Belzec, Treblinka and Sobibor, were constructed in southeast Poland, featuring large gas chambers with adjacent crematories or burial pits for the disposal of corpses. After they became operational, the ghettos were bypassed and Jews went directly by train to the new death camps.
In June 1941 Germany attacked the Soviet Union and began the "Final Solution." Four mobile killing groups were formed called Einsatzgruppen A, B, C and D. Each group contained several commando units. The Einsatzgruppen gathered Jews town by town, marched them to huge pits dug earlier, stripped them, lined them up, and shot them with automatic weapons. The dead and dying would fall into the pits to be buried in mass graves. In the infamous Babi Yar massacre, near Kiev, 30,000-35,000 Jews were killed in two days. In addition to their operations in the Soviet Union, the Einsatzgruppen conducted mass murder in eastern Poland, Estonia, Lithuania and Latvia. It is estimated that by the end of 1942, the Einsatzgruppen had murdered more than 1.3 million Jews.
The Majdanek camp served from time to time as a killing site for Jews residing in the Generalgouvernement. In its gas chambers, the SS killed tens of thousands of Jews, primarily forced laborers too weak to work. The SS and police killed at least 152,000 people, mostly Jews, but also a few thousand Roma (Gypsies), in gas vans at the Chelmno killing center about thirty miles northwest of Lodz. In the spring of 1942, Himmler designated Auschwitz II (Auschwitz-Birkenau) as a killing facility. SS authorities murdered approximately one million Jews from various European countries at Auschwitz-Birkenau.
Sources: C.A.N.D.L.E.S; Kor, Eva Mozes. Echoes from Auschwitz. IN.: C.A.N.D.L.E.S. 1995; Lifton, Robert Jay. The Nazi Doctors. The United States: Basic Books. 1986; Nyiszli., Dr. Miklos. Auschwitz: A Doctor's Eyewitness Account. New York: Fawcett Crest. 1960; Posner, Gerald L. and John Ware. Mengele: The Complete Story. New York: Dell Publishing. 1986; Ramati, Alexander. And the Violins Stopped Playing
One of the Auschwitz survivors who was selected by Dr. Josef Mengele for his cruel and horrific experiments was Yitzchak Ganon, a Greek Jew who was deported, along with his parents and 5 brothers and sisters to Auschwitz in 1944, according to a news article by Alan Hall, published on December 11, 2009. Ganon told reporter Alan Hall that he was selected for an experiment in which Dr. Mengele removed one of his kidneys without an anesthetic: "He cut into me without an anesthetic. The pain was indescribable. I felt every slice of the knife. Then I saw my kidney pulsating in his hand. [...] After the operation I was given no painkillers and put to work. I cleaned up after the bloody operations carried out by Mengele."
In early 1942 the Nazis built killing centres at Treblinka, Sobibor, and Belzec in occupied Poland. The death camps were to be the essential instrument of the “final solution.” The Einsatzgruppen had traveled to kill their victims. With the killing centres, the process was reversed. The victims were taken by train, often in cattle cars, to their killers. The extermination camps became factories producing corpses, effectively and efficiently, at minimal physical and psychological cost to German personnel. Assisted by Ukrainian and Latvian collaborators and prisoners of war, a few Germans could kill tens of thousands of prisoners each month. At Chelmno, the first of the extermination camps, the Nazis used mobile gas vans. Elsewhere they built permanent gas chambers linked to the crematoria where bodies were burned. Carbon monoxide was the gas of choice at most camps. Zyklon-B, an especially lethal killing agent, was employed primarily at Auschwitz and later at Majdanek.
The first killing center set up in occupied Polish lands was the camp at Chełmno on the Ner; Jews brought in from the ghettos in the Wartheland were being killed there from December 1941. Three more camps, somewhat larger, were opened at Bełżec, Sobibor, and Treblinka (in what was known as “Aktion Reinhard”) somewhat later, between March and July 1942.