Phase two: deportations to extermination camps
When the Wehrmacht invaded the Soviet Union in June 1941, the area of the General Government was enlarged by the inclusion of regions that had been annexed by the Soviet Union since the 1939 invasion. The killings of Jews from the Łódź Ghetto in the Warthegau district began in early December 1941 with the use of gas vans [approved by Heydrich] at the Kulmhof extermination camp. The deceptive guise of "Resettlement in the East" organised by SS Commissioners, was also tried and tested at Chełmno. By the time the European-wide Final Solution was formulated two months later, Heydrich's RSHA had already confirmed the effectiveness of industrial killing by exhaust fumes, and the strength of deception.
Construction work on the first killing centre at Bełżec in occupied Poland began in October 1941, three months before the Wannsee Conference. The new facility was operational by March the following year. By mid-1942, two more death camps had been built on Polish lands: Sobibór operational by May 1942, and Treblinka operational in July. From July 1942, the mass murder of Polish and foreign Jews took place at Treblinka as part of Operation Reinhard, the deadliest phase of the Final Solution. More Jews were killed at Treblinka than at any other Nazi extermination camp apart from Auschwitz. By the time the mass killings of Operation Reinhard ended in 1943, roughly two million Jews in German-occupied Poland had been murdered. The total number of people killed in 1942 in Lublin/Majdanek, Bełżec, Sobibór, and Treblinka was 1,274,166 by Germany's own estimation, not counting Auschwitz II Birkenau nor Kulmhof. Their bodies were buried in mass graves initially. Both Treblinka and Bełżec were equipped with powerful crawler excavators from Polish construction sites in the vicinity, capable of most digging tasks without disrupting surfaces. Although other methods of extermination, such as the cyanic poison Zyklon B, were already being used at other Nazi killing centres such as Auschwitz, the Aktion Reinhard camps used lethal exhaust gases from captured tank engines.
The Holocaust by bullets (as opposed to the Holocaust by gas) went on in the territory of occupied Poland in conjunction with the ghetto uprisings, irrespective of death camps' quota. In two weeks of July 1942, the Słonim Ghetto revolt, crushed with the help of Latvian, Lithuanian, and Ukrainian Schutzmannschaft, cost the lives of 8,000–13,000 Jews. The second largest mass shooting (to that particular date) took place in late October 1942 when the insurgency was suppressed in the Pińsk Ghetto; over 26,000 men, women and children were shot with the aid of Belarusian Auxiliary Police before the ghetto's closure. During the suppression of the Warsaw Ghetto Uprising (the largest single revolt by Jews during World War II), 13,000 Jews were killed in action before May 1943. Numerous other uprisings were quelled without impacting the pre-planned Nazi deportations actions.
About two-thirds of the overall number of victims of the Final Solution were killed before February 1943, which included the main phase of the extermination programme in the West launched by Eichmann on 11 June 1942 from Berlin. The Holocaust trains run by the Deutsche Reichsbahn and several other national railway systems delivered condemned Jewish captives from as far as Belgium, Bulgaria, France, Greece, Hungary, Italy, Moravia, Netherlands, Romania, Slovakia, and even Scandinavia. The cremation of exhumed corpses to destroy any evidence left behind began in early spring and continued throughout summer. The nearly completed clandestine programme of murdering all deportees was explicitly addressed by Heinrich Himmler in his Posen speeches made to the leadership of the Nazi Party on 4 October and during a conference in Posen (Poznan) of 6 October 1943 in occupied Poland. Himmler explained why the Nazi leadership found it necessary to kill Jewish women and children along with the Jewish men. The assembled functionaries were told that the Nazi state policy was "the extermination of the Jewish people" as such.
We were faced with the question: what about the women and children? – I have decided on a solution to this problem. I did not consider myself justified to exterminate the men only – in other words, to kill them or have them killed while allowing the avengers, in the form of their children, to grow up in the midst of our sons and grandsons. The difficult decision had to be made to have this people disappear from the earth.
— Heinrich Himmler, 6 October 1943
On 19 October 1943, five days after the prisoner revolt in Sobibór, Operation Reinhard was terminated by Odilo Globocnik on behalf of Himmler. The camps responsible for the killing of nearly 2,700,000 Jews were soon closed. Bełżec, Sobibór, and Treblinka were dismantled and ploughed over before spring. The operation was followed by the single largest German massacre of Jews in the entire war carried out on 3 November 1943; with approximately 43,000 prisoners shot one-by-one simultaneously in three nearby locations by the Reserve Police Battalion 101 hand-in-hand with the Trawniki men from Ukraine. Auschwitz alone had enough capacity to fulfill the Nazis' remaining extermination needs.
Auschwitz II Birkenau
Unlike Belzec, Sobibor, Treblinka, and Lublin-Majdanek, which were built in the occupied General Government territory inhabited by the largest concentrations of Jews, the killing centre at Auschwitz subcamp of Birkenau operated in Polish areas annexed by Nazi Germany directly. The new gas chambers at Bunker I were finished around March 1942 when the Final Solution was officially launched at Belzec. Until mid-June 20,000 Silesian Jews were killed there using Zyklon B. In July 1942, Bunker II became operational. In August, another 10,000–13,000 Polish Jews from Silesia perished, along with 16,000 French Jews declared 'stateless', and 7,700 Jews from Slovakia.
The infamous 'Gate of Death' at Auschwitz II for the incoming freight trains was built of brick and cement mortar in 1943, and the three-track rail spur was added. Until mid-August, 45,000 Thessaloniki Jews were murdered in a mere six months, including over 30,000 Jews from Sosnowiec (Sosnowitz) and Bendzin Ghettos. The spring of 1944 marked the beginning of the last phase of the Final Solution at Birkenau. The new big ramps and sidings were constructed, and two freight elevators were installed inside Crematoria II and III for moving the bodies faster. The size of the Sonderkommando was nearly quadrupled in preparation for the Special Operation Hungary (Sonderaktion Ungarn). In May 1944, Auschwitz-Birkenau became the site of one of the two largest mass murder operations in modern history, after the Großaktion Warschau deportations of the Warsaw Ghetto inmates to Treblinka in 1942. It is estimated that until July 1944 approximately 320,000 Hungarian Jews were gassed at Birkenau in less than eight weeks. The entire operation was photographed by the SS. In total, between April and November 1944, Auschwitz II received over 585,000 Jews from over a dozen regions as far as Greece, Italy, and France, including 426,000 Jews from Hungary, 67,000 from Łódź, 25,000 from Theresienstadt, and the last 23,000 Jews from the General Government. Auschwitz was liberated by the Red Army on 27 January 1945, when the gassing had already stopped.