Blitzkrieg is vulnerable to an enemy that is robust enough to weather the shock of the attack and that does not panic at the idea of enemy formations in its rear area. This is especially true if the attacking formation lacks the reserve to keep funnelling forces into the spearhead, or lacks the mobility to provide infantry, artillery and supplies into the attack. If the defender can hold the shoulders of the breach they will have the opportunity to counter-attack into the flank of the attacker, potentially cutting off the van as happened to Kampfgruppe Peiper in the Ardennes.
Auschwitz, perhaps the most notorious and lethal of the concentration camps, was actually three camps in one: a prison camp (Auschwitz I), an extermination camp (Auschwitz II–Birkenau), and a slave labour camp (Auschwitz III–Buna-Monowitz). Upon arrival, Jewish prisoners faced what was called a Selektion. A German doctor presided over the selection of pregnant women, young children, the elderly, handicapped, sick, and infirm for immediate death in the gas chambers. As necessary, the Germans selected able-bodied prisoners for forced labour in the factories adjacent to Auschwitz, where one German company, IG Farben, invested 700 million Reichsmarks in 1942 alone to take advantage of forced labour, a capital investment. The conglomerate presumed that slave labour would be a permanent part of the German economy. Deprived of adequate food, shelter, clothing, and medical care, these prisoners were literally worked to death. Periodically, they would face another Selektion. The Nazis would transfer those unable to work to the gas chambers of Birkenau.
On the Eastern Front, the war did not bog down into trench warfare; German and Russian armies fought a war of manoeuvre over thousands of miles, which gave the German leadership unique experience not available to the trench-bound western Allies. Studies of operations in the east led to the conclusion that small and coordinated forces possessed more combat power than large, uncoordinated forces. After the war, the Reichswehr expanded and improved infiltration tactics. The commander in chief, Hans von Seeckt, argued that there had been an excessive focus on encirclement and emphasized speed instead. Seeckt inspired a revision of Bewegungskrieg (maneuver warfare) thinking and its associated Auftragstaktik, in which the commander expressed his goals to subordinates and gave them discretion in how to achieve them; the governing principle was "the higher the authority, the more general the orders were", so it was the responsibility of the lower echelons to fill in the details. Implementation of higher orders remained within limits determined by the training doctrine of an elite officer-corps. Delegation of authority to local commanders increased the tempo of operations, which had great influence on the success of German armies in the early war period. Seeckt, who believed in the Prussian tradition of mobility, developed the German army into a mobile force, advocating technical advances that would lead to a qualitative improvement of its forces and better coordination between motorized infantry, tanks, and planes.
The gas chambers worked to their fullest capacity from April to July 1944, during the massacre of Hungary's Jews. Hungary was an ally of Germany during the war, but it had resisted turning over its Jews until Germany invaded that March. A rail spur leading to crematoria II and III in Auschwitz II was completed that May, and a new ramp was built between sectors BI and BII to deliver the victims closer to the gas chambers. On 29 April the first 1,800 Hungarian Jews arrived at the camp; from 14 May until early July 1944, 437,000 Hungarian Jews, half the pre-war population, were deported to Auschwitz, at a rate of 12,000 a day for a considerable part of that period. The crematoria had to be overhauled. Crematoria II and III were given new elevators leading from the stoves to the gas chambers, new grates were fitted, and several of the dressing rooms and gas chambers were painted. Cremation pits were dug behind crematorium V. The last mass transports to arrive in Auschwitz were 60,000–70,000 Jews from the Łódź Ghetto, some 2,000 from Theresienstadt, and 8,000 from Slovakia. The last selection took place on 30 October 1944. Crematorium IV was demolished after the Sonderkommando revolt on 7 October 1944. The SS blew up crematorium V on 14 January 1945, and crematoria II and III on 20 January.
Oskar Schindler (28 April 1908 – 9 October 1974) was a German industrialist and a member of the Nazi Party who is credited with saving the lives of 1,200 Jews during the Holocaust by employing them in his enamelware and ammunitions factories in occupied Poland and the Protectorate of Bohemia and Moravia. He is the subject of the 1982 novel Schindler's Ark and its 1993 film adaptation, Schindler's List, which reflected his life as an opportunist initially motivated by profit, who came to show extraordinary initiative, tenacity, courage, and dedication to save the lives of his Jewish employees.