However, the route to a professorship was interrupted in 1938-1939 when he began his military experience by serving six months with a specially trained mountain light-infantry regiment. In 1940 he was placed in the reserve medical corps, following which he served three years with a Waffen SS unit. It was during this time period he was wounded and declared medically unfit for combat. Because he had acquitted himself brilliantly in the face of the enemy during the Eastern Campaign, he was promoted to the rank of captain.

"Dr. Mengele had always been more interested in Tibi. I am not sure why - perhaps because he was the older twin. Mengele made several operations on Tibi. One surgery on his spine left my brother paralyzed. He could not walk anymore. Then they took out his sexual organs. After the fourth operation, I did not see Tibi anymore. I cannot tell you how I felt. It is impossible to put into words how I felt. They had taken away my father, my mother, my two older brothers - and now, my twin ..."
“I am marshalling my last remaining strength in order to die peacefully as one who will not surrender and who will not ask for forgiveness. The historical fact that Israel became the leading social political superpower in the 19th century lies before us. We have amongst us a flexible, tenacious, intelligent foreign tribe that knows how to bring abstract reality into play in many different ways. Not individual Jews but the Jewish spirit and Jewish consciousness have overpowered the world. All this is the consequence of a cultural history so unique in its way, so grand that every day polemic can achieve nothing against it. With the entire force of its armies the proud Roman Empire did not achieve that which Semitism has achieved in the West and particularly in Germany.”
When in 1941 the Wehrmacht forces attacked the Soviet positions in eastern Poland during the initially successful Operation Barbarossa, the area of the General Government was enlarged by the inclusion of regions that had been occupied by the Red Army since 1939.[72] 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,[73] 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.[74]

^ Jump up to: a b Dan Stone (Histories of the Holocaust, 2010): "Europe's Romany (Gypsy) population was also the victim of genocide under the Nazis. Many other population groups, notably Poles, Ukrainians, and Soviet prisoners of war were killed in huge numbers, and smaller groups such as Jehovah's Witnesses, Black Germans, and homosexuals suffered terribly under Nazi rule. The evidence suggests that the Slav nations of Europe were also destined, had Germany won the war, to become victims of systematic mass murder; and even the terrible brutality of the occupation in eastern Europe, especially in Poland, can be understood as genocidal according to the definition put forward by Raphael Lemkin in his major study, Axis Rule in Occupied Europe (1944), the book that introduced the term 'genocide' to our vocabulary. Part of the reason for today's understanding, though, is a correct assessment of the fact that for the Nazis the Jews were regarded in a kind of 'metaphysical' way; they were not just considered as racially inferior (like Romanies), deviants (like homosexuals) or enemy nationals standing in the way of German colonial expression (like Slavs). ... [T]he Jews were to some extent outside of the racial scheme as defined by racial philosophers and anthropologists. They were not mere Untermenschen (sub-humans) ... but were regarded as a Gegenrasse: "a 'counter-race', that is to say, not really human at all. ... 'Holocaust', then, refers to the genocide of the Jews, which by no means excludes an understanding that other groups—notably Romanies and Slavs—were victims of genocide. Indeed ... the murder of the Jews, although a project in its own right, cannot be properly historically situated without understanding the 'Nazi empire' with its grandiose demographic plans."[32]
AT AUSCHWITZ, on 24th December, 1942, I was paraded in company with about 19,000 other prisoners, all of them women. Present on parade were Doctors Mengele and Konig and Rapportfuhrer Tauber. I was one of the 3000 prisoners picked out of the 19,000 by the doctors and taken to our huts, where we were stripped naked by other prisoners and our clothes taken away. We were then taken by tipper-type lorries to the gas chamber chute. They were large lorries, about eight in all and about 300 persons on each lorry. On arrival at the gas chamber the lorry tipped up and we slid down the chute through some doors into a large room. The room had showers all around, towels and soap and large numbers of benches. There were also small windows high up near the roof. Many were injured coming down the chute and lay where they fell. Those of us who could sat down on the benches provided and immediately afterwards the doors of the room were closed. My eyes then began to water, I started to coughing and had a pain in my chest and throat. Some of the other people fell down and others coughed and foamed at the mouth. After being in the room for about two minutes the door was opened and an S.S. man came in wearing a respirator. He called my name and then pulled me out of the room and quickly shut the door again. When I got outside I saw S.S man Franz Hoessler, whom I identify as No. 1 on photograph 9. He took me to hospital, where I stayed for about six weeks, receiving special treatment from Dr. Mengele. For the first few days I was at the hospital I found it impossible to eat anything without vomiting. I can only think that I was taken out of the gas chamber because I had an Aryan husband and therefore was in a different category from the other prisoners, who were all Jews. I now suffer from a weak heart and had two attacks since being at Belsen. I do not know the names of any persons who went into the gas chamber with me.
Lay Catholics, such as the German Dr. Gertrude Luckner, who headed the Caritas Catholica, also extended help to Jews and non-Aryan Christians in Germany. She was deported to Ravensbruck for her aid to the persecuted. After the war, Dr. Luckner was honored for her courage by the Israeli government. It must be noted that much of this Christian help was actually rendered to fellow Christians (converted Jews), who were classified as Jews due to their descent under Nazi racial laws.

When war erupted, Mengele was a medical officer with the SS, the elite squad of Hitler’s bodyguards who later emerged as a secret police force that waged campaigns of terror in the name of Nazism. In 1943, Mengele was called to a position that would earn him his well-deserved infamy. SS head Heinrich Himmler appointed Mengele the chief doctor of the Auschwitz death camps in Poland.
How, when, and why the Nazis’ decision to exterminate Europe’s Jews was made remains one of the most vexed and disputed of all important questions concerning the Holocaust. There was not simply an order from Hitler commanding the killing of the Jews, and there is general agreement that the genocide evolved in stages, steadily becoming more comprehensive. The Origins of the Final Solution by the universally respected historian Christopher R. Browning, now at the University of North Carolina at Chapel Hill, is a magisterial examination of this subject in the wider context of the overall evolution of Nazi policy towards the Jews between the outbreak of the Second World War in September 1939 and the opening of the first extermination camps early in 1942.
While Clauberg and Schumann were busy with experiments designed to develop methods for the biological destruction of people regarded by the Nazis as undesirable, another medical criminal, SS-Hauptsturmführer Josef Mengele, M.D., Ph.D., was researching the issues of twins and the physiology and pathology of dwarfism in close cooperation with the Kaiser Wilhelm Institute of Anthropology, Genetics, and Eugenics in Berlin-Dahlem. He was also interested in people with different colored irises (heterochromia iridii), and in the etiology and treatment of the gangrenous disease of the face known as noma Faciei (cancrum oris, gangrenous stomatitis), a little understood disease endemic to the Gypsy prisoners in Auschwitz.
The memory of this slightly built man, scarcely a hair out of place, his dark green tunic neatly pressed, his face well scrubbed, his Death's Head SS cap tilted rakishly to one side, remains vivid for those who survived his scrutiny when they arrived at the Auschwitz railhead. Polished boots slightly apart, his thumb resting on his pistol belt, he surveyed his prey with those dead gimlet eyes. Death to the left, life to the right. Four hundred thousand souls - babies, small children, young girls, mothers, fathers, and grandparents - are said to have been casually waved to the lefthand side with a flick of the cane clasped in a gloved hand.

While concentration camps were meant to work and starve prisoners to death, extermination camps (also known as death camps) were built for the sole purpose of killing large groups of people quickly and efficiently. The Nazis built six extermination camps, all in Poland: Chelmno, Belzec, Sobibor, Treblinka, Auschwitz, and Majdanek. (Auschwitz and Majdanek were both concentration and extermination camps.)
Following the invasion of Poland, German occupation policy especially targeted the Jews but also brutalized non-Jewish Poles. In pursuit of lebensraum, Germany sought systematically to destroy Polish society and nationhood. The Nazis killed Polish priests and politicians, decimated the Polish leadership, and kidnapped the children of the Polish elite, who were raised as “voluntary Aryans” by their new German “parents.” Many Poles were also forced to perform hard labour on survival diets, were deprived of property and uprooted, and were interned in concentration camps.
Peter Hayes (How Was It Possible? A Holocaust Reader, 2015): "The Holocaust, the Nazi attempt to eradicate the Jews of Europe, has come to be regarded as the emblematic event of Twentieth Century ... Hitler's ideology depicted the Jews as uniquely dangerous to Germany and therefore uniquely destined to disappear completely from the Reich and all territories subordinate to it. The threat posted by supposedly corrupting but generally powerless Sinti and Roma was far less, and therefore addressed inconsistently in the Nazi realm. Gay men were defined as a problem only if they were German or having sex with Germans or having sex with Germans and considered 'curable' in most cases. ... Germany's murderous intent toward the handicapped inhabitants of European mental institutions ... was more comprehensive ... but here, too, implementation was uneven and life-saving exceptions permitted, especially in Western Europe. Not only were some Slavs—Slovaks, Croats, Bulgarians, some Ukrainians—allotted a favored place in Hitler's New Order, but the fate of most of the other Slavs the Nazis derided as sub-humans ... consisted of enslavement and gradual attrition, not the prompt massacre meted out to the Jews after 1941."[20]
"Dr. Mengele had always been more interested in Tibi. I am not sure why - perhaps because he was the older twin. Mengele made several operations on Tibi. One surgery on his spine left my brother paralyzed. He could not walk anymore. Then they took out his sexual organs. After the fourth operation, I did not see Tibi anymore. I cannot tell you how I felt. It is impossible to put into words how I felt. They had taken away my father, my mother, my two older brothers - and now, my twin ..."
Auschwitz is the most famous because there the killing machine was the most efficient. There, between the end of 1941 and 1944, as many as 12,000 Jews a day could be gassed to death and cremated. In addition to the Jews, hundreds of thousands of others deemed threats to the Nazi regime or considered racially inferior or socially deviant were also murdered.
The Nazis used the phrase Lebensunwertes Leben (life unworthy of life) in reference to the disabled and mentally ill.[92] On 14 July 1933, the Law for the Prevention of Hereditarily Diseased Offspring (Gesetz zur Verhütung erbkranken Nachwuchses), the Sterilization Law, was passed, allowing for compulsory sterilization.[93][94] The New York Times reported on 21 December that year: "400,000 Germans to be sterilized".[95] There were 84,525 applications from doctors in the first year. The courts reached a decision in 64,499 of those cases; 56,244 were in favor of sterilization.[96] Estimates for the number of involuntary sterilizations during the whole of the Third Reich range from 300,000 to 400,000.[97]
First, the rescuer must have been actively involved in saving Jews from the threat of death or deportation to concentration camps or killing centers. Second, the rescuer must have risked their own life or liberty in their attempt to save Jews. Third, the original motive for rescue must have been to protect and save Jews from the Holocaust. Other motivations, not considered for qualification, include financial gain, protecting Jews in order to convert them to Christianity, taking a Jewish child with the intention of adoption, or rescuing individuals during resistance activities that were not explicitly geared towards rescuing Jews. Finally, there must be first-hand testimony from those rescued to verify the individual's role in the rescue. If testimony does not exist or cannot be found, there must be irrefutable documentation of the individual's participation in the rescue and the conditions surrounding it.
At Auschwitz, a large new camp was already under construction to be known as Auschwitz II (Birkenau). This would become the future site of four large gas chambers to be used for mass extermination. The idea of using gas chambers originated during the Euthanasia Program, the so-called "mercy killing" of sick and disabled persons in Germany and Austria by Nazi doctors.
Anti-Jewish measures were introduced in Slovakia, which would later deport its Jews to German concentration and extermination camps.[175] Bulgaria introduced anti-Jewish measures in 1940 and 1941, including the requirement to wear a yellow star, the banning of mixed marriages, and the loss of property. Bulgaria annexed Thrace and Macedonia, and in February 1943 agreed to deport 20,000 Jews to Treblinka; all 11,000 Jews from the annexed territories were sent to their deaths, and plans were made to deport an additional 6,000–8,000 Bulgarian Jews from Sofia to meet the quota.[176] When the plans became public, the Orthodox Church and many Bulgarians protested, and King Boris III canceled the deportation of Jews native to Bulgaria.[177] Instead, they were expelled to the interior pending further decision.[176] Although Hungary expelled Jews who were not citizens from its newly annexed lands in 1941, it did not deport most of its Jews[178] until the German invasion of Hungary in March 1944. Between 15 May and 9 July 1944, 440,000 Hungarian Jews were deported to Auschwitz.[179] In late 1944 in Budapest, nearly 80,000 Jews were killed by the Hungarian Arrow Cross battalions.[180]
Mengele joined the Nazi Party in 1937 and the Schutzstaffel (SS; protection squadron) in 1938. He received basic training in 1938 with the Gebirgsjäger (light infantry mountain troop) and was called up for service in the Wehrmacht (Nazi armed forces) in June 1940, some months after the outbreak of World War II. He soon volunteered for medical service in the Waffen-SS, the combat arm of the SS, where he served with the rank of SS-Untersturmführer (second lieutenant) in a medical reserve battalion until November 1940. He was next assigned to the SS-Rasse- und Siedlungshauptamt (SS Race and Settlement Main Office) in Poznań, evaluating candidates for Germanization.[18][19]