What was the purpose of Nazi extermination camps?

I'm fairly surprised nobody mention the main purpose of concentration camps wasn't the execution. If was, the prisoners would go to showers as they arrive in the camp.

The camps where useful economically, as the prisoners works every day, as slaves, with production quotas et all. So they are moved to camps not for extermination, but for slavery, then extermination.

Then the showers have other advantage: they are silent. You don't want a prisoner uprising in a camp where there outnumber you by orders of magnitude.

The problem with shooting people on the fly is that word gets around very quickly that you are doing that and it becomes much more difficult to capture victims in the future.

Cost is not really a factor, because it is relatively cheap to kill people compared to say, fielding a military division.

The means of execution is also relatively unimportant. For example, in the 1930s the way the Soviets killed people is that in each county that made a fenced off area and dug trenches in it. Throughout the night they would arrest people on the lists and bring them in sedans called "black Marias" (or a truck if it was large families) to the special area. Then they would line them up over the trench and shoot them in the back of the head. Then the trench was covered over and during the day a new trench was dug for the next night. Similar methods were used in Cambodia under Pol Pot.

The biggest advantage of using remote death camps was that they were very secret, so this made it a lot easier to lull the victims into a false sense of security and hence capture more of them. It also was beneficial in avoiding negative publicity abroad. Hitler was very sensitive to Germany's "image" and read translated American newspapers regularly. Naturally, he did not want stories of mass executions appearing in those papers.

just complementing the good answers already given:

After the "Action Groups" proved difficult (as explained above: too slow, to visible, too demanding psychologically - who wants more drunk depressed demotivated soldiers roaming around? ), and before the camps/gas chambers, they had [gas vans1. Prisoners were crammed in the back of a sealed van, and the exhaust gases were rerouted to the inside. They learned:

• gas would be less demanding psychologically to the guards, as they would not directly shoot or see the deaths.
• exhaust gases were not fast (20 min) or silent enough. A better gas was needed.
• a bigger space would be more efficient, more dead in less time.
• obviously, corpse disposal was still an issue.

You can see that the gas chamber + cremation ovens idea had a direct precedent. It is not possible to kill trainloads of people with a couple of vans.

Also concentration camps allowed the Nazis to exploit the prisoners as workforce. There were not just Jews. See the prisoner color system. Another forerunner were the camps were they housed political prisoners since the 30's. So, they just had to put together the pieces they already had and increase the scale.

Even basic robbery of valuables was made easy. Prisoners would bring their valuables in their bags, and the guards could process the valuables in controlled rooms. Compare with rounding people around in the country, and having soldiers look for valuables on their houses - consider also how easy it would be for a soldier to pocket a valuable.

There are good movies about the Wansee Conference. Watch them (or read the minutes), they give a good view of the mindset.

Why did they spend money and effort to build the infrastructure and organization, collect, transport and house the prisoners while execution on the spot would presumably be easier and less costly?

Execution on the spot was indeed the policy practiced by Nazis on the Soviet territory, known as Holocaust by Bullets, which accounts for at least one and a half millions of the notorious 6 millions murdered Jews.

It is necessary to point out that Nazi treatment of Jews evolved over time - from extra-judicial abuse perpetrated by the Sturmabteilung (Brown Shirts) in early 1930s, to more systematic legal restrictions, to stripping Jews from citizenship and finally exterminating them. Thus, while Nazis came to power in 1933, the Final Solution was formally decided upon in 1942, well into the WW2.

Hanna Arendt in Eichmann in Jerusalem discusses how the audacity of Nazis grew, as they saw no reaction from Western governments and few protests among the non-Jewish population. They however took a number of precautions, such as:

• Keeping the destination and the purpose of deportations in secret - the very term deportation was intended to suggest resettlement to the east, rather than extermination. This also helped to avoid/reduce the resistance from the deportees, who willingly loaded the trains.
• Starting with Jews in the occupied western states (rather than in Germany), and typically demanding first deportation of the Jewish refugees from Germany, and only later the deportation of the Jews native to these countries.
• Placing the extermination camps in the east - e.g., the reason for placing Auschwitz in Poland was not only that this country used to have a significant Jewish population (most of its inmates came from other countries), but also because it was well hidden from the westerners.

A notorious example is that of Kastner train - Rudolph Kastner, a prominent Hungarian journalist of Jewish origin, negotiated with Eichmann an exit for about a thousand of his Jewish relatives and acquaintances - supposedly in exchange for keeping secret the planned deportation of 400,000 Hungarian Jews to Auschwitz (three quarters of whom died there.)

I recall a line from the World at War, episode 20 in which a commander remarks that the method of execution on the spot was producing a German nation of brutes and that another means of [genocide] would be preferable.

Adding two things to some good points from the other answers:

1) While the Nazis as an organization did horrible things they did not at all encourage individual cruelty as they understood it (i.e. as a Nazi you were supposed to kill Jews as a "necessity" but not supposed to have fun with it). There was a certain fear that exposing the general population to mass murders executed in the streets would corrupt the (alleged) higher morality of the german "Volk" [a]. So the murder of Jews from the area of the "Reich" was relegated to an elite force (which was lauded by Himmler in one of his "Posen speeches" for "having done that [killing the jews] while still remaining decent people").

Note that outside the area of the Reich the Nazis didn't much bother, at least 1,25 mio Jews were rounded up, shot and buried on the spot in the occuppied eastern terriories, and another ca. 400 000 killed in gas wagons [b].

2) Another important factor was disposal of the bodys. There did not exist any facilities that could have dealt with additional (to natural deaths) millions of bodys. This lead to the constructions of the notorious "ovens" in the annihilation camps. The engineers at the german company Topf und Söhne constructed a crematory that could completely incinerate a human body with as little as four kilograms of fuel (coke). This worked only as long as the bodys where properly stacked and the oven was not allowed to go cold, so an influx of bodys at a predictable rate was needed.

So one of the purposes of concentration camps relating to the holocaust was to have a buffer of future victims that could be funneled into the annihilation process according to available capacities for disposal (certainly there were other goals, especially since not everyone who went into a concentration camp was destined to go to a death camp; e.g. the non-jewish inmates would often be places in forced labour camps. For jewish victims forced labour usually meant "Vernichtung durch Arbeit" (annihilation by labour), i.e. they were given jobs that would most certainly kill them).

This applied till end of 1943/ beginning 1944 - when the Nazis realized the war effort wasn't going well they decided to kill as many jews as possible before they lost the war, and the destruction process became a lot more haphazardly (i.e. people were shot and burned in masses under the open sky because victims arrived quicker than they could be disposed in the previously employed manner).

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[a] Individual Motivations probably did not always match the ideological framework - for example Eichmann, who for a long time was portrayed as a bureaucratic figure, was later revealed to hold a visceral hatred against jews.

[b] Benz, Graml, Weiß (Editors), "Enzyklopädie des Nationalsozialismus" , München 1997, Page 50ff

Originally they were tried to just shoot the people in the ghettos/prisons, but it was having a demoralising effect on their soliders. There's only so many times the average soilder can shoot people at point blank range and not suffer psycological consequences.

Hence they came up with the extermination camps. The "gas showers" thing was helpful for the Nazis because the people would strip off all their clothes themselves (rather than the soliders stripping the corpses).

Goldhagen (Hitler's Willing Executioners), while drawing controversial conclusions, uses standard evidence. Goldhagen's evidentiary basis matches what I've read in Police Battalion studies, for example. So I am using Goldhagen as a handy, widely published, monographical account of modern German genocide studies.

The German genocide in Europe involved three significant components resulting in mass deaths: a) Actions b) Ghettos, concentration camps, extermination camps c) Death marches

In all instances, policy and execution evolved in relation to the concrete situation. Prior to 1941, the scale of the problem with excess undesirable populations was primarily limited to German controlled Poland. Poland had seen limited actions, but primarily saw population transfers into ghettos.

1941 and the invasion of the Soviet Union brought a new scale of problems into being. German war plans for the first year were to occupy everything West of the Leningrad, Moscow, Rostov-on-Don line. Some planning involved the use of forced extraction before winter to starve undesirable populations (all Slavs and Jews). They were highly fanciful plans.

The reality of the situation combined the use of rear area forces with specific anti-Jew and anti-Commissar actions (einsatzgruppen), with supplemental support from wehrmacht units and police battalion units to conduct primarily political pogroms. While there was a great deal of initial success in this method, the problems of excess undesirable population were compounded by Soviet POWs captured in large and increasing numbers. At the same time, the einsatzgruppen started showing signs of overwork, including extreme alcoholism and suicide. Alternatives to the action system were needed as "craft" style genocide was not sufficient for the planned goals.

While Soviet POW camps showed an extremely high mortality rate through deliberate neglect and starvation, this wasn't viewed as adequate. The Wannsee conference authorised the requirement that had already become apparent on the ground: a need for an industrial method of killing large numbers of human beings.

Killing was already systematic, that system of localised actions had become inefficient, and the system put in place mirrored on a larger scale the industrial and homicidal logic behind the mere concentration camps and the Soviet POW camps. As noted above, and in other posts, a significant volume of deaths occurred in late war death marches, or in continued actions or concentration camp starvation and disease deaths during the operation of extermination camps.

The purpose of to industrialize the mass execution of Jews and other "undesirables". Prior to creating the execution camps, the Nazis had executed considerable numbers of people "on the spot". This was a time consuming process not only for the actual execution but the sanitary disposal of bodies afterward. Considering that the regime was planning on executing between 12-15 million people, industrialization made sense.

Also, there was concern about the public reaction to performing the mass murder out in the open. By creating the convenient fiction that they were being sent to "relocation" camps, it allowed the German public to pretend not to notice what was really going on. Public outcry would be an even greater risk in occupied/allied nations like France, Romania and Hungary.

If you want to get some further info on it, read about the Wannsee Conference and watch the fairly accurate docu-drama Conspiracy that depicts this meeting.

1) It's much easier to hide the killings if they occur at a remote camp rather than executing people on the spot. The latter would probably have meant a much higher chance of rebellion amongst the Jews, Roma and other people who were killed. Most of the people who were deported to the camps did not know they would be killed.

2) The manpower required is much less compared to executing on the spot. For executing you need lots and lots of soldiers. For the gas chambers, you only need one person to flip the switch.

3) Psychologically, it's easier on the people doing the killing.

That said, counting the number of Jews killed in extermination camps (see here) compared to the total numer of Jews killed, almost 3 million were not killed in extermination camps but via other means.