POLAND: Adolf Hitler's Germany created a machine which ultimately devoured over 11 million people, writes Daniel McLaughlin.
When, a decade before invading Poland as undisputed leader of Nazi Germany, Adolf Hitler warned against "maintaining the weak at the expense of the healthy", he had a many-headed monster in mind. But no one could have imagined the weapon he would use to slay it.
A machine, evolving over time, which devoured those whom the Fuhrer deemed a burden or threat to the Third Reich: elderly and handicapped people; prisoners of war; dissidents and democrats; Jews and Gypsies and homosexuals.
A machine to create "lebensraum" - "living space" for a master race - by enslaving foreigners and annihilating Jews, and which ultimately devoured 11 million people.
But what became a web of prison camps across central and eastern Europe, including extermination centres like Auschwitz and Treblinka, grew from six, unprepossessing clinics in rural Germany that called their work "mercy killing".
As many as 100,000 people with physical and mental illnesses were murdered at the so-called T4 centres between 1939-'41, giving grim substance to long-running discussions in Nazi circles over the elimination of "life not worthy of life".
Such talk also covered eugenics - the search for ways to improve a nation's bloodstock, which underpinned a 1933 law making sterilisation compulsory for - in the ominously vague Nazi phrasing - carriers of "inherited mental or physical defects".
Germany was fertile ground for a right-to-life debate that was taking place across Europe, a continent forced to examine its most fundamental values after witnessing the industrial-scale killing power of poison gas and machine guns in the first World War.
Now, shorn of land, crippled by reparations and humiliated by the post-war settlement at Versailles, Hitler told Germany that mass sterilisation and "euthanasia" would strengthen the nation's bloodstock while saving money on health and welfare.
But the T4 centres did more than legitimise state-sponsored killing, and nudge German doctors down the slope that would lead some to the train platform at Auschwitz, sending prisoners to work or execution.
In the shower rooms where German patients were poisoned with carbon monoxide, and the crematoria where their bodies burned, the extermination camps had their seed.
With time and attention, the Nazis' "mercy killing" machine would be big enough to consume millions.
When T4 operations were wound down in August 1941, the doctors and SS men who ran it were not idle for long.
They and their methods offered a definitive, practical answer to Hitler's problem of what to do with the millions of Jews and other "asocial elements" who had come under his control as German forces occupied most of Europe.
Just three weeks after Germany invaded Poland on September 1st, 1939, Security Police chief Reinhard Heydrich had devised a series of steps towards a secret "final aim".
His plan was to concentrate eastern Europe's Jews in ghettos in the main Polish cities, governed by German officials through local councils of Jewish elders, and close to main railway lines for ease of transport. In the countryside, meanwhile, mobile SS Einsatzgruppen units were dispatched to mop up: they operated with grim efficiency, killing more than a million Jews in Poland and the Soviet Union before the end of the war.
But as the squalid Jewish ghettoes became potential sources of rebellion, and German industry and prison camps struggled to utilise the available slave labour, Hitler wondered what to do with the human "trash" accumulated by his pursuit of lebensraum.
By late 1940, Britain's continuing naval threat had convinced him to shelve a tentative scheme to deport Europe's Jews to Madagascar - whose combination of remoteness and tropical disease he found appealing - and another answer took shape.
As German troops pushed into Yugoslavia and Greece in April 1941, and then invaded the Soviet Union in June, hundreds of thousands more Jews came under their control, and the ghettos were already at bursting point.
In Belorussia, a roving Einsatzgruppen unit, sick of countless executions by shooting, found a new way to kill the inmates of a mental asylum: after consulting a veteran of the T4 "euthanasia" programme, they gassed them all with carbon monoxide.
The success of the venture encouraged Dr Walter Rauff, one of the Nazi's leading technicians, to hand an efficient new tool to the overworked Einsatzgruppen: the gas van.
These trucks, sometimes painted in Red Cross livery, were put to work at Chelmno in eastern Poland in late 1941.
Dozens of Jews and suspected communists could be loaded into each zinc-lined lorry and driven to a prepared grave. On the way, carbon monoxide fumes from the engine were pumped in, and they were usually dead on arrival.
"Did I think twice about employing the gas vans?" Rauff mused after the war. "I couldn't say. At the time the most important consideration for me was the psychological stress felt by the men involved in the shootings. This problem was overcome by the use of gas vans."
The practical and psychological benefits of gassing were now clear, and the Nazis accelerated towards the "final aim" to which Heydrich had alluded two years before.
In October 1941 - a month after Czech Jews had assassinated Heydrich in Prague - Gestapo chief Heinrich Himmler ordered the construction of Belzec, the first of three Polish camps built solely for extermination.
Jewish prisoners built Belzec, Sobibor and Treblinka, and old medical and SS hands from the T4 programme were enlisted to man the gas chambers and crematoria, with help from Ukrainians who often outdid the Germans for brutality. With the killing houses ready, the Jewish ghettos of Poland could now be emptied.
Nazi officials told Jewish elders to organise the orderly evacuation of the miserable, horrendously overcrowded ghettos, so their residents could be "resettled" somewhere to the east. Fetid cattle trucks took thousands of Jews to the extermination camps each day. Those who survived the journey were again promised resettlement after a hot shower.
The guards moved them with maximum, disorientating speed to the "bathrooms". When the door was closed, a simple truck engine pumped its exhaust fumes inside. Some 1.7 million people died of carbon monoxide poisoning this way, on a conveyor belt of murder that was named in honour of Heydrich: "Operation Reinhard".
Hitler had created thousands of labour camps since taking power in 1933 - the year he opened Dachau near Munich - and major German companies like Volkswagen, Siemens and Daimler all used concentration camp labour.
In 1941, some of these labour camps were infused with the macabre expertise of the "mercy killing" programme, to execute the so-called 'Final Solution' of the Jewish problem. Auschwitz and Majdanek, both in southern Poland, were two such places.
Unimpressed by the carbon monoxide method - which sometimes left doomed prisoners screaming in a locked gas chamber while a faulty motor engine was fixed - Auschwitz commandant Rudolf Hoess found that a pest control chemical called Zyklon B could be an efficient killer in high-enough doses.
It was this prussic acid that asphyxiated more than a million people in Auschwitz, and 230,000 more at Majdanek.
A death certificate was filed for most of them. It was a typical affectation of a regime that sought to make mass murder a cold matter of duty, science and bureaucracy.