After June 1941, the Nazi Einsatzgruppen experimented with gas vans for mass killing. Gas vans were hermetically sealed trucks with engine exhaust diverted to the interior compartment. Use of gas vans began after Einsatzgruppe members complained of battle fatigue and mental anguish caused by shooting large numbers of women and children.
Gassing also proved to be less costly. Einsatzgruppen gassed hundreds of thousands of people, mostly Jews, Roma (Gypsies), and mentally ill people.
In 1941, the SS concluded that the deportation of Jews to extermination camps was the most efficient way of achieving the Final Solution. That same year, the Nazis opened the Chelmno camp in Poland. Jews from the Lodz area of Poland and Roma were killed there in mobile gas vans.
In 1942, systematic mass killing in stationary gas chambers began at Belzec, Sobibor, and Treblinka, Poland. The victims were unloaded from cattle cars, they were told that they had to be disinfected in showers. The victims were ordered to enter the showers with raised arms to allow as many people as possible to fit into the gas chambers. The tighter the gas chambers were packed, the faster the victims suffocated.
The Nazis constantly searched for more efficient means of extermination. At the Auschwitz camp in Poland, they conducted experiments with Zyklon B by gassing some 600 Soviet prisoners of war and 250 ill prisoners in September 1941.
Zyklon B pellets, converted to lethal gas when exposed to air. They proved the quickest gassing method and were chosen as the means of mass murder at Auschwitz.
At the height of the deportations, up to 6,000 people were gassed each day at Auschwitz – a figure which equals one death every 15 seconds. To put that in perspective: about four people would have died in the time you read this article.