Vans used by the Nazis to murder Jews and other prisoners through asphyxiation by carbon monoxide. About 700,000 people were victims of gas vans. The Nazis first experimented with gas vans in 1940 in Kochanowka, Poland; they locked mentally ill children inside a sealed van and choked them to death with carbon monoxide. Soon, the Nazis performed further experimentation that involved piping carbon monoxide from a truck's engine into a sealed chamber. When the Einsatzgruppen began the extermination of Soviet Jewry in mid-1941, they shot their victims to death. However, this was not a quick or secret enough method. Thus, the Reich Security Main Office (Reichssicherheitshauptamt, RSHA) ordered that gas vans be employed for murder on a large scale. The first gas vans in the Soviet Union were used in Poltava, in November 1941, and in Kharkov in December. That same month, gas vans were also used in the Chelmno extermination camp. By June 1942 there were 20 gas vans in operation, and another ten were being prepared.Some of the trucks could hold up to 50--60 victims; others could only handle 25--30 people. In March 1942, 7,000 prisoners, mostly Jewish women and children, were put to death by gas van in the Yugoslavian concentration camp called Sajmiste. Vans were also employed in Lublin, where they were used to kill Polish and Jewish prisoners in the Lublin fortress prison. The vans were then driven to Majdanek, where the corpses were burned in the crematorium. Fifteen vans were put at the disposal of the Einsatzgruppen operating in German-occupied Soviet Union. However, after several months of use, the Germans realized that the gas van method of extermination was rather troublesome. The men who unloaded the vans suffered mental stress due to their extremely close contact with murder. In addition, the back roads of the Soviet Union were very bad and caused the vans to break down quite frequently. Ultimately, the gas vans could not handle the large number of Jews that the Nazis intended to murder, so the more effective gas chambers were developed.