As the first death camp, Belzec was used to test the efficiency of different methods of mass execution. The commanders of the camp, Josef Oberhauser and Christian Wirth, had originally been involved in the Nazi euthanasia program and decided to introduce gas chambers there. These used carbon monoxide gas, but since the sudden shipment of large quantities of gas to the area would evoke suspicion, the gas was supplied by gasoline through the exhaust pipes of normal vehicles. In this way, it mimicked the gas vans used in Chelmno (Kulmhof).
The camp commanders experimented with various ways to make the extermination process as efficient as possible. The wooden gas chambers were disguised as the barracks and showers of a labor camp, so that the victims would not realize the true purpose of the site, and the process was conducted as quickly as possible: people were forced to run from the trains to the gas chambers, leaving them no time to absorb where they were or to plan a revolt. Finally, a handful of Jews were selected to perform all the manual work involved with extermination (removing the bodies from the gas chambers, burying them, sorting the victims' clothing, etc.). The extermination process itself was conducted by Ukrainian guards. The Jewish Sonderkommandos were killed periodically and replaced by new arrivals, so that they would not organize in a revolt either.
Eventually, the extermination camp consisted of two subcamps: Camp I, which include the administration and reception areas, and Camp II, which contained the gas chambers. The two camps were connected by a narrow corridor called the Schlauch, or "Tube." The German guards and adminstrators were housed in barracks outside the camp, near the local railway station.
Belzzec's three gas chambers began operating officially on March 17, 1942, the date given for the start of Operation Reinhard. Its first victims were Jews deported from Lublin.
There were many technical difficulties in this first attempt at mass extermination. The gas chamber mechanisms were problematic, and usually only one or two were working at any given time, causing a backlog. Furthermore, the corpses were buried in pits covered with only a narrow layer of earth. The bodies often swelled in the heat as a result of putrefaction and the escape of gases, and the covering of earth actually split. This latter problem was corrected in other death camps with the introduction of crematoria.
It was soon realized that the original three gas chambers were insufficient for completing the task at hand, especially with the growing number of arrivals from Cracow and Lvov. They were dismantled and a new complex with six gas chambers, each 4 x 8 meters, was built instead. The new facility, which could handle 2,000 victims at a time, was imitated by the other two Operation Reinhard extermination camps: Treblinka and Sobibor. Nevertheless, by December 1942, the last shipment of Jews arrived in Belzec, and in March 1943 Heinrich Himmler decided to dismantle the camp, along with Treblinka and Sobibor. By that time, the Jews in the area served by Belzec had been almost entirely exterminated, and it was felt that the newly completed facility at Auschwitz could handle the rest.
It is believed that some 800,000 people were killed in Belzec, mainly Jews, though some evidence Gypsies were exterminated there too. Only two Jews are known to have survived Belzec: Rudolf Reder and Chaim Herszman. The camp's commander, Christian Wirth, was killed by partisans in Trieste in 1944. Josef Oberhauser was brought to trial in Germany in 1965 and sentenced to four and a half years in prison. He later gave an interview about the camp in Claude Lanzmann's documentary film Shoah.