In 1933 the Nazi police and SA set up about fifty concentration camps. In 1936 the SS began to rebuild or erect new concentration camps, each as an organized whole, with permanent headquarters, camp, SS barracks, and SS housing. Once the war started the Nazis rooted out even more thoroughly opponents in Germany and abroad. In some camps with a much smaller gas chamber and where the Nazis used carbon monoxide, such as at Belzec, they might force so many victims into the chamber that there was no room to move. Like the Japanese militarists and the Soviets, the Nazis also conducted horrible medical experiments on the living and conscious: freezing experiments, bone grafting experiments, vacuum experiments, infection experiments, disease experiments, surgical experiments, and so on and on. The Nazis sought to develop an inexpensive, unobtrusive and rapid method of sterilization that could be used to wipe out Russians, Poles, Jews, and other people.