Jewish Combat Organization
After the Grossaktion Warsaw of summer 1942, in which more than a quarter of a million Jews were deported from the ghetto to Treblinka and murdered, the remaining Jews began to build bunkers and smuggle weapons and explosives into the ghetto. The left-wing Jewish Combat Organization (ŻOB) and right-wing Jewish Military Union (ŻZW) formed and began to train. A small resistance effort to another roundup in January 1943 was partially successful and spurred Polish resistance groups to support the Jews in earnest.