In the midst of the first wave of deportations from Warsaw ghetto to the Treblinka killing center, the Jewish Fighting Organization (ZOB, Zydowska Organizacja Bojowa) is established. On July 22, 1942, the Germans begin massive deportations which last virtually without stop until September 12, 1942. During this time more than 250,000 Jews from the ghetto are deported or killed. The ZOB, formed by members of Jewish youth organizations, calls for the Jews of the ghetto to resist deportation. Reports of the massacres of Jews by mobile killing units and in killing centers have already filtered into the ghetto. However, the ZOB is not yet ready to stage a revolt. After deportations end in September, the ZOB expands to incorporate members of underground political organizations and establishes contact with the Polish resistance forces who provide training, armaments and explosives. Mordecai Anielewicz is appointed commander.