The Warsaw ghetto In 1942 he joined the Jewish Fighting Organization (ŻOB). Rotem became particularly useful as a courier for the Warsaw Ghetto fighters. The nickname "Kazik"—an abbreviation of a Polish name "Kazimierz" (Casimir), which means in Polish "someone who destroys opponent's prestige/glory during battle". The Warsaw Ghetto Uprising and aftermath As a ŻOB member, Kazik took part in the Warsaw ghetto uprising. He became the head courier, reporting directly to the ŻOB commander on the Gentile side, Yitzhak Zuckerman. The ŻOB commander in general was Mordechai Anielewicz. When it became apparent that the Germans would prevail, he was sent via a secret passageway to the Gentile side of Warsaw where he met with Zuckerman to arrange an escape for the fighters. However, the passageway was discovered by the Nazis. Unable to return, he and Zuckerman were trapped on the Gentile side while the fighting raged and the ghetto burned. Desperate to reach his comrades, Rotem made several attempts to enter the ghetto through the sewers before finally succeeding. There he encountered Zivia Lubetkin, one of the last surviving leaders of the ghetto uprising, and he led her with her team of approximately 80 fighters through the sewers to the Gentile side and then to the forests outside of the city. Throughout the rest of the war he continued his underground activities with the resistance, in particular helping to care for the several thousand Jews, who still remained in Warsaw in hiding. In August 1944, he took part in the Polish Warsaw Uprising.