The Jewish Combat Organization was established in the Warsaw Ghetto on 28 July 1942, assuming its final shape in December of the same year.
Its objective was to put up active resistance and conduct an armed struggle against the Germans. The consolidation of the organization was closely connected with the commencement of the so-called Grossaktion a few days earlier. It was created by young people originating from three groupings: Hashomer Hatzair, Dror, and Agudat Hanoar Haiwri “Akiba”, which were all seated in the building at No. 34 Dzielna Street. They realized only too well that they stood no chance of actually winning the fight against the excellently trained and well-armed German SS units. Thus, the emphasis was placed on simply opposing the invader with weapon in hand. The founding members of the Jewish Combat Organization included Mordechaj Anielewicz, Icchak Cukierman, Cywia Lubetkin, Mordechaj Tenenbaum, Arje Wilner, and Józef Kapłan. Over time, it set up field branches in Białystok, Częstochowa, Sosnowiec and Będzin. In Kraków, no “Jewish Combat Organization” was formally established as such, however those united in the resistance operated under the name “Jewish Organization of HeHalutz Youth”. In the autumn of 1942, the organization was joined by members of the Bund, Poale Zion, and the Communists. Mordechaj Anielewicz, pseudonym “Aniołek”, became the commander of the Jewish Combat Organization in Warsaw. Its organizational department was headed by Icchak Cukierman, pseudonym “Antek”, with Jochanan Morgenstern supervising intelligence affairs. Outside the ghetto, the Jewish Combat Organization was represented by Izrael Chaim Wilner, pseudonym “Jurek”.
The members of the Jewish Combat Organization carried out assassinations of collaborationists and spies, killing, among others, Jakub Lejkin, a Jewish policeman and deputy commandant of the Jewish Order Service (Jüdischer Ordnungsdienst), and Alfred Nossig, who was suspected of being an informer. In fact, one of the first such operations was organized less than a month after the formation of the Jewish Combat Organization. On 20 August 1942, Izrael Kanał made an assassination attempt (ultimately unsuccessful) on Józef Szeryński, the commandant of the Jewish police in the Warsaw Ghetto. Smaller-scale actions were also carried out, such as bringing people out of the ghetto or setting fire to workshops and sabotaging their activities.