Fareynikte Partizaner Organizatsye

The Fareynikte Partizaner Organizatsye (Yiddish: פֿאַראײניקטע פּאַרטיזאַנער אָרגאַניזאַציע‎; "United Partisan Organization"; referred to as FPO by its Yiddish initials) was a Jewish resistance organization based in the Vilna Ghetto in German-occupied Lithuania and founded on January 21, 1942. The clandestine organisation was established by Communists as well as left- and right-wing Zionists. Their leaders were the Communist Yitzhak Wittenberg, Socialist Abba Kovner, and revisionist Betar member Josef Glazman.

After the creation of the ghetto in Vilnius, Jewish youth organizations were mainly involved in rescuing Jews during the extermination operations. There were disagreements between the various organizations regarding the goals of their activities and methods of work. The main proposals were to continue operating in Vilnius, to transfer their activities to the ghettos of Białystok or Warsaw, where the possibility of an uprising seemed more realistic (and where they did take place in August 1943 and April-May 1943, respectively), or to go into the forests as partisans. In the end, most of the organizations, with the exception of Mordechai Tenenbaum's Ha-Halutz-Dror group, decided to continue operating in Vilnius.

On December 31, 1941, Abba Kovner's appeal "We will not go like sheep to the slaughter" was published, calling for armed resistance to the Nazis.

On January 21, 1942, the FPO was created. Representatives of Jewish youth organizations – Yitzhak Wittenberg from the communists, Abba Kovner from Hashomer Hatzair (Socialist Zionism), Nissan Reznik from the Zionist youth and Josef Glazman from Betar (right-wing Revisionist Zionism) - gathered in the ghetto and decided to create a united organization. Yitzhak Wittenberg was elected its commander, Kovner, Resnick and Glazman as members of the staff. In the spring of 1942, the Bundists also joined the FPO. Representatives of Ha-Halutz-Dror created a separate organization under the leadership of Yechiel Sheinbaum. It advocated fleeing to the forests rather than revolt, but it united with the FPO in spring 1943 when the end of the ghetto's continued existence was in plain sight.

The FPO was formed in the Vilna Ghetto on January 21, 1942, three weeks after Kovner's manifesto, at Rūdninkų (Rudnicka) street no. 6, which was the office building of the Judenrat. This was the first Jewish resistance organization established in the ghettos of Nazi-occupied Europe in World War II, followed by Łachwa underground in August 1942. Unlike in other ghettos – where the underground resistance was coordinated to some extent with the officials of the local Jewish establishment – Vilna's Jacob Gens, head of the ghetto, cooperated with German officials in stopping armed resistance.

The goals of the FPO were to establish self-defense in the ghetto, to sabotage German industrial and military activities and to join the partisan and Red Army’s fight against the Nazis. Abba Kovner, the movement's leader, and 17 members of the local Zionist group Hashomer Hatzair, stationed at a Polish Catholic convent for an order of Dominican Sisters, sheltered from the Nazis by Mother Superior Anna Borkowska (Mother Bertranda), who was the first to supply hand grenades and other weapons to the Vilnius ghetto underground.

During 1942, the FPO was mainly engaged in acquiring weapons and attempting to transmit information about the extermination of Lithuanian Jews in Lithuania. Based on their place of residence in the ghetto, the members of the organization were divided into fives, 3 fives made up a platoon (roughly 15), and 6–8 platoons made up a battalion (ranging from 100 to 120 in strength). Representatives of all the parties and movements that were part of it were at the organization's headquarters. Grenades and Molotov cocktails were produced in the ghetto itself. Rifles and other weapons were purchased from the local population. The organization sent messengers to the ghettos of Grodno, Warsaw, and Bialystok, with news of the extermination of the Jews in Vilnius.

At this stage of the struggle, there were no disagreements between the underground and the Judenrat leadership. The head of the Judenrat, Jacob Gens, a former Lithuanian army officer, knew about the existence of the FPO and maintained contacts with it, supporting the organization as long as it did not fight the Judenrat and did not harm the productivity of the labour in the ghetto.