Kovner, Yitzhak Wittenberg, Alexander Bogen and others formed the United Partisan Organization ("Fareynikte Partizaner Organizatsye", or FPO), one of the first armed underground organizations in the Jewish ghettos under Nazi occupation.[7] Kovner became its leader in July 1943, after Wittenberg was named by a tortured comrade and turned himself in to prevent an attack on the ghetto.[8] The FPO planned to fight the Germans when the end of the ghetto came, but circumstances and the opposition of the ghetto leaders made this impossible and they escaped to the forests.[9]