In 1941 Pontecorvo joined the Italian Communist Party. He traveled to northern Italy to help organize partisans. Going by the pseudonym "Barnaba", he became a leader of the Resistance in Milan from 1943 until 1945. Pontecorvo broke ties with the Communist party in 1956 after the Soviet intervention to suppress the Hungarian uprising. He did not, however, renounce his dedication to Marxism.