The aforementioned secret group set up by the Jews working in the Sonderkommando was of the greatest significance in the history of the Jewish resistance movement at Auschwitz. Its leaders included Załmen Gradowski, Jankiel Handelsman and Kamiński. Its clandestine activity encompassed all the four crematoria with gas chambers in Birkenau. The group also established contacts with the organisation of Russians in the camp, mostly to agree on cooperation in case of an uprising.