 During the Second World War he fought the Nazis as a member of the Polish Underground, leading the grouping Konfederacja Narodu (merged into the Armia Krajowa in 1943) and taking part in the fighting around Vilnius.Afterwards, he was arrested by the Soviet NKVD, and in a drastic conversion from his previous stance began to cooperate with the Communist government in Poland.After the war, in 1945, he cofounded and directed a so-called social progressive movement of lay Catholics, grouped around the weekly publication "Dziś i Jutro" (Today and Tomorrow).