During the Invasion of Poland with the rank of captain he took part in the Battle of Modlin. He organized a chapter of Służba Zwycięstwu Polski (later transformed into Związek Walki Zbrojnej and then into Armia Krajowa) in Pomorze. He was instrumental in coordinating the activities of various Polish resistance organizations in the Pomorze region, until the majority of them merged into Armia Krajowa. After the death of Józef Ratajczak in May 1940, he was the unofficial commander of Polish resistance in Pomorze. From 1943 he was commander of staff of Komenda Okręgu Armii Krajowej Pomorze under Komendant Okręgu Jan Pałubicki (codename 'Janusz'). During that time, he lived mostly in Toruń, although every few months he traveled to Warsaw for meetings with commanders of AK (Stefan Rowecki and Tadeusz Komorowski).