Returning to Vilnius, he joined a Polish underground resistance movement, and in 1942 he submitted to Lieutenant Gracjan Fróg "Góral" of the National Radical Camp (ONR-Falanga). In September 1943 he joined the "Goral" partisan group, which from March 1944 was known as the 3rd Brigade of Vilinus Home Army. Commanding the first assault company, his unit had a reputation for successful combat operations. Rajs led by example, often serving as the lead attacker in his group. He is noted for his successful defense of the village of Mikuliszki during a German manhunt, in which heavy losses were inflicted on the Germans. In July 1944 Rajs took part in Operation Ostra Brama against the Germans. However, he was also known for unscrupulous actions, personally killing prisoners of war.