As Germany began to prepare for war with the Soviet Union in early 1941, "Schlesien" was reactivated on 30 April to protect minelayers along with "Schleswig-Holstein" as they laid a series of minefields in the Baltic to prevent the Soviet Baltic Fleet from attempting to break out to Britain. The Soviet fleet did not attempt to leave port after Germany invaded in June, and so "Schlesien" was detached from the force guarding the minefields in October. She returned to Gotenhafen and resumed training duties there. Icebreaker service again summoned the vessel to active service from January to April 1942. On 4 April, "Schlesien" sailed back to Gotenhafen in company with the battleship and the icebreaker . "Schlesien" thereafter saw limited training duties in the Baltic in 1943 and 1944, owing to the increasingly limited supplies of fuel oil available to Germany by this stage in the war. During this period, her armament was revised several times. In 1943, a pair of twin anti-aircraft guns were installed, one on each side of her bridge.