Finland fought the Soviet Union in the Winter War of 1939–1940 after the Soviet Union attacked Finland and in the Continuation War of 1941–1944, following Operation Barbarossa, when Finland aligned with Germany following Germany's invasion of the Soviet Union. For 872 days, the German army, aided indirectly by Finnish forces, besieged Leningrad, the USSR's second-largest city. After Finnish resistance to a major Soviet offensive in June and July 1944 led to a standstill, the two sides reached an armistice. This was followed by the Lapland War of 1944–1945, when Finland fought retreating German forces in northern Finland. Perhaps the most famous war heroes during the aforementioned wars were Simo Häyhä, Aarne Juutilainen, and Lauri Törni.