Unternehmen Barbarossa (or Operation Barbarossa, originally Fall Barbarossa) was the code name for the German Wehrmacht's war of aggression against the Soviet Union during the Second World War. The military invasion planned and prepared by the Nazi regime on June 22, 1941 opened the German-Soviet War. With 3 million soldiers crossing the border of the Soviet Union, Operation Barbarossa was the largest and most destructive military campaign in history.

see: https://de.wikipedia.org/wiki/Unternehmen_Barbarossa