 On 5 December 1940 , Hitler received the final military plans for the invasion on which the German High Command had been working since July 1940 under the codename " Operation Otto " . Hitler , however , was dissatisfied with these plans and on 18 December issued Führer Directive 21 , which called for a new battle plan , now codenamed " Operation Barbarossa " . The operation was named after medieval Emperor Frederick Barbarossa of the Holy Roman Empire , a leader of the Third Crusade in the 12th century . The invasion was set for 15 May 1941 , though it was delayed for about 7 weeks in favor of further time for preparation because of the war in the Balkans . 
