 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.
