 Hitler intervened on 4 November 1940 , four days after British troops arrived at Crete and Lemnos . Although Greece was neutral until the Italian invasion , the British troops that were sent as defensive aid created the possibility of a frontier to the German southern flank . He ordered his Army General Staff to attack Northern Greece from bases in Romania and Bulgaria in support of his master plan to deprive the British of Mediterranean bases . On 12 November , the German Armed Forces High Command issued Directive No. 18 , in which they scheduled simultaneous operations against Gibraltar and Greece for the following January . However , in December 1940 , German ambition in the Mediterranean underwent considerable revision when Spain 's General Francisco Franco rejected the Gibraltar attack . Consequently , Germany 's offensive in southern Europe was restricted to the Greek campaign . The Armed Forces High Command issued Directive No. 20 on 13 December 1940 , outlining the Greek campaign under the code designation Operation Marita . The plan was to occupy the northern coast of the Aegean Sea by March 1941 and to seize the entire Greek mainland , if necessary . During a hasty meeting of Hitler 's staff after the unexpected 27 March Yugoslav coup d 'état against the Yugoslav government , orders for the campaign in Kingdom of Yugoslavia were drafted , as well as changes to the plans for Greece . On 6 April , both Greece and Yugoslavia were to be attacked . 
