 The German strategy was based on using so @-@ called " blitzkrieg " methods that had proved successful during the invasions of Western Europe . Their effectiveness was confirmed during the invasion of Yugoslavia . The German command again coupled ground troops and armour with air support and rapidly drove into the territory . Once Thessaloniki was captured , Athens and the port of Piraeus became principal targets . Piraeus , was virtually destroyed by bombing on the night of the 6 / 7 April . The loss of Piraeus and the Isthmus of Corinth would fatally compromise withdrawal and evacuation of British and Greek forces . 
