plan an invasion of Greece via Yugoslavia. The American historians Allan Millett and Williamson Murray wrote from the Greek perspective, it would have had been better if the Yugoslav coup d'état had not taken place as it would have forced the Wehrmacht to assault the Metaxas Line without the option of outflanking the Metaxas Line by going through Yugoslavia. On 6 April, both Greece and Yugoslavia were to be attacked. British Expeditionary Force Little more than a month later, the British reconsidered. Winston Churchill aspired to reestablish a Balkan Front comprising Yugoslavia, Greece and Turkey, and instructed Anthony Eden and Sir John Dill to resume negotiations with the Greek government. A meeting attended by Eden and the Greek leadership, including King George II, Prime Minister Alexandros Koryzis—the successor of Metaxas, who had died on 29 January 1941—and Papagos took place in Athens on 22 February, where it was decided to send an expeditionary force of British and other Commonwealth forces. German troops had been massing in Romania and on 1 March, Wehrmacht forces began to move into Bulgaria. At the same time, the Bulgarian Army mobilised and took up positions along the Greek frontier. On 2 March, Operation Lustre—the transportation of troops and equipment to Greece—began and 26 troopships arrived at the port of Piraeus. On 3 April, during a meeting of British, Yugoslav and Greek military representatives, the Yugoslavs promised to block the Struma valley in case of a German attack across their territory. During this meeting, Papagos stressed the importance of a joint Greco-Yugoslavian offensive against the Italians, as soon as the Germans launched their offensive. By 24 April more than 62,000 Empire troops (British, Australians, New Zealanders, Palestine Pioneer Corps and Cypriots), had arrived in Greece, comprising the 6th Australian Division, the New Zealand 2nd Division and the British 1st Armoured Brigade. The three formations later became known as 'W' Force, after their commander, Lieutenant-General Sir Henry Maitland Wilson. Air Commodore Sir John D'Albiac commanded British air forces in Greece. Prelude Topography To enter Northern Greece, the German army had to cross the Rhodope Mountains, which offered few river valleys or mountain passes capable of accommodating the movement of large military units. Two invasion courses were located west of Kyustendil; another was along the Yugoslav-Bulgarian border, via the Struma river valley to the south. Greek border fortifications had been adapted for the terrain and a formidable defence