The entry of Greece into the war was assured by Mussolini on May 5th 1940, when Italian troops garrisoned in Albania launched an invasion through the mountains of North-western Greece.
Though small and inadequately equipped, the Greek army inflicted a series of crushing defeats on the Italians driving them back through the mountains and over the border into Albania. By mid January 1941, after a series of stunning counteroffensives, the Greeks had crossed the Albanian frontier and driven the Italians from the southernmost quarter of the country.
The humiliation of Italy infuriated Hitler who had long opposed Mussolini’s Balkan ambitions, and had planned to secure peace in the region through diplomacy. These plans had now become untenable. The attack on Greece had driven that country into the arms of Britain, and brought British troops back onto the continent of Europe. The security of Greece and the Balkans had become a priority for Hitler. Since the Autumn of 1940 he had been preparing in secret for an invasion of the Soviet Union in the Spring of 1941.
To secure the flank of his offensive a German conquest of Greece had now become inevitable. A coup in Yugoslavia on March 26th and the subsequent defection of that country from the axis required that it too be conquered.
On April 6th the campaign began with attacks on Greece and Yugoslavia from Austria, Hungary, Rumania and Bulgaria. Code-named ‘Operation Punishment’ , the invasion of Yugoslavia was supported by air attacks on Belgrade which lasted almost uninterrupted for two days. As the Axis troops drove relentlessly towards the capital, the Luftwaffe attacked vital centres and installations disrupting communications and defences.
The attack was quickly joined by Italian offensives across the Italian-Yugoslav border and from Albania. Under such weight of arms Yugoslav resistance began to falter. Within a week of the offensive Belgrade had fallen. In the air offensive on the capital 17,000 civilians had been killed, the city centre reduced to rubble. By April 17th the last units of the Yugoslav army had surrendered. The campaign in Yugoslavia had been an unqualified success for the Wehrmacht. At a cost of 151 killed and less than 400 wounded, the Germans had taken more than a quarter of a million prisoners.
But the conquest of Yugoslavia was to prove merely the first act in a long drama of resistance. The defection of the Balkan state from his system of Alliances, Hitler had taken as a personal slight. His savage vengeance shocked the Yugoslavs and drove many to seek refuge in the mountainous interior of the country. Within weeks of the German occupation partisan units had begun to be forged and the nucleus of a partisan army established.
In the South, the Greeks put up stiffer resistance. Invading from Bulgaria, the Germans were held for three days at the fortifications of the Metaxas line. But on the 9th of April, despite heroic Greek resistance and heavy casualities on both sides, the Germans broke through the lines capturing Salonika and cutting off 70,000 Greek troops in Eastern Thrace.
West of the Mataxas line armoured and mechanised units of the German 12th Army, including the elite, mechanised S.S. Leibstandarte Division crossed into Greece from Yugoslavia and began a rapid encirclement of the Greek 1st Army in Albania.
With most of the Greek forces cut off or captured, all that stood between the advancing axis divisions and Athens were the 70,000 troops of the British Expeditionary force. Hopelessly outmatched, the British were driven Southwards fighting a series of desperate rearguard actions, most notably at the passes of Thermopilae and Thebes.
By April 27th the Germans had reached Athens and raised the swastika over the ancient heart of the city. In the ports of the Peloponese to the South-West, the British had begun reenbarking and, despite repeated attacks from the air, the evacuation from Greece was largely successful. By May 1st 51,000 troops had been rescued at the cost of four transports and two destroyers.
But the campaign had been a setback for Britain. Unable to affect the outcome of the conflict, the British had been shocked by the energy and efficiency of the German advance. Vital equipment had had to be abandoned in the rout, and, although less than a thousand British soldiers lost their lives in battle, more than 7,000 were left behind and captured.