German XVII Mountain Corps, comprising the eastern prong of the Axis offensive, reached Volos on April 21, 1941. Three days later, a German advance using battle tanks through the Thermopylae Pass was stopped by British rear guard artillery and armored units. On April 25, a German flanking maneuver around the pass forced the British to withdraw to avoid encirclement. A final, hastily formed defensive line at Thebes, located 60 miles from Athens, also became threatened by a German flanking maneuver, forcing the British rear guard there to retreat toward the Peloponnesus, Greece’s southernmost region. On April 27, 1941, advance units of the German Twelfth Army entered Athens without meeting any resistance.
At this time, the British High Command had been carrying out troop evacuations at various points, including at Volos and Piraeus. The Germans, determined to capture the whole W Force, did away with its infantry units because of their lack of mobility, and tasked the ground pursuit to their armored, motorized infantry, and mountain units. To cut off W Force’s retreat to the Peloponnesus, on April 26, 1941, German paratroopers were air-dropped into the Isthmus of Corinth to seize the bridge connecting the Greek mainland to the Peloponnesus. The bridge was taken, but a stray projectile from a British anti-aircraft gun struck the explosives on the bridge that the British had placed earlier but had failed to set it off. The resulting explosion destroyed the bridge, but German engineering crews quickly built a temporary replacement span. The German paratroopers had also arrived late, as W Force had already crossed into the Peloponnesus and had moved south to Kalamata and other southern ports for evacuation to Crete and Egypt.
(Taken from Invasion of Greece – Wars of the 20th Century – World War II in Europe)
In early March 1941, as German forces massed at the Bulgarian-Greek border, Greek Prime Minister Ioannis Metaxas was convinced that an invasion was imminent. Metaxas then requested military assistance from the British government. Britain sent a force consisting of British, Australian, and New Zealander units from Egypt, a total of 60,000 troops that arrived in Greece in March 1941 under Operation Lustre. This contingent was commonly called W Force (named after its commander, British General Henry Maitland Wilson).
Disagreement immediately arose between General Wilson and the Greek top commander General Alexander Papagos, regarding the deployment of their combined forces to confront the German invasion. By March 1941, some 70% (or 14 divisions) of the Greek Army was still locked in combat with Italian forces in southern Albania (Greco-Italian War, separate article), leaving an insufficient six Greek divisions and the W Force to defend the rest of Greece’s northern frontier. Greek and British commanders concluded that their combined forces were inadequate to stop the Germans coming from the northeast; for example, 12 Allied divisions alone were needed to adequately defend the Greek-Bulgarian border. Furthermore, more units were needed to guard the Greek-Yugoslav border, although at this time, Yugoslavia had announced its neutrality in the emerging crisis. Also because Yugoslavia might remain a non-belligerent, and Greek-Yugoslav relations were friendly since both were pro-British to varying degrees, Greece kept its border with Yugoslavia only lightly defended. Nearly the whole Greek Army was deployed at both ends of the country’s northern frontier, in the west at the Albanian front, and in the east at the Metaxas Line, the vaunted 125-mile series of fortifications facing the Bulgarian border. As in much of Greece, the northern frontier was dominated by rugged mountain ranges, with the Rhodope Mountains in the east and the Pindus Mountains in the west, with few passes whose steep, narrow roads allowed only the movement of pack animals. Consequently, Greek military planning incorporated these excellent natural barriers in the defense of the northern frontier. However, Greece was vulnerable along two areas, both in the Yugoslav-Greek border, at the Vardar River Valley and the so-called Monastir Gap, where a major invasion could potentially be launched into Greece.
On March 25, 1941, Yugoslavia became allied with Germany and Italy by signing the Tripartite Pact, which clearly was an ominous development for Greece. But two days later, a coup in Belgrade toppled the pro-Axis Yugoslav government, and a military regime took over that had pro-British leanings. In Germany, a livid Hitler ordered hasty preparations for an invasion of Yugoslavia (called Operation 25), which was to be launched together with the attack on Greece. Ironically, the two-day alliance of Yugoslavia with the Axis gave Greece full security along the Greek-Yugoslav border, since in the corresponding secret German-Yugoslav protocol, Germany promised to respect Yugoslavia’s sovereignty, and German troops would not enter Yugoslavian territory. But with the March 27 Belgrade coup, Hitler decided that Germany was not anymore bound by the secret protocol and indeed, that the main German attack on Greece would be made through Yugoslavia, particularly through the Vardar River Valley and Monastir Gap.
Meanwhile, Yugoslavia was unaware of German preparations for Operation 25, and continued to espouse its neutrality, and announced its desire to maintain friendly relations with Germany. The Yugoslav military also did not fully mobilize its forces so as not to provoke Hitler. And on April 3, 1941 (just three days before Germany invaded), in a meeting of British, Greek, and Yugoslav military leaders, the Yugoslav High Command vowed to resist a German invasion, and also agreed with its Greek counterparts to launch a joint offensive against the Italians in Albania. The success of the latter action would free up considerable numbers of Greek troops (14 divisions) to confront the German invasion in northeastern Greece. Even then, the Yugoslav government did not believe that a German attack was imminent, and that it still had many months to prepare, and was also confident in its military strength, as its army boasted one million troops, 200 tanks, and 600 planes. As it turned out during the war (previous article), Yugoslavia’s theoretical military capability was severely overpowered by the Germans in terms of firepower, technology, and tactics.
In the lead-up to the German invasion of Greece, British planners proposed to their Greek counterparts of setting up a shorter line of defense equivalent to their limited manpower and resources. As such a plan would require the Greek Army in Albania to relinquish its hard-won territories to the Italians, General Papagos refused, stating that such a move would be devastating to Greek civilian and military morale. The British also saw that although the Metaxas Line in the northeast was sound against a frontal attack from Bulgaria, it could be outflanked through southern Yugoslavia, and that in any case, the strength of the combined British-Greek forces was insufficient to successfully hold the Metaxas Line. Only four Greek divisions were assigned to defend the Line. In the Greek northeast, the idea of relinquishing the Metaxas Line was even more unacceptable to the Greeks, as Salonika, Greece’s second largest city, and the whole region of Western Thrace and Eastern Macedonia, would be exposed to attack.
In the end, the British acquiesced to Greek sentiments, and established their own defensive line, called the Vermion Position, a forty-mile series of fortifications stretching along the slopes of the Olympus and Pieria Mountains to the Vermion Mountain range in the Yugoslav-Greek border. Manned by W Force as well as two Greek divisions, the Vermion Position was strategically situated in central Macedonia, and was aimed at sealing the northern frontier between the two main Greek formations in Albania and the Metaxas Line.
Invasion On April 6, 1941, Germany launched Operation Marita, the invasion of Greece, with the German 12th Army in Bulgaria launching offensives into southern Yugoslavia, whose capture would achieve the strategic objective of cutting off the rest of Yugoslavia in the north with Greece in the south. In the northern sector, units of the German XL Panzer Corps advanced along two points: the 9th Panzer Division for Kumanovo and the 73rd Infantry Division for Stip. Both met strong Yugoslav resistance, but they reached their objectives that same day. On April 7, the German 9th Panzer Division reached Skopje, and then Prilep the next day. On April 9, the Germans took Monastir. These thrusts cut the rail and road lines between Belgrade, Yugoslavia’s capital, and Salonika. More important, the Germans were now poised to invade Greece through the Monastir Gap.
Also on August 6, 1941, the Germans in western Bulgaria attacked from further south, with the German 2nd Panzer Division entering southern Yugoslavia and advancing to Strumica, which it captured that same day. After breaking off a Yugoslav counter-attack, on April 7, the Germans turned south for the border and, passing through the mountainous frontier, crossed into Greece and then overwhelmed the Greek 19th Motorized Infantry Division south of Lake Doiran. Now unopposed, the Germans continued south and entered Salonika on April 9, 1941.
The German XVIII Mountain Corps crossed into Greece directly through the Metaxas Line. Here, strong Greek resistance, difficult terrain, and alpine weather conditions slowed the advance. But the Germans broke through at various points: the 6th Mountain Division through a 7,000-foot mountain that the Greeks had deemed impassable; the 5th Mountain Division at Neon Petritsi, and the 72nd Infantry Division from Nevrokop to Serres. Assaults on Greek fortifications along the Metaxas Line resulted in heavy casualties to the German 125th Infantry Regiment. The deeply entrenched Greek fortifications were finally subdued only after intense German air and artillery bombardment. Greek forces then surrendered to the Germans, who disarmed and released the Greek soldiers. East of the Metaxas Line, the German XXX Infantry Corps invaded Western Thrace, seizing Greece’s easternmost region by April 9. By then, all regions east of the Vardar River, including Salonika, Eastern Macedonia, and Western Thrace, were in German hands.