In March 1941, a major Italian counterattack against Greek forces failed, and Germany came to the aid of its ally. Operation Marita began on 6 April 1941, with German troops invading Greece through Bulgaria and Yugoslavia in an effort to secure its southern flank. Reich was ordered to leave France and head for Romania, and the was ordered to Bulgaria. The , attached to the XL Panzer Corps, advanced west then south from Bulgaria into the mountains, and by 9 April had reached Prilep in Yugoslavia, 30 miles from the Greek border. Further north the SS Reich, with the XLI Panzer Corps, crossed the Romanian border and advanced on Belgrade, the Yugoslav capital. Fritz Klingenberg, a company commander in the Reich, led his men into Belgrade, where a small group in the vanguard accepted the surrender of the city on 13 April. A few days later the Royal Yugoslav Army surrendered. The had now crossed into Greece, and on 10 April engaged the 6th Australian Division in the Battle of the Klidi Pass. For 48 hours they fought for control of the heights, often engaging in hand-to-hand combat, eventually gaining control with the capture of Height 997, which opened the pass and allowed the German Army to advance into the Greek interior. This victory gained praise from the OKW: in the order of the day they were commended for their "unshakable offensive spirit" and told that "the present victory signifies for the a new and imperishable page of honour in its history." The continued the advance on 13 May. When the Reconnaissance Battalion under the command of Kurt Meyer came under heavy fire from the Greek Army defending the Klisura Pass, they broke through the defenders and captured 1,000 prisoners of war at the cost of six dead and nine wounded. The next day, Meyer captured Kastoria and took another 11,000 prisoners of war. By 20 May, the had cut off the retreating Greek Army at Metsovon and accepted the surrender of the Greek Epirus-Macedonian Army. As a reward, the was nominally redesignated as a full motorised division, although few additional elements had been added by the start of the Russian campaign and the "Division" remained effectively a reinforced brigade. Soviet Union Operation Barbarossa, the German invasion of the Soviet Union, started on 22 June 1941, and all the Waffen-SS formations participated (including the SS Reich, which was formally renamed