the Wehrmacht and Waffen-SS encountered resistance from the British Expeditionary Force (BEF) and Greek Army. The fighting was intensified by the mountainous terrain, with its heavily defended narrow passes. The LSSAH was at the forefront of the German push. The BEF evacuated by sea to Crete, but had to flee again in late May when the Germans arrived. Like Yugoslavia, the conquest of Greece brought its Jews into danger, as the Nazis immediately took a variety of measures against them. Initially confined in ghettos, most were transported to Auschwitz concentration camp in March 1943, where they were killed in the gas chambers on arrival. Of Greece's 80,000 Jews, only 20 percent survived the war. War in the east On 22 June 1941, Hitler launched Operation Barbarossa, the invasion of the Soviet Union. The expanding war and the need to control occupied territories provided the conditions for Himmler to further consolidate the police and military organs of the SS. Rapid acquisition of vast territories in the East placed considerable strain on the SS police organizations as they struggled to adjust to the changing security challenges. The 1st and 2nd SS Infantry Brigades, which had been formed from surplus concentration camp guards of the SS-TV, and the SS Cavalry Brigade moved into the Soviet Union behind the advancing armies. At first, they fought Soviet partisans, but by the autumn of 1941, they left the anti-partisan role to other units and actively took part in the Holocaust. While assisting the Einsatzgruppen, they formed firing parties that participated in the liquidation of the Jewish population of the Soviet Union. On 31 July 1941, Göring gave Heydrich written authorization to ensure the cooperation of administrative leaders of various government departments to undertake genocide of the Jews in territories under German control. Heydrich was instrumental in carrying out these exterminations, as the Gestapo was ready to organize deportations in the West and his Einsatzgruppen were already conducting extensive murder operations in the East. On 20 January 1942, Heydrich chaired a meeting, called the Wannsee Conference, to discuss the implementation of the plan. During battles in the Soviet Union in 1941 and 1942, the Waffen-SS suffered enormous casualties. The LSSAH and Das Reich lost over half their troops to illness and combat casualties. In need of recruits, Himmler began to accept soldiers that did not fit the original SS racial profile. In early 1942, SS-Leibstandarte, SS-Totenkopf, and