a measure to compensate for the losses in the Wehrmacht (unlike Poles, Deutsche Volksliste members were eligible for military conscription). In a top-secret memorandum, "The Treatment of Racial Aliens in the East", dated 25 May 1940, Heinrich Himmler, head of the SS, wrote: "We need to divide the East's different ethnic groups up into as many parts and splinter groups as possible". Forced labour Almost immediately after the invasion, Germans began forcibly conscripting laborers. Jews were drafted to repair war damage as early as October, with women and children 12 or older required to work; shifts could take half a day and with little compensation. The labourers, Jews, Poles and others, were employed in SS-owned enterprises (such as the German Armament Works, Deutsche Ausrustungswerke, DAW), but also in many private German firms – such as Messerschmitt, Junkers, Siemens, and IG Farben. Forced labourers were subject to harsh discriminatory measures. Announced on 8 March 1940 was the Polish decrees which were used as a legal basis for foreign labourers in Germany. The decrees required Poles to wear identifying purple P's on their clothing, made them subject to a curfew, and banned them from using public transportation as well as many German "cultural life" centres and "places of amusement" (this included churches and restaurants). Sexual relations between Germans and Poles were forbidden as Rassenschande (race defilement) under penalty of death. To keep them segregated from the German population, they were often housed in segregated barracks behind barbed wire. Labor shortages in the German war economy became critical especially after German defeat in the battle of Stalingrad in 1942–1943. This led to the increased use of prisoners as forced labourers in German industries. Following the German invasion and occupation of Polish territory, at least 1.5 million Polish citizens, including teenagers, became labourers in Germany, few by choice. Historian Jan Gross estimates that "no more than 15 per cent" of Polish workers volunteered to go to work in Germany. A total of 2.3 million Polish citizens, including 300,000 POWs, were deported to Germany as forced laborers. They tended to have to work longer hours for lower wages than their German counterparts. Concentration and extermination camps A network of Nazi concentration camps were established on German-controlled territories, many of them in occupied Poland, including one of the largest and most infamous, Auschwitz (Oświęcim). Those camps were officially designed as labor camps, and many displayed the