The victories of Operation Barbarossa in the summer and fall of 1941 against Hitler's new enemy, the Soviet Union, led to dramatic changes in Nazi anti-Jewish ideology and the profile of prisoners brought to Auschwitz.  Construction on Auschwitz II-Birkenau began in October 1941 to ease congestion at the main camp. Reichsführer-SS Heinrich Himmler , head of the Schutzstaffel (SS), intended the camp to house 50,000 prisoners of war , who would be interned as forced laborers. Plans called for the expansion of the camp first to house 150,000 and eventually as many as 200,000 inmates.  An initial contingent of 10,000 Soviet prisoners of war arrived at Auschwitz I in October 1941, but by March 1942 only 945 were still alive, and these were transferred to Birkenau, where most of them died from disease or starvation by May.  By this time Hitler had decided to annihilate the Jewish people, so Birkenau was changed to a labor camp– extermination camp .   The Auschwitz-Birkenau Memorial and Museum estimates that million people, million of them Jewish, were sent to the camp during its existence.