That's a historical myth. The Holocaust *was* known during the war and condemned during it, while the Soviet discoveries of Majdanek and Sobibor helped fuel further the Soviet rampages in Germany after the end of the war. Germans didn't simply rape millions of Soviets and kill millions of them, they had their abbatoirs on Soviet soil. All of the Allied leaders knew the Camps were there, Soviet partisans in 1943-4 included Jewish resistance fighters, some who lasted following the breakout at Sobibor, and this was a reason the British Empire, itself prone to Jew-hatred formed the Jewish Legion (aka the reality behind Inglorious Basterds).