On This Day in History Marks the Beginning of Operation Barbarossa   On 22 June 1941, Hitler unleashed Operation Barbarossa the biggest military operation in human history. With a force of over 3 million Axis soldiers surging into the heartland of the Soviet Union, a conflict of scale and savagery was set into motion.   The initial stages of Operation Barbarossa unfolded with unparalleled success, as the Wehrmacht and its allies achieved resounding triumphs, leaving in their wake a trail of devastation and death. Millions of Soviet soldiers were killed or captured in the opening months, which seemed to foresee a march towards victory for the Axis powers.   But by the winter of 1941 the mighty German war machine, previously unstoppable in its conquest, found itself halted just outside the gates of Moscow, marking the beginning of the end for the Nazi regime.