Drawing on remarkable and never-before-seen material, the extraordinary story of one of the most horrific and devastating encounters of the Second World War. On June 22nd, 1941 the largest military invasion in human history was launched  an attack on the Soviet Union by almost four million men of Nazi Germany's brutal war machine. Operation Barbarossa led to the bloodiest military campaign mankind has ever known. The statistics of death and destruction are almost impossible to believe. The cruelty, suffering and destitution it wrought are unimaginable over forty million people lost their lives.