April 1945, three years after Stalingrad, 2.5 million Russian troops attacked along the Oder Neisse front, psychologically crushing the 'invincible' Nazi Germany. The battle was one of the most terrifying examples of fire and sword recorded, with mass rape, murder, pillage and destruction. Ensconded deep in his concrete bunker, Hitler could only scream at his military staff, denouncing the cowardice of the Wehrmacht. The award-winning historian tells the story.