Clarence Smoyer's index finger caressed the trigger. Sweat poured down the leather flaps of his helmet. No one in his tank moved or even whispered. It was March 6, 1945, and Smoyer was part of the Allies' last push into Nazi Germany. The lanky 19-year-old with a mop of curly hair was part of a tank crew that had crawled into the German city of Cologne for what would become the US Army's biggest house-to-house fight in Europe. The Germans called it "Endkampf," the final battle for their homeland. "Gentlemen, I give you Cologne," Smoyer's commander announced over the radio....