In 1942, as Hitler’s forces swept through the Soviet Union, the Red Army went underground. Outside the city of Kerch in Crimea, 10,000 Russian, Belarusian and Ukrainian soldiers dug into the caves of a limestone quarry, ready to defend their position to the last man. Intent on flushing them out, the Nazis bombed them from the skies, flooded the complex and, according to testimony from survivors, pumped noxious gas into the tunnels.