For many outside the battle zones of Europe, the Second World War is a matter of textbooks and faded black-and-white photographs.

But for those whose roots lay in the paths of Adolf Hitler’s conquest, the war remains close, a tactile connection to tragedy and loss even 75 years and three generations removed from 85 million deaths and untold suffering. Siblings, children, grandchildren feel the pang of lost relatives many never knew.

In Germany, where the war began and ended, the fate of more than a million soldiers and citizens remains unknown. Many were taken prisoner by Red Army troops, never to be seen again...