I don’t usually talk about my great-uncle Walter. Gen Walter Warlimont, as my grandfather’s brother was formally known, was head of the national defence department in the high command of the Wehrmacht, the armed forces of Nazi Germany. Only two people were between him and the Führer in the chain of command. Walter worked so closely with Hitler that the failed assassination attempt in July 1944 injured his arm. The orders he signed during wartime – about who to shoot to kill, about how to treat prisoners – meant he had hundreds of thousands of lives on his conscience. Not...