Robert Asher was leaning casually against the bunker wall in a distant corner, taking it all in. British Prime Minister Winston Churchill hadn’t earned the moniker “the Lion of London” for nothing. Watching him run a meeting never got old.

Churchill was standing, a cigar clamped between his pudgy fingers, a stern expression etched on his face. He was listening to a general explain that the weather was supposed to clear on June Sixth, which meant that in about twenty-four hours, ...