On a bright, windy day in March 2000, I stood on a cliff in France looking down at Omaha Beach, site of some of the bloodiest fighting on D-Day, through the firing slit of a preserved German bunker. My view of the beach was so clear and unimpeded that I could read the writing on the sweatshirt of a boy strolling on the sand a hundred feet below. There had been a storm the night before, and the English Channel heaved angrily, just as it did on June 6, 1944. That anyone burdened with weapons and equipment could jump off a ship into the roiling sea, make his way across the shelterless beach,…