Near midnight on March 26, 1961, dark waters lapped at the hull of a converted naval barge as it queasily rocked in the Pacific Ocean. The ship had just arrived at this spot, some 240 kilometers off the Baja peninsula, after three days of fighting seas so rough the crew had lashed gear to the deck with heavy chains, “like a rogue elephant,” the novelist John Steinbeck, who was aboard the vessel...