Since the Sparrowhawk sank off Orleans in 1626, the Cape and Islands have seemingly crooned siren songs to thousands of ships, luring them to destruction in their shifting shoals. While “Cape Cod Girls” may be the best known of local sea shanties, “The Mermaid” may be the most apt, with its closing lines: “Three times around spun our gallant ship/And she sank to the bottom of the sea.” One of the most infamous of these lost vessels is the Andrea Doria, which rests on the ocean floor today about 53 miles southeast of Nantucket. She sank at 10:09 a.m. on July 26, 1956, some 11 hours after a freak collision with the Stockholm, a Swedish passenger liner. Nearly six decades later, mystery continues to drive interest in the Andrea Doria—because the collision never should have happened. After all, how can two large luxury liners crash into each other on the wide-open ocean?