Anders Franzén lived for shipwrecks. An engineer and expert on the naval warfare of the 16th and 17th centuries, he was especially obsessed with the old Swedish men-of-war that had once menaced the Baltic Sea. When he wasn’t busy at his day job with the Swedish Naval Administration, he’d spend hours combing through archives in search of maps and documents, hoping they might reveal the location of Sweden’s great sunken warships. And when he learned that one wreck might still be trapped, undiscovered, not far from his home in Stockholm, he was hungry to find it.