For almost 40 years, more than five tons of gold sat at the bottom of the Barents Sea. The treasure was locked inside the hull of a British World War II cruiser named HMS Edinburgh, 800 feet beneath the surface. Finding the wreck was difficult enough. Getting 465 bars of gold out of a sunken warship was a whole other problem. Pulling it off would require specialized divers, cutting-edge equipment, and somehow finding a way inside a ship that had…