Summary:
- The article discusses the mysterious disappearance of a revolutionary submarine called the Hunley, which was the world's first successful combat submarine.
- The Hunley was developed during the American Civil War and successfully sank a Union warship, but then disappeared without a trace after its historic mission.
- Scientists are now preparing to return to the site where the Hunley was last seen, in hopes of uncovering more clues about what happened to this groundbreaking and enigmatic submarine.