The Hunley’s air circulation system didn’t work or was disconnected the night she and her eight-man crew vanished in 1864. The finding suggests difficulty getting oxygen inside crew compartment.

According to the scientists studying the submarine, the crew did not operate the emergency keel release mechanisms the night they lost their lives in the experimental, 40-foot vessel. The blocks represent a significant breakthrough in conservation as well as an important clue for those working to solve the mystery of the Hunley’s disappearance.

The Hunley has finally come out of her shell. For the first time in over a century, you can actually see the original surface of the world’s first successful combat submarine. Using small hand tools, drills, and chisels, conservators have removed approximately 1200 pounds of concretion, roughly the same weight as a grand piano. This material is being removed so the submarine can be preserved for generations to come. With the exterior now completely exposed, they will start to chisel away the concretion covering the inside of the crew compartment.