I am skeptical of the sub being an unknown civil war design. It seems too unlikely that it "floated" around for 30 or more years. It also seems unlikely that something so "cool" could have been forgotten. While touring the Vicksburg area I took a side trip down to the abandoned town of Grand Gulf. Interestingly, they have a similarly designed prohibition era Rum runner sub. The Rum runner was even believed to be a CW ship at 1st. Could this sub have been a similar style smuggler boat that got lost? Obviously, the owner would not have claimed it.