Known as the “Bayou St. John submarine”, this vessel was discovered when the Bayou St. John, in New Orleans was dredged by the US Government in 1878. For years, the vessel was thought to be the Confederate submarine Pioneer, but research in the 20th century showed it was of a different design. There is no surviving documentation from the Civil War about the construction of this submarine. It was presumably scuttled by the Confederacy during the Civil War when the Union capture of New Orleans was immanent.
It is being displayed in New Orleans in this picture, with what appears to be a local policeman in the photo.
That explains how they got it. Is there anywhere to read about what (if anything) it was used for during the war?
Not really. The submarine is something of a mystery, since as of yet historians haven’t found any documentation about it.