Because of the H.L. Hunley's short service and problematic testing phase, its maximum diving depth was not fully established. The H.L. Hunley is supposedly the world's first and operational combat submarine credited with the sinking of the USS Housatonic in February 1864. After the successful mission, the H.L. Hunley failed to return from the mission and was lost until it was discovered in 1995.
The H.L. Hunley had an eight-man crew, was crank operated, civil-war era submarine built in 1862 and launched in July 1863. It sank 1 month later in a freak accident that sent the Hunley diving with its hatch still open, killing five crew members. In October of the same year, the H.L. Hunley sank again, this time killing eight crew members including its inventor Horace Hunley. The submarine was raised after both accidents and returned to service.