Scientists can't say what caused HL Hunley to go under
                                
                                
                                    (Newser) -
                                    A revered Confederate submarine was recently commemorated by military reenactors in Charleston, South Carolina, but a key mystery still hung in the air, the  Christian Science Monitor  reports. The HL Hunley made history on February 17, 1864, when it became the first sub to ever sink an enemy ship—in...