The coal torpedo was a hollow iron casting filled with explosives and covered in coal dust, deployed by the Confederate Secret Service during the American Civil War, and intended for doing harm to Union steam transportation. When shoveled into the firebox amongst the coal, the resulting explosion would at the very least damage the boiler and render the engines inoperable. At worst, a catastrophic boiler explosion would kill crewmen and passengers, start a fire, or even sink the vessel.