Complex sentence: A torpedo car or bottle car is a type of railroad car used in steel mills to haul molten pig iron from the blast furnace to begin the process of primary steelmaking.
Split into simpler sentences: A torpedo car or bottle car is a special type of railroad car used in steel mills to haul molten hot metal. Torpedo cars are usually used to haul pig iron from the blast furnace to begin the process of primary steelmaking.