Iron ore rains into the hold of a U.S.-Flag "Laker" (so called as these ships are built exclusively for service on the Great Lakes). Iron ore is the primary raw material used to make steel, the foundation of our standard of living and national defense capabilities. The U.S.-flag Lakes fleet can move more than 60 million tons of iron ore during the 10-month season (ice largely closes the Lakes from late January until late March.