When the U.S. Department of Transportation—the federal agency that funds things like ports, highways, and transit projects—pays for equipment or materials that need to travel by ocean vessel, this bill says all of that cargo must go on U.S.-flagged ships (vessels registered and crewed under American rules) instead of foreign ships. This applies not just to DOT itself, but to any state, city, company, or organization that receives DOT money and needs to ship stuff overseas with those funds. Right now, similar rules usually only require about half of such cargo to travel on American ships; this bill would raise that to the full 100%, though it still allows exceptions if U.S.-flagged ships aren't available at reasonable prices.