it packs down tighter than foam seats for storage U-BOAT DESIGN - The OSG Super Fat Cat sports a classic Outcast U-boat design that makes it one of the most efficient float tubes on the water LCS ...

In that same vein, all U-boats are submarines, but not all submarines are U-boats. What you call them depends on where they're made. A U-boat is nothing more than the Anglicized term for a German ...