Northrop TAB Vericraft
I wasn't quite sure which thread to include this in - truck, airplane or boat.
Northrop's 1960's plan for a multimode triphibian vehicle for the US army, capable of flying at 130 mph, driving at 50 mph, and airboating at 35 mph, able to carry a jeep, and able to be airlifted into theatre in a C130 Hercules. Scale air models were created, but no full-size vehicle was ever constructed.