sentences:  The semi-trailer increased the capacity of trucks, but it was the fifth wheel that brought the flexibility for drivers to keep moving while receivers unloaded the loads they just delivered.The Fruehauf Trailer Corporation helped to make the Martin Rocking 5th Wheel a success by installing them on their popular new semi-trailer design.August Fruehauf invented the semi-trailer in 1914 with their own 5th wheel hitch.