One example of this is the fender line. Earl's goal here, as it was for many other stylists, was to merge fenders into the overall body shape, having them extend from front to rear rather than being discrete elements. The first step he took was to have his stylists change the basic front fender from a "teardrop" curved shape to a more squared-off "suitcase" form. The following step was to move the rear of the suitcase fender from in front of the front door opening to a point over the door itself. This took some engineering work on body panels and door hinging, but by the late 1930s these problems had been solved and extended fenders could now appear on General Motors production cars.
That's Harley Earl himself in the driver's seat of GM's first true concept car, the Buick Y-Job of 1938. The over-the-door front fender is clearly visible.
American buyers first encountered production extended front fenders of the Y-Job variety on the 1941 Cadillac Sixty Special. The body dates from the 1938 model year and had been extensively facelifted by 1941.
The 1942 model year saw this fender concept throughout the rest of GM's line, though some Buick models featured front fenders that extended so far that they touched the rear fenders.
Another example of extended fenders. Surely another case where American cars took the styling lead in those days.
Actually, no. Earl's extended fenders first appeared in production on General Motors' 1939 Opel Kapitän. This might have been intended as a trial run by GM management. In any case, Earl is known to have sent Frank Hershey, one of his ace stylists, over to Germany and Opel, perhaps with this fender styling concept in mind.
Here is a photo of a 1939 Kapitän showing what the car really looked like, because the publicity illustrations above are clearly distorted.