DePalma had been let go by the Mercer Automobile Co. racing team in favor of Barney Oldfield. In a Mercedes "Gray Ghost," he showed he was a master tactician in beating Oldfield's much faster car. He ended 1914 by winning his second U.S. national driving championship. The following year, 1915, he drove to victory at 1915 Indianapolis 500 with a Mercedes 4.5 liter GP car.