Martin Winterkorn, Volkswagen’s chief executive, took the stage four years ago at the automaker’s new plant in Chattanooga, Tenn., and outlined a bold strategy. The company, he said, was in the midst of a plan to more than triple its sales in the United States in just a decade — setting it on a course to sweep by Toyota to become the world’s largest automaker.

“By 2018, we want to take our group to the very top of the global car industry,” he told the two United States senators, the governor of Tennessee and the other dignitaries gathered for the opening of Volkswagen’s first American factory in decades.

One way Volkswagen aimed to achieve its lofty goal was by betting on diesel-powered cars — instead of hybrid-electric vehicles like the Toyota Prius — promising high mileage and low emissions without sacrificing performance. Ray LaHood, the transportation secretary, endorsed the company’s commitment to diesel that day, calling it an “ingredient in the recipe for our long-term energy security.”

Volkswagen’s unbridled ambition is suddenly central to what is shaping up as one of the great corporate scandals of the age. On Tuesday, Volkswagen said it had installed software in 11 million diesel cars that cheated on emissions tests, allowing the vehicles to spew far more deadly pollutants than regulations allowed. About 500,000 of the cars were sold in the United States, including Passats that rolled off the assembly lines in Chattanooga.