This became the prevalent design for body-on-frame cars in the United States, but not in the rest of the world, until the unibody gained popularity. For instance Hudson introduced this construction on their 3rd generation Commodore models in 1948. This frame type allowed for annual model changes, and lower cars, introduced in the 1950s to increase sales – without costly structural changes. The Ford Panther platform, discontinued in 2011, was one of the last perimeter frame passenger car platforms in the United States. However, the fourth to seventh generation Chevrolet Corvette used a perimeter frame integrated with an internal skeleton that serves as a clamshell.