One of the literal shortcomings of some WWII fighter planes was their range. They simply couldn't hold enough gas for some of the missions they were required to fly. That's where drop tanks, or belly tanks, came in. Belly tanks were supplemental gas tanks. They'd be strapped to the belly of the plane to provide extra fuel, which in turn provided additional flying range. When the tank was empty, the pilot would simply jettison it.
And while this military hardware was built for a specific purpose, it turns out that those belly tanks are very good at something entirely different. Belly tanks make great race cars, especially if you're trying to set a land speed record on a dry lake bed. And not surprisingly, their preferred racing locale is also how belly tank racers got their other name: lakesters.
The original purpose of a belly tank helped make it ideally suited for use as a race car body. If you're strapping something the to the belly of a plane to increase its flying range, the last thing you want to do is have a negative impact on how far the plane can fly. That is, you don't want to add so much wind resistance that you end up burning more fuel by carrying the belly tank than the tank itself can hold. In order to minimize wind resistance and maximize fuel economy, belly tanks had to be very aerodynamic. Belly tanks look like giant bullets and are about as aerodynamic as they come.
After World War II ended, belly tanks ended up in surplus and scrap yards. Hot rodders took notice. Beyond the belly tank's super-fast shape, car builders noticed that the rear of the belly tank was just wide enough to install a car engine block and rear end. Given that hot rodders were already building and racing their own creations made from a hodgepodge of car parts, adding an airplane fuel tank wasn't that farfetched — especially when the surplus tanks could be bought for about $35 [sources: Wise; Wilkinson].