Editor's Note: The following is the third in a series of stories by FOXNews.com on "Obama Chic: The Changing Face of the White House."

When he was just a U.S. senator, he had a HEMI in his Chrysler 300. As a candidate for the White House, his ride was a Ford Escape Hybrid. But when President-elect Barack Obama moves to Pennsylvania Avenue in January, he will be handed the keys to what looks to be the most potent presidential limousine ever to carry the American head of state.

Spy photos taken at an undisclosed location, and obtained by FOXNews.com, show a vehicle undergoing testing that is believed to be the next version of "Cadillac One," the unofficial code name of the President's limousine.

Although a spokesman would not discuss any details, the Secret Service did confirm with FOXNews.com that such a vehicle is in development by General Motors, adding only that it will afford "the highest level of protection."

At first glance, the unfinished limo looks a lot like the current model used to ferry President Bush around town: an armored Cadillac sedan with a modest stretch job, raised roof line, and mounts on the front fenders to carry the American and presidential flags. But eyewitnesses say the new vehicle is actually much larger, and rides on large wheels similar to those found on commercial grade GMC TopKick trucks. The vehicle was being escorted by two of those big boys at the time it was spotted, leading to speculation that the car is in fact one of them in disguise.

Photos show doors that appear to be nearly 8 inches deep, with thick, fixed windows. Only the driver's window has a small slot that can slide open, which we assume is for paying tolls. With so much armor on board, it would be no surprise if GM needed to resort to using the bones of a truck to support the added weight.

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A source at one of the world’s premier security vehicle manufacturers says that armored cars of this magnitude are capable of withstanding not only armor-piercing bullets, but also attacks from IEDs. A number of electronic countermeasures are known to exist that can do things like jam enemy communications and prevent them from detonating roadside bombs remotely, but many others remain top secret and are available only to customers at the highest levels of government.

The real mystery is what will be under the hood when the first family pulls up to the Capitol building to watch dad take the oath of office. Although the photos of the vehicle were taken long before the outcome of the election was known, both John McCain and Obama made the development of greener, more fuel-efficient automobiles hallmarks of their campaigns.

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Nevertheless, a vehicle that needs to withstand a direct hit from an asteroid is likely to get the kind of gas mileage that would make Toyota Prius owners weep, so there are no expectations of it being anything less than a certified gas guzzler. That said, GM does have a number of ethanol-burning powerplants available in its parts bin, and even offers hybrid versions of its full-size SUVs. Interestingly, the photographer who caught the beast in the wild reports hearing what sounded like the distinctive exhaust note of a diesel engine coming from the Caddy, which would give it at least a few extra miles per gallon over gasoline and bring a smile to every Teamster along the motorcade route.

In any case, we'll get a better look at it when it goes into service on Inauguration Day, Jan. 20, 2009. Whether it will come with a rebate, or low interest financing, is on a need-to-know basis.