In Call of Duty: World at War the vehicle is untextured, crudely modelled and shaped like a typical modern automobile. It has exhaust pipes, six wheels and a spoiler. The vehicle differs from a normal car simply because it's armed with World War II-era weaponry.
In Call of Duty: Modern Warfare 2 the vehicle appears almost insect-like, with no wheels or any resemblance at all to any conventional vehicle. The appendage at the top was most likely used for turret testing.