1958 Jaguar XK D-type rear 3/4 action. The Jaguar D type, like its predecessor was a factory-built race car. Although it shared the basic straight-6 XK engine design (uprated to 3.8 litres) with its predecessor, the majority of the car was radically different. Perhaps its most ground-breaking innovation was the introduction of a monocoque chassis, which not only introduced aircraft-style engineering to competition car design, but also an aeronautical understanding of aerodynamic efficiency. The