The Jaguar D-Type shares many of its mechanical components with the C-Type, including the basic straight-6 XK engine design (initially 3.4 litres and uprated to 3.8 litres in the late fifties), but the structure of the car was radically different. The innovative monocoque construction brought aviation industry technology to competition car design, together with an aeronautical understanding of aerodynamic efficiency.
Jaguar D-Types won the Le Mans 24-hour race in 1955, 1956 and 1957. After Jaguar temporarily retired from racing as a factory team, the company offered the remaining unfinished D-Types as XKSS versions whose extra road-going equipment made them eligible for production sports car races in America. In 1957 25 of these cars were in various stages of completion when a factory fire destroyed nine of them.
Total D-Type production is thought to have included 18 factory team cars, 53 customer cars, and 16 XKSS versions.
Source: Wikipedia (original)