From time to time Jaguar's thoughts had turned to competition and [Malcolm] Sayer had wanted to build a mid-engined car. Heynes and colleagues had realised that if Jaguar was to remain competitive it would need to design a completely new engine, preferably of 12 cylinders. In 1965, with the Lightweight E-types uncompetitive, a small team including Sayer and Mike Kimberley, later to head Lotus Cars, drew up plans for a mid-engined sports racing car. To power it, they designed a four cam V12 of 5 litres.
The car, the XJ13, was built in great secrecy in 1966 but there was an unfortunate lack of urgency about the project. It was eventually run in 1967. Sadly it was never to race and has become a museum piece for enthusiasts. The shape was another Sayer masterpiece. Of obvious ancestry, it was one of the most beautiful cars ever conceived, and a lasting tribute to this brilliant man who prematurely died in 1970.
-from Jaguar's website
Malcolm Sayer was one of the first engineers to apply principles of aerodynamics to car design. His designs include the C-Type, D-Type, E-Type, and the XJS.