In 1966 Malcolm Sayer produced a prototype for Project XJ21 which was heavily based on the existing E-type. But this along with other proposals were pushed aside by a new Project XJ27/28 which Malcolm Sayer should be based on the XJ4 platform (the as yet unlaunched Jaguar XJ6 saloon). At the same time it was decided to give this car the V12 engine which had yet to used in a production vehicle although the E-type would soon receive it. The 'Flying Buttresses' were given to the XJ27 at this point, for aerodynamic and strength purposes. Launched as the XJ-S in September 1975, the XJ-S struggled against a world recession but hung on, gaining the 'fireball head' modifield V12 HE engine in 1981. In 1983 Jaguar introduced the AJ6 3.6 six cylinder engine and this soon became available in the XJ-S. The first Jaguar 'convertible' version appeared in 1983 as the XJ-SC, but this retained the side windows and frames. For 1991 the XJ-S was restyled by Geoff Lawson who decided to keep the buttresses, and the car became 'XJS'. Underneath the car was re-engineered, and the AJ6 engine enlarged to 4-litre, and V12 enlarged to 6-litres in 1993. A true convertible was also introduced, and in 1996 the XJS gave way to the XK8.