1973, Triumph, GT6 MK3

In early 1963 Giovanni Michelotti was commissioned by Standard-Triumph to design a GT version of their recently introduced Spitfire 4 (also designed by Michelotti). An unmodified Spitfire 4 was delivered to Michelotti's design studios in Italy and late in 1963 the prototype Spitfire GT was returned to England for evaluation. The styling of the vehicle was a success but the extra weight of the GT bodyshell resulted in extremely poor performance from the Spitfire's 1,147 cc (70 cu in) Standard SC engine, and plans for producing the Spitfire GT were shelved.

Michelotti's fastback design for the Spitfire GT prototype was adopted by the Triumph racing programme for the 1964 season, as it was deemed to provide an aerodynamic benefit over the standard Spitfire body shape. Fibreglass copies of the Spitfire GT's fastback were grafted on to the race-modified Spitfires destined for competition. The Spitfire racing programme was successful, and in 1965 resulted in 13th overall and a 1st in class at the prestigious 24 Hours of Le Mans (beating their main rivals, the MG Midgets). The Spitfire's competitive success and the continuing commercial success of the production vehicle led Triumph to re-evaluate its shelved plans for a GT version of the Spitfire. To overcome the lack of performance inherent in the heavier body style the Spitfire's 4-cylinder engine was replaced with the more powerful 2.0 L (1,996 cc) Triumph inline 6 originally derived from the SC and then in use in the Triumph Vitesse (which shared a similar chassis with the Spitfire and Triumph Herald). The car was further developed and refined and eventually launched as the Triumph GT6 (dropping the "Spitfire" prefix and adding the 6) to emphasise its GT styling and its 6-cylinder engine.