In December 1963 Triumph decided to return to competition for 1964. This time the focus was on the Spitfire, which seem to be the most competitive of the range. An ambitious programme was launched to bring Triumph back to Le Mans and to the famous tarmac rallies on the continent.  In a development time of less than 6 month 9 cars were built. 4 of them for the Le Mans race (ADU 1B, ADU 2B, ADU 3B, ADU 4B) and 4 destined to rallies (ADU 5B, ADU 6B, ADU 7B, ADU 467B). The 9th car, ADU 8B, was a test and development car and took never part in any works competition events. ADU 467B was built for the use of the SMART racing team of Stirling Moss and this car was raced with less success by his secretary Valerie Pirie.

For the 1965 season a 10th car was built in left-hand-drive rally specification for the Finn driver Simo Lampinen (AVC 654B) who was successful in the Monte Carlo Rally, Geneva Rally and with a 1296cc prototype engine in the Alpine Rally.

An early development car from 1962, 412 VC, was actually the first Spitfire who take part in a works entry in the Welsh International Rally in January 1964, where it achieved a 2nd place overall. This car was used then for further development of components for the rally cars.

The Le Mans cars were run in the prototype category, this allowed a higher degree of development. The main differences to the standard Spitfire were the aluminium body, a glassfibre top which style was taken from the already finished GT6 prototype (therefore the GT6 was not born in Le Mans as the sales brochures later told), the aluminium TR4 gearbox with a Salisbury limited slip differential and an E-Type-style bonnet with faired headlamps.

The rally cars starts their life with an aluminium paneled steel body, an aluminium standard style bonnet, a close ratio Vitesse gearbox and the standard steel hardtop. After their first event, the Alpine rally 1964, they received a similar glassfibre top like the Le Mans cars. For the following Tour de France they borrowed the bonnets from the Le Mans cars, because of the many high speed circuit racing involved with this event.  For 1965 they received a bonnet with 2 additional build-in auxiliary headlamps and a center spot lamp.

The main problem was to get sufficient power out of the 1147cc engine. To reach the target of 100+ bhp a completely new cylinder head was developed to overcome the limitations of the standard 6-port head. The result was a high compression 8-port head. They were built in cast iron and aluminium. With 45 DCOE Weber carburettors the engine developed 109 bhp @ 7.300 rpm. At Le Mans they reached a top speed of 134 mph (214 km/h).

ADU 2B achieved a 21st overall and a 3rd place in class at the 1964 Le Mans race, ADU 1B and ADU 3B retired, caused by accidents. For 1965 the Le Mans cars received further development. The aluminium cylinder heads, now more reliable, were used and further weight was saved by using a thinner-gauge chassis frame, lighter gearbox and brakes. All 4 cars were entered and ADU 4B finished 1st in class and 13th overall, ADU 3B 2nd in class and 14th overall. The other two retired.

The rally cars were also very successful. ADU 7B finished 3rd in class at the 1964 Alpine Rally. In that year ADU 7B also finished 1st in class and 10th overall in the 6000km Tour de France. A class win in the 1000km race at Paris followed for ADU 5B. In 1965 a 2nd and 3rd in class was won by ADU 6B and AVC 654B at the rally Monte Carlo.

A unique racing Spitfire was built in 1965 for the Triumph distributor in Hong Kong. It was built from remains of the Le Mans project and was styled like a Jaguar D. It was raced successfully at the Grand Prix of Macao and was later used in the US by the Kastner team with a GT6 engine.

Another car was prepared from the remains of the Le Mans project, ERW 412C, which had a modified Lotus style rear suspension. This car was very competitive in the hands of the former works driver Bill Bradley.