Jaguar wasn't used to losing, having won five times in seven years at the 24 hours of Le Mans through 1957. When the rules changed for the next season, effectively obsoleting the D-Type, it ended Jaguar's attempts in sports car racing. In the 1960s, they did develop the XJ13, even taking it so far as to test it, but the project was quietly dropped.
With the Coventry-based company not interested, that meant if the Jaguar marque was going to go racing, it was up to privateers to make it happen. Enter Bob Tullius. His team, Group 44, first started racing Jaguars in 1974. He won the SCCA B Production category with a lightly modified Jaguar E-Type V12.
Over time, he kept utilizing the V12 Jaguar in increasingly larger series, including the Trans-Am series. So when IMSA announced a new GTP class, Tullius made a decision to build a prototype racer around the V12 he so expertly understood.
There was a class established at Lemans for the IMSA GTP cars. In an odd twist of fate, the ability to have the Jaguar marque appear at Le Mans piqued the interest of the folks in Coventry. They started to back the development work out of the Group 44 racing headquarters in Winchester Virginia early in 1981.
The new car, named the XJR-5, was fully drawn up and being built in clay models by January 1982. The Lee Dykstra-designed coupe had very effective aerodynamics with significant ground effect elements. The chassis was an aluminum monocoque design with honeycomb floor sections and tubular reinforced bulkheads. The underfloor Venturi tunnels extended from the cockpit to the rear, exiting underneath the full width rear wing of the sleek car. The first engine to find its way in the car was a fully stressed-member 5.3 liter V12. The elegant bodywork was constructed in carbon fiber and Kevlar.
The XJR–5 made its debut at Road America in late August. Tullius and Bill Adam co-drove to a third-place podium finish behind two Porsches. Not a bad first event.
After a series of endurance events as a test, in 1984 Jaguar became comfortable supporting a return to Lemans in 1984 with the XJR-5 after a 22 year hiatus. While they were no competition for overall speed versus the turbocharged Lancias and Porsches, the two factory cars ran in sixth and seventh place before they retired around the midway point of the race. They returned the following year, claiming 13th overall and the winners of the GTP class.
Lee Dykstra perpetually redesigned the car, which would be concluded in full with the XJR-5's last iteration of the car in the summer of 1985. Although it carried the same name, the claim is that by the conclusion of the XJR-5 program, 99.9% of the original car had been redrawn. The engine displacement ultimaltey increased to 6.0 L by 1984, with output of around 650 hp pushing a chassis that weighed around 2050 pounds.
Despite the continued improvement and evolution, by 1985, Group 44 lost their factory backing to Tom Walkinshaw's TWR team. Despite this, Tullius continued to develop the XJR-7.
The XJR-7 featured Kevlar reinforcement in the chassis and more refined aerodynamics. By 1987, they were scoring victories at Riverside in Palm Beach. By 1988, the Group 44 Jaguars were in their last race. They had been outright replaced by the TWR teams, who finished out the 1988 and 1990 seasons very strongly for Jaguar.
Despite much of the historical glory going to the TWR teams, if it weren't for the efforts of Bob Tullius and Group 44, Jaguar may not have returned back to endurance racing.