The V12 began life as Claude Bailey's 1951 proposal for a Le Mans prototype, the Jaguar XJ13. Bailey's original design was a quad-cam unit displacing around 5.0 litres, intended to recapture Jaguar's glory years at Le Mans. After the XJ13 project was cancelled in 1967, engineers Walter Hassan and Harry Mundy reworked the DOHC design into a simpler single-overhead-camshaft layout better suited to road car production. The resulting 5.3-litre (5,344 cc) unit, with a 90 mm bore and 70 mm stroke, debuted in the Jaguar E-Type Series 3 in 1971 — the only mass-produced V12 in the world at the time.
The production block used an all-aluminium construction with removable wet steel cylinder liners, single overhead camshafts, and two valves per cylinder. Electronic Lucas OPUS ignition was fitted from the outset. Output ranged from 242 hp to 295 hp depending on emission calibration and market specification.
In 1981 a significant revision produced the High Efficiency (HE) variant. Swiss racing driver Michael May designed new cylinder heads incorporating a swirl chamber at the exhaust valve, which pushed air into turbulent motion around the spark plug during the compression stroke. This stratified-charge combustion allowed an unusually high compression ratio — up to 12.5:1 in some markets — on a lean mixture, improving fuel economy by nearly 50 percent with little penalty to power output. The HE heads replaced the earlier dished pistons with flat-topped items and introduced a new digital fuel injection system in place of the older Bosch-derived analogue unit.
From 1982 Tom Walkinshaw Racing developed the V12 for motorsport competition under Jaguar's factory backing. Running the XJ-S coupé in the European Touring Car Championship, TWR progressively extracted 450 hp from the 5.3-litre unit. With drivers including Tom Walkinshaw, Win Percy, Hans Heyer, and a young Martin Brundle, the big XJ-S became competitive and TWR won the 1984 ETCC title as well as the 1984 Spa 24 Hours.
TWR then moved to the World Sportscar Championship, fielding the XJR series of sports prototypes. The first WSC car, the XJR-6, used a 6.0-litre version of the V12. Displacement was progressively increased as the racing programme matured: the engine grew to 6.9 litres for 1987, and then to the iconic 7.0-litre (6,995 cc) specification used in the XJR-9 that won Le Mans outright in 1988. By 1991, inside the XJR-12, the V12 had been expanded to 7.4 litres, developing approximately 750 hp.
The 1988 Le Mans victory, with Jan Lammers, Johnny Dumfries, and Andy Wallace sharing the XJR-9LM, marked Jaguar's return to La Sarthe after an absence of more than three decades. A second overall win followed in 1990 with the XJR-12.
Alongside the outright endurance programme, TWR produced upgraded road and semi-competition versions of the Jaguar XJR-S. From 1989 the company offered a 6.0-litre XJR-S to customers through Jaguar dealerships, pre-dating Jaguar's own factory-produced 6.0-litre road car by several years.
Lister Cars also exploited the V12 platform extensively. Working from a long history of Jaguar collaboration, Lister fitted the 7.0-litre V12 — producing a claimed 546 hp and 580 lb-ft of torque — to a heavily modified XJ-S bodyshell rebadged as the Lister Le Mans in 1991. From 1993, Lister's first in-house design, the Lister Storm, carried the V12 into FIA GT Championship competition.
The 5.3-litre HE evolved into a 6.0-litre (5,993 cc) road unit in 1992, achieved by lengthening the stroke to 78.5 mm. This version produced 318 hp at 5,400 rpm and 336 lb-ft at 3,750 rpm in standard form, with a higher-output XJR-S specification reaching 333 hp. The 6.0-litre road V12 featured a Nippondenso distributorless ignition system. The last Jaguar V12 engine was assembled on 17 April 1997, ending a production run spanning 26 years.
The Jaguar V12 racing engine represented a rare case of a road-car powerplant being directly evolved, without switching to a purpose-built racing unit, into a Le Mans winner. The progressive displacement increases — from 5.3 to 7.4 litres — reflected the creative latitude of Group C and IMSA GTP regulations, and the TWR development programme demonstrated that a production-based block could be made competitive against purpose-designed prototypes from Porsche, Nissan, and Toyota. The twin Le Mans victories of 1988 and 1990 remain the high-water mark of the V12 in international motorsport.