Jaguar D-Type

The Jaguar D-Type is a sports racing car that was produced by Jaguar Cars Ltd. between 1954 and 1957. Designed specifically to win the Le Mans 24-hour race, it shared the straight-6 XK engine and many mechanical components with its C-Type predecessor. Its structure, however, was radically different, with innovative monocoque construction and slippery aerodynamics that integrated aviation technology, including in some examples a distinctive vertical stabilizer.

Engine displacement began at 3.4 litres, was enlarged to 3.8 L in 1957, and reduced to 3.0 L in 1958 when Le Mans rules limited engines for sports racing cars to that maximum. D-Types won Le Mans in 1955, 1956 and 1957. After Jaguar temporarily retired from racing as a factory team, the company offered the remaining unfinished D-Types as street-legal XKSS versions, whose perfunctory road-going equipment made them eligible for production sports car races in America. In 1957 25 of these cars were in various stages of completion when a factory fire destroyed nine of them.

Total production is thought by some to have totaled 71 D-Types, including 18 for factory teams and 53 for privateers^{[citation needed]} (plus an additional 16 D-Types were converted into road-legal XKSS versions). Jaguar is quoted as claiming it built 75 D-Types.

The design applied aeronautical technology, revolutionary at the time. The "tub", or cockpit section, was of monocoque construction, mostly comprising sheets of aluminium alloy. Its elliptical shape and comparatively small cross-section provided torsional rigidity and reduced drag. To the front bulkhead was attached an aluminium tubing subframe for the engine, steering assembly, and front suspension. Rear suspension and final drive were mounted to the rear bulkhead. Fuel was carried in the tail and the designers followed aviation practice by specifying a deformable Marston Aviation Division bag in place of a conventional tank.

The aerodynamic influence was partly the work of Malcolm Sayer, who had joined Jaguar following a stint with the Bristol Aeroplane Company during the Second World War and later worked on the C-Type. The D-Type required a minimal frontal area. To reduce the XK engine's height dry sump lubrication was developed, and it has been said that the car's frontal area was also a consideration in canting the engine at 8½° from the vertical (which necessitated the offset bonnet bulge). Philip Porter, in his book Jaguar Sports Racing Cars, says that "[a] more likely reason was to provide extra space for the ram pipes feeding the three twin-choke Weber carburettors." Reducing underbody drag contributed to the car's high top speed; for the long Mulsanne Straight at Le Mans, a fin was mounted behind the driver for aerodynamic stability. For the 1955 season, factory cars were fitted with a longer nose, which lengthened the car by 7½ inches and further increased maximum speed; and the headrest fairing and aerodynamic fin were combined as a single unit that smoothed the aerodynamics and saved weight.

Mechanically, many features were shared with the outgoing C-Type. Its front and rear suspension and innovative all-round disc brakes were retained, as was the XK engine. Apart from the new lubrication system, the engine was further revised as development progressed during the D-Type's competition life. Notably in 1955, larger valves were introduced, together with asymmetrical cylinder heads to accommodate them.

Elements of the body shape and many construction details were used in the Jaguar E-Type from 1961 to 1969.

Jaguar D-Types fielded by a team under the leadership of Jaguar's racing manager Lofty England were expected to perform well in their debut at the 1954 24 Hours of Le Mans race. In the event, the cars were hampered by fuel starvation caused by problems with the fuel filters, necessitating pit stops for their removal, after which the entry driven by Duncan Hamilton and Tony Rolt speeded up to finish less than a lap behind the winning Ferrari. The D-Type's aerodynamic superiority is evident from its maximum speed of 172.8 mph (278.1 km/h) on the Mulsanne Straight compared with the 4.9 litre Ferrari's 160.1 mph (257.7 km/h). Three weeks later the D Type won the Rheims 12 hour endurance race.