rear picnic tables, and a front seat pull-out picnic table stowed beneath the instrument cluster. Later, air conditioning and a sound-proof glass division between the front and rear seats were added as options. The substantial doors required helical torsion springs inside the door pillars to enable them to be opened from the inside with an acceptably low level of effort. From its introduction in mid-October 1961 until the arrival in 1992 of the low-slung XJ220, the Mark X stood as one of the widest production Jaguars ever built. Asked in 1972 if he thought the Mark X had grown rather too large, Jaguar chairman William Lyons, agreed that it "definitely" had: he opined that the then recently introduced and notably more compact Jaguar XJ6 was, by contrast an "ideal size". Mechanical The Mark X was the first Jaguar saloon to feature independent rear suspension designed by William Heynes, who was Jaguar's Technical Director and Chief Engineer. It differed from earlier large Jaguar saloons in having 14" wheels instead of the more common 15". It used a wider-track version of Jaguar's IRS unit first seen on the E Type, which was subsequently used on Jaguar vehicles until XJ-S production ended in 1996. The front suspension used double wishbones with coil springs and telescopic dampers. Power initially came from the E-type's version of Jaguar's 3781 cc XK in-line six-cylinder engine designed by W Heynes, developing either or , depending on compression ratio. A 9:1 compression ratio was standard, but an alternative 8:1 compression ratio was available as an option. For the London Motor Show in October 1964 the enlarged 4,235 cc unit took over, although the 3.8-litre unit could still be specified until October 1965. Triple SU carburettors were fitted, fed from an AC Delco air filter mounted ahead of the right hand front wheel. Transmission options were manual, manual with overdrive, or automatic . The arrival of the 4.2-litre power unit coincided with the introduction of a newly developed all-synchromesh four-speed gear box, replacing the venerable box inherited by the 3.8-litre Mark X from the Mark IX, which had featured synchromesh only on the top three ratios. Many domestic market cars and almost all cars destined for the important North American markets left the factory with a Borg Warner automatic gear-box. The 4.2-litre engine's introduction was also marked by a transmission upgrade for buyers of the automatic cars, who saw the