The XK120, manufactured by Jaguar between 1948 and 1954. It was Jaguar’s first sports car since SS 100 production ended in 1939.

The XK120 was launched in open two-seater or (US) roadster form at the 1948 London Motor Show as a testbed and show car for the new Jaguar XK engine designed by Jaguar Chief Engineer William Heynes . The display car was the first prototype, chassis number 660001. It looked almost identical to the production cars except that the straight outer pillars of its windscreen would be curved on the production version. The sports car caused a sensation, which persuaded Jaguar founder and Chairman William Lyons to put it into production.

With a high-temperature, high-strength aluminum alloy cylinder head, hemispherical combustion chambers, inclined valves and twin side-draft SU carburetors, the dual overhead-cam 3.4 L straight-6 XK engine was highly advanced for a mass-produced unit of the time. Using 80 octane fuel a standard 8:1 compression ratio developed 160 bhp (119 kW). Most of the early cars were exported; a 7:1 low-compression version, with commensurately reduced performance, was reserved for the UK market, where the post-war austerity measures then in force restricted buyers to 70 octane “pool petrol”. The Jaguar factory’s access to 80 octane fuel allowed it to provide cars with the higher compression ratio to the press, enabling journalists to test the model’s optimum performance in Belgium, on a long, straight stretch of road between Jabbeke and Ostend. The XK engine’s basic design by William Heynes, later modified into 3.8 and 4.2-litre versions, survived until 1992.

All XK120s had independent Heynes designed torsion bar front suspension, semi-elliptic leaf springs at the rear, recirculating ball steering, telescopically adjustable steering column, and all-round 12-inch drum brakes which were prone to fade. Some cars were fitted with Alfin (ALuminium FINned) brake drums to help overcome the fade.

The open two-seater’s lightweight canvas top and detachable sidescreens stowed out of sight behind the seats. Its doors had no external handles. There was an interior pull-cord accessed through a flap in the sidescreens when the weather equipment was in place. The windscreen could be removed for aeroscreens to be fitted. All models had removable spats (“fender skirts” in America) covering the rear wheel arches, which enhanced the streamlined look. On cars fitted with optional center-lock wire wheels (available from 1951), the spats were omitted as they gave insufficient clearance for the chromed, two-eared Rudge-Whitworth knockoff hubs. Chromium-plated wire wheels were optional from 1953.