Originally, so the story goes, the sports car Jaguar showed at the 1948 London Motor Show at Earls Court was intended to be an appetite-whetter for the Mark VII saloon car due to go on sale the following year.
The two cars, the Super Sports (which became the XK120 two-seat roadster), and the Mark VII both used the same engine, a 3.4-litre double overhead camshaft six-cylinder.
The motor had a seven-bearing crankshaft and in the XK120 developed 160bhp.
Jaguar had planned to build 200, but public interest was so great that the sports car went into full-scale production.
It had a sleek body that is as ageless as its descendent the E-Type’s; spats smoothed the airflow over the rear wheels.
Export markets were supplied from mid-1949, and British buyers had to wait until 1951 to get their hands on this revolutionary sports car that blended a competitive price with outstanding performance.
Motor magazine clocked its test XK at 125mph (around 200km/h), and a version with an aerodynamic undertray went 132.6mph in a test run on a Belgian motorway.
More usually the XK120’s top speed was a genuine 120mph, which made it the world’s fastest production car at that time. Acceleration was equally impressive: 0-96km/h took 10 seconds and the car would reach 160km/h in a shade over 35 seconds. Average fuel economy was 22 miles per gallon.
Original cars had hand-built aluminium-bodies but tooling for steel-bodied cars was in place by 1950.
Jaguar raced the car from the outset, and XK120s took the first three places in the 1949 production car race on the ultra-fast Silverstone track in England.
Ian Appleyard drove one to victory in the Alpine Rally, and the legendary Stirling Moss won the Tourist Trophy in an XK.
A fixed-head coupe version (our cover car) arrived in 1951, followed by a droptop coupe two years later.
The XK120 had a separate chassis, twin SU carburettors, and a four-speed Moss gearbox with synchromesh on the upper three ratios.
Front suspension was by wishbones and torsions bars, and the solid rear axle rode on semi-elliptic springs.
The standard wheels were steel, though wire wheels were a popular option. Brakes were 12-inch diameter drums.
In 1954, the 120 was replaced by the similar-looking XK140 with 190bhp motor, laying the foundations for the elegant XK150 of 1957 and the most desirable of all Jaguar sports cars, the E-Type of 1961.
Like the E-Type, the XK is an ageless design, a superb and ground-breaking vehicle that paved the way for some of the world’s most desirable sports cars.