With peace returned to Europe in 1945, William Lyons could focus on producing cars again. For obvious reasons, he could no longer use the SS brand name used before the War, but with the already frequently used 'Jaguar' he had another strong brand name. The first production models were very similar to the late 1930s line-up and featured two four cylinder and one 3.5 litre six cylinder engines. This gave Lyons' engineers some time to develop a complete new sportscar with a state of the art engine. Initially two versions were planned, but the four cylinder model was abandoned and all the focus was on the new six cylinder.
The engine's development team was headed by William Heynes, but he was helped in no small part by Walter Hassan and Claude Bailly. They came up with a straight six cylinder engine displacing just over 3.4 litres. Unlike the push-rod and side-valve engines previously used, the new 'XK' featured twin overhead camshafts. In street tune the engine was good for 160 bhp and in competition spec with the compression increased to 9.0:1, the six cylinder happily developed 180 bhp. Both versions used a twin SU Carburetor setup. Power was fed to the rear wheels through a four speed gearbox, bolted directly to the engine.
Just like the new Mk V model introduced a few months earlier, the sportscar used Jaguar's new box type chassis, but with a simpler and lighter construction. Suspension was by wishbones and torsion bars at the front and a live axle with transverse leaf springs. Lockheed drum brakes were fitted all around. The brand new package was covered in a simple, but very elegant two seater roadster body. Lyons planned to build only 200 examples of the new sportscar and the very first examples featured hand beaten aluminium body panels.
Dubbed the XK120 after its claimed top speed of 120 mph, Jaguar's new sportscar debuted to much acclaim at the 1948 Earl's Court show. Not surprisingly the public's positive reaction led to the introduction of a production model, but problems with getting the moulds for the steel body right delayed the full time manufacturing of the XK120 until the second half of 1950. In the mean time the proposed 200 aluminium bodied cars were produced and due to the popularity another 40 were completed. These proved particularly successful in racing and in 1949 a virtually standard car achieved a speed of 126.594 mph to prove the type indication was not an overestimation.
With the production finally underway, it was time to expand the line-up and in 1951 two distinctly different models were added. First up was the beautiful fixed-head coupe version that was reminiscent of the great designs of the 1930s. The other was a proper competition version, first known as the XK120 C, but today generally referred to as the C-Type. Although sharing the XK-engine with the production, the C-Type was an XK120 in name only as it featured a unique tubular chassis and aluminium body. It easily eclipsed the racing successes of the aluminium XK120s with two Le Mans victories. A final edition to the XK120 line-up was a more luxurious drop-head coupe.
At the end of the XK120 production run, the high compression 180 bhp competition engine was offered in the 'SE' (Special Equipment) model. A 190 bhp version of this engine was standard equipment in the XK140 launched in 1954. At first glance it was very similar to its predecessor, but closer inspection revealed changes to most chrome parts like the grill and bumpers. The handling was greatly improved by the adoption of rack-and-pinion instead of the recirculating ball used in the XK120. A 210 bhp C-Type derived engine was available as an option. As before the small sportscar was available as a roadster and a fixed and drop head coupe.
In 1957 a third and final evolution of the very successful XK model was launched; the XK150. Again it was more powerful, heavier and better equipped than its predecessor. The slightly more spartan roadster model was dropped altogether. In the XK150 S model the 3.4 litre engine reached its peak power of 250 bhp with a 9.0:1 compression ratio and a triple SU setup. The final version featured the D-Type derived 3.8 litre, which produced 265 bhp. After being produced for over a decade, the XK finally each the end of the line in 1961, but found a very worthy replacement in the E-Type.