Grace in Motion: The Jaguar XK120

Some cars are recognized as milestones only after the fact, dismissed and overlooked in their own times. Others, like this one, are standouts from the moment they first appear. This car stunned the world when it debuted at Earls Court Motor Show in October 1948 — one of the fastest and loveliest cars offered by any manufacturer at any price a dramatic statement of what the British auto industry was capable of achieving. This is the history of the Jaguar XK120, XK140, and XK150.

1953 Jaguar XK120-FHC badge


The story of Jaguar begins with its founder, Sir William Lyons. Lyons was born in Blackpool on September 4, 1901, the son of a music shop owner. As a teenager, he was a motorcycle enthusiast, buying his first Sunbeam in 1919. In 1922, he bought himself a stylish custom-built sidecar from neighbor William Walmsley, who called his creation the Swallow. Lyons soon convinced Walmsley that they should go into business together and the two formed a partnership known as the Swallow Sidecar Company.

The company proved to be very successful and Lyons and Walmsley soon branched out into coachbuilding, crafting stylish two-seat roadster and coupe bodies on the ubiquitous Austin Seven chassis. In 1928, they renamed the company SS Cars Ltd. and moved to larger facilities in Coventry. Before long, they were producing 50 cars a week.

At first, the SS cars were simply custom bodies built on chassis from other companies, but in 1931, Lyons and Walmsley introduced their first complete car, the S.S. I, with a chassis of their own design. Offering an appealing mix of performance and luxury, the S.S. I was a commercial success and was followed in 1932 by the S.S. II, which also did very well.

The prestige of these cars was limited, however, by the fact that the company still had to purchase engines from outside manufacturers, primarily the Standard Motor Company. Lyons had ambitious visions of making SS a full-fledged automaker, rather than simply a customer, but Walmsley’s enthusiasm had begun to wane. He was more of a tinkerer than a tycoon and his partner’s ambitions were beyond his scope. Walmsley allowed Lyons to buy out his share of SS in 1934.

Now in sole control of the company, Lyons began laying ambitious plans for a line of stylish, high-performance cars, which he dubbed SS Jaguars.


Lyons was a canny businessman and an adroit stylist, but he was not an engineer. To rectify that shortcoming, he began hiring experts to bolster the company’s technical operations: Cyril Holland to oversee coachbuilding and William Heynes, formerly of Rootes, as chief engineer.

SS did not yet have the resources for a completely new engine to replace the Standard side-valve engines they had been using for the past few years, but Lyons hired engine designer Harry Weslake to develop new cylinder heads for the existing six, offering to pay him a bonus for each additional horsepower he could extract from the 2,664 cc (162 cu. in.) six. Weslake responded with a new, free-breathing overhead-valve cylinder head, which boosted the Standard engine’s output by nearly 50%. Rather than build the new heads in-house, Lyons arranged to have Standard manufacture them to his specifications, avoiding the need to tool up for engine production.

Using this engine, Lyons launched the company’s first true sports cars, the SS 90 and SS 100. The latter eventually received a 3,485 cc (213 cu. in.) version of the modified Standard six, giving it scalding performance for its era: 0-60 mph (0-97 km/h) in less than 11 seconds and a top speed of 100 mph (160 km/h). It was reasonably priced as well; £445 (about $1,800) for a 3-½ Litre SS 100 was not cheap, but it was far less expensive than any rival with comparable performance.


Lyons’ ambitions were interrupted by World War II, which saw the company’s efforts shifted to war materiel, principally aircraft parts. It was a harrowing time, since Coventry’s factories were heavily targeted by German bombardment. Lyons was undaunted. During the Blitz, he told chief engineer Bill Heynes that if they survived the war, he wanted the company to produce its own engines, rather than buying them from outside suppliers. Although military work occupied most of their time, Jaguar engineers continued to work on postwar designs.

1940 BMW 328 Mille Miglia front 3q © 2006 Lars-Göran Lindgren Sweden (CC BY-SA 3.0 Unported)
A principal stylistic influence on the Jaguar XK120 was the 1940 BMW 328 coupe, a rally car built for the 1940 Mille Miglia rally. With its higher beltline and slab sides, it’s less voluptuous than the Jaguar, but the similarities are apparent. (Photo: “BMW 328 Mille Miglia Coupe 1940” © 2006 Lars-Göran Lindgren Sweden; resized 2009 by Aaron Severson and used under a Creative Commons Attribution-ShareAlike 3.0 Unported license)

In February 1945, Lyons changed the name of the company from SS Cars — which now had very sinister connotations — to Jaguar, a model name they had used since 1934. When civilian production resumed that fall, Jaguar reintroduced its prewar sedans (now known as Mark IVs), but the SS 100 sports car became a casualty of the war. The Mark IV was followed in 1948 by the Mark V, which had a new chassis with Citroën-inspired independent front suspension, but retained the Standard-derived prewar engines.

By the time peace returned, Lyons had become more interested in sedans than sports cars. His great goal was to offer a good-looking sport saloon with 100 mph (160 km/h) performance for less than £1,000. In the late 1940s, it was no small feat. Most contemporary European sedans weren’t good for much more than 75 mph (120 km/h) and reaching 60 mph (97 km/h) took a half a minute or more. Even the big-capacity Americans needed the better part of 20 seconds for the 0-60 mph run and could seldom manage much over 90 mph (144 km/h). Lyons also wanted the car to be relatively fuel efficient, recognizing that gasoline was still in short supply after the war. A 1947 fuel crisis led the government to ask the public to save fuel at all costs; petrol rationing was not phased out until 1950.


During the war, Bill Heynes, Harry Weslake, Walter Hassan, and Claude Bailey began work on a completely new engine, later dubbed the XK. Fuel economy concerns made big engines in the American fashion impractical, so the engineers focused instead on specific output, getting the most power out of a modest displacement. Bill Heynes strongly advocated dual overhead camshafts, which had been used very successfully in racing, but were rarely seen on street cars because of their cost and complexity.

The DOHC layout dovetailed neatly with the cross-flow heads that Harry Weslake wanted for better volumetric efficiency. The eventual result was a prototype four-cylinder engine with dual overhead cams and hemispherical combustion chambers. The prototype had excellent performance, but the engineers soon determined that a six-cylinder version would cost no more to produce, but have far better performance. The design ultimately evolved into a seven-bearing straight six, displacing 3,442 cc (210 cu. in.).

American engineers of the era were starting to favor oversquare engines, with big cylinder bores and short strokes, which allowed greater rev potential, but the XK was notably undersquare with a bore of 83 mm (3.27 in.) and a stroke of 106 mm (4.17 in.). The long stroke provided good low-end torque while high-RPM power was ensured by Weslake’s cross-flow heads and hemispherical combustion chambers. Hemispherical combustion chambers make for bulky, heavy cylinder heads, particularly with dual overhead cams, but Jaguar accounted for this by casting the cylinder head in aluminum, which kept engine weight within reason.

The XK six made an interesting comparison with Cadillac’s new overhead-valve V8, introduced at around the same time. Despite giving up nearly two liters of displacement to the Cadillac, the Jaguar engine made the same 160 gross horsepower (119.3 kW), albeit far less torque: 195 lb-ft (264 N-m), compared to the Cadillac’s 312 lb-ft. (423 N-m). In compensation, the Jag engine was 128 pounds (58 kg) lighter and could return over 20 mpg (11.8 L/100 km) in gentle cruising.


The plan for the XK engine, which began production in 1948, was to mate it with the chassis of the Mark V to create Lyons’ new sport sedan. (This ordinarily would have been dubbed Mark VI, but to avoid confusion with the contemporary Bentley Mark VI, Lyons opted to skip directly to Mark VII.) Since the XK was Jaguar’s first wholly original engine, however, Lyons wanted more field experience with it before putting it into large-scale production in a bread-and-butter product.

His solution was to develop a limited-production sports car sharing its basic chassis design with the Jaguar Mark V, but with an entirely new body. As was customary for sports cars of that vintage, it was a roadster, with a folding windscreen and detachable side curtains, rather than roll-up windows. To avoid the tooling cost for a steel body, it had a composite wood and metal frame, with hand-formed aluminum body panels. It was about 18 inches (457 mm) shorter than the sedan and was some 600 pounds (272 kg) lighter.

1950 Jaguar XK120-OTS front
The Jaguar XK120’s narrow ribbed grille is undeniably elegant, but it doesn’t really allow enough air flow for adequate cooling, and overheating could be a problem in slow traffic. Other than a tendency to consume oil, the XK engine is fairly sturdy, particularly compared to other contemporary sports car engines, which were much more finicky. Many Jaguar enthusiasts consider the 3,442 cc (210 cu. in.) iteration the best version of this long-lived engine, less powerful than the later 3,781 cc (231 cu. in.) and 4,235 cc (258 cu. in.) versions, but smoother and sweeter-sounding.

The sports car’s styling inspired by the prewar BMW 328 Mille Miglia, refined in no small way by Lyons himself. It was longer, lower, and more curvaceous than the BMW, with a dramatic beltline dip below the doors. Thanks to its light weight and powerful engine, its performance was as exciting as its looks. The sports car took its name from the engine and its claimed top speed: Jaguar XK120.


The Jaguar XK120 was introduced to the public at Earls Court Exhibition Centre in West London in October 1948. To say that it was the star of the show is an understatement. The XK120 thoroughly upstaged every other car there — including Jaguar’s own Mark V sedan, which now seemed decidedly ordinary.

In 1948, there were few cars of any price that were capable of 120+ mph (195+ km/h). Fewer still could be had for less than £1,000 (although that didn’t include the onerous postwar purchase tax). Representatives of other manufacturers were jeeringly skeptical that Lyons could really offer the car for such a modest price. Like the prewar SS100, the XK120 was expensive, but far from unattainable. The fact that it was also one of the world’s most beautiful cars was icing on an extremely desirable cake.

1950 Jaguar XK120-OTS front 3q
The Jaguar XK120 is rather large for a vintage sports car, 173 inches (4,369 mm) long on a 102-inch (2,591mm) wheelbase and even in roadster form, it weighs over 2,800 pounds (1,300 kg). Its size, however, does nothing to dilute its peerless looks, which rivals anything from Italy or America.

The critics were ecstatic, so enraptured by the car’s performance and looks that they willingly overlooked its various shortcomings. The Jaguar XK120 inspired no small amount of patriotic, Rule Britannia fervor, proving that only three years after the end of the war, Britain could still produce cars rivaling any in the world.

Lyons had intended to build only 200 of the roadsters, but the public reaction was so strong that it would have been foolish to stop there. The body was hastily redesigned for large-scale production in steel.


The steel-bodied Jaguar XK120 bowed in April 1950. The steel-bodied cars were about 120 pounds (54 kg) heavier than the early, alloy-bodied roadsters, which blunted their performance slightly. Still, 0-60 mph (0-97 km/h) in less than 12 seconds was not slow in 1950 and it kept the XK120 in a very elite performance category.

1950 Jaguar XK120-OTS rear 3q
The Jaguar XK120 roadster had only the most minimal weather protection and lacked even exterior door handles. On the other hand, it’s far racier than the later drophead coupé, whose more practical convertible top is bulkier and more obtrusive. Although the fenders and body are steel, this 1950 roadster retains aluminum doors, decklid, and hood, helping to minimize the weight gain from the steel body.

The XK120 was also fairly easy to live with, at least in some respects. Unlike many high-performance rivals of the period, the XK engine was not particularly peaky and it would happily lug down to 10 mph (16 km/h) in top gear, something that would raise all manner of hell with, for example, a Porsche 356 Carrera.

The XK120’s handling was secure, if not brilliant, and it had a relatively agreeable ride. Its principal dynamic shortcomings were inadequate brakes and the Moss four-speed gearbox, which was sturdy, but slow and clumsy. The roadster’s driving position also left something to be desired, a reflection of the car’s limited development; it was created as a show car, rather than a production model.

Jaguar was at some pains to prove their grandiose performance claims for the XK120. In May 1949, test driver Ron Sutton achieved 126.5 mph (202.4 km/h) on a Belgian autoroute, although the car was fitted with a non-standard aluminum belly pan to reduce drag and there is some question as to whether the engine was truly stock. Either way, with the top down and the windscreen replaced by a small airflow deflector in front of the driver, the car achieved 136.6 mph (218.6 km/h), making the XK120 the world’s fastest production car.


With such performance, it’s no wonder that the Jaguar XK120 was soon bound for the racetrack. It scored a one-two victory in a one-hour production car race at Silverstone in August 1949. In January 1950, one of the Silverstone XK120s won the production class at Palm Beach Shores, its first racing victory in America. Driver Leslie Johnson made a good showing in the 24 Hours of Le Mans in 1950, although clutch failure made him a DNF. The XK120 also competed in the Targa Florio, the Mille Miglia rally, and the Tourist Trophy, where three XK120s — one driven by a young Stirling Moss — scored an impressive one-two-three victory. William Lyons’ daughter Pat and her husband, Ian Appleyard, also won France’s Alpine Rally in 1950 and 1951.

In 1951, Jaguar introduced a new variation on the XK120, the XK120C, or “C-Type.” Its relationship to the XK120 was tenuous — the C-Type had an aluminum body, a tubular steel frame, rack-and-pinion steering, and many performance features not shared with the standard XK120. Only 53 of these cars were built between 1951 and 1953.

1956 Jaguar XK140 C-type Engine
While the Jaguar C-Type was quite rare, its uprated engine was offered as an option on street cars; one is seen here in a 1956 Jaguar XK140.

For owners who couldn’t afford a C-Type (or who didn’t have the connections to get one), Jaguar offered a variety of performance parts, including twin spare wheels and a 24-gallon (91-liter) fuel tank. Jaguar XK120s competed to good effect throughout the decade, favored by drivers like future world champion Phil Hill.


Although Lyons was always wary of the vagaries of the U.S. market, many Jaguar XK120s inevitably went to America, which proved to be far more important to Jaguar’s survival than the domestic market. The XK120 was extremely popular with the rich and famous on both sides of the Atlantic, with owners that included actors Humphrey Bogart and Clark Gable.

About 85 percent of all XK120s built were left-hand drive and most of those went across the pond, due in part to the 1949 devaluation of the British pound. The XK120’s U.S. price — initially $3,945 POE — was set based on the prevailing dollar-to-sterling exchange rate of $4.03. In September 1949, the UK’s Labour government devalued the pound to $2.80, but Jaguar’s U.S. prices did not change. Even accounting for the cost of importation, the exchange rate now made each U.S. sale a very lucrative proposition for the company. As a result, the XK120 became comparatively rare in the home market, particularly in right-hand-drive form.

The demands of the American market led to the addition of a closed coupe (fixed-head coupé, or FHC) model in 1951. The FHC was a good deal more civilized than the roadster, with wind-up windows, outside door handles, a heater, and other minor changes. A new convertible model (drophead coupé, or DHC) followed in 1953, with a padded top, side windows, and equipment similar to the fixed-head coupé’s. It was both the heaviest and the most expensive version of the Jaguar XK120, with U.S. prices of about $175 more than the coupe.

1953 Jaguar XK120-FHC front3q
With far more amenities than the roadster, the Jaguar XK120 fixed-head coupé weighed 130 pounds (59 kg) more, which reduced its acceleration somewhat. If that was a problem, you could specify the “special equipment” package (known in the U.S. as the XK120M), which added bigger carburetors, dual exhaust, and other minor tweaks to bump horsepower to 180 hp (134 kW).


The Jaguar XK120 became the XK140 in 1954, receiving various mechanical and stylistic revisions that improved its functionality, if not its aesthetics. In 1957, the XK140 underwent an even more significant metamorphosis, becoming the XK150. By most standards, the XK150 was still a beautiful car, but it had lost something of its original elegance thanks to the elimination of the beltline dip and a higher cowl. Its straight-line performance was much improved, however, and Jaguar addressed the earlier cars’ mediocre brakes with the world’s first production four-wheel discs. Still, compared to its stunning 1948 predecessor, the Jaguar XK150 seemed a little flabby and middle-aged.

1953 Jaguar XK120-FHC rear 3q
The easiest way to tell a Jaguar XK120 coupe from an XK140 is the rear roofline. Although both have the same curvy greenhouse (a scaled-down version of that of the Mark VII sedan), the XK140’s roof was extended toward the back, creating more interior space at the cost of making its profile slightly clumsier.

The Jaguar XK150 survived until 1961, when it was replaced by the E-Type. Total production for the XK line was 12,061 XK120s (including 240 of the original aluminum-bodied roadsters), 8,935 XK140s, and 9,385 XK150s — a respectable total for what Lyons had originally assumed would be a limited-production special.


The conservatism that crept into the Jaguar sports car line with the XK150 was decisively addressed by the 1961 E-Type, which was just as dramatic as the XK120 had been 13 years earlier. Like its processor, the E-Type offered a combination of looks and performance that could scarcely be matched by cars two and three times its price.

1953 Jaguar XK120-FHC front
U.S. prices on the Jaguar XK120 line fell sharply late in the 1953 model year, probably to help clear out stocks prior to the introduction of the XK140. In the U.S., a fixed-head coupé could be had for $3,875, a superb value for a high-performance sports car; by comparison, a contemporary Porsche 356 Super, which was far slower, would cost you $4,284, while an Alfa Romeo 1900C coupe ran to $7,200 and a Ferrari 212 Inter cost around $11,000.

Sir William Lyons remained as chairman of the company until 1972, some 50 years after he and William Walmsley originally founded SS. He retired to his country estate at Wappenbury, where he occupied much of his time tending sheep. He remained close with Jaguar stylists and took an involvement in several pet projects, including the short-lived XJ coupe and the controversial XJ-S. He died on February 8, 1985, at the age of 83.

Like many of Sir William’s creations, Jaguar XK120s remain highly desirable cars, with the early aluminum-bodied roadsters particularly prized. As with all Jaguars, they can be very expensive (and exasperating) to own, but such drawbacks haven’t dissuaded enthusiasts. For many devotees of these cars, their beauty is its own reward.



Our sources for this article included Martin Buckley, Jaguar: Fifty Years of Speed and Style (Haynes Classic Makes) (Sparkford, Somerset: Haynes Publishing, 1998); Craig Burlingame, “There’s a Lyon Behind Every Jaguar: The Story of Sir William Lyons,” Jag-lovers Web, n.d.,, accessed 4 March 2009; Roger Bywater, “XK engine,” Jaguar World, 30 March 2001,, accessed 10 March 2009; the Auto Editors of Consumer Guide, “1949-1961 Jaguar XK Sports Cars,”, 15 October 2007, auto.howstuffworks. com/ 1949-1961-jaguar-xk-sports-cars.htm, accessed 10 March 2009; Mike Covello, Standard Catalog of Imported Cars 1946-2002, Second Edition (Iola, WI: Krause Publications: 2001); and “1951 Jaguar XK120” in Road & Track Vol. 21, No. 6 (February 1970), pp. 90-95.

Historical exchange rates for the dollar to the pound came from Werner Antweiler, “PACIFIC Exchange Rate service, Foreign Currency Units per 1 British Pound, 1948-2007” (2007, University of British Columbia, fx.sauder.ubc. ca), and Lawrence H. Officer, “Exchange Rates Between the United States Dollar and Forty-one Currencies,” MeasuringWorth, 2009,, used with permission. Exchange rate values cited in the text represent the approximate equivalency of British and U.S. currency at the time, not contemporary U.S. suggested retail prices, which are listed separately. All such figures are approximate and are provided for informational purposes only; this is an automotive history, not a treatise on the historical value of money, and nothing in this article should be taken as financial advice of any kind!


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  1. I’ve heard that Lyons wasn’t good in drawing, so he usually hires an assistant in making designs using clay, or metal or wood models ( I’m not sure which one.) He gives the things what the car should look like, and the assistant will put those to the model. We can see his talent of styling with the XK120.

    1. That is true. Nevertheless, he certainly set the aesthetic direction for Jaguar’s cars, even more than Harley Earl did at GM.

  2. "The XK120 became the XK140 in 1954, with various mechanical and stylistic revisions that improved its functionality, if not its aesthetics."

    What the XK 140 fixed, more than anything, was the XK 120’s horrific ergonomics. The XK 120 began life as a styling exercise, and nowhere is this more evident than the driving position! If you were a diminutive Brit it might work, but anyone over 5′ 9" tall is in for a shock when they climb in. The pedals are too high and the seat far too forward.

    I’ve driven an XK 120 well over 5,000 miles in various car rallies and tours, and at 5′ 11" it was torture. Plenty of pleasure to go with the pain however as that XK engine is a joy to run! Pulls like a freight train, in any gear.

  3. Nice write-up as always, I just doubt the following conversion: 120+ mph (256 kph).

    The Imperial Mile is 1,609.344 meters, so 120+ mph should be approx. 195 kph, while 256 kph would be roughly 160mph.

    1. Oops — that was a typographical error and a rather odd one, at that. As you’ll see, the other conversions in the text are more reasonable, so I’m not sure where THAT one came from! I’ve amended the text.

  4. Didn’t the Jaguar factory in Coventry build Spitfires during WW2?

    1. Possibly — I’ve never looked into which of the shadow factories was making what during the war.

  5. no were can I find who designed that wonderful best looking in the world body I had a 1954 XK120m fixed head coupe back in 1960 .I’m 5’11” and the cockpit was tight but mastering heal and toeing the pedals was a art

  6. I bought a ’51 XK-120 OTS (roadster) in 1958 while (believe it or not) working my way through college. It was white (various names) with red leather. I drove it to my first job out of college from Illinois to California on the “Mother Road” and later back again. That was a few years BEFORE the Rt. 66 TV show. I loved the car but a mechanic “took it for a ride” after tuning it up, the safety catch on the bonnet was broken and the bonnet flew open and was torn off the car. My dad (who was caretaker of the car at the time) sold it. Last month I finally got my XK-120 back. Another ’51 OTS this time white with biscuit interior … fully restored. Real a hoot to drive, of course. Driving shoes help and 2 inches in spine compression compared to back when I was 21 years old helps as well. :-) :-)

  7. It would have been interesting to see how things would have been different at Jaguar had they produced both 4-cylinder and 6-cylinder versions of the XK engine.

    Jaguar during the mid/late-60s had plans to develop an XJ Junior (prior to the project being cancelled upon the formation of BL), which was of similar dimensions to the Alfa Romeo Giulia and intended to challenge both the Rover P6 and Triumph 2000/2500.

    However since rivals from Rover and Triumph are roughly similar to the Mk1/Nk2 in terms of size, Jaguar could have potentially anticipated the grow of the 2-litre+ or so Executive saloon sector by producing 1.8-2.0-litre+ XK4 engined variants, whose lack of grunt compared to the XK6 engined Jaguars would likely be offset by being significantly lighter.

    One thing that perplexes me is why Jaguar found it difficult to develop a full production version of the 3-litre XK6 engine.

  8. It seems difficult to believe that the XK120’s styling wasn’t influenced by the 1941 Chrysler Newport, whether the XK120’s designer gave credit or not.

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