1950 Jaguar XK120 roadster on later wire wheels; leather strap and bonnet louvres also unoriginal
12,055 made 
|Assembly||Holbrook Lane, Coventry, England, United Kingdom (1948-1951)
Browns Lane, Coventry, England, United Kingdom (1951-54)
|Body style||2-seat roadster (OTS)
2-seat Drop Head Coupé
|Engine||3.4 L XK I6|
|Wheelbase||102 in (2,591 mm)|
|Length||173 in (4,394 mm)|
|Width||61.5 in (1,562 mm)|
|Height||52.5 in (1,334 mm)|
The XK120 was launched in roadster form at the 1948 London Motor Show as a testbed and show car for the new Jaguar XK engine. The display model was the first prototype, chassis number 670001. 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 roadster caused a sensation, which persuaded Jaguar founder and design boss William Lyons to put it into production.
Beginning in 1948, the first 242 cars were aluminium-bodied roadsters. Production switched to steel in early 1950. The "120" in the name referred to the aluminium car's 120 mph (193 km/h) top speed (faster with the windscreen removed), which made it the world's fastest production car at the time of its launch. In 1949 the first production roadster, chassis number 670003, was delivered to Clark Gable.
The XK120 was ultimately available in two open versions, first as the roadster (designated OTS, for open two-seater, in America), then also as a drophead coupé (DHC) from 1953; and also as a closed, or "fixed-head" coupé (FHC) from 1951.
A smaller-engined version intended for the UK market was cancelled prior to production.
In 1949, on a motorway in Belgium, a prototype XK120 achieved over 132 mph with the windscreen removed. In 1950 and 1951, at a banked oval track in France, XK120 roadsters averaged over 100 mph for 24 hours and over 130 mph for an hour, and in 1952 a fixed-head coupé took numerous world records for speed and distance when it averaged 100 mph for a week.
Roadsters were also successful in racing and rallying.
The first roadsters, hand-built with aluminium bodies on ash frames mounted on modified Jaguar Mark V chassis, were constructed between late 1948 and early 1950. To meet demand, and beginning with the 1950 model year, all subsequent XK120s were mass-produced with pressed-steel bodies. They retained aluminium doors, bonnet, and boot lid. The DHC and FHC versions, more luxuriously appointed than the roadsters, had wind-up windows and also wood veneers on the dashboard and interior door caps.
With alloy cylinder head and twin side-draft SU carburetors, the dual overhead-cam 3.4 L straight-6 XK engine was comparatively advanced for a mass-produced unit of the time. With standard 8:1 compression ratio it developed 160 bhp (119 kW), using 80 octane fuel. Most of the early cars were exported; a 7:1 low-compression version, with consequently 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, with access to 80 octane fuel, provided roadsters with the higher compression ratio to the press. Journalists could then 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, later modified into 3.8 and 4.2 litre versions, survived into the late 1980s.
All XK120s had independent 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 that were prone to fade. Some cars were fitted with Alfin (ALuminium FINned) brake drums to help overcome the fade.
The roadster's lightweight canvas top and detachable sidescreens stowed out of sight behind the seats, and its barchetta-style doors had no external handles; instead there was an interior pull-cord which was accessible through a flap in the sidescreens when the weather equipment was in place. The windscreen could be removed for aeroscreens to be fitted.
The drophead coupé (DHC) had a padded, lined canvas top, which folded onto the rear deck behind the seats when retracted, and roll-up windows with opening quarter lights. The flat glass two-piece windscreen was set in a steel frame that was integrated with the body and painted the same colour.
Dashboards and door-caps in both the DHC and the closed coupé (FHC) were wood-veneered, whereas the more spartan roadster's were leather-trimmed. All models had removable spats ("fender skirts" in America) covering the rear wheel arches, which enhanced the streamlined look. On cars fitted with optional centre-lock wire wheels (available from 1951), the spats were omitted as they gave insufficient clearance for the chromed, two-eared Rudge-Whitworth knockoff hubs.
In addition to wire wheels, upgrades on the Special Equipment, or SE, version (called the M version in the United States) included increased power, stiffer suspension and dual exhaust system.
All XK models are collectible.
Engine specifications 
|XK 120 3.4||1948–1954||
||Double SU H6||160 bhp (119 kW; 162 PS) @ 5000 rpm|
|XK 120 3.4 SE ("M" in USA)||1951–1954||
||Double SU H6||180 bhp (134 kW; 182 PS) @ 5300 rpm|
|XK 120 3.4 SE (C-Type Head) ("MC" in USA)||1951–1954||
||Double SU H8||210 bhp (157 kW; 213 PS) @ 5750 rpm|
The Motor magazine road-tested an XK120 roadster in November 1949. This pre-production car, chassis number 670001, road-registered as HKV 455, was the first prototype built. It was also the 1948 London Motor Show display model, and had been driven by Prince Bira in the 1949 Silverstone Production Car Race. When tested, it had the 8:1 compression ratio, was fitted with an undertray, and ran with hood and sidescreens in place. The magazine reported a top speed of 124.6 mph (200.5 km/h), acceleration from 0–60 mph (97 km/h) in 10.0 seconds and fuel consumption of 19.8 miles per imperial gallon (14.3 L/100 km; 16.5 mpg-US). The car as tested cost £1263 including taxes.
Racing and rallying 
XK120s were active in racing and rallying:
- First race victory: In the Daily Express-sponsored One-Hour Production Car Race held on 30 August 1949 at Silverstone Circuit, England, Leslie Johnson drove the Jabbeke car to the XK120's first-ever race victory (despite an early collision with a spinning Jowett Javelin which dropped the Jaguar to fifth). The car, road-registered HKV 500, was converted to right-hand drive for Silverstone. Two other XK120s took part. One, driven by Peter Walker, finished second and the other, driven by Prince Bira, spun out of contention when a tyre punctured.
- First victory in America: In January 1950 Johnson also scored the model’s first competition success in America, winning the production class in a race at Palm Beach Shores, Florida with the car that had finished second at Silverstone. The Jaguar lost its brakes but finished fourth overall. John Lea, Jaguar’s Experimental Department mechanic who attended the race, reported: "The conditions at Palm Beach were wet, windy and sandy. Water and sand gained entry into the brake drums at the front, and the mixture had the effect of accelerating the wear very considerably. Our car finished with no linings and with the steel shoes bearing on the brake drums."
- Le Mans: Three of the allocated cars, extensively modified, were entered for the 1950 Le Mans 24 Hours race. Johnson, who spearheaded this factory-supported assault on the race with co-driver Bert Hadley, never ran lower than seventh place, and held second for two hours, but in the 21st hour had to retire from third place with clutch failure caused by using the gears to slow the car in the absence of brakes. (As a result the clutch was revised to a more robust design for production models.) The Jaguar had been closing the gap to leader Louis Rosier, whose Talbot's pace was significantly slower, at a rate that would have secured victory. Haines, with co-driver Peter Clark, finished 12th, and Walker’s car, driven by Peter Whitehead and John Marshall, was 15th. The results convinced William Lyons it was worth investing in future success at Le Mans.
- Targa Florio: Biondetti's car, the first XK120 to contest the Targa Florio, lay second to Alberto Ascari’s Ferrari when a connecting rod broke, ending the Jaguar’s run.
- Mille Miglia: Johnson took fifth place in the Mille Miglia, with John Lea as his riding mechanic, while Biondetti and co-driver Gino Bronzoni finished eighth. Fifth was an outstanding achievement for a production car, with Johnson's Jaguar beaten only by Fangio's works Alfa Romeo and the works Ferraris of Serafini, Bracco and winner Marzotto. It was Jaguar's best-ever finish in the Mille Miglia; also the best by a British car and driver combination, a feat that only Reg Parnell ever equalled, driving an Aston Martin DB3 in 1953.
- Silverstone Production Car Race: Five XK120s entered the race, which Peter Walker won from Tony Rolt, with Johnson recovering to eighth after spinning on oil. Jaguar won the team prize.
- Tourist Trophy: XK120s also achieved a 1–2–3 victory in the TT, held at Dundrod in heavy rain. On the eve of his 21st birthday Stirling Moss drove Tom Wisdom's car to a brilliant win ahead of Whitehead and Johnson, and Jaguar once again took the team prize.
- Alpine Rally: Ian Appleyard's XK120, road-registered as NUB 120, won the Alpine Rally with his wife Pat, who was the daughter of Sir William Lyons, navigating. They also won a coveted Coupe des Alpes.
- Alpine Rally: NUB 120 and the Appleyards repeated their previous year's success.
- Tulip Rally: The Appleyards took first place in the Tulip Rally, with Swiss fighter pilot Rolf Habisreutinger’s XK120 finishing second.
- Alpine Rally: Although the Appleyards’ XK120 did not win its third Alpine, it completed the rally without incurring a single penalty point, winning the first-ever Coupe d'Or (Gold Cup).
- Mount Druitt 24 Hours Road Race: On 1 February 1954, an XK120 FHC driven by Geordie Anderson, Chas Swinburne and Bill Pitt won Australia's first 24-hour motor race, the 1954 Mount Druitt 24 Hours Road Race from a Bristol 400 and a Humber Super Snipe.
- NASCAR road race: In America, an XK120 FHC was the first imported car to achieve victory in NASCAR, when Al Keller won the first NASCAR road race, held at Linden Airport, New Jersey, on 13 June 1954.
High-speed runs and records 
- 132.596 mph (213.393 km/h) through the flying mile: in May, Jaguar demonstrated an XK120 roadster to the press on the high-speed autoroute between Jabbeke and Aeltre in Belgium. The road was closed for the occasion. The white left-hand drive car, chassis number 670002, was the second XK120 built. Jaguar's development engineer Walter Hassan was to have driven but fell ill, so Jaguar test-driver Ron "Soapy" Sutton substituted. With hood and sidescreens erected, and the airflow under the car improved by the addition of a full-length aluminium undertray, the Jaguar was timed through the flying mile by the Royal Automobile Club of Belgium at 126.448 mph (203.498 km/h). With hood, sidescreens and windscreen removed, a metal airflow deflector fitted in front of the driver, and a tonneau cover fastened over the passenger side of the cockpit the speed improved to 132.596 mph (213.393 km/h). The Observer's Book of Automobiles said it was the fastest production car in the world.
- 107.46 mph (172.94 km/h) for 24 hours (including stops for fuel and tyres): Leslie Johnson sharing his XK120 roadster, road-registered JWK 651, with Stirling Moss at the Autodrome de Montlhéry, a steeply banked oval track near Paris. The first time a production car had averaged over 100 mph (160.93 km/h) for 24 hours. Changing drivers every three hours, the Jaguar covered 2579.16 miles, with a best lap of 126.2 mph (203.10 km/h).
- 131.83 mi (212.16 km) for one hour: Johnson solo in JWK 651 at Montlhéry. "No mean feat...driving at almost twice today's maximum (UK) speed limit into a steep turn, assaulted by the G-Force induced by 30 degree banking twice every minute, using Forties technology, leaf spring suspension and narrow crossply tyres...Johnson remarked that the car felt so good it could have gone on for another week, an off-the-cuff comment that sowed the seed for another idea. Flat out for a week..."
- 100.31 mph (161.43 km/h) for 7 days and 7 nights, again at Montlhéry: XK120 fixed-head coupé driven by Johnson, Moss, Hadley and Jack Fairman. William Lyons, mindful of the considerable kudos and advertising mileage that had already accrued from Johnson's exploits, commandeered a brand new XK120 FHC for him: bronze-colored, and fitted with wire wheels, it was Jaguar chief engineer Walter Hassan's car, the second right-hand drive coupé made. The car broke a spring on the track's rough concrete surface when already well into the run. No spare was carried, and regulations stipulated that a replacement from outside would make the car ineligible for any further records beyond those already achieved before the repair. Johnson drove nine hours to save the other drivers from added risk while the speed had to be maintained on the broken spring. When he finally stopped to have it replaced, the car had taken the world and Class C 72-hour records at 105.55 mph (169.87 km/h), world and Class C four-day records at 101.17 mph (162.82 km/h), Class C 10,000-kilometer record at 107.031 mph (172.250 km/h), world and Class C 15,000-kilometer records at 101.95 mph (164.07 km/h), and world and Class C 10,000-mile (16,000 km) records at 100.65 mph (161.98 km/h). After the repair the car went on to complete the full seven days and nights, covering a total of 16,851.73 mi (27,120.23 km) at an average speed of 100.31 mph (161.43 km/h).
Jaguar XK100 
A 2-litre four-cylinder version of the twin cam XK engine was to have powered an XK100 variant of the XK120 for the UK market. Details of the model were included in an “Advance Particulars” brochure for the XK  but Jaguar's managers were dissatisfied with the engine and the project was cancelled prior to production.
- Robson, G (2006). A-Z of British Cars 1945–1980. Devon, UK: Herridge. ISBN 0-9541063-9-3.
- "The Jaguar 2-seater Type XK120 Road Test". The Motor. 1949.
- Holloway, Hilton;Buckley, Martin (2002). 20th Century Car Design. Carlton Books. ISBN 1-84222-835-8.
- Porter, Philip (1998). Jaguar Sports Racing Cars, Bay View Books. ISBN 1-901432-21-1
- "3½-litre XK120 Jaguar Super Sports (road test)". Autocar. September 2, 1949.
- Jaguar XK120 Specifications – Retrieved on 4 November 2008
- The Jaguar Database – Retrieved on 4 November 2008
- Buckley, Martin: Jaguar: Fifty Years of Speed and Style p.120. Haynes Publishing 2003, ISBN 1-85960-872-2
- Nevinson, Tim: "Flat out for a week" Thoroughbred and Classic Cars June 2008 p. 84.
- Photograph of Biondetti's XK120 prepared for the 1950 Mille Miglia.
- Al Keller, Legends of NASCAR website; includes photo of Keller with XK120
- The Observer's Book of Automobiles, Fifteenth Edition, 1969, page 137
- Generation X – Jaguar’s XK Heritage Retrieved from www.classicmotor.co.uk on 18 November 2009
- Advance Particulars of the new Jaguar Type XK “100” & “120” Super Sports Models Retrieved from www.badgers-british.com on 18 November 2009
|Wikimedia Commons has media related to: Jaguar XK120|
- XKData.com volunteer maintained online registry with thousands of cars and over 10,000 photos
|Jaguar Cars road and race car timeline, 1940s–1970s — next »|
|Sports||XK120||XK140||XK150||E-type S1||E S2||E-type S3||XJ-S|
|Saloon||Mark 1||Mark 2, 240, 340|
|420||XJ6 S1||XJ6 S2|
|Mk IV||Mk V||Mk VII||Mk VIII||Mk IX||Mk X||420G||XJ12 S1||XJ12 S2|
|Racing||C-Type||D-Type||E-Type||XJ13||XJ-C||XJ41 / XJ42|