The Jaguar XJ13 was a prototype racing car developed by Jaguar Engineering Director William Heynes to compete at Le Mans in the mid 1960s.
It never raced, and only one was produced. The car has not been officially valued, but a £7 million bid for it was declined by the owners in 1996. It was more than 3 times the price of a Ferrari 250 GTO at the time.
Jaguar had considered the manufacture of a DOHC V12 engine as far back as 1950, initially for racing purposes, and then developing a SOHC road going version, unlike the XK which was designed as a production engine and later pressed into service for racing. The engine design was essentially two XK 6-cylinder engines on a common crankshaft with an aluminium cylinder block, although there were differences in the inlet porting, valve angles and combustion chamber shape. The first engine ran in July 1964.
The design structure of a mid-engined prototype was first mooted in 1960 by William Heynes, but it was not until 1965 that construction began, with the first car running by March 1966. The aluminium body exterior was designed by Malcolm Sayer, the aerodynamicist responsible for aerodynamic air flow work on the Jaguar C-type, D-type, who used his Bristol Aeroplane Company background to build it using techniques borrowed from the aircraft industry. The task of building the car was entrusted by Heynes to Engineer Derick White, Ted Brookes, Mike Kimberley, Bob Blake in the Browns Lane experimental department's "competition shop" - Blake described by his contemporaries as "An Artist in Metal". William Heynes recognised as early as 1964 that a car such as the XJ13 needed an experienced race driver to help develop it. Jack Brabham was approached in this regard  but the challenge was eventually taken up by ex-Jaguar Apprentice David Hobbs. David Hobbs was recruited as the XJ13's main test driver. In 1969 Hobbs was included in a FIA list of 27 drivers who were rated the best in the world. Hobbs achieved an unofficial UK closed lap record with the XJ13 which stood for 32 years. The XJ13’s main test and development driver, Hobbs, was joined at Silverstone for the XJ13’s final test at full racing speed by another racing driver (and ex-Jaguar apprentice) Richard Attwood.
The XJ13 had mid-engine format with the 5.0 litre V12 engine designed by Heynes and Claude Bailey, mounted behind the driver, used as a stressed chassis member together with the five-speed manual ZF Transaxle driving the rear wheels.
The front suspension wishbones were similar to that of the E-Type, however where the E-Type used longitudinal torsion bars, the XJ13 had more conventional coil spring/damper units. At the rear there again remained similarities with the E-Type—the use of driveshafts as upper transverse links—however the rest was quite different, with two long radius arms per side angling back from the central body tub together with a single fabricated transverse lower link.
The development of the XJ13, although treated seriously by the designers, was never a priority for company management (despite assistant MD Lofty England's Le Mans success in the 1950s), and became less so following the 1966 merger with BMC. By that time Ford had developed the 7.0 litre GT40, and so the XJ13 was considered obsolete by the time the prototype was complete. The prototype was tested at MIRA and at Silverstone, which confirmed that it would have required considerable development to make it competitive. The prototype was put into storage and no further examples were made.
In 1971 the Series 3 E-type was about to be launched with Jaguar's first production V12 engine. The publicity team wanted a shot of the XJ13 at speed for the opening sequence of the film launching the V12 E-Type. On 21 January 1971, the XJ13 was taken to MIRA for the filming with Jaguar test driver Norman Dewis at the wheel. Sadly, the car was driven by Dewis at speed on a damaged tyre, against the instructions of Jaguar director England. The resultant crash heavily damaged and nearly destroyed the car, although Dewis was unharmed. The wreck of the car was put back into storage.
Some years later, Edward Loades spotted the crashed XJ13 in storage at Jaguar and made the offer to 'Lofty' England that his company Abbey Panels should rebuild the car. The car was rebuilt, to a specification similar to the original, using some of the body jigs made for its original construction and at a cost of £1,000 to Jaguar. In Jaguar's own words, "The car that can be seen today is not an exact reproduction of the original."  The XJ13 made its public debut in July 1973 when 'Lofty' drove it around Silverstone at the British Grand Prix meeting. It is now displayed at the British Motor Museum at Gaydon, UK.
Neville Swales, Building the Legend, creates "exact replicas" of the pre-crash 1966 Jaguar XJ13. His first recreation, powered by an original quad-cam prototype engine, was built with the knowledge of the Jaguar Heritage Trust and under the guidance of surviving XJ13 Team members. The car, painted and with its engine running, was shown in February 2016 at the London Classic Car show. The completed car made its first track appearance, in the company of surviving members of the original XJ13 project team, and members of William Heynes' and Malcolm Sayer's family, Jaguar VIPs and enthusiasts at Curborough (UK) on 9 August 2016. The car has been nominated as a finalist in the International Historic Motoring Awards 2016 in the category Car of the Year 
Other replicas have been produced of the post-crash (current) car:
- Proteus P90 
- Proteus XJ13-inspired coupé 
- Charles Motors Ltd replica 
- The Sports Car Factory / TWRR 
- "Jaguar XJ13". 9 November 2007. Retrieved 7 May 2018.
- Frankel, Andrew (1 October 2006). "The finest Jaguar that never was". The Sunday Times. London.
- "How many quad-cam V12s were built and where are they now?". UK. 21 October 2011. Archived from the original on 27 September 2016.CS1 maint: BOT: original-url status unknown (link)
- "Bob Blake - "An Artist in Metal"". UK. 21 October 2011. Archived from the original on 14 April 2013.CS1 maint: BOT: original-url status unknown (link)
- "Letter from Jack Brabham to William Heynes". UK. 23 March 1965. Archived from the original on 5 October 2017. Retrieved 5 October 2017.
- "David Hobbs - Jaguar XJ13's Test Driver". UK. 2013. Archived from the original on 24 October 2016.CS1 maint: BOT: original-url status unknown (link)
- "Jaguar Heritage Trust - XJ13". UK. 2000.
- "Building The Legend Limited".
- "London Classic Car Show stars".
- "The Jaguar XJ13". www.xj-13.co.uk.
- "Hofmann's - Jaguar XJ13 recreation by Proteus". www.hofmanns.co.uk. 5 March 2014. Archived from the original on 17 April 2016. Retrieved 5 April 2016.
- Needell, Tiff; David Wheeler (director). "Proteus Jaguar XJ13". Top Gear. BBC. (YouTube, 2013 March 27)
- "Charles Motors Ltd.; Jaguar XJ13". www.ciltd.co.uk.
- "Archived copy". Archived from the original on 9 July 2015. Retrieved 5 April 2016.CS1 maint: archived copy as title (link)
- "The Sports Car Factory". www.sportscarfactory.com.
- XJ13 page at the Jaguar Daimler Heritage Trust
- The finest Jaguar that never was Andrew Frankel of the Sunday Times tests the Jaguar XJ13
- Building The Legend
|Sports||SS 90||SS 100||Production interrupted by World War II||XK120||XK140||XK150||E-Type S1||E-Type S2||E-Type S3||XJ-S|
|Saloon||SS 1 / SS 2||Mark 1||Mark 2, 240, 340|
|SS 1½ litre||Jaguar 1½ litre||S-Type||XJ-C|
|SS 2½ litre||Jaguar 2½ litre||420||XJ6 S1||XJ6 S2|
|SS 3½ litre||Jaguar 3½ litre||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|
|Ownership||Independent (SS Cars Ltd)||Independent (renamed Jaguar Cars)||BMH||British Leyland|