William Munger Heynes (31.12.1903 – 11.07.1989)

William Heynes was born at 11 Percy Terrace, Leamington Spa, one of a family of five boys. He was educated at Warwick School from 1914 to 1921, when he started as an apprentice draughtsman at the Humber Car Company in Coventry. He worked in the design department, learning every aspect of the motor business from design to completed car.  By 1930, he was head of the technical department and responsible for preparing for the production of significant models such as the Humber Snipe and Humber Pullman.

In April 1935, following the takeover of Humber by the Rootes Group, William Heynes joined SS Cars Ltd as Chief Engineer, at the invitation of William Lyons himself. Discovering that SS did not have a drawing office, and that there was only one draughtsman on the staff, he quickly established a dedicated engineering office and recruited additional staff. Initially, Heynes and his small team worked on the chassis, and as a result, they produced a new chassis in less than six months. The chassis was designed for independent front suspension and a new 2.6-litre engine (2663) with an overhead valve 103 hp. (77 kW). The new engine and new chassis fitted perfectly into the company’s first four-door saloon. The powerful, well-equipped sedan became the cornerstone of the company’s development for many decades. Later, Heynes was involved in increasing the production of Standard Motor Company engines, which were then used in SS vehicles.

Sir William Lyons & William Heynes at Browns Lane 1955

William Heynes & Claude Baily







After World War II, SS Cars was renamed Jaguar and Heynes persuaded William Lyons that the company should create its own line of engines. The result was the legendary XK engine. This power unit became the mainstay for Jaguar for forty years and was used extensively for military purposes after this.  Heynes also worked on preparations for the production of many vehicles, including the Mk V, the C-type racing car and D-type, Mk VII, E-type, Jaguar XJ13 and Mk X.   With another exceptional engineer, Claude Baily, he continued to modify and develop engines, chassis and suspension throughout his working life.  Perhaps his greatest innovation came about in 1952 as a result of collaboration with Dunlop, – the development of the disc brake, for use on normal road-going cars, after their success in Jaguar C-Type and later D-Type at Le Mans.  [Jaguar were winners at Le Mans in 1952/53 with the C-Type, and in 1955/56/57 with Heynes’ monocoque-designed D-Type].  Disc brakes were subsequently used extensively in the automotive world, potentially saving thousands, possibly millions of lives worldwide.

Appointed Commander of the British Empire (CBE) for his achievements in July 1969,

William Heynes retired as Vice-Chairman and Technical Director of Jaguar Cars later that year. He remained at his farm just outside Stratford upon Avon until shortly before his death, but still kept in touch with former colleagues who remembered him for his role in creating a world brand. Following his departure from Jaguar Cars, two men took on his responsibilities: RJ (“Bob”) Knight and “Wally” Hassan.


David G P Morse  February 2022

Acknowledgements: Jonathan Heynes (Son); Bob Beecham (Chairman Jaguar Drivers Club Midands Area; Tony Merrygold (Jaguar Daimler Heritage Trust); Jaguar Driver July 2021