The Railton Special, later rebuilt as the Railton Mobil Special, is a one-off motor vehicle built for John Cobb's successful attempts at the land speed record.
It was powered by two supercharged W12-block Napier Lion VIID (WD) aircraft engines. These engines were the gift of Betty 'Joe' Carstairs, who had previously used them in her powerboat Estelle V. Multiple engines was not a new technique, having already been used by the triple-engined White Triplex and the Railton Special's contemporary rival, Captain Eyston's twin-engined Thunderbolt. With the huge powers thus available, the limitation was in finding a transmission and tyres that could cope. Reid Railton found a simple and ingenious solution to this by simply splitting the drive from each engine to a separate axle, giving four wheel drive.
On 15 September 1938, the Railton Special took the land speed record from Thunderbolt at 353.30 mph (568.58 km/h), also being the first to break the 350 mph (560 km/h) barrier. Eyston re-took the record within 24 hours (357.50 mph / 575.34 km/h), holding it again until Cobb took it a year later on 23 August 1939 at a speed of 369.70 mph (594.97 km/h).
After the Second World War further development and sponsorship by Mobil Oil led to renaming as the 'Railton Mobil Special'. It was the first ground vehicle to break 400 mph (640 km/h) in a measured test. On September 16, 1947 John Cobb averaged 394.19 mph (634.39 km/h) (385.6 & 403.1) over the measured mile in both directions to take the world land speed record.
It weighed over 3 tonnes and was 28 ft 8 in (8.74 m) long, 8 ft (2.4 m) wide and 4 ft 3 in (1.30 m) high. The front wheels were 5 ft 6 in (1.68 m) apart and the rear 3 ft 6 in (1.07 m). The National Physical Laboratory's wind tunnel was used for testing models of the body.
It was designed by Reid Railton and is currently on display at the Thinktank museum in Birmingham, England.