Thomas at the wheel. Thomas, Guyot, and Duray returned to the French Grand Prix with 4½-liter twin-cam desmodromic valved racers featuring twin carburettors, five-speed gearbox, and four-wheel brakes. While quick, they proved unreliable; only one finished, Duray's, in eighth. In 1914, Delage emphasized its focus on competition by creating the type O Lyon Grand Prix, while at the same time moving towards the luxury car market with 6 cylinders of a large class. However, racing was severely curtailed during World War One. In 1923, Louis Delage returned to competition with the innovative 12-cylinder 2-liter type 2 LCV. This car won the 1924 European Grand Prix in Lyon and the 1925 Grand Prix of ACF Montlhéry. The 12-cylinder DH (10.5 liters) of 1924 beat the world speed record on the highway, at . A Delage 155 B won the first Grand Prix of Great-Britain in 1926, driven by Louis Wagner and Robert Senechal. The production of cars continued with the DI and the DI S SS. The DM evolved into the DMS and DML, equipped with a 6-cylinder 3-liter engine designed by Maurice Gaultier. Delage's Grand Prix effort saw a Plancton-designed () four overhead cam V12. The car, driven by Thomas, fell out of the French Grand Prix in 1923, but went on to perform well for the bulk of the 1923 and 1924 season. With supercharger added in 1925, bringing output to , it won at Montlhéry and Lasarte, proving as fast as the Alfa Romeo P2, but rarely racing it directly. This car was supplanted in 1926 by a Lory-designed supercharged 1.5-liter twincam straight eight of ; capable of , it was the company's last Grand Prix entrant. Always passionate about racing, Louis Delage designed an 8-cylinder 1500 cc, the type 15 S 8. This car won four European Grands Prix races in 1927, and won Delage the title "World Champion of Car Builders" that same year. A -powered D6 won the 1938 Tourist Trophy at Donington Park and came second at Le Mans. A single V12-powered car, intended for Le Mans, caught fire at the 1938 International Trophy at Brooklands. Postwar, the best results Delage had were seconds at the 1949 Le Mans and 1950 Paris Grand Prix. The D6 and the D8: The Classic Era 1930 saw the launch of the 6-cylinder Delage D6 which would form the mainstay of the manufacturer's passenger car range until 1954.