Lorraine-Dietrich was founded in 1896 in Lunéville, Lorraine, when railway locomotive manufacturer Société Lorraine des Anciens Etablissements de Dietrich et Cie branched into automobiles. After World War I, under new technical director Marius Barbarou — formerly of Delaunay-Belleville — the company introduced a family of six-cylinder models starting in 1919 with the A1-6 and B2-6. The B3-6 followed in 1922, available in both short and long wheelbase forms.
All variants in this family shared a 3,445 cc six-cylinder engine featuring overhead valves, a hemispherical combustion chamber, aluminium pistons, and a four-bearing crankshaft. They fell into the 15 CV fiscal horsepower category. The B3-6 designation distinguished the third body series on the six-cylinder platform.
Lorraine-Dietrich's sporting ambitions became clear as early as 1923, when three B3-6 tourers entered the inaugural 24 Hours of Le Mans and put up a creditable performance against outright racing machinery. This result encouraged the factory to develop a dedicated competition variant, the 15 CV Sport.
The 15 CV Sport was a performance-focused evolution of the B3-6 platform. It featured twin carburetion, larger valves, and Dewandre-Reprusseau servo-assisted four-wheel brakes — an advanced feature at a time when four-wheel brakes of any kind were still a rarity on production-derived competition cars. At the 1924 Le Mans, works 15 CV Sports finished second and third overall, proving themselves comparable to the 3-litre Bentleys that dominated that era.
In 1925, the 15 CV Sport reached its highest point, winning the 24 Hours of Le Mans outright, with a sister car finishing third. The following year, 1926, Bloch and Rossignol won again at an average speed of 106 km/h (66 mph), leading a 1-2-3 sweep by Lorraine-Dietrich cars — the most dominant team result the fledgling race had seen to that point.
By winning Le Mans in consecutive years, 1925 and 1926, Lorraine-Dietrich embedded itself in the early history of endurance racing. The marque became the benchmark against which the Bentley Boys and other period factory efforts were measured. Its success at Le Mans drove the commercial reputation of the touring 15 CV family, with coachwork for the road cars supplied by builders including Gaston Grümmer of Argenteuil.
Racing activities for the 15 CV Sport wound down after 1930, with the car's final competition appearance being the 1931 Monte Carlo Rally, where Jean-Pierre Wimille finished within a tenth of a point of the winner. Automobile production at Lorraine-Dietrich ceased entirely in 1935, ending a marque that had also produced notable aircraft engines used by Breguet, IAR, and Aero. The B3-6 and its Sport derivative remain significant as the cars that established France's most famous endurance circuit as an international proving ground for touring machinery.