Cadillac Runabout and Tonneau

The first Cadillac automobiles were the 1903 Model built in the last quarter of 1902. These were 2-seater "horseless carriages" powered by a reliable and sturdy 10 hp (7 kW) single-cylinder engine developed by Alanson Partridge Brush and built by Leland and Faulconer Manufacturing Company of Detroit, of which Henry Leland was founder, vice-president and general manager.

Reformed as the Cadillac Automobile Company in August 1902, it began manufacturing the runabouts and named them "Cadillac" after the city's founder Antoine Laumet, the self-styled Antoine Laumet de La Mothe, sieur de Cadillac at the re-purposed Detroit Assembly. The 1904 Model B was a refinement of the 1903 and while still a mid-engined, one cylinder automobile, it now had an extended front and transverse front suspension. With the introduction of the Model B, the 1903 style became known as the Model A . Both the Model A and B were available as a two-passenger runabout or four passenger rear tonneau. Catalogs also show a light delivery.

The one cylinder Cadillac continued to be offered through 1908 in the runabout, tonneau or delivery bodies under a variety of Model designations which are delineated below.