The Cadillac Type 51 was a large, luxurious automobile introduced in September 1914 as a 1915 model. It was Cadillac's first V8 automobile, replacing the four-cylinder Model 30. The similar Types 53, 55, 57, 59, and 61 lasted through 1923, when the design was substantially updated as the Type V-63.
All of these models used a new L-head V8 engine, one of the first V8 engines ever mass produced and a substantial differentiator for the marque. All bodies were built by Fisher. The Type 51 was also the first left-hand drive Cadillac—all previous models had been right-hand drive, which was continued as an option. Wheelbases varied in those years, with 122 in (3099 mm) at the low end and 145 in (3683 mm) as the longest.
In May 1916, Erwin "Cannonball" Baker and William Sturm drove a Cadillac from Los Angeles to New York in 7 days, 11 hours, and 52 minutes.