The Cadillac Model D was a vintage car introduced in January 1905, and sold throughout that year. It was a large automobile, the first four-cylinder car from Cadillac. Priced at $2800, it can be seen as the first luxury car from the company.

The engine was a 300.7 in³ (4.9 L) four-cylinder L-head design producing a claimed 30 hp (22 kW). The car used a complicated 3-speed planetary transmission and had a governed throttle, essentially a primitive cruise control. The engine was designed by Alanson P. Brush, who left Cadillac shortly afterwards.

Model H/L

The Model D was replaced for 1906 with the Model H and larger Model L. Both were based on the Model D, though the departure of Brush lead Henry Leland to begin to purge his patented designs from the cars. Thus, the variable intake valve lift system and hydraulic governor were abandoned for more conventional designs.

The Model L used a large 392.7 in³ (6.4 L) engine with 5 in (127 mm) square bore and stroke, rated at 40 hp (30 kW). The smaller Model H continued with the 30 hp (22 kW) 300.7 in³ (4.9 L) engine size used in the Model D.

The Model H continued in production through 1908, while the Model L was cancelled.

Model G

The Model G was a smaller version of the Model H, with a wheelbase of 100 in (2540 mm).

The engine was a 226.2 in³ (3.7 L) four-cylinder L-head design producing 20 hp (15 kW), which was re-rated to 25 for 1908 with no changes made. The Model G eschewed the complicated planetary transmission used on other luxury four-cylinder cars of the era for a less-complicated sliding gear system.

The entire Cadillac range was replaced for 1909 with a single model — the Model Thirty. This new car was based on the Model G.