Aerial combat advanced at an astonishing rate during World War I, and though it seems unimaginable today, there were no American-designed aircraft deemed suitable for battle in the skies over Europe. There was a U.S.-designed engine in the fight, however: the Liberty V-12, or L-12.

The L-12 engine was America’s greatest technological contribution to the aerial war effort. Its initial assignment was powering the “Liberty Plane” — a version of the British-designed De Havilland/Airco DH-4 bomber produced in the U.S. by Dayton-Wright in Ohio, Fisher Body Corporation in Michigan, and Standard Aircraft in New Jersey. In addition to powering the DH-4 and a variety of other airplanes, over its long service life the L-12 powered tanks, high-speed watercraft and land-speed racers.

The L-12 came about because Packard’s head of engineering, Jesse G. Vincent, recognized the need for a standardized line of aircraft engines that could be mass produced during wartime. The government assigned Vincent to the task of creating this engine and teamed him up with Elbert J. Hall of the Hall-Scott Motor Company. The two met in Washington, D.C., on May 29, 1917, and with the help of volunteer draftsmen, created detailed drawings and a full report by May 31. This original design was a V-8, but in their report Vincent and Hall outlined how the engine could be configured as a 4-, 6-, 8- or 12-cylinder.

By July 3, a V-8 prototype assembled by Packard was running, and a V-12 soon followed. Due to its superior horsepower potential, the 1,650-cu.in. V-12 was given the nod for mass production.

Not only did the Liberty engine mark a great achievement for American aviation, it was responsible for creating a landmark car company: Lincoln. Henry Leland, who founded Cadillac, and his son Wilfred started Lincoln with a $10 million government contract awarded to build Liberty engines. The Lelands left Cadillac to form Lincoln because General Motors President William C. “Billy” Durant was a pacifist and initially rejected the government’s call for GM to build L-12s. (Liberty engines were later manufactured by GM). Production numbers seem to vary for output before and after the war but, in total, Ford, Lincoln, Packard, Marmon and Buick produced 20,748 L-12 engines.

The L-12 was a liquid-cooled, single-overhead-camshaft, V-12 rated to make 400-plus horsepower. The deep box-section crankcase was two-piece — upper and lower — and cast out of aluminum. The cases were joined together by bolts around the perimeter as well as by bolts on each side of the main bearings. The cylinders were individual with welded-on cooling jackets and they extended down into the crankcase for increased rigidity. The stroke was 7 inches while the bore was 5 inches, and aluminum pistons on floating pins helped pump up 5.4:1 compression. The cylinders breathed through 2.5-inch valves (one intake, one exhaust) with exposed rockers and valve springs, while carburetion was handled by a pair of Zenith model US52s.

The Liberty is a fascinating engine built with many advanced features. A full report about the L-12 presented in 1919 to the Society of Automotive Engineers by Jesse G. Vincent is available as a free download.