The Liberty L-4 was a four-cylinder, water-cooled, inline engine for aircraft developed in the United States during World War I. Designed by Jesse G. Vincent and Elbert J. Hall, the Liberty L-4 was an experimental engine of 102 hp, built by the Hudson Motor Co. and intended primarily for use in training airplanes. Only two were produced since other types of engines were available and already in production. It is unknown if the L-4 was ever test-flown.