Harley-Davidson models. In the late summer of 1929, Harley-Davidson introduced its 45 cubic inches (737 cm³) flathead V-Twin to compete with the Indian 101 Scout and the Excelsior Super X. This was the "D" model, produced from 1929 to 1931. Riders of Indian motorcycles derisively referred to this model as the "three cylinder Harley" because the generator was upright and parallel to the front cylinder. The Great Depression began a few months after the introduction of their 45 cubic inch (737 cm³) model. Harley-Davidson's sales fell from 21,000 in 1929 to 3,703 in 1933. Despite this, Harley-Davidson unveiled a new lineup
Harley-Davidson I was the first time the motorcycle had been adopted for military issue, first with the British Model H, produced by British Triumph Motorcycles Ltd in 1915. After the U.S. entry into the war, the U.S. military purchased over 20,000 motorcycles from Harley-Davidson. Harley-Davidson launched a line of bicycles in 1917 in hopes of recruiting customers for its motorcycles. Besides the traditional diamond frame men's bicycle, models included a step-through frame 3-18 "Ladies Standard" and a 5-17 "Boy Scout" for youth. The effort was discontinued in 1923 because of disappointing sales. The bicycles were built for Harley-Davidson in Dayton, Ohio,