Harley-Davidson had been building motorcycles since 1904. During World War I the War Department purchased about 20,000 from Harley. ( Indian supplied the most motorcycles for the War, approximately 50,000.) The Harley military motorcycle was based on their series J and had a 15 horsepower engine. The electric headlamp was replaced with a gas powered one. At the time this was a fairly complicated piece of machinery for an army that was going from the horse age to the engine age in one bound. Harley founded the Harley-Davidson Quartermasters School which gave a three week crash course in the construction and maintenance of the motorcycles for Army quartermasters and mechanics. The course was so successful that Harley made it a permanent part of its operation after the War as the Harley Davidson Service School.