Glenn Curtiss began his career as a bicycle mechanic. In 1902 he opened his own shop, making motors for motorcycles. Later, he designed and built a motor for the dirigible California Arrow, which led to a similar assignment for the U.S. Army's Dirigible No. 1. Moving to heavier-than-air craft, in 1908 he made the June Bug, which he flew for one kilometer. Three years later, he built a seaplane, with which he demonstrated takeoffs and landings on water at San Diego, CA. At the beginning of World War I, his factory was making military planes for the United States, England, and Russia. It produced 5,000 training Curtiss "Jennies" and the NC-4, which in May 1919 made the first transatlantic flight. His most important contribution to aerodynamics is the aileron, the movable control surface on the trailing edge of the airplane wing that permits a plane to roll. He designed the first land-sea plane with a retractable landing gear.