The Airco DH.4 was a British two-seat biplane day bomber of the First World War. It was designed by Geoffrey de Havilland for Airco, and was the first British two-seat light day-bomber to have an effective defensive armament. The United States possessed no combat-worthy aircraft upon entry into World War I in 1917. Several European aircraft were considered. The British DH-4 was selected because of its comparatively simple construction and its apparent adaptability to mass production. It was also well-suited to the new American 400-horsepower Liberty V-12 engine. American-built DH-4s were dubbed the "Liberty Plane." By war's end, 13 Army Air Service squadrons, five of them bomber squadrons, were equipped with them. In addition, four combined Navy-Marine squadrons were flying DH-4s along the Belgian coast. Of the 4,346 DH-4s built in the United States, 1,213 were delivered to France, but of those only 696 reached the Zone of Advance. In the postwar period, the DH-4 was the principal aircraft used by the U.S. Government when air mail service began in 1918. Length 5:00.