Häfeli DH-4
The Häfeli DH-4 was a Swiss fighter prototype in the late 1910s, build by the Eidgenoessische Konstruktionswerkstaette. The DH-4 was a single-seat fighter based on the successful Häfeli DH-3 design. It was made of wood with fabric covering, and carried one machine gun. Operational history. The Swiss Air Force trialled it from May 1918 to August 1918, but the DH-4 was found to possess disappointing performance and poor handling. As such only one was ever produced and production ceased in late 1918.