The Airco DH.4 was a British two-seat biplane day-bomber of the First World War. It was designed by Geoffrey de Havilland (hence "DH") for Airco, and was the first British two seat light day-bomber to have an effective defensive armament. It first flew in August 1916 and entered service with the Royal Flying Corps (RFC) in March 1917. The majority of DH.4s were actually built as general purpose two-seaters in the USA, for service with the American forces in France.