High Quality Content by WIKIPEDIA articles! High Quality Content by WIKIPEDIA articles! The Airco DH.9 (from de Havilland 9) - also known after 1920 as the de Havilland DH.9 - was a British bomber used in the First World War. A single-engined biplane, it was a development of Airco's earlier, highly successful DH.4 and was ordered in very large numbers for Britain's Royal Flying Corps and Royal Air Force. Its engine was unreliable, and failed to provide the expected power, giving the DH.9 poorer performance than the aircraft it was meant to replace, and resulting in heavy losses, particularly over the Western Front. The subsequently-developed DH.9A had a more powerful and reliable American Liberty L-12 engine. The DH.9 was designed by de Havilland for the Aircraft Manufacturing Company in 1916 as a successor to the DH.4. It used the wings and tail unit of the DH.4 but had a new fuselage. This enabled the pilot to sit closer to the gunner/observer and away from the engine and fuel tank.