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.
Read more about Airco DH.9: Design and Development, Operational History, Civilian Use, Variants, Survivors, Specifications (D.H.9 (Puma Engine))