In 1917 the first production de Havilland DH9 bombers, from the aircraft manufacturers Airco, joined the ranks of the Royal Flying Corps, with the intention of replacing their predecessor the DH4. The new type's construction inherited many of the successful features of the DH4; the fuselage had an improved design; and the new more powerful BHP Puma engine should have given the DH9 substantial advantages. However, in practice, all the hopes of the designers were ruined very quickly, both literally and figuratively. The faulty construction of the new engine together with lower than expected flying performance figures, led to catastrophe. Total losses of the DH9 during a few months in 1918 on the Western Front quickly reached a three figure count, and pilots of the German fighter squadrons frequently perpetrated massacres when they met the DH9 in the air. The situation appeared so dire, that the general in command Hugh Trenchard ordered an immediate withdrawal of these airplanes from the front line.
The sheer numbers of DH9's already built up to that moment, in accordance with signed contracts, was already so considerable, that in spite of all the type's difficulties the military authorities simply could not give up its operational use. Gradually, the DH9 began to be transferred to the secondary fronts and the colonies, where they would not meet such great opposition in the air as in the air of the Western Front. Small numbers of machines were occasionally used during the Great War for non-combat purposes, such as transportation of loads or communications.
At the end of the war some of them were rebuilt as passenger airplanes and even as an air ambulance. For the ambulance role, a special installation was built behind the cockpit over the former gunner's position in the widest part of the fuselage, where it was possible to fasten stretchers keeping the injured in a steady position. The construction of the fuselage itself was little changed, there simply appeared a prominent fuselage fairing. Only a single machine of this variant was built, and its operational use was short, because from the mid 1920's more capacious ambulances were produced, converted from more modern twin-engined bombers or transport airplanes.

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