The Airco D.H.9 was an unsuccessful single engined day bomber designed to replace the D.H.4 but that was let down by its original engine. The D.H.9 was very similar to the D.H.4, and shared ninety percent of the same airframe. A number of changes were made to eliminate flaws in the D.H.4, the most obvious of which saw the fuel tank and the pilot swap places so that the pilot's cockpit was located close the observer/ gunners position behind the wings. This meant that the two crew members could communicate more easily, and reduced the chance of the pilot being caught in a sudden fire.
The first prototype of the D.H.9 was produced from an existing D.H.4. This aircraft underwent its flight trails at Hendon in July 1917, and its performance was impressive enough for it to be ordered into mass production.
As was so often the case it was its engine that let down the D.H.9. The aircraft was designed around the 300hp B.H.P. engine, which was to be mass produced by the Siddeley-Deasy Motor Car Company as the Siddeley Puma. When the first batch of aluminium cylinder blocks was delivered they turned out to have a fault that could not easily be corrected. Siddeley decided to reduce the engine's power output to 230hp in the hope that the cylinder blocks would be able to cope with the lower power levels. Unfortunately this was not the case. Not only did the lower-powered Puma reduce the performance of the D.H.9 to the point where it was actually lower than that of the D.H.4, it was still prone to failure. With its full military load the new aircraft had a service ceiling of only 13,000ft and was much slower than the more powerful versions of the D.H.4.
The engine problems delayed the combat debut of the D.H.9 until the summer of 1918, by which point nine squadrons in France and thirteen in Britain were equipped with the type. The D.H.9 had a disastrous combat record on the Western Front – between May 1918 and the end of the war Nos.99 and 104 Squadrons lost 148 aircraft in 848 sorties, two thirds of them after accidents.
The majority of D.H.9 squadrons never left Britain and instead were used for coastal patrols, often replacing the D.H.6 trainer. The aircraft's unreliable engines were still a problem but at least its poor performance wasn't such an issue.
The D.H.9 was more useful on less dangerous fronts. Its long range with lighter loads meant that it was used in attempts to bomb Constantinople and it was also used in the last stage of the campaign in Palestine.
A number of attempts were made to equip the D.H.9 with better engines. These proved that there was no problem with the basic design. Eventually the D.H.9 was given the American Liberty 12 engine to produce the much more successful D.H.9A, which saw limited service in the last months of the war before becoming the main bomber of the post-war RAF.
Despite its problems a huge number of D.H.9s were built. 4,630 were ordered, of which 3,204 had been delivered by the end of 1918. By the time production ended 4,091 had been built, although not all were fully completed and many of the last 800 were delivered straight into storage. The RAF struck the last D.H.9s off its strength in July 1919, leaving a vast number of aircraft surplus to requirements. As a result the D.H.9 was available in large numbers for export and in the post-war years was used by the air forces of Belgium, Poland, South Africa, New Zealand, Australia, Canada, India, Afghanistan, Greece, Irish Free State, Holland, Latvia, Chile, Estonia the Netherlands and Spain.
Engine: Siddeley Puma
Wing span: 42ft 4 3/8in
Length: 30ft 5in
Height: 11ft 3.5in
Tare Weight: 2,230lb
All-up Weight: 3,325lb
Max Speed: 109.5mph
Service Ceiling: 15,500ft
Endurance: 4h 30min
Armament: One forward firing Vickers Gun, one rear Lewis guns
Bomb-load: two 230lb or four 112lb bombs