The D.H.9A was a single-engined day bomber produced by matching the fuselage of the unsuccessful Airco D.H.9 with a 400hp Liberty 12 engine. The resulting aircraft was one of the most successful bombers of its period and remained in front line service with the RAF until 1931.
The D.H.9 had been designed by Geoffrey de Havilland to replace his own D.H.4, itself probably the most effective British bomber of the First World War. The failure of the Siddeley Puma engine left the D.H.9 badly underpowered, and with a worse performance than the D.H.4. When the D.H.9 entered front line service the squadrons operating it suffered very heavy losses.
A number of different engines were tested in the D.H.9 in an attempt to solve the problem. The Rolls Royce Eagle VIII had the power but wasn't available in sufficient numbers. The answer was found in the United States, where the new 400hp Liberty 12 engine went from the drawing board to a working engine in only six weeks. Three months later, in October 1917, the Liberty was test-flown in a D.H.4, and it was decided to mount the new engine in the D.H.9.
Airco themselves were working on the D.H.10 twin engined bomber, and so Westland, who already had some experience of building the D.H.9, were given the task of designing the D.H.9A. task. Over the winter of 1917-1918 the Westland design team adapted the basic aircraft for the new larger engine, although they didn't actually receive a Liberty engine until March 1918 and so the prototype D.H.9A was powered by an Eagle VIII.
Westland made two main changes on the D.H.9A. The wing span was increased to just under 46 feet, from just over 42ft 4in, resulting in a 12% increase in wingspan. In the fuselage the plywood partitions of the D.H.9 were replaced by wire cross-bracing, increasing its strength.
The D.H.9 was ordered in very large numbers. By the end of the war 2,250 had been ordered and by December 1918 885 had been completed. Production continued after the end of the war, and eventually around 1,730 were completed from the wartime orders and 267 from post-war orders.
The D.H.9A arrived a little too late to have a significant impact on the course of the First World War. Only four squadrons operated the aircraft on the Western Front, starting with No.110 Squadron, which flew its aircraft to France on 31 August-1 September 1918. Between then and the end of the war the squadron dropped a total of ten and a half tons of bombs in daylight raids on Coblenz, Frankfurt and Mannheim. In two months of operations the squadron lost 17 aircraft to enemy action and 28 in accidents, although seven of those losses came on a single raid over Frankfurt on 21 October. By the end of the war Nos.205, 99 and 18 Squadrons were also operating the D.H.9A in France and Nos.25 and 120 Squadrons were in the process of converting to the type. The D.H.9A was also used by Nos.212 and 273 squadrons at Great Yarmouth to carry out anti-submarine patrols.
The D.H.9A was one of the main aircraft of the post-war RAF, although none of the wartime squadrons continued to operate the type. It was used by Regular and Auxiliary day bomber squadrons, Flying Training Schools and as a general purpose aircraft on the North West Frontier and in Iraq. As a result of the continuing demand for the aircraft from the RAF it was much less widespread in other country's air forces than the basic D.H.9, although some were used by Australia and Canada. The D.H.9A was finally phased out towards the end of the 1920s, and the last aircraft were struck off the RAF's strength in 1931.
Two later aircraft – the Westland Walrus fleet spotter and Westland Wapiti general purpose aircraft – were designed to take advantage of the vast stocks of D.H.9A parts available to the post-war RAF.
Plans had been put in place to produce vast numbers of D.H.9As in the United States, but in the end only four prototypes were completed, with the designation USD-9. Another nine slightly modified aircraft were built as the USD-9A, and on 8 June 1921 one of these became the first aircraft to fly with a pressurised cockpit. Two more became infantry liaison aircraft as the Ordnance IL-1.
Engine: Liberty 12
Wing span: 45ft 11 3/8in
Length: 30ft 3in
Height: 11ft 4in
Tare Weight: 2,800lb
All-up Weight: 4,645lb
Max Speed: 114.5mph at 10,000ft
Service Ceiling: 16,750ft
Duration: 5h 15min
Armament: One fixed forward firing Vickers gun, one or two Lewis guns on rear Scarf ring
Bomb-load: 660lb of bomb under fuselage and lower wing