The AMC DH.9a (Aircraft Manufacturing Company de Havilland design 9a) bomber arrived late in the Great War and was borne out of the necessity to find a replacement for the underperforming DH.9. Intended as a replacement for the 275-350hp Rolls Royce Eagle powered DH.4, with the pilot and gunner repositioned closer together for improved communications, the DH.9 was in fact a great leap backwards due in no small part to the inferior performance and unreliability of its 230hp Puma engine.
Due to the workload at AMC, the initial design work for the improved DH.9a was undertaken at Westland Aircraft Works. AMC built DH.9 C6350 was modified to accept a 350hp Rolls Royce Eagle VIII engine in anticipation of the immanent arrival of the plentiful 400hp Liberty V12 engine from America. With its larger wings and re-designed nose C6350 started flight testing in February 1918. The 2nd prototype, and the 1st to be fitted with a Liberty engine, was AMC built C6122 which took to the air on 19 April 1918. In July 1918 it appeared that the supply of Liberty engines could dry up so a 3rd prototype, Westland built B7644, was produced to accept the 350hp Eagle VIII, but as it turned out the supply of Liberty engines proved to be enough for RAF needs.
Remarkably, an initial production order for 400 DH.9a was placed with the Whitehead Aircraft Co in January 1918, a month before the 1st prototype flew. The DH.9a was manufactured by Whitehead, AMC, Mann Eggerton & Co and The Vulcan Motor & Engineering Co as well as numerous rebuilds and small post war production orders from the likes of the de Havilland Aircraft Co, Handley Page Ltd, HG.Hawker Engineering Co Ltd and Short Bros amongst others. An American order for 4000 USD-9A was placed with the Curtiss Aeroplane and Motor Company but was cancelled due to the armistice and it appears that only 13 USD-9A were built, all prototypes. At least 2700 unlicensed copies were built in the newly formed Soviet Union as the Polikarpov R-1.
The DH.9a ‘Ninak’ (Nin = 9, ack = A) entered front line service with 110 Sqn Independent (strategic bombing) Air Force (IAF) of the Royal Air Force (RAF) at the end of August 1918. While 110 Sqn was the only squadron in France to be fully equipped with the DH.9a before the armistice, it also saw active service with 99 Sqn IAF, 18 Sqn RAF and 55 Sqn RAF. Additionally 53 DH.9as were used by United States Marine Corps (USMC) Northern Bombing Group from September 1918. Post war the DH.9a served with the RAF in Germany, Russia and the Middle East and saw service in Canada, the Australian Air Corps and the Soviet Union and China (as the R-1).