FS2004 The D.H.9 was designed to be the successor to the DH-4, with higher speed and greater load-carrying capability. Although it was structurally only a modest revision of the earlier model, higher performance was anticipated from use of the 300HP Siddeley-Puma engine. Development troubles with the Puma engine produced performance that was inferior to the earlier DH-4. Yet the DH-9 was constructed in large numbers (over 3,000 airframes) with the intent that it form the backbone of the Independent Force, the RAF strategic bombing group. Model, Panel & Texters By Chris Herring.